Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.

PART TWO – General Approach to Pediatric Anesthesia

Chapter 11 – Pediatric Intraoperative and Postoperative Management

Ira T. Cohen,Etsuro K. Motoyama

  

 

Intraoperative Management, 359 

  

 

Early Postinduction Period, 359

  

 

Ventilation, 361

  

 

Monitoring, 363

  

 

Temperature Maintenance, 366

  

 

Fluid Maintenance, 366

  

 

Blood Loss and Blood Component Therapy,367

  

 

Pharmacologic Agents, 368 

  

 

Inhaled Anesthetics, 368

  

 

Intravenous Agents, 371

  

 

Adjuvant Agents, 372

  

 

Regional Anesthesia,375

  

 

Emergence and Extubation, 377 

  

 

Emergence, 377

  

 

Extubation of the Trachea, 378

  

 

Transport to the Postanesthetic Care Unit (PACU),380

  

 

Postanesthetic Recovery, 380 

  

 

Recovery in the Postanesthetic Care Unit, 381

  

 

Common Problems in the Postanesthetic Care Unit,382

  

 

Discharge From Postanesthetic Care Unit, 386

  

 

Short-Stay Recovery Unit, 387

  

 

Summary, 387

The anesthetic plan should be designed as a continuous process that cares for the patient from preinduction to discharge, anticipating the patient's intraoperative requirements and postoperative recovery. Each step in the continuum is interrelated and interdependent. All factors, including the patient's age, medical history, surgical procedure, and discharge disposition, must be considered in selecting drugs and techniques to ensure safe induction, a stable intraoperative course, and comfortable, rapid recovery.

Once anesthesia is induced, the anesthesiologist is responsible for maintaining a state of analgesia, amnesia, adequate muscle relaxation, and autonomic nervous system stability, while communicating with the surgeon closely and providing the optimum working conditions for surgical procedures. To achieve this goal, the anesthesiologist chooses appropriate anesthetics and adjuvant drugs and carefully and continually monitors anesthetic depth, oxygenation, ventilation, cardiovascular function, fluid balance, body temperature, and glucose and electrolyte levels. For critically ill patients or those undergoing major or prolonged procedures, more extensive and invasive monitoring may be required. The pediatric anesthesiologist must use appropriate positioning and protective measures with soft pads to avoid soft tissue injury. Management of all factors, from the choice of pharmacologic agents to the use of regional anesthetic adjuncts to the adjustment of ambient temperature, is the role of the pediatric anesthesiologist.

Postoperatively, the pediatric anesthesiologist should plan a relatively swift awakening to ensure adequate airway maintenance, protective reflexes, and hemodynamic stability while avoiding emergence delirium, agitation, and pain. A rapid return to the preoperative level of consciousness, although ideal for ambulatory and short-stay patients, may be frightening and disorienting to a child who is not prepared to awaken in a new and unfamiliar environment among strangers. Pain, however slight, magnifies these responses dramatically. Nonambulatory and critically ill patients may not need a rapid emergence and can benefit from an extended period of sedation and analgesia. If they are being transferred directly to an intensive care unit (ICU), continuous monitoring is indicated. Once the patient is in the postanesthetic care unit (PACU or recovery room) or ICU, the anesthesiologist must assess airway patency, cardiovascular status, body temperature, and level of discomfort. Nausea, vomiting, and pain should be assessed and treated appropriately.

▪ INTRAOPERATIVE MANAGEMENT

▪ EARLY POSTINDUCTION PERIOD

Airway Protection

After anesthetic induction, securing the pediatric airway, maintaining patency, and reducing the risk of aspiration are crucial. Healthy, supine children over the age of 1 year who are having elective surgical procedures not involving the head and neck can safely be breathed spontaneously or by assisted breathing through a face mask. Suctioning of gastric contents, avoiding insufflation of gas into the stomach, and maintaining an appropriate level of anesthesia decrease the risk of regurgitation and pulmonary aspiration. Typically a handheld mask is adequate for short cases while the head is positioned in a sniffing position to maintain upper airway patency. Both the insertion of an oral airway and moderate levels of continuous positive airway pressure (CPAP) improve the upper airway patency and reduce inspiratory work of breathing ( Keidan et al., 2000 ) (see Chapter 10 , Induction of Anesthesia). Head straps are usually not necessary. If the use of straps is chosen, however, the anesthesiologist must be extremely careful not to press too tight on the face because soft tissues and neurovascular structures are more easily damaged in pediatric patients.

The advent of the laryngeal mask airway (LMA) has added an important alternative for managing the pediatric airway ( Brain, 1983 ). LMAs offer the advantage of securing the airway without the need for additional manipulation, head straps, or instrumentation; an addition of a low CPAP further improves the patency of the pharyngeal airway and is recommended ( Keidan et al., 2000 ). Ranging in sizes of 1 to 4 with half-sizes between 1 and 2 and 2 and 3, LMAs can be used in most pediatric patients over 6 months of age ( Haynes and Morton, 1993 ; Pennant and White, 1993 ). These devices are designed for insertion into the pharynx by sliding over the tongue, imitating the swallowing motion. At times, inserting the LMA upside down and then rotating the devices 180 degrees is necessary for placement (Nakayama et al., 2002 ). After inflation of the cuff, one must check the position and fit of the mask over the larynx by confirming airway patency. Securing the LMA to prevent inadvertent displacement is essential (see Chapter 10 , Induction of Anesthesia).

For infants, especially those younger than 6 months, endotracheal (ET) intubation is indicated because upper airway obstruction occurs commonly and is often unrecognized. In addition, vigorous manual ventilation with a mask by inexperienced hands tends to inflate the stomach with anesthetic gases, resulting in compression of the lower lungs and an increase in the dangers of regurgitation and aspiration of gastric secretions. Between 7 and 12 months of age, ET intubation is optional, although it is still recommended unless one is well experienced in the management of infant airways.

After intubation, the ET tube should be properly secured with adhesive tapes. For patients who are to be turned or have extensive movement of the head before or during the surgical procedures, the ET tube and adhesive tape should be secured to the face with the aid of adherent adjuncts, such as tincture of benzoin. In all patients, the corrugated delivery tubing of the anesthesia breathing circuit should be anchored securely near the ET tube connection to prevent to-and-fro movement with positive pressure ventilation, a major source of laryngeal injury. Most nonrebreathing circuits are relatively heavy and bulky, placing tension on the ET tube. Immobilizing the circuit with an anesthesia circuit stabilizing device ( Fig. 11-1 ) or a drape sheet folded to about 1 foot wide and then rolled from both ends and held together by an elastic band can prevent laryngeal injury and accidental extubation ( Fig. 11-2 ).

 
 

FIGURE 11-1  Circuit immobilized with an anesthesia circuit stabilizing device.

 

 

 
 

FIGURE 11-2  A rolled drape sheet held together by a rubber band (“jelly roll”) provides a convenient stabilizer for a nonbreathing anesthesia delivery tube.

 

 

The stomach should be evacuated by using a lubricated suction catheter after the patient is well anesthetized. Usually a 12F catheter passes easily through the mouth in children younger than 6 years; in older children and adolescents, a regular nasogastric tube (12F to 18F) with side holes seems easier to insert, either orally or nasally.

If auscultation of the chest after intubation indicates the presence of secretions in the tracheobronchial lumen, the anesthesia apparatus is briefly disconnected, and an appropriate suction catheter with a proximal side vent is passed through the ET tube for tracheobronchial toilette. The patient is ventilated with a high inspired concentration of oxygen and air without nitrous oxide before and after ET suction to prevent hypoxemia. Sometimes the air leakage around the ET tube with positive airway pressure is mistaken for rhonchi caused by increased airway secretions. Gentle pressure applied by the thumb and index finger over the intubated trachea, just above the sternal notch (resembling the Sellick maneuver but lower and with less pressure), minimizes air leak and noise and helps to identify the presence of airway secretions. The duration of apnea during ET suctioning should be kept to a minimum, especially in infants, since PaCO2 in apneic infants increases at a rate of 9 to 11 mm Hg/min ( Motoyama et al., 2001 ). Furthermore, the suction catheter should be sufficiently small in relation to the ET tube to leave enough space between the two to avoid the direct application of high negative pressure to the airway system and inadvertent collapse of the lungs.

Protection of the Eyes

General anesthesia eliminates protective eyelid and corneal reflexes and decreases tear production with the eyelids partially open ( Krupin et al., 1977 ). To prevent injury and desiccation, the eyelid should be completely closed and carefully sealed with hypoallergenic clear tape ( Batra and Bali, 1977 ). Taping partially opened eyes can result in corneal abrasion from the tape adhesive itself. The eye tape should be placed horizontally, not diagonally, to ensure a complete seal. Orkin and Cooperman (1983) suggest placing artificial tears in the eyes before taping. Petroleum-based ophthalmic ointment may also protect against abrasions but is more irritating than water-soluble artificial tears ( Boggild-Madsen and Schmidt, 1981 ), although Cucchiarra and Black (1988) were not able to demonstrate a significant difference with its use. Eye irritation and resultant mucosal edema can be severe when halothane (presumably other inhaled anesthetics as well) is used, probably because the anesthetic is absorbed into the ointment through the capillaries ( Boggild-Madsen et al., 1981 ). Ointments also cause blurring of vision and should be avoided in ambulatory patients. In addition, these ointments support combustion and should never be used during laser surgery.

Intravenous Catheters

In children undergoing elective surgery, intravenous access is commonly established after an inhalation induction. These catheters should be large enough to allow the delivery of necessary fluids as indicated by the patient's medical status and surgical procedure. Unless excessive fluid or blood loss is anticipated, a 20-gauge catheter for children and a 22- to 24-gauge catheter for infants and small children fulfill the need for routine elective procedures. It is an error to use small-gauge catheters in infants and children merely because of their size. This is especially true for patients who come to the operating room with previously placed catheters that are typically small in size and may be inappropriate for major surgical procedures. If adequate percutaneous sites are not available, use of a central venous catheter or surgical cut-downs may be indicated.

In response to the growing concern in the medical community regarding percutaneous injury and exposure to blood-borne pathogens, needleless intravenous systems and self-sheathing needles and catheters have been developed and are now mandated in the United States and other countries. Limitations and complications secondary to the use of these catheters have been reported ( Asai et al., 2002 ; Coté et al., 2003 ). The technical problems encountered with these self-sheathing catheters are of particular concern in preterm and young infants.

Securing the intravenous insertion site is particularly important in children because they often emerge in an uncooperative and agitated state. The extremity in which the catheter is inserted should be taped to a cushioned board with a loop of intravenous tubing to prevent accidental removal of the catheter. If a scalp vein is used, caution is advised. Inadvertent subcutaneous injection of certain drugs, such as thiopental or calcium, can cause tissue destruction and sloughing of the scalp.

Positioning

The relative lack of subcutaneous adipose tissue, poorly developed musculature, and more superficially located neurovascular structures place infants and children at greater risk for injuries caused by incorrect positioning. Cushioning with a sponge rubber cushion (“egg crating”) or cotton towels to soften the otherwise hard surface of the operating room table can prevent pressure injuries, especially during procedures that require a long period of time. The patient must be prevented from lying on any monitoring cords, cables, or tubing, with particular attention to areas such as the distal humerus and femur where superficial nerves are at increased risk for injury. Extra precautions should be taken when placing infants and children in special positions, such as the prone, lateral, and lithotomy positions. Incorrectly sized rolls and straps can do more harm than good if they press or pull on delicate structures. Infants typically have large abdomens and require ample elevation of the pelvis and shoulders when prone. An infant's underdeveloped muscles and more elastic tendons and ligaments allow for greater flexibility and abnormal positioning of the extremities. As in adults, upper extremities should not be extended more than 90 degrees, hips should not be hyperextended, and bony prominences should not be allowed to press against each other. Head rings and horseshoe devices must be appropriately sized for the patient's head, preventing pressure on the globes or ears. Occasional turning of the patient's head is necessary during long surgical procedures to ensure the protection of soft tissues.

▪ VENTILATION

Partial Rebreathing Versus Circle Systems

To maintain alveolar ventilation in infants and small children, partial rebreathing or nonrebreathing Mapleson D- or F-type circuits (such as the Bain or Jackson-Rees systems) are most commonly used and are desirable because of their relatively light weight, lower flow resistance, and easy access to heated humidifiers, although adult circle systems with lightweight pediatric circuits are increasingly used for convenience. The adult circle system should be used with caution for young infants because it does not provide adequate humidity, especially when fresh CO2 absorbers are added to the circuit. Relative humidity of at least 50% at body temperature is necessary to maintain normal ciliary activity in the trachea and bronchi ( Forbes, 1974 ; Mercke, 1975 ). A low dead space heat and moisture exchanging filter (artificial nose) should be used at the anesthesia circuit'ET tube junction to maintain humidity, although the artificial nose is far less effective than the heated humidifier, particularly during the first hour after induction of anesthesia ( Bissonnette et al., 1989 ). Adequate humidification of inspired gas mixtures also decreases heat loss and increases thermal stability ( Bissonnette and Sessler, 1989 ) (seeChapter 5 , Thermoregulation: Physiology and Perioperative Disturbances). Adult circle systems may also add extra airway resistance to breathing, especially when the inspiratory valve is wet and sticky; circuit compliance may diminish the accuracy of measured tidal volume, although in vitro experiments using an infant lung model did not report major problems (Stevenson et al., 1998, 1999a, b [396] [397] [398]).

In older children, an adult circle system can be used satisfactorily with a smaller anesthesia bag (0.5 to 3 L capacity) and pediatric corrugated tubing. The infant circle systems, although once popular, have become obsolete because of their lack of a built-in scavenging system and the availability of disposable coaxial circuits and effective, easy-to-use humidifiers. The advantages and disadvantages of pediatric anesthesia circuits are discussed in Chapter 9 (Anesthesia Equipment and Monitoring).

Fresh Gas Flow

There has been controversy as to what fresh gas flow rate is needed for the Mapleson D or F (Jackson Rees) systems to maintain adequate alveolar ventilation in different pediatric age groups. For adults with moderately increased artificial ventilation, Bain and Spoerel (1973) found that a fresh gas flow of 70 mL/kg was sufficient to maintain eucapnia. In a later study, Bain and Spoerel (1977) proposed a minimum flow of 3.5 L/min for children weighing 10 to 35 kg and 2 L/min for infants weighing 10 kg or less.

Using a Mapleson D circuit, Nightingale (1965) demonstrated that, with adequate controlled ventilation, a fresh gas flow of 220 mL/kg (50% to 100% of minute ventilation depending on age) was adequate to maintain eucapnia or mild hypocapnia in all children studied (aged 5 months to 10 years). Although end-tidal carbon dioxide with this fixed fresh gas flow decreased significantly with increasing age, the gas flow rate was not adjusted for age.

Rayburn and Graves (1978) ventilated children at three times the calculated minute ventilation with a Mapleson D system and found that, on the basis of body surface area (BSA), a fresh gas flow of 2500 mL/m2 per min was needed to maintain eucapnia (2900 to 3000 mL/m2 per min for mild hypocapnia). Their data imply that the fresh gas flow needed to maintain eucapnia in a newborn weighing 3 kg (BSA, 0.2 m2) would be 170 mL/kg per min; for a typical 10-year-old child (weight, 30 kg; BSA, 1 m2), it would be 80 mL/kg per min.

Rose and Froese (1979) studied the factors determining PaCO2 during controlled ventilation with either a Bain circuit or an Ayre T-piece in a lung model and substantiated their findings with data obtained in children under general anesthesia. They found that, at a fixed minute ventilation, assuming constant carbon dioxide production, PaCO2 varied inversely with fresh gas flow until it reached a plateau as the circuit became completely nonrebreathing. When the fresh gas flow was kept constant, PaCO2 decreased with increasing ventilation, but it reached a plateau at high levels of minute ventilation, apparently because of increased carbon dioxide rebreathing. The formulas by Rose and Froese (1979) for the fresh gas flow needed to achieve PaCO2 of 37 mm Hg are as follows:

For optimum predictability, the minute ventilation should be set at 1.5 to 2.0 times the fresh gas flow. Most of these studies, however, included only small numbers of children and no young infants.

Badgwell and others (1987a) reported that a fresh gas flow of approximately 270 mL/kg per min in infants weighing less than 10 kg and 240 mL/kg per min in children weighing 10 to 20 kg was needed to maintain mild hypocapnia (end-tidal PCO2, 38 mm Hg). These flow rates were not significantly different.

The variation in the fresh gas flow rates recommended by a number of investigators for pediatric partial rebreathing circuits is considerable. Such discrepancies are related to a number of factors, including the difference in minute ventilation used, variations in metabolic rate resulting from anesthetic technique and depth, measurement of arterial versus end-tidal PCO2, site and method of end-tidal gas sampling, and differences in experimental design. Table 11-1 compares fresh gas flow rates needed to maintain mild hypocapnia as calculated from the data of various investigators.


TABLE 11-1   -- Fresh gas flow rate for Mapleson D system[*]

 

Newborn

1 Year

10 Years

Weight (kg)

3.0

10

30

Body surface area

0.2

0.5

1.0

Fresh gas flow (mL/kg per min)

 

 

 

Nightingale and others (1965)

220

220

220

Rayburn and Graves (1978)

200

150

100

Rose and Froese (1979)

––

200

133

Badgwell and others (1987a, 1987b)

270

230

––

*

Minute ventilation moderately increased to maintain mild hypocapnia.

 

In clinical practice, the fresh gas flow is adjusted to 200 mL/kg with a minimum flow of 3 to 4 L/min after the induction of anesthesia, while ventilation is usually maintained manually. Once a steady state of general anesthesia and controlled ventilation is established, the fresh gas flow rate is fine-tuned with the aid of end-tidal PCO2 readings on a capnograph. To maintain mild hypocapnia with the use of a partial rebreathing system with recommended gas flow rates, the patient's minute ventilation must be increased considerably. Note that the end-tidal gas concentrations do not necessarily represent alveolar concentrations and that an end-tidal–to–arterial PCO2 difference of 5 mm Hg or more exists in anesthetized patients ( Nunn and Hill, 1960 ; Rayburn and Graves, 1978 ). End-tidal PCO2 measurements are not reliable unless there is a plateau on the capnographic waveform (see Fig. 9-33 in Chapter 9 , Anesthesia Equipment and Monitoring). Indeed, Badgwell and others (1986, 1987a) [20] [18] have shown that when a Mapleson D system is used, reliable end-tidal PCO2 measurements cannot be obtained in children less than 8 kg in body weight unless the end-tidal gas is sampled at the tip of the ET tube (Badgwell et al., 1987b ). Alternatively, the accurate end-tidal or alveolar PCO2 can be obtained by temporarily turning off completely the fresh gas flow, having the pop-off valve closed, and having the child rebreathed by manual ventilation for five or six breaths or until the end-tidal CO2 waveform reaches a plateau.

For sevoflurane using adult circle systems with a conventional CO2 absorber, a minimum fresh gas flow of 2 L/min is recommended to minimize the accumulation of a sevoflurane degradation product, fluoromethyl-2-2-difluoro-1-(trifluoromethyl)vinyl ether (Compound A). More breakdown occurs with barium hydroxide (Baralyme) than with soda lime; the breakdown increases with decreasing gas flow, increasing sevoflurane concentrations, CO2 production, temperature, and the drying of the absorbent ( Biebuyck and Eger, 1994 ; Meakin, 1999 ).

Several new CO2 absorbers, which do not react with sevoflurane, have been developed ( Lerman, 2004 ). The new products, such as Amsorb and Dragersorb-Free, have eliminated the problem of sevoflurane degradation by replacing CO2 absorbers containing sodium, barium, and potassium bases with calcium hydroxide ( Kharasch et al., 2002 ; Kobayashi, 2003 ). When this new class of CO2absorbers becomes available, it is likely that low-flow sevoflurane anesthesia with semiclosed or closed circle ventilation will become a reality in the very near future, with considerable cost savings ( Peters et al., 1998 ; Meakin, 1999 ).

For controlled ventilation in infants and children without major respiratory dysfunction, the ventilator can be set initially at a tidal volume of 10 mL/kg or peak pressure of 16 to 18 cm H2O. The respiratory rates between 20/min for infants and 12/min for older children are sufficient as long as one maintains adequate positive end-expiratory pressure (PEEP) between 5 and 6 cm H2O, although much higher respiratory rates have been recommended for young infants ( Peters et al., 1998 ). The PEEP of at least 5 cm H2O is necessary to prevent airway closure and atelectasis in anesthetized infants and young children ( Thorsteinsson et al., 1994 ; Motoyama, 1996 ; Serafini et al., 1999 ). A lower level of PEEP (3 cm H2O), often used in the past for pediatric patients under general anesthesia or in intensive care settings, is inadequate to counteract the reduction in functional residual capacity (FRC) and prevent atelectasis under general anesthesia or paralysis ( Motoyama, 1996 ) (see Chapter 2 , Respiratory Physiology). Once the steady state of ventilation is established, tidal volume and respiratory rate can be fine-tuned to adjust end-tidal PCO2 between 35 and 40 mm Hg.

Ventilators

Traditionally, anesthesia machines were equipped with only a volume-control mode system. For decades, the advantages of pressure-controlled or pressure-limited ventilation in premature infants, neonates, and patients with pulmonary pathology have been recognized. Badgwell and others (1996) described varying success in infants using volume control-mode ventilators with large compression volumes and compliant breathing systems. Tobin and others (1998) reported on a pressure-limited ventilation system on the Narkomed 2B (North America Draeger) anesthesia machines using infant lung models. This group's findings (Stevenson et al., 1999a, 1999b [397] [398]) support the use of this system with adult circuits in infants with pulmonary disease when the appropriate level of peak inspiratory pressure is selected. Ventilation was comparable to free-standing NICU ventilators (Servo 3000 and Babylog 8000). Intraoperative ventilation of children has been reviewed in detail ( Marraro, 1998 ).

▪ MONITORING

In children, close, fastidious observation of the patient's clinical signs is crucial. Physiologic changes can be both subtle and sudden in this age group, and their rapid detection is of paramount importance. Monitoring devices alone are not sufficient in caring for these patients. Changes in chest movement and symmetry, breath sounds, heart tones, skin color, capillary refill, and muscle tone can be perceived only with a precordial stethoscope and careful and continuous clinical observation. Although Spears and others (1991) found that manual ventilation may not provide an anesthesiologist with information as precise as once thought, it still allows for earlier detection of changes in respiratory system compliance resulting from ET tube obstruction caused by kinking or anesthesia circuit disconnection.

Routine monitoring devices include a precordial or esophageal stethoscope, pulse oximeter, capnograph, electrocardiogram, automated blood pressure–measuring device, and temperature probe. Of particular importance is the use of the precordial stethoscope, which is indispensable for continuous monitoring of heart and breath sounds ( Smith, 1980 ), and the use of the pulse oximeter, which allows for rapid detection of oxygen desaturation ( Coté et al., 1988 ). For surgical procedures lasting longer than 3 hours or those in which a major shift in fluid balance is anticipated, an indwelling urinary (Foley) catheter and monitoring urinary output provide useful information in assessing the state of hydration and adequacy of circulatory blood volume. Invasive monitors such as arterial, central venous, and pulmonary artery catheters are indicated only when the benefits of their use exceed the risks.

Standards of Intraoperative Monitoring

To reduce anesthesia-related catastrophes, minimum standards for intraoperative monitoring were initially proposed by the Harvard teaching hospitals in 1986 (Einhorn et al., 1986) and were adopted and amended as guidelines by the American Society of Anesthesiologists (ASA) (1986, 1999, 2004 [8] [9] [10]; http://www.asahq.org/publicationsAndServices/stantards/02.pdf#2). These standards are realistic, rather than idealistic, and must be attainable by average practicing anesthesiologists. The monitoring standards must be technologically attainable and affordable in terms of personnel and utilization (that is, not dependent on state-of-the-art technology). It should be noted that the fundamental focus of the standards is on behavior rather than on technology ( Eichhorn, 1988a ). For example, the ASA standards mandate the “continual” (means intermittent versus continuous) monitoring of ventilation. Initially, a list of methods to achieve this goal was given, including qualitative clinical signs such as chest excursion and observation of the reservoir breathing bag or breath sounds by means of a precordial stethoscope, as well as the use of capnography (see Chapter 9 , Anesthesia Equipment and Monitoring). The updated guidelines, which now state that “continual monitoring for the presence of expired carbon dioxide shall be performed unless invalidated by the nature of the patient, procedure, or equipment” (ASA, 1999), still leave monitoring practices to the discretion of the practitioner.

The ASA standards specifically mandate that oxygenation, ventilation, circulation, and body temperature be evaluated “continually” (meaning frequently at regular intervals, as opposed to “continuously,” as stated in Harvard's standards). For each component, the clear objectives, to ensure adequacy and specific methods, are stated. There is a strong emphasis on combining clinical evaluation and technological methods. Although no specific methodology or instrumentation is mandated for monitoring these components, ASA standards strongly encourage quantitative methods, such as pulse oximetry and capnography, over qualitative clinical assessment with inspection and auscultation for monitoring cardiopulmonary functions. These recommendations are meant to be minimal requirements and are expected to be routinely exceeded ( Eichhorn, 1988b ). Since the late 1980s, the use of a pulse oximeter and capnography in all patients has become a part of standard anesthesia practice in the United States. Indeed, the routine use of pulse oximetry and capnography has been mandated by law in a number of states ( New York State Hospital Code, 1988 ). Although the benefit of government-imposed regulation of anesthetic practice is debatable, these standards should be observed by practicing anesthesiologists to further the desirable goal of minimizing unfortunate anesthesia-related mishaps (seeChapter 34 , Safety and Outcome). The potential medicolegal consequences of ignoring these standards are also an incentive for compliance ( Eichhorn, 1988a ). Standard monitoring and supplemental measures recommended in pediatric anesthesia are shown in Box 11-1 .

BOX 11-1 

Standard Monitors and Supplementary Measurements in Pediatric Anesthesia

Standard Monitors

Physiology

Clinical observation by qualified anesthesiologist

Oxygenation: pulse oximeter

Ventilation: stethoscope, capnograph, gas flow meter

Circulation: stethoscope, blood pressure cuff

Electrocardiograph

Temperature probe: rectal, esophageal, or axillary

Anesthetic depth: BIS monitor

Safety

Oxygen analyzer with low concentration alarm

Ventilator with low pressure and disconnect alarm

Supplemental Measurements

Continual

Fluids given

Urine output (catheterization and urinometer)

Blood loss

Direct arterial pressure

Central venous pressure

Pulmonary arterial pressure and wedge pressure

Cardiac output (noninvasive or invasive)

Electroencephalogram

Somatosensory-evoked potentials

Intermittent

Train-of-four twitch response on nerve stimulator

Arterial blood gas tensions, pH hematocrit

Serum levels of Na+, K+, Ca2+, glucose

Colloid oncotic pressure

Coagulation profile

Clinical Observation

To evaluate various factors that determine the child's condition, the anesthesiologist should rely on continuous clinical observation in addition to information provided by various monitoring devices. In pediatric anesthesia, it is mandatory to be fully aware of surgical progress at all times; consequently, the anesthesiologist should remain standing or positioned so that the whole patient is in view throughout the procedure.

Even with the modern technology of noninvasive monitoring, such as pulse oximetry or infrared capnography, it is indispensable to have continual clinical assessment of information and interpretation with experience. Perhaps with the exception of pulse oximetry, this continual clinical assessment is often more valuable than what is provided by monitors. The anesthesiologist should observe, both visually as well as with a precordial stethoscope, the rate and depth of ventilation, whether assisted or controlled'that it is without obstruction, with equal expansion of both sides of the chest, and with good compliance and normal color of the skin and blood.

Stridor indicates a narrowing of the extrathoracic airways, most commonly at the glottis. Expiratory stridor usually denotes light anesthesia with tightening of the vocal cords, whereas inspiratory stridor indicates narrowing caused either by flaccid soft tissue being sucked together with inspiration during deep anesthesia or by impending laryngospasm.

Manual ventilation of the patient, as opposed to mechanical ventilation, is encouraged, at least intermittently or whenever possible, because the hand on the anesthesia bag is an additional and an excellent monitor for detection of changes in the patient's dynamic compliance and respiratory resistance resulting from air leaks in the anesthesia circuit, airway obstruction of various origins, or movement of the diaphragm.

Normal cardiovascular function is evident in suitable heart tone and rate, rhythm, pulse volume, vascular tone, capillary refill, and skin color. Blood loss can be quantified reasonably well by visual estimation of bleeding in the surgical field and on drapes, pulse rate and volume, color of the conjunctivas, the counting and weighing of blood-soaked sponges, and measuring the volume of blood in suction bottles. With continuous monitoring with a precordial or an esophageal stethoscope, changes in the heart tone can readily be heard even before a reduction in the systemic blood pressure as indicated by automated blood pressure measurements by cuff.

The amended guidelines from the ASA (1999) state that “every patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated or suspected.” The standards for monitoring temperature should be applied more strictly in the pediatric patient, especially infants, because of their greater susceptibility to temperature change. Temperature should be monitored directly, but heating and cooling of the skin often can be sensed by touch. This helps to detect a faulty thermistor probe, avoiding initiation of treatment for false hypothermia or hyperthermia. Neuromuscular tone in infants (without relaxants) is easily assessed by just sensing changes in respiratory compliance while manually compressing the anesthesia bag or passively extending the child's flexed arm or fingers.

Depth of anesthesia can be difficult to assess in the pediatric patient. Bispectral index analysis (BIS) monitoring measures the effects of anesthetic agents on electroencephalography (see later). Extensively validated in adults and children, BIS monitoring can effectively estimate the level of sedation/anesthesia ( Denman et al., 2000 ; Bannister et al., 2001 ; Choudhry and Brenn, 2002 ; McCann et al., 2002 ). In addition, central nervous system responses, such as pupillary responses and lid reflexes and autonomic responses such as sweating, vasomotion, and vagal activity, are informative and easily recognizable by clinical observation. Again, clinical observation, if properly used, provides a great deal of information that cannot be obtained by electronic monitors.

Monitoring Apparatus

Perioperative monitoring of patients receiving general anesthesia can be subdivided into physiologic monitoring and safety (accident prevention) monitoring. Both types are included in the ASA basic standards discussed previously. Safety monitoring is primarily the monitoring of the anesthesia delivery system, but this often overlaps with physiologic monitoring. Monitoring can also be classified as noninvasive or invasive. Most noninvasive monitors are mandated by the ASA standards as described earlier. These and some additional noninvasive monitors are considered mandatory for all pediatric procedures; others are indicated for special situations or procedures. Invasive monitors should be used only if they give truly essential information without exposing the child to undue risk ( Smith, 1980 ). Various monitoring devices, together with their mechanism of action and clinical use, are detailed in Chapter 9 , Anesthetic Equipment and Monitoring. In the current chapter, additional brief comments are made only on the most essential monitors, namely, the stethoscope, pulse oximeter, and anesthesia record.

Stethoscope

The use of a precordial stethoscope as an intraoperative monitoring device was first advocated by Smith in the late 1940s ( Smith, 1953 ). It was gradually recognized and its use expanded in the United States and abroad over the next two decades ( Ploss, 1955 ; Smith, 1962, 1978 [378] [379]; Bosomworth et al., 1963 ; Domette, 1963, 1973 [105] [106]; Bethune, 1965 ; Patterson, 1966 ). By the 1970s, the precordial (or esophageal) stethoscope was established as the most important monitoring device in pediatric anesthesia, essential for all procedures involving general anesthesia ( Smith, 1980 ).

Several types of stethoscope heads without a diaphragm are available for adult and pediatric patients. The most convenient and popular have double-sided adhesive tape (see Fig. 10-3 in Chapter 10 , Induction of Anesthesia). Before the stethoscope is fixed to a child's chest, the site should be determined by where both heart tones and breath sounds can be heard most distinctly. This usually is near the left sternal border at the nipple line (the fourth intercostal space), bordering the heart and major airways ( Smith, 1980 ). Alternatively, the stethoscope may be placed over the third or second interspace at the left sternal border or over the second interspace at the right sternal border (to transmit pulmonic valve sounds). Auscultation of heart and breath sounds is satisfactory at these alternative sites in all ages but especially in muscular or obese adolescents. A disposable, soft, compressible foam rubber earpiece, attached to lightweight tubing, is commercially available as a convenient connector to the precordial stethoscope head, although, because of the small diameter of the tubing, the heart and breath sounds are often excessively attenuated. A large-bore silicone rubber tubing, attached to a custom-molded earpiece, gives more satisfactory results.

An esophageal stethoscope is valuable when children are placed in the prone position or when the precordium cannot be used because of surgery or injury. Esophageal stethoscopes are available commercially in sizes 12F, 18F, and 24F, which are suitable for most infants and children.

Pulse Oximeter

The pulse oximeter, which became available clinically in the mid 1980s, measures the arterial oxygen saturation of hemoglobin continuously and noninvasively. Within 5 years, it was widely accepted as an essential (if not mandatory) monitoring device for clinical anesthesia. Its probe, usually affixed to a fingertip or a toe, senses changes in light absorption of two wavelengths (saturated and unsaturated hemoglobin) that occur synchronously with arterial pulsation. Thus, the oxygen saturation detected by this device (SpO2) represents arterial, rather than capillary, hemoglobin saturation on a beat-to-beat basis without previous heating or arteriorization ( Yelderman and New, 1983 ; Motoyama and Glazener, 1986 ). The pulse oximeter accurately reflects SaO2 in all age groups with various hematocrit values, including premature infants with fetal hemoglobin, over the range of 60% to 100% SaO2 ( Deckardt and Steward, 1984 ).

Pulse oximetry is the most important advancement in perioperative monitoring in pediatric anesthesia, since the precordial stethoscope was introduced by Smith more than 50 years ago ( Smith, 1953 ). Coté and others (1988) found that the use of a pulse oximeter significantly reduced the occurrence of major hypoxic events during general anesthesia and surgery in children. The pulse oximeter detected hypoxemia before its signs and symptoms were apparent. Not surprisingly, hypoxemic events occurred more frequently in children younger than 2 years of age and in those with ASA physical status 3 or 4. A greater number of children not monitored by the pulse oximeter (not visible for the anesthesiologists administering anesthesia) experienced borderline hypoxemia (SpO2 <90%, estimated PaO2 <58 to 60 mm Hg) while breathing room air at the end of anesthesia than those with the monitor visible to the anesthesiologist. In a subsequent single-blind study of combined pulse oximetry and capnography in children, Coté and others (1991) showed that, of all major hypoxemic events, nearly 70% were first discovered with the pulse oximeter, 22% by the anesthesiologist (clinical signs), and only 8% with the capnograph. Thus, compared with changes in clinical signs and capnography, pulse oximetry provides by far the most sensitive warning of developing hypoxemia in anesthetized children.

The limitations of pulse oximetry have been noted. Accuracy of measurement is greatest in the range of 90% to 100%. Schmitt and others (1993) observed that accuracy was compromised in children with cyanotic congenital heart disease. Advances have been made in pulse oximetry by Masimo Signal Extraction Technology (SET). This device minimizes the effect of motion artifact, improves accuracy, and has been shown to have advantages over the existing systems, especially when used in neonates and with low-flow states, mild hypothermia, and in moving patients ( Malviya et al., 2000 ; Hay et al., 2002 ;Irita et al., 2003 ).

Anesthesiologists should be aware that the most commonly used pulse oximetry system in the United States and elsewhere is artificially modified to read SpO2, 2% to 3% higher than real values and, consequently, gives a false sense of security regarding patients' oxygenation (see Chapter 2 , Respiratory Physiology). The reason for the built-in “deception” is not clear (it probably is for the convenience of reading SpO2 of 100% in room air in the healthy individual). In reality, true oxygen saturation of hemoglobin at PO2 of 100 mm Hg is 97% to 98% (arterial PO2 of 130 to 150 mm Hg is necessary for 100% hemoglobin saturation). Unfortunately, the newer pulse oximetry system has also adopted the practice of raising SpO2 readings by 2% to 3% above the true pulse oximetry reading, presumably in response to consumer demands and to avoid discrepancies between the two pulse oximeter systems. It is not clear if these pulse oximeters read falsely higher values at lower oxygen saturation where the accuracy of pulse oximeter diminishes markedly.

Bispectral Index

Bispectral analysis, comparing paired wave activity, quantifies the level of synchronization in an electroencephalogram, along with the traditional measurements of amplitude and frequency. BIS monitors compress electroencephalographic signals by a sophisticated algorithm into a digital readout ranging from 0 to 100. By comparing the reading with previously measured results in conscious, sedated, and anesthetized patients, a normogram for level of sedation has been generated. Studies in infants and children have confirmed the validity of this instrument and have demonstrated that more accurate titration of general anesthesia in children is achieved with the use of a BIS monitor ( Denman et al., 2000 ; Bannister et al., 2001 ; Choudhry and Brenn, 2002 ; McCann et al., 2002 ). Davidson and others (2001) did not find the usual BIS–MAC relationship in children less than 1 year old. Attempts to refine this technology by interpreting high-frequency electroencephalographic data are in the initial phase.

Anesthesia Record

The anesthesia record or chart is extremely valuable as a data sheet during anesthesia, as a source of information for anesthetic management at a later date, and as a legal document (see Chapter 36 , Medicolegal and Ethical Aspects). It should be considered an essential part of monitoring for the anesthesiologist, particularly when caring for infants and children. The record should contain all the important information obtained preoperatively:

  

   

Patient's systemic disease or condition and ASA physical status (PS)

  

   

Hemoglobin and hematocrit, when applicable

  

   

Time of the last food and liquid intake

  

   

Preanesthetic state of anxiety, if any

  

   

Premedication, time and its effect

  

   

Calculated fluid deficit, estimated blood volume, and allowable blood loss

  

   

Completed preinduction and postinduction checklists

The chart should be properly documented and signed by the trainee as well as by the attending anesthesiologist legally responsible for administering anesthetic.

After induction a brief description of induction and intubation should be recorded, noting the drugs given, the size of the ET tube, whether cuffed or uncuffed, and verification of proper air leak around the ET tube. Subsequently, gas flow rates, maintenance concentrations and doses of anesthetic and adjuvant drugs, blood pressure, pulse, respiratory rate, temperature, oxygen saturation readings from the pulse oximeter, and end-tidal PCO2 should be entered at frequent intervals.

With advances in computer technology, attempts have been made to elaborate the anesthesia record into a fully automated data entry system ( Stanley and Reves, 1994 ). Computerized systems seem to increase efficiency by automatically entering cardiorespiratory and other data from various monitors into the anesthesia record and improving the accuracy and security of records. A number of automated charting systems have become commercially available but have not been widely used in clinical practice. Studying data collected from automated anesthesia records, Sanborn and others (1996) found that electronic scanning recorded a higher incidence of intraoperative incidents than those reported voluntarily. Lubarsky and others (1997) applied data collected toward management practice and cost containment. In review, Dorman and Fackler (2000) state that available automated anesthesia information systems are primitive, focusing only on the charting process. They believe that until these systems can be integrated with the care process, they will be of no true benefit. Others have reported improvements in patient safety and care with automated systems ( Junger et al., 2001 ; Merry et al., 2001 ).

▪ TEMPERATURE MAINTENANCE

Control of thermal regulation requires special consideration in infants and small children because of their relative lack of subcutaneous adipose tissue and increased BSA in relation to body weight. Vasodilation, exposure to the cold operating room environment, insensible heat losses, and infusion of cold intravenous fluid often result in loss of heat and resultant hypothermia ( Smith, 1969 ). The mechanisms of thermoregulation in infants and children are discussed in detail in Chapter 5 (Thermoregulation: Physiology and Perioperative Disturbances).

To prevent excessive heat losses, a heated humidifier in the anesthetic circuit should always be turned on to humidify anesthetic gas mixtures (with 0% humidity) to prevent evaporative heat loss, damage to the ciliated airway epithelia, and postoperative pulmonary complications ( Chalon et al., 1979 ). A warming mattress on the operating table is helpful for infants weighing less than 10 kg ( Goudsouzian et al., 1973 ). Additional measures for heat conservation, such as increasing room temperature, use of a radiant warming lamp, use of a forced air warmer, and wrapping the child's head and other exposed areas with plastic sheet, should be practiced as needed to maintain normal body temperature. Kurz and others (1993) found in both adults and children that forced-air warming maintains intraoperative normothermia better than circulating-water mattresses. Intravenous fluids should be prewarmed with a fluid warmer, especially in infants and young children. Conversely, prolonged periods in a warmed environment with plastic drapes and wraps can sometimes cause hyperthermia. To reduce elevated temperature, reversing the measures of heat conservation is often sufficient.

Accurate and close monitoring of body temperature is essential for keeping pediatric patients in the normothermic range. Rectal or esophageal thermistor probes reliably measure core and peripheral temperature. Axillary probes, which are more easily placed, record temperatures 0.7° to 1.0°C less than core readings and are more appropriate for older children undergoing surgery without expected major hemodynamic changes. For the best results with this method, the sensing tip should be located as near the axillary artery as possible by taping the probe to the lateral chest wall and then adducting the arm down close to the body. The safe range for a child's core temperature is approximately 35.5° to 37.5°C (96° to 100°F). To minimize temperature changes under general anesthesia, action should be taken as soon as or before the temperature deviates from this narrow range (see Chapter 5 , Thermoregulation: Physiology and Perioperative Disturbances).

▪ FLUID MAINTENANCE

Regulation of fluids and electrolytes is detailed in Chapter 4 (Regulation of Body Fluids and Electrolytes). Intraoperative fluid and glucose management in children was reviewed ( Leelanukrom and Cunliffe, 2000 ). The maintenance fluid requirement is most commonly based on the energy needs proposed by Holliday and Segar (1957) . The basal caloric needs of infants and children dictate their fluid requirement. Infants weighing up to 10 kg use 100 kcal/kg per day; those weighing 10 to 20 kg require 1000 kcal plus 50 kcal/kg above 10 kg; and those weighing more than 20 kg need 1500 kcal plus 20 kcal/kg above 20 kg. For every 100 kcal consumed, these authors estimate that 67 mL of water is needed for solute excretion, plus an average of 50 mL/100 kcal is associated with insensible loss, while 17 mL/100 kcal is produced by oxidation. Thus, an infant needs 100 mL (67 + 50 - 17 = 100) of water per 100 kcal of caloric expenditure. On the basis of 1 mL of fluid per 1 kcal of caloric requirement, the fluid requirements in infants and children can be approximated as follows:

Body Weight Fluid Requirement

Alternatively, Oh (1980) proposed a modification of this formula as follows:

Body Weight Fluid Requirement

An increase or decrease in metabolic rate changes the fluid requirement. For each 1°C increase in body temperature, an 8% to 10% increase in fluid requirement occurs. For every 100 calories of energy expenditure or 100 mL of water, a child needs 3 mmol of sodium, 2 mmol of potassium, 5 mmol of chloride, and 5 g of dextrose. Usually 5% dextrose in ¼ or ½ normal saline solution (0.2% or 0.45% NaCl) suffices; potassium is not replaced routinely because of the hazard of accidental rapid infusion.

Pediatric patients are usually kept fasting (NPO status) for 2 hours for clear fluids and 4 to 8 hours for solid food, depending on the age (and sometimes much longer by default) before induction of anesthesia for elective surgery (see Preoperative Fasting Guidelines in Chapter 10 , Induction of Anesthesia). With the exception of simple, same-day surgery procedures of short duration, half of the estimated fluid deficit, plus the hourly maintenance fluid requirement, should be given during the first hour of anesthesia, with a balanced salt solution such as lactated Ringer's solution; one quarter of the fluid deficit plus the hourly maintenance fluid is infused during the second and third hours of anesthesia and surgery, along with the hourly maintenance fluid and the replacement of any third-space fluid loss ( Furman et al., 1975 ). While the fluid deficit should be replaced by a balanced salt solution not containing glucose, 5% dextrose in 0.2% or 0.45% NaCl may be used for the hourly fluid maintenance. Infants and occasionally healthy children who have fasted for a prolonged period become hypoglycemic during general anesthesia and surgery without apparent clinical symptoms ( Welborn et al., 1986 ). The intraoperative monitoring of blood glucose levels is recommended in infants and toddlers who have not received glucose supplementation for prolonged periods.

The intraoperative use of glucose supplementation has been reevaluated ( Seiber et al., 1987 ). Administration of fluid containing 5% dextrose invariably produces hyperglycemia and causes osmotic diuresis. Hyperglycemia may worsen neurologic outcome in cerebral ischemia ( Lanier et al., 1987 ). On the other hand, hypoglycemia is known to cause cerebral ischemia and brain damage, particularly in infants, and is difficult to detect during general anesthesia unless the blood glucose level is determined directly.

Welborn and others (1986, 1987) [452] [453] reassessed the need for intravenous glucose in otherwise healthy children undergoing outpatient surgery for minor procedures with minimal blood loss. They found that children who were given 5% dextrose in lactated Ringer's solution consistently developed hyperglycemia, whereas those given 2.5% dextrose in lactated Ringer's solution maintained a normal blood glucose level. At the infusion rate given, children who had intravenous fluid containing less than 2.5% dextrose did not meet the glucose maintenance requirement of 5 mg/kg per min. On the basis of these studies, these authors recommended the use of 2.5% dextrose rather than the 5% glucose solution (given routinely back in the 1980s) for healthy children undergoing minor surgical procedures.

A urethral catheter allows continual monitoring of urine output and the state of hydration and blood volume during major surgical procedures or with injuries that involve large loss of blood and fluid. Urethral catheterization is usually recommended in surgical procedures lasting for 3 hours or longer. In newborn and small infants, it is safest to use a soft 6F or 8F infant feeding tube. This avoids the retention balloon, which may contribute to bladder irritability and spasm. Even in premature infants weighing less than 1 kg, the feeding tube, when connected to a small syringe, provides an accurate measure of urine output and the state of hydration. In older infants and children, urine output can be read ultrasonically on a minute-to-minute basis with a urinometer ( Lilly et al., 1980 ). Urine output of more than 0.5 mL/kg per hr should be maintained to avoid damage to the renal tubules (see Chapter 4 , Regulation of Body Fluids and Electrolytes). Foley catheters sizes 8F to 10F made of nonreactive silicone rubber are generally used in the 6-month- to 6-year-old age group ( Litvak et al., 1976 ). Although urethral catheterization can be achieved safely for intraoperative monitoring, the risk of complications increases with longer periods of drainage, so every effort is made to shorten its duration ( Kaplan and Brock, 1983 ).

▪ BLOOD LOSS AND BLOOD COMPONENT THERAPY

Accurate and continuous monitoring of blood loss and accurate assessment of acceptable blood loss and its timely replacement are essential in pediatric patients. Seemingly small losses in infants can cause significant changes in hemoglobin concentration and hemodynamic stability. Careful assessment of blood loss by weighing blood-soaked sponges, tallying blood and fluid losses using calibrated miniaturized suction bottles, and making a visual estimation of blood lost on surgical drapes allow determination of the extent of total blood loss. Factors that determine allowable blood losses include the patient's estimated blood volume, which is age dependent, preoperative and intraoperative hematocrit, cardiopulmonary and general medical conditions to provide adequate oxygen transport, and risk versus benefit of the transfusion. Estimated blood volumes in pediatric patients of different ages are listed in Table 11-2 .


TABLE 11-2   -- Estimates of circulating blood volume

Patient

Blood Volume (mL/kg)

Premature newborn

90 to 100

Full-term newborn

80 to 90

3 mo to 1 yr

75 to 80

3 to 6 yr

70 to 75

>6 yr

65 to 70

 

 

As mentioned earlier, estimated blood volume and maximal allowable blood loss should be computed before the induction of anesthesia. There have been several methods proposed to estimate allowable blood loss based on blood volume, body weight, and hematocrit using a simple proportion, an approximation of circulating red blood cell (RBC) mass, and a logarithmic function ( Bourke and Smith, 1974 ;Kallos and Smith, 1974 ; Furman et al., 1975 ). The results from these equations are compatible. The following simple formula can be used to estimate allowable blood loss (ABL):

where EBV is the estimated blood volume, HO is the original hematocrit, HL is the lowest acceptable hematocrit, and HA is the average hematocrit (that is, [HO + HL]/2) ( Bennett, 1975 ). The estimated blood volume can be determined by the patient's age using Table 11-2 . For example, in an 8-kg, 10-month-old infant whose original hematocrit (HO) is 35% and blood volume is approximately 80 mL/kg, EBV is 80 × 8, or 640 mL. Allowing the lowest hematocrit (HL) to fall to 25% yields an ABL of 640 × (35 - 25)/(35 + 25)/2, or 213 mL.

Whether a crystalloid or a colloid solution should be used to replace blood volume as the hematocrit is allowed to decrease has been debated. If a colloid solution (albumin, plasma protein, fresh frozen plasma) is used, blood loss is replaced milliliter for milliliter. If a crystalloid solution is used, two to three times the volume of the blood loss is replaced because the intravascular volume cannot be sustained with crystalloid solutions (Shires et al., 1961, 1964 [375] [376]). In most cases the replacement of ABL with crystalloid alone is safe and effective, provided the patient is healthy otherwise. The replacement of blood loss with colloid solutions may be more physiologic but is much more expensive and exhibits no clear-cut evidence of superiority over crystalloid replacement. With excessive blood loss and large volumes of crystalloid replacement, however, hypoproteinemia would result. Furman and others (1975) recommend that continuing blood loss be replaced with an equal volume of lactated Ringer's solution until the serum total protein concentration decreases to 5 g/dL. Then blood volume is maintained with 5% albumin until the ABL has occurred.

Until the early 1980s, 10 g/dL of hemoglobin was used as a guideline for the minimal adequate level for elective anesthesia and surgery. This guideline began long before the physiologic effects of organic phosphates and the different oxygen affinities of fetal and adult hemoglobins were discovered (see Chapter 2 , Respiratory Physiology). With the exception of patients in the early neonatal period (with high oxygen affinity of fetal hemoglobin and decreased oxygen unloading at tissue levels) and those with cyanotic cardiopulmonary disease, it is evident that 10 g/dL of hemoglobin is not a prerequisite in healthy, normovolemic patients for elective surgery.

A study on acute normovolemic hemodilution in animals indicated that hemoglobin values of 6 to 7 g/dL may be acceptable ( Stehling and Zander, 1991 ). In another study of acute normovolemic hemodilution in dogs at hematocrit levels below 20%, hemodynamic stability was maintained with colloid solution but crystalloids caused massive whole body edema and hemodynamic instability (Brinkmeyer, Safar, and Motoyama, 1983 ). Furthermore, Dong and others (1986) demonstrated that normovolemic hemodilution to a hematocrit of 15% for 1 hour was associated with depression of evoked brain activities (somatosensory evoked potentials); the combination of hemodilution with hypotension resulted in either death or permanent brain damage.

Based on these limited findings, the best recommendation to date appears to be that of the National Institutes of Health Consensus Conference on Perioperative Red Cell Transfusion (1988) : Healthy patients with hemoglobin values of 10 g/dL or greater rarely require transfusion, whereas those with values less than 7 g/dL frequently require transfusion. Thus, to keep operative hemorrhage and blood volume under control in a situation such as spinal fusion, hemoglobin may be decreased temporarily to as low as (but not below) 7 g/dL (hematocrit 20%), with proper monitoring of blood pressure, arterial and mixed venous PO2, etc. The hemoglobin level should be increased (i.e., to 8 g/dL with a hematocrit of ≥25%) postoperatively when the patient needs more oxygen uptake for increased metabolic needs.

When the estimated blood loss approaches or exceeds the ABL, transfusion, most commonly with packed RBCs, becomes necessary. The hematocrit of packed RBCs varies between 60% and 80% and can be adjusted according to the need of the physician administering the blood. If the packed RBCs have a hematocrit of 75% and the patient's hematocrit is to be maintained at 30%, the volume of packed RBCs needed to replace the blood loss beyond ABL can be calculated as follows:

Using the example given earlier of the 8-kg infant and a total blood loss of 270 mL, or about 60 mL above ABL, the volume of packed RBCs needed would be as follows:

When the blood loss exceeds one blood volume (massive blood loss), labile clotting factors are significantly diminished. In patients with massive blood loss, packed RBCs are often given with 1 to 2 volumes of normal saline solution to achieve desired hematocrit, reduce viscosity, and facilitate transfusion. In patients with clinical signs of nonsurgical bleeding or abnormal activated clotting time, fresh frozen plasma (FFP) is given in place of crystalloid solution, with equal volumes of packed RBCs. The management of blood component therapy and massive blood loss is detailed elsewhere ( Chapter 12 , Blood Conservation).

Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com

Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.

Copyright © 2005 Mosby, An Imprint of Elsevier

▪ PHARMACOLOGIC AGENTS

▪ INHALED ANESTHETICS

A majority of general anesthetics administered to pediatric patients still involves the use of inhaled anesthetics. The pharmacokinetics and pharmacodynamics of inhaled anesthetics are detailed in Chapter 6(Pharmacology of Pediatric Anesthesia). Nitrous oxide is commonly used for the initiation of mask induction and as an adjunct agent during inhalation and intravenous anesthetics, although its use has been decreasing considerably.

Since its introduction in North America in 1995, sevoflurane has replaced halothane as the preferred agent for inhalation induction and is commonly used in relatively simple and short procedures. The bronchodilating action and longer, smoother emergence of halothane offer advantages over the less-soluble agent when managing patients with reactive or difficult airways. Isoflurane, desflurane, and sevoflurane provide better cardiovascular stability with less or minimal biodegradation in the liver and are preferred for most other procedures. Each of these agents, however, has properties that may limit their use in certain patients and situations. Their effect on induction and emergence should be of particular consideration. Physical and pharmacologic characteristics of volatile anesthetics are shown inTable 11-3 .

TABLE 11-3   -- Characteristics of volatile anesthetics

 

Molecular Weight (Da)

Boiling Point (°C)

Vapor Pressure at 20°C (mm Hg)

Blood Gas Partition Coefficient

MAC (%)

 

 

 

 

 

Infant (1 to 6 mo)

Child (3 to 10 yr)

Adult

Halothane

197.4

50.2

244

2.3

1.1

0.9

0.7

Enflurane

184.5

56.5

172

1.9

––

––

1.6

Isoflurane

184.5

48.5

239

1.4

1.7

1.6

1.2

Desflurane

168.0

23.5

664

0.4

9.4

8.0

6.0

Sevoflurane

200.1

58.5

160

0.6

3.3

2.5

2.0

Adapted in part from Jones RM: Desflurane and sevoflurane; inhalation anesthetics for this decade? Br J Anaesth 65:527, 1990. Copyright © The Board of Management and Trustees of the British Journal of Anaesthesia. Reproduced by permission of Oxford University Press/British Journal of Anaesthesia.

MAC, Minimum alveolar concentration.

 

 

 

 

Nitrous Oxide

Nitrous oxide has been the most widely used anesthetic in adults and children because of its inoffensive odor; low solubility, which results in rapid uptake and distribution (blood-gas partition coefficient of 0.47); hypnotic and analgesic action; and relatively minimal depressant effects ( Smith, 1971 ). Nitrous oxide requires a concentration greater than 100% to achieve 1 MAC, making its use as a sole anesthetic agent impossible at normal atmospheric pressures (Hornbien et al., 1982). Its use with volatile agents reduces the risk of untoward effects and the duration of emergence by lowering their MAC requirements. When intravenous anesthetics are used, nitrous oxide potentiates the analgesic effect of opioids and the amnesic actions of hypnotics.

In several situations, however, its use demands special consideration. In adults with moderate pulmonary hypertension, nitrous oxide increased pulmonary artery and pulmonary capillary wedge pressures (Schulte-Sasse et al., 1982 ). In healthy infants, however, Hickey and others (1986) observed no increase in pulmonary artery pressure or vascular resistance. Mild but significant decreases in heart rate, systemic blood pressure, and cardiac index were seen. These effects of nitrous oxide on systemic hemodynamics may be clinically insignificant in healthy infants but may affect the hemodynamic stability of sick infants, particularly those with pulmonary hypertension. Furthermore, the presence of nitrous oxide in blood may increase the oxygen affinity of hemoglobin, decreasing the P50 by as much as 8 mm Hg and thereby reducing the oxygen-unloading capacity of blood at the tissue level ( Fournier and Major, 1984 ).

Of greater concern is the accumulation of nitrous oxide in a closed, gas-containing space such as an obstructed loop of bowel or a pneumothorax. In situations where maximal oxygen delivery is essential, as in bronchoscopy, massive blood loss, severe anemia, shock, and compromised cerebrospinal blood flow, the use of high concentrations of nitrous oxide is not recommended. Other possible undesirable side effects include risk to operating room personnel, inhibition of methionine synthetase, and teratogenic effects, as demonstrated in experimental animals.

The role of nitrous oxide in causing postoperative nausea and vomiting (PONV) has been reexamined since Watcha and others (1991) reported an increased incidence when it was used with propofol.Crawford and others (1998) confirmed this finding. A meta-analysis by Sneyd and others (1998) , however, found that nitrous oxide had no effect on the incidence of PONV when propofol was compared with inhalation agents for the maintenance of general anesthesia. In children, no difference was seen in the incidence of PONV with or without nitrous oxide when general anesthesia was administered with sevoflurane ( Bortone et al., 2002 ) or desflurane ( Kuhn et al., 1999 ). This evidence supports avoiding the use of nitrous oxide to reduce the incidence of PONV only when propofol is the primary anesthetic agent.

Sevoflurane

Sevoflurane is an excellent induction agent in infants and children because of its relatively pleasant aroma, minimal airway irritation, and rapid induction time. Systolic blood pressure and heart rate are unchanged during the induction with nitrous oxide–sevoflurane anesthesia compared with nitrous oxide– halothane anesthesia, and hemodynamic stability is retained during the maintenance of anesthesia (Sarner et al., 1995 ). Concentrations can be increased rapidly to 8% during induction in healthy ASA I/II children without laryngospasm or hypotension ( Baum et al., 1997 ).

Sevoflurane is a fluorinated methyl isopropyl ether with a blood-gas partition coefficient of 0.60 to 0.69 ( Strum and Eger, 1987 ). One MAC of sevoflurane is 3.3% in neonates and infants 1 to 6 months of age ( Lerman et al., 1994 ), 2.5% in younger children ( Katoh and Ikeda, 1992 ), and 2.0% in older children and adults ( Scheller et al., 1988 ; Inomata et al., 1994 ). The biotransformation of sevoflurane in humans is about 3%, roughly one fifth that of halothane ( Holaday and Smith, 1981 ) and significantly greater than that of desflurane and isoflurane (see Chapter 6 , Pharmacology of Pediatric Anesthesia).

Sevoflurane has minimal effect on hemodynamic parameters. Wodey and others (1997) , using echocardiographic studies, found that sevoflurane at 1 and 1.5 MAC did not alter the heart rate or cardiac index. They did find a significant change from baseline when measuring blood pressure and vascular resistance but no abnormal values when assessing myocardial contractility. Unlike halothane, sevoflurane does not sensitize the myocardium to epinephrine ( Hayashi et al., 1987 ).

Sevoflurane has been observed to profoundly depress ventilation (Doi and Ikeda, 1988). In comparison to halothane, minute ventilation and respiratory frequency were significantly lower in infants on 1 MAC of sevoflurane, although end-tidal PCO2 values were only moderately increased ( Brown et al., 1998 ). The bronchodilatory effect of sevoflurane appears to be similar to that of halothane ( Hashimoto et al., 1996 ; Rooke et al., 1997 ). Neurologic effects of sevoflurane include decreasing cerebral blood flow compared with halothane ( Monkhoff et al., 2001 ) and eliciting epileptiform electroencephalographs in adults and children ( Yli-Hnankala et al., 1999 ; Vakkuri et al., 2001 ).

Metabolism of sevoflurane in vivo produces inorganic fluoride, the level of which may be proportional to the concentration and duration of exposure to sevoflurane (MAC-hour). There have been no reports of renal toxicity with sevoflurane, although serum fluoride concentrations in excess of 50 μmol/L have been reported in adults ( Frink et al., 1992 ). It has been suggested that sevoflurane exposures up to 15 MAC-hours are safe in adults ( Sarner et al., 1995 ). Sevoflurane is not stable in soda lime, and the rate of degradation (especially accumulation of Compound A) increases with increasing sevoflurane concentrations, decreasing fresh gas flow, and increasing temperature ( Strum et al., 1987 ); this degradation may not be of clinical significance with a semiclosed anesthesia breathing circuit with moderate to high flows (i.e., >2 L/min of fresh gas flow). Ebert and others (1998) reported no sign of renal or hepatic toxicity in healthy volunteers exposed to 3% sevoflurane for 8 hours. In addition, as described previously, a new class of CO2 absorbers, which do not react with sevoflurane, may solve the problem of sevoflurane breakdown in the near future (Karasch et al., 2002; Kobayashi et al., 2003 ; Lerman, 2004 ).

Another infrequent but potentially catastrophic problem with sevoflurane is its extreme exothermal reaction with desiccated CO2 absorbers, especially with Baralyme, producing spontaneous ignition, fire, and even explosion, and the production of carbon monoxide, first reported in Europe ( Baum et al., 1998 ) and more recently in the United States ( Olympio and Morell, 2003 ; Castro et al., 2004 ; Wu et al., 2004 ).

Degradation of sevoflurane increases as the water content of the CO2 absorber with strong monovalent base contents (KOH and NaOH) decreases. Complete desiccation occurs within several days of constant flow of dry gas at room temperature, such as oxygen flowing through the canister over the weekend (Woehlck et al., 2001; Wu et al., 2004 ). Fatheree and Leigon (2004) reported an unfortunate case of a patient developing acute respiratory distress syndrome (ARDS) and tracheobronchial burn with increased carboxyhemoglobin (29%) in arterial blood following an exposure to an apparent exothermic reaction (without explosion) between sevoflurane and Baralyme. Wu and others (2004), in reporting an explosion in an unused, unattended anesthesia machine in which oxygen and sevoflurane were left running, identified several areas where CO2 absorbent desiccation may be of concern. These areas include infrequently used anesthesia machines at off-site locations and in the operating rooms where high fresh gas flows relative to body size are used (such as myringotomies and tube insertions) and for bronchoscopy ( Wu et al., 2004 ).

After an incidence of explosion during sevoflurane anesthesia for rigid bronchoscopy, Castro and others changed CO2 absorbers from KOH- and NaOH-based Baralyme to soda lime (less carbon monoxide production than Baralyme) or Ca(OH)2-based Amsorb ( Castro et al., 2004 ; Fatheree and Leighton, 2004 ). In an editorial in Anesthesiology that accompanied these case reports, Woehlck (2004)recommended the monitoring of canister temperature intraoperatively using a skin temperature probe, which is readily available in the operating room. Alternatively, one should consider using a Mapleson D (Bain or Jackson-Rees) circuit with a humidifier, which totally circumvents the problems related to the use of adult circle systems with CO2 absorbers, especially for infants and small children who are too small to produce enough exhaled CO2 to humidify adult circle systems.

There have been case reports of hepatitis possibly associated with the administration of sevoflurane in Japan, with the estimated incidence of less than 1:250,000. These reports included three children between the ages of 1 to 18 months, all of whom recovered from hepatic dysfunction, although several deaths were reported among adult patients. Hepatic microsomal induction and its potential for hepatotoxicity may be no greater than those associated with isoflurane ( Stoelting et al., 1987 ). Clinical case reports have noted malignant hyperthermia occurring with sevoflurane anesthesia in both adults and children and with or without the use of succinylcholine for intubation ( Otsuka et al., 1991 ; Ochiai et al., 1992 ; Maeda et al., 1997 ; Kinouchi et al., 2001 ).

Postanesthetic emergence and the time for attaining discharge criteria are significantly shorter with sevoflurane than with halothane, consequently requiring the administration of postoperative analgesics sooner ( Naito et al., 1991 ; Sarner et al., 1995 ). Approximately 40% to 50% of children experience emergence agitation depending on anesthetic technique and diagnostic criteria. Severe agitation often necessitates the use of sedatives and prolonging the recovery time ( Greenspun et al., 1994 ). Intraoperative use of analgesics without delaying emergence and recovery has met varying success in minimizing this untoward response ( Davis et al., 1999 ; Cohen et al., 2001 ).

Halothane

Although abandoned in Japan (within 6 months after introduction of sevoflurane in clinical use) and in most of Europe, halothane still offers some advantages over other agents, including excellent airway conditions and low cost. The relative lack of airway response (secretion, spasm) is a favorable characteristic of halothane, and, together with its bronchodilatory effect, halothane had been the drug of choice for inhaled anesthetics in the presence of airway pathology such as bronchopulmonary dysplasia or bronchial asthma. Pharyngeal reflexes are obtunded sufficiently by halothane to allow the use of an oral airway relatively early in induction. Its longer duration of action makes it a useful agent during procedures that require spontaneous respiration and instrumentation of the airway.

The MAC of halothane varies during infancy and childhood. It is highest in infants 1 to 6 months of age at 1.1%, measures 0.97% for children 1 to 2 years of age, and progressively decreases with increasing age until reaching adult values at around 10 years of age ( Gregory et al., 1969 ; Nicodemus et al., 1969 ). A subsequent study showed that the MAC of halothane in neonates (0.87%) is much lower than that in older infants ( Lerman et al., 1983 ).

As with other potent inhaled anesthetics, halothane depresses the neural respiratory drive and increases PCO2 progressively with increasing depth of anesthesia in children ( Graff et al., 1964 ; Wren et al., 1987 ). Spontaneous breathing under light halothane anesthesia increases alveolar dead space and wasted ventilation ( Hulse et al., 1984 ). It is not unusual to find the end-tidal PCO2 increased to 60 mm Hg and beyond in infants and children breathing spontaneously under halothane anesthesia. Although infants and children seem to tolerate mild to moderate hypercapnia, the extent of stress response to severe hypercapnia and respiratory acidosis in anesthetized infants and children is not known. It is therefore recommended that ventilation be assisted in infants and children as needed to keep end-tidal PCO2below 60 cm H2O, especially to avoid myocardial irritability (see later).

Halothane depresses stroke volume, cardiac output, and mean arterial blood pressure in proportion to the depth of anesthesia (Eger et al., 1970, 1971 [114] [115]), primarily because of a direct negative inotropic effect on the myocardium ( Goldberg, 1968 ). Barash and others (1978) found that a halothane concentration greater than 2% can result in severe cardiac depression. This effect can be attenuated or even reversed by intravenous atropine (0.02 mg/kg).

Cardiac arrhythmias, particularly premature ventricular contractions, are much more likely to occur with halothane than with isoflurane ( Rodrigo et al., 1986 ). Children, however, appear to tolerate epinephrine better than adults ( Melgrave, 1970 ; Wallbank, 1970 ). While the hazard of arrhythmias with epinephrine may be less in children than in adults, a smaller dose of epinephrine (up to 5 mcg/kg in less than 10 minutes) during halothane anesthesia is recommended as a precautionary measure. It is also important to maintain adequate alveolar ventilation to reduce the effects of hypercapnia and resultant increases in endogenous catecholamines on the myocardium ( Joas and Stevens, 1971 ).

Halothane, like other volatile anesthetics, causes cerebral vasodilation, increases cerebral blood flow and volume ( Wollman et al., 1964 ; Todd and Drummond, 1984 ), and, at high concentrations, abolishes autoregulation of cerebral blood flow in response to changes in arterial blood pressure ( Miletich et al., 1976 ). At concentrations greater than 1%, these agents increase intracranial pressure ( DiGiovanni et al., 1974 ). Such effects present a definite danger in patients with increased intracranial pressure. Use of an opioid and a muscle relaxant technique with mild hypocapnia is the method of choice in these patients.

Hepatitis secondary to exposure to halothane is rare in children. A few documented accounts exist of fatal posthalothane hepatic necrosis in pediatric patients ( Walton, 1986 ; Kenna et al., 1987 ). Retrospective studies have identified only a few cases of possible halothane-related hepatitis in children'1:82,000 halothane anesthesia procedures in one study ( Wark, 1983 ) and 1:>200,000 cases in the other ( Warner et al., 1984 ). In contrast, the estimated incidence in adults is between 1:6000 and 1:35,000 cases ( Summary of the National Halothane Study, 1966 ; Inman and Mushin, 1978 ; Brown, 1985). Thus, although children cannot be assumed to be immune to acute halothane hepatic necrosis, the incidence is extremely rare.

Isoflurane

Isoflurane is a stable, colorless liquid requiring no stabilizing agent. Isoflurane undergoes minimal biotransformation in vivo ( Holaday et al., 1975 ). It has an unpleasant, pungent odor and often causes cough and laryngospasm during inhalation induction when the concentration is increased too rapidly. Its blood-gas partition coefficient (1.4) is lower than that of halothane (2.4) but much higher than that of desflurane (0.42) and sevoflurane (0.66). As with halothane, the MAC of isoflurane is age dependent, ranging from 1.3% in preterm infants ( LeDez and Lerman, 1987 ) to 1.7% in infants 6 to 12 months of age and decreasing to 1.6% in children 1 to 5 years of age, compared with 1.2% in adults ( Cameron et al., 1984 ). Clinically, emergence from isoflurane anesthesia in children is similar to that from halothane despite the lower solubility of isoflurane. This apparent discrepancy between solubility and clinical effect may be related to different extents of biotransformation of these agents, which may affect their alveolar concentration and their washout during emergence ( Eger, 1984 ).

Isoflurane depresses ventilation progressively with increasing concentration but more so than does halothane at equipotent concentrations in adults as well as in children. The depression of minute ventilation and respiratory frequency with isoflurane in children is more than that with halothane, but the degree of tidal volume depression and hypercapnia is similar ( Wren et al., 1987 ). Because of its potent ventilatory depressant effect, isoflurane anesthesia requires controlled ventilation.

During isoflurane anesthesia, as with other volatile agents, systemic arterial blood pressure decreases progressively with increasing anesthetic depth. In contrast to halothane, however, clinical concentrations of isoflurane maintain cardiac output; hypotension is caused primarily by a reduction in peripheral vascular resistance ( Wolf et al., 1986 ). With minimal negative inotropic effect and decreased myocardial oxygen consumption, isoflurane may have a wider margin of safety than halothane. Isoflurane increases heart rate but does not precipitate arrhythmias. In adults, when exogenous epinephrine is used for subcutaneous hemostasis during isoflurane anesthesia, three times the dose that precipitates arrhythmias with halothane anesthesia is well tolerated.

Isoflurane causes more potentiation of pancuronium than does halothane ( Miller et al., 1972 ). Vecuronium is less affected by the choice of inhalation anesthetic ( Miller et al., 1984 ). The dose of nondepolarizing muscle relaxants should be adjusted accordingly.

Desflurane

Desflurane, a polyfluorinated methyl ethyl ether, has a blood-gas solubility coefficient (0.42) similar to that of nitrous oxide (0.47) ( Yasuda et al., 1989 ). As with other inhaled anesthetics, the MAC of desflurane is age dependent. Taylor and Lerman (1991) report that MAC in neonates is 9.2%, in infants 1 to 6 months of age is 9.4%, in infants 6 to 12 months of age is 9.9%, and then progressively decreases to 8.0% in older children. These differences are similar to those reported for halothane and isoflurane but smaller in magnitude. Desflurane appears to be similar to isoflurane in terms of negligible biodegradation, absence of myocardial sensitization to epinephrine, and effect on electroencephalography. Because of its lower boiling point (23.5°C), desflurane requires a heated pressurized vaporizer.

Desflurane has a strong pungent odor and is highly irritating to the airways ( Rampil et al., 1991 ; van Hemelrijck et al., 1991 ). Among infants and children undergoing inhalation induction with desflurane without premedication, severe laryngospasm occurred in 73% of patients ( Fisher and Zwass, 1992 ). Zwass and others (1992) concluded that desflurane should be limited in its use as an anesthetic for maintenance.

Desflurane causes dose-related respiratory depression, with the major effect being a reduction in tidal volume and minute ventilation, whereas the respiratory rate is increased ( Lockhart et al., 1991 ).Behforouz and others (1998) documented similar results in children when concentrations were greater than 1 MAC. The blunted ventilatory response to carbon dioxide is dose dependent and is qualitatively similar to that with isoflurane. Desflurane does not appear to have similar bronchodilating properties as halothane or sevoflurane ( Goff et al., 2000 ).

The cardiovascular effects of desflurane have been extensively studied in healthy adult volunteers ( Cahalan et al., 1991 ; Weiskopf et al., 1991a, 1991b [446] [447]). During steady-state anesthesia, desflurane provides a high degree of cardiovascular stability, although it markedly decreases systemic vascular resistance, leading to a significant decrease in systemic blood pressure without changes in cardiac output. Heart rate increases with desflurane in a dose-dependent manner. The myocardial depressant effect of desflurane is mild. In children, cardiovascular stability is well maintained if anesthesia is induced by sevoflurane, halothane, or intravenous agents. Bradycardia and arrhythmias are uncommon. At 1 MAC, heart rate and systolic blood pressure are decreased by 20% to 25% from awake controls ( Taylor and Lerman, 1991 ).

Because of its low blood-gas partition coefficient, desflurane should allow for a more rapid emergence and recovery than halothane, isoflurane, or even sevoflurane. Indeed, in two studies in adults, emergence from desflurane anesthesia was significantly faster than emergence from sevoflurane, especially after prolonged anesthesia ( Eger et al., 1998 ). The time to eye opening and orientation following anesthesia and the time to being ready for discharge were significantly shorter in the desflurane group ( Mahmoud et al., 2001 ). The use of desflurane in pediatric patients, however, is complicated by a high incidence (50% to 80%) of emergence agitation, often characterized by violent thrashing and inconsolability. This necessitates the use of sedation with opioids and/or hypnotic medications ( Davis et al., 1994 ). Moderate doses of fentanyl (average, 2.8 mcg/kg) have been successful in reducing the incidence of emergence agitation in pediatric patients, but postoperative vomiting incidence was high (75%) in this study ( Cohen et al., 2001 ). On the other hand, the original multicenter study of desflurane in children reported a significantly lower incidence of PONV in children induced with halothane who were switched over to desflurane than those with halothane alone (10% versus 26%) ( Zwass et al., 1992 ).

▪ INTRAVENOUS AGENTS

There has been an increased use of intravenous anesthesia in infants and children as a result of an improved understanding of pediatric pharmacokinetics and the introduction of new shorter-acting agents, such as propofol and remifentanil. In general, neonates and infants have larger volumes of distribution and decreased rates of elimination. The density of receptors, blood-brain barrier permeability, and pharmacodynamic effects of various drugs also vary greatly during the early postnatal period. These differences are discussed in greater detail in Chapter 6 (Pharmacology of Pediatric Anesthesia). In general, the newer opioids with shorter durations, as well as hypnotic and anesthetic agents, have all been shown to be safe and effective in infants and children. Their increased use has changed pediatric anesthetic practice from a classic single-agent inhalation anesthetic to a vast array of possible techniques that can be specifically tailored to the patient's needs.

Total intravenous anesthesia (TIVA) offers both advantages (rapid recovery, cleaner environment, and portability) and disadvantages (awareness, vagal reflexes, movement, and need for supplemental analgesia) for the pediatric patient. The cost of TIVA compared with an inhalation technique, which is an important consideration, is difficult to assess. Often, in the pediatric age group, an inhalation induction precedes TIVA, which negates some of its advantages. Of the available agents, propofol has been the most widely adopted.

Propofol is a short-acting intravenous anesthetic with high lipid solubility and a short elimination half-life, can be used as an induction agent as well as a maintenance anesthetic when given as a continuous infusion. Propofol is increasingly the agent of choice for general anesthesia and sedation in and outside of the operating room settings. Often, it is the sole anesthetic agent used in magnetic resonance imaging (MRI), endoscopy, bronchoscopy, and “painful procedure” suites ( Keengwe et al., 1999 ; Elitsur et al., 2000 ; Jayabose et al., 2001 ).

Hannallah and others (1994) demonstrated that children have higher dose requirements than adults. With a background of 60% nitrous oxide, pediatric patients require a dose of approximately 250 to 300 mcg/kg per min to prevent movement in response to surgical stimulation, and a dose of approximately 150 to 200 mcg/kg per min to stabilize the hemodynamic indices of those who received muscle relaxants. The higher dose requirement in children may be secondary to a 50% increase in the volume of distribution ( Marsh et al., 1991 ) and a shorter elimination half-life ( Valtonen et al., 1989 ). A shorter recovery period and decreased incidence of PONV have been described in children receiving propofol infusions compared with those receiving halothane anesthetics ( Marsh et al., 1991 ; Watcha et al., 1991 ; Hannallah et al., 1994 ). Watcha and others (1991) found the incidence of nausea and vomiting to be even lower when nitrous oxide was not administered. Emergence times are reduced in infants and children when propofol is used as the induction agent for short procedures. Schrum and others (1994) found this to be especially true of infants aged 1 to 6 months. Cohen and others (2003) found in patients aged 2 to 36 months that propofol at 200 mcg/kg with analgesic supplementation had the same hemodynamic, recovery, and antiemetic profile as sevoflurane. Emergence delirium has not been described as occurring after the use of propofol in children.

Similar to adults, hypotension and bradycardia are associated with the use of propofol. These responses are accentuated by the concurrent use of opioids and attenuated with the use of an anticholinergic drug, such as atropine. Pain during injection, possible allergic reactions, and the need for intravenous access are additional problems related to propofol use, especially in children who have distinct fear and dislike of a needle stick. These disadvantages can usually be easily overcome by choosing inhalation induction or using a small dose of thiopental or lidocaine before or mixed with propofol to abolish or minimize pain at the injection site. Propofol is an excellent agent for the maintenance of anesthesia that permits rapid recovery not associated with agitation and disorientation on emergence and decreased PONV.

▪ ADJUVANT AGENTS

There are numerous agents available to the pediatric anesthesiologist that can be incorporated into the maintenance anesthetic for both intraoperative and postoperative effects. Opioids and other analgesics are discussed in detail in Chapter 6 (Pharmacology of Pediatric Anesthesia). Reducing the amount of inhaled agent required during the anesthetic, a smooth, calm emergence, a comfortable patient, and appreciative family are just some of the benefits. Much discussion has been addressed to the issue of preemptive analgesia. Although, theoretically, preventing the reception and/or transmission of noxious stimuli in an organism should reduce the overall experience, the timing of analgesics, blocks, and paraxial opioids (i.e., presurgical versus postsurgical) has not been shown to effect acute postoperative pain measurements. Moiniche and others (2002) performed an extensive review of the available literature and found no benefit to pretreating patients undergoing surgical procedures. Studies in children that examined preemptive analgesia using axillary blocks ( Altintas et al., 2000 ) or new-generation nonsteroidal anti-inflammatory drugs (NSAIDs) ( Kokki and Salomen, 2002 ) for tonsillectomy also failed to show any difference in postoperative scores or analgesic requirements. Preemptive analgesia, however, may play an important role in preventing chronic pain syndromes.

Opioids

Opioids and their synthetic analogs have been widely used for infants and children as adjuncts to inhaled anesthetics, as the primary or major anesthetic component for “balanced anesthesia” techniques, or as analgesics for postoperative pain. Morphine, fentanyl, and, more recently, remifentanil are the opioids most commonly used in pediatric anesthesia. The dosage used varies a great deal, depending on the purpose and plan for postoperative management (spontaneous breathing versus mechanical ventilation) ( Table 11-4 ).


TABLE 11-4   -- Intravenous dosage of opioids in children

Drug

As Major Anesthetic

As Adjunct

As Postoperative Analgesic

Morphine

2 to 3 mg/kg

0.05 to 0.1 mg/kg per hr

0.05 to 0.1 mg/kg

Fentanyl

50 to 100 mcg/kg

1 to 3 mcg/kg per hr

1 to 2 mcg/kg

Sufentanil

10 to 15 mcg/kg

0.1 to 0.3 mcg/kg per hr

Alfentanil

150 to 200 mcg/kg

1 to 3 mcg/kg per min

Remifentanil

0.2 to 1.0 mcg/kg per min

0.1 to 0.4 mcg/kg per min

Hydromorphone

5 to 10 mcg/kg

3 to 5 mcg/kg per hr

3 to 5 mcg/kg

 

 

Morphine is a long-acting, hydrophilic analgesic that initially appeared to be unsafe in infants. Kupferberg and Way (1963) and Way and others (1965) demonstrated increased sensitivity to morphine in neonatal rats and humans, respectively. An increased permeability of the infant blood-brain barrier, which was suggested by both groups, is supported by evidence cited by Cook and Marcy (1988) . Lynn and Slattery (1987) described lower clearance and longer elimination half-life in neonates. Because of greater drug availability to the central nervous system and longer pharmacologic half-life, morphine dosing in the newborn should be reduced in amount and given at increased intervals. Morphine can be used safely in older infants and children who have pharmacokinetics similar to those of adults. In high doses, morphine can cause hypotension as a result of bradycardia, vasodilation, and histamine release as well as hypertension ( Conahan et al., 1973 ; Moss and Roscow, 1983 ). Urticaria (frequent) and bronchospasm (rare) are also described. As with other opioids, morphine may cause nausea and vomiting postoperatively. Because of its longer duration of action and euphoric effect, however, morphine is commonly used for inpatients who require postoperative analgesia and sedation.

Hydromorphone is a hydrogenated ketone derivative of morphine that is 7 to 10 times more potent. Hydrophilic in nature, its time to onset and duration of action are shorter than those of morphine. In addition, it manifests less sedation, nausea, and vomiting but is still capable of inducing pronounced respiratory depression. Both morphine and hydromorphone are widely used in patient controlled and epidural analgesia.

Meperidine is about one tenth as potent as morphine. It does not have the same marked increased narcotic effect in the newborn as morphine ( Way et al., 1965 ). In newborn animals, the plasma half-life of meperidine is about twice that of the adult, but because it is lipophilic, its active plasma level may not differ in infants ( Mirkin, 1970 ). In older infants and children, meperidine offers the same advantages as morphine. Histamine release is also associated with its use. Relatively small doses of meperidine (≤0.5 mg/kg) continue to be a reliable treatment of postanesthesia shivering ( Macintyre et al., 1987 ; Tsai and Chu, 2001 ).

Fentanyl is a lipophilic synthetic opioid with a relatively short duration of action, 1 to 2 hours, but a plasma half-life similar to that of morphine. It is about 100 times as potent as morphine. From 20 to 50 mcg/kg is suggested for general anesthesia in neonates and infants for cardiac surgery, but there is great variability found in kinetic studies. Koehntop and others (1986) measured decreased elimination times and increased volumes of distribution in neonates, whereas Singleton and others (1987) described values similar to those in older infants and children. Hertzka and others (1989) demonstrated, in infants older than 3 months, no increased risk of respiratory depression, but Koehntop and others (1986) found the need for postoperative ventilatory support in some neonates and evidence of rebound in fentanyl serum levels. Fentanyl appears to be safe in infants and children as a primary anesthetic agent and as a supplementary analgesic during an inhalation anesthetic. Pharmacokinetic studies of fentanyl in neonates have demonstrated a highly variable volume of distribution, rate of clearance, and half-life. Because the effect is less predictable in neonates and premature infants, postoperative ventilatory support should be considered.

Two common side effects of high-dose fentanyl are bradycardia and chest wall rigidity. Bradycardia is typically beneficial in adults, because they rarely experience hemodynamic changes with these doses, even with poor ventricular function ( Stanley and Webster, 1978 ). However, bradycardia is undesirable in infants, who are unable to accommodate the increased preload by increasing stroke volume. Vagolytic agents or muscle relaxants that cause tachycardia should be administered concurrently. Muscle relaxants also reduce the difficulty of mask-bag ventilation experienced with chest wall rigidity. If mask-bag ventilation is planned, then fentanyl doses should be limited to 2 to 3 mcg/kg.

Fentanyl is ideal for patients needing short-term anesthesia and analgesia. It is useful for patients who require rapid recovery to baseline ventilatory function and respiratory drive, such as patients having same-day surgery, neurosurgical procedures, and airway instrumentation. Unless administered as a continuous infusion, fentanyl is not the drug of choice for patients requiring extended periods of analgesia.

Sufentanil is about 1000 times as potent as morphine and has an elimination half-life of approximately half that of fentanyl. The neonatal pharmacokinetics profile is similar to that of fentanyl (Davis et al., 1987a, 1987b [90] [91]). Bradycardia is not as prevalent and can be minimized with muscle relaxants that cause tachycardia ( Hickey and Hansen, 1984 ).

Alfentanil is about 25 to 100 times as potent as morphine, with a small volume of distribution and an elimination half-life about one third that of fentanyl. Davis and others (1989) found that in neonates, alfentanil, like fentanyl, has a prolonged elimination time and increased volume of distribution that markedly prolong its pharmacologic half-life. Alfentanil has great patient-to-patient variability, and its effect can be difficult to predict. Alfentanil is associated with a high incidence of PONV.

Remifentanil is an ultrashort-acting opioid with an elimination half-life about one sixth that of fentanyl ( Egan et al., 1993 ; Westmoreland et al., 1993 ). Davis and others (2000) describe an infusion at 0.25 mcg/kg per min as being effective for general anesthesia for children undergoing adenotonsillectomy. Rapid emergence and the need for supplementary postoperative analgesia were also noted. Ross and others (2001) found a consistent pharmacokinetic profile of remifentanil in the pediatric population. Infants had the largest volume of distribution and the most rapid clearance, but the elimination half-life (3.4 to 5.7 minutes) was the same for all age groups. Pinsker and Carrol (1999) found in children undergoing dental restoration a low incidence of PONV in those patients anesthetized with remifentanil. When used for general anesthesia in premature and full-term infants undergoing pyloromyotomy, remifentanil provided safe and stable intraoperative and postoperative conditions ( Davis et al., 2001 ). No new-onset postoperative apnea was reported. Remifentanil, with predictable pharmacokinetic and hemodynamic effects, is extremely well suited for intraoperative anesthesia and analgesia in infants and children but typically requires analgesic supplementation for emergence and recovery.

Methadone is a long-acting synthetic opioid with an elimination half-life of about 35 hours. It is equipotent to morphine when given intravenously. It can be administered as part of a general anesthetic for prolonged surgical procedures (such as anteroposterior spinal fusions) and when protracted postoperative pain relief is anticipated.

Nonsteroidal Anti-inflammatory Drugs

NSAIDs have no known role in the maintenance of anesthesia but may be used intraoperatively to decrease postoperative pain and discomfort. Intraoperative treatment with ketorolac has been shown to be effective in decreasing postoperative pain and the incidence of nausea and vomiting associated with opioid use ( Watcha et al., 1992 ; Cohen et al., 1993 ; Munro et al., 1994 ). Unfortunately, ketorolac's interference with platelet function has been reported to increase the risk of bleeding, especially in surgeries with an increased risk of bleeding, such as tonsillectomy ( Gunter et al., 1995 ; Splinter et al., 1996 ). Ketorolac should also be avoided in patients with compromised renal and hepatic function.

Cyclooxygenase-2 (COX-2) inhibitors offer the advantage of having minimal to no effect on renal, gastrointestinal, and platelet function. By selectively blocking prostaglandin production in response to inflammation, this group of drugs is more selective in treating pain. In a review, parecoxib (40 mg PO) was found to be more effective than placebo for pain after laparoscopic cholecystectomy in adults (Joshi et al., 2004 ). Rofecoxib (50 mg PO) was also found to be effective for postoperative pain relief after outpatient inguinal herniorrhaphy in adults ( Ma et al., 2004 ). Romsing and Moiniche (2004)reported significant decreases in postoperative pain in 33 studies, including 62 comparisons of four COX-2 inhibitors with placebo. However, rofecoxib, a COX-2 inhibitor, given orally, did not decrease the postoperative use of opioids compared with placebo in children following adenotonsillectomies, although there was no increase in postoperative bleeding ( Sheeran et al., 2004 ). An intravenous formulation, parecoxib, is available and a preinduction dose of 40 mg intravenously was reported to be more effective compared with placebo ( Gan et al., 2004 ; Joshi et al., 2004 ) but not as effective as ketorolac (30 mg IV) after laparoscopic procedures in adult patients ( Ng et al., 2004 ). The use of COX-2 inhibitors is being re-evaluated at the time of this writing due to increased mortalities reported among long-term users, in high doses ( Lenzer, 2005 ).

Acetaminophen has for many years been given per rectum intraoperatively to supplement opioid analgesia. Birmingham and others (1997, 2001) [40] [39] demonstrated that doses of 40 mg/kg and an onset time of 2 hours were necessary to achieve antipyretic levels with this mode. They also reported marked interpatient variability. It should be noted that these one-time doses are at near toxic levels and subsequent doses should be modified.

Hypnotics and Sedatives

Benzodiazepines, commonly used for premedication and preinduction medication, can be used intraoperatively to ensure amnesia during “balanced anesthetics” and to prevent emergence delirium. Diazepam has a slower elimination time in neonates ( Morselli et al., 1974 ) and greater blood-brain barrier penetration in newborn rodents ( Marcucci et al., 1973 ). The shorter serum half-life of midazolam makes it better suited for intraoperative use. Davis and others (1995b) found that intranasal midazolam premedication did not prolong recovery from ultrashort procedures, such as bilateral myringotomies.

Antiemetics

The introduction of a serotonin receptor (5-HT3) antagonist has markedly improved the anesthesiologist's ability to decrease the incidence of and treat PONV ( Litman, Wu, and Catanzaro, 1994 ; Patel et al., 1997 ; Khalil et al., 1996 ). Ondansetron, compared with droperidol (the most effective antiemetic at that time), was shown to be equally effective with a minimum of side effects causing no delay in emergence or discharge ( Davis et al., 1995a ; Splinter et al., 1995 ). The half-life of ondansetron in infants and children under 2 years of age is 50% greater than in adults, so this age group should not require repeat dosing in the PACU. Other 5-HT3 antagonists, granisetron and tropisetron, have been shown to be equally efficacious ( Fuji et al., 1996 ; Ang et al., 1998 ).

Broadman and others (1990) found metoclopramide (0.15 mg/kg) to be an effective antiemetic in a similar group of pediatric patients. Its effects may be both central, where it antagonizes dopamine receptors, and peripheral, where it increases gastroesophageal sphincter tone and gastric emptying ( Taylor, 1985 ). Other agents with demonstrated effectiveness include dimenhydrinate at 0.5 mg/kg (Kranke et al., 2002 ) or perphenazine at 70 mcg/kg ( Splinter et al., 1998 ).

Dexamethasone has also been shown to be effective in reducing the incidence of vomiting in children recovering from tonsillectomy ( Splinter and Roberts, 1996 ; Pappas et al., 1998 ). In addition, dexamethasone appears to decrease postoperative pain in this patient population ( Elhakim et al., 2003 ). In a meta-analysis of antiemetic studies, Henzi and others (2000) found that dexamethasone is effective for a prolonged period of time. They concluded that the best available treatment for patients at increased risk for PONV is a combination of a 5-HT3 antagonist and dexamethasone.

Muscle Relaxants

Muscle relaxants are discussed in greater detail in Chapter 6 (Pharmacology of Pediatric Anesthesia). The following overview briefly discusses the advantages and disadvantages of the different agents available. Table 11-5 summarizes recommended doses, duration, and sites of metabolism.


TABLE 11-5   -- Intravenous doses of muscle relaxants in children

 

MAINTENANCE

ED95 (mg/kg)

Drug

Intubation (mg/kg)

Bolus (mg/kg)

Continuous Infusion (mcg/kg/m)

Infants

Children

Mivacurium

0.2 to 0.3

0.1

10 to 20

0.1

0.1

Cisatracurium

0.15

0.1

1 to 5

0.05

0.05

Vecuronium

0.05 to 0.1

0.025

1

0.024

0.026

Rocuronium

0.8 to 1.0

0.3 to 0.5

15

0.2

0.3

Pancuronium

0.1

0.5

0.05

0.05

Pipecuronium

0.1

0.035

0.05

 

 

Succinylcholine is a depolarizing, fast- and short-acting muscle relaxant that offers important advantages but has important disadvantages compared with other available muscle relaxants. Succinylcholine is still the only muscle relaxant that dependably creates muscle relaxation for intubation conditions within 1 minute. It is also the only relaxant available approved for intramuscular use. Meakin and others (1989) recommend that 3 mg/kg in infants and 2 mg/kg in children intravenously dependably produce the profound degree of paralysis needed for ET intubation. Atropine (0.02 mg/kg) should always be infused before the use of succinylcholine to prevent bradyarrhythmias. Liu and others (1981) recommend a dose of 4 mg/kg for intramuscular use for an onset time of 30 seconds to relieve laryngospasm and 3 to 4 minutes to achieve intubating conditions. Serious complications of succinylcholine include hyperkalemia in patients with neuromuscular disorders and burns, dysrhythmias, muscle rigidity, masseter spasm, postoperative myalgias, and triggering of malignant hyperthermia in susceptible patients. Due to these serious complications, the use of succinylcholine in children should be limited to emergency situations.

Mivacurium is a short-acting nondepolarizing muscle relaxant-with a structure similar to that of d-tubocurarine and with a fairly rapid onset of action ( Sarner et al., 1989 ). It is metabolized by plasma cholinesterase but more slowly than is succinylcholine. If needed, its neuromuscular effects can be satisfactorily antagonized by edrophonium or neostigmine. Histamine release and patient-to-patient variability can be seen with its use, particularly in pediatric patients (Gronert et al., 1993a, 1993b [159] [160]; Gronert and Brandom, 1994 ). Brandom and others (1998) described intubating conditions to be acceptable 90 seconds after a dose of 0.3 mg/kg. Infants were found to require a higher rate than adults for mivacurium infusion secondary to greater clearance (Marakakis et al., 1998).

Vecuronium is an intermediate-acting steroidal nondepolarizing muscle relaxant similar to pancuronium in structure. The vagolytic response and hemodynamic alterations do not occur with its use. Vecuronium in children has a higher ED95 than in infants and adults ( Meretoja et al., 1988 ). At an equipotent dose (2 × ED95), the duration of its effect is much more prolonged in infants (73 minutes) compared with in children (35 minutes) or adults (53 minutes) ( Meretoja, 1989 ). Because its duration of action is similar to that of pancuronium in infants, vecuronium cannot be considered as an intermediate-acting muscle relaxant for this age group.

Rocuronium is an intermediate-acting steroidal nondepolarizing agent similar in structure to vecuronium but with about one-tenth the potency. It produces a more rapid onset of paralysis than other nondepolarizing muscle relaxants. Woelfel and others (1992) described, at a dose of 0.6 mg/kg, that onset of maximal block was 1.3 (± 0.2) minutes in children 1 to 5 years of age and the time to recovery (T25) was 26.7 ± 1.9 minutes. Increases in heart rate have been reported with its use. Meretoja and others (1995) found that the ED95 of rocuronium in infants was considerably less than that in adults and children but that the recovery times were similar in all age groups. In lightly anesthetized patients, intravenous injection is associated with pain and tachycardia ( Shevchenko Y et al., 1999 ).

Cisatracurium, an intermediate nondepolarizing agent, is one of the 10 optical and geometric isomers (1R-isomer) of atracurium with four times the potency but a slower onset of action ( Wastila et al., 1996; Brandom et al., 1998 ). Taivainen and others (2000) found at a dose of 0.15 mg/kg that onset of maximal block was 2 ± 0.8 and 3 ± 1.2 minutes in infants and children, respectively. Time to recovery (T25) was longer in infants (43.3 ± 6.2 minutes) than in older children (36.0 ± 5.4 minutes). cis-Atracurium under goes hydrolysis at body temperature and physiologic pH (Hoffmann elimination), but this accounts for about only 23% of its elimination. Histamine is not an issue with this isomer, and hemodynamic stability is reported with its use.

Pancuronium is a long-acting steroidal nondepolarizing agent and is about 5 to 10 times more potent than d-tubocurarine with a comparative duration of action. Pancuronium causes tachycardia by blocking vagal activity at the ganglionic level and by releasing norepinephrine. The tachycardia may be advantageous in pediatric patients, who often demonstrate decreased heart rates and blood pressures caused by inhaled agents or synthetic opioids. Pancuronium is in part metabolized in the liver and the kidney excretes the rest; its effect is prolonged in patients with hepatic or renal failure.

Pipecuronium is an analogue of pancuronium with minimal or no cardiovascular effects. The duration of neuromuscular action is similar to that of pancuronium. The effective dose (ED95) of pipecuronium in children with nitrous oxide–halothane anesthesia is 50 mcg/kg, and the dose during nitrous oxide–fentanyl anesthesia is 80 mcg/kg. The ED95 in infants under nitrous oxide–halothane anesthesia is only 35 mcg/kg ( Pittet et al., 1989 ; Sarner et al., 1990 ). Pipecuronium is largely excreted by the kidneys.

▪ REGIONAL ANESTHESIA

The reintroduction and adaptation of regional anesthetic techniques in the 1980s have helped advance pediatric pain management. The caudal approach is the simplest and most popular, but other methods, including peripheral nerve blocks, epidural anesthesia, and neuroaxial opioid use, have also become common practice. As in adults, the treatment course can be extended with the placement of catheters. Extensive experience with these methods intraoperatively and postoperatively has shown their efficacy and safety. The various regional analgesia techniques and the choice and dosage of local anesthetics and opioids for regional analgesia are detailed in Chapter 13 (Pain Management in Infants and Children). The volumes (and doses) of local anesthetics recommended for various regional blocks are summarized in Table 11-6 .


TABLE 11-6   -- Volumes of local anesthetic solutions for peripheral nerve blocks and regional anesthesia in children

Block

Volume (mL/kg)

Axillary

0.2 to 0.5[*]

Interscalene

0.33[*]

Sciatic

0.15 to 0.2[*]

Femoral

0.5[*]

Intravenous

0.5 to 10[†]

Caudal

0.5 to 1.0[‡]

Intrapleural (infusion)

0.5 (per hr)[§]

*

Broadman and Rice, 1988.

Yaster and Maxwell, 1989 .

Armitage, 1979 .

§

McIlvaine and others, 1989.

 

Caudal Anesthesia

Caudal blocks are most often used as an adjunct to general anesthesia and for postoperative analgesia for surgical procedures involving the lower abdomen, pelvis, or lower extremities. The combination of inhalation anesthesia and regional block allows the anesthesiologist to lower anesthetic concentrations and facilitate postoperative emergence from general anesthesia. The caudal block is easily performed with minimal associated complications, such as dural puncture and intravascular injection (Dalens and Hasnaoui, 1989 ). Anatomical features that contribute to these occurrences are the caudal position of the dural sac in infants (S3), the high degree of vascularity of the region, and the development of the sacral fat pad in school-aged children. Awareness of these factors should reduce the risk of untoward events.

A caudal block in infants and children is most often performed after the induction of general anesthesia. After the airway is secured with an ET tube or the insertion of an oral airway, the child is turned to a lateral decubitus position and the sacral hiatus is identified, cleaned, and prepared. (If LMA is chosen for airway maintenance, it is safer to wait until the caudal block is completed, the patient turned back to the supine position, and the stomach emptied with a gastric tube before LMA is inserted. This is because LMA in infants and children tends to dislodge with the changes in the neck or body position.) A short beveled needle (22 gauge) is inserted through the sacrococcygeal ligament and advanced into the caudal space. Although different needle types and sizes are recommended ( Broadman and Rice, 1988; Yaster and Maxwell, 1989 ), the only difference in outcome observed is that shorter needles result in fewer inadvertent intrathecal and intravascular injections. The syringe is withdrawn before injecting to make sure that an intravascular or intrathecal space is not inadvertently entered. Tobias (2001) reviewed the available literature on the efficacy of test doses, with epinephrine-containing solutions, for detecting the signs and symptoms of intravascular injection and concluded that they may be of limited benefit depending on anesthetic technique and previous use of anticholinergic medications.

Bupivacaine is the most widely used local anesthetic because of its relative safety and longer duration of action. Takasaki and colleagues (1977) recommended a volume of 0.056 mL/kg per segment, whereas Armitage (1979) uses 0.5 mL/kg for a sacral or saddle block and 1.0 mL/kg for an upper abdominal blockade. The optimal concentration of bupivacaine is one that provides adequate analgesia without producing postoperative motor blockade of the lower extremities ( Wolf et al., 1990 ). Both 0.125% and 0.175% of bupivacaine have been shown to be appropriate concentrations, whereas 0.25% bupivacaine may occasionally produce a motor blockade in the lower extremities ( Gunter et al., 1991 ). The (S)-isomer of bupivacaine, levo-bupivacaine, which has less cardiac toxicity with similar local anesthetic properties, may afford some benefit in at risk patients ( Ivani et al., 2002 ).

Ropivacaine, a congener of bupivacaine with less toxicity and, at concentrations of 0.2%, with a lower incidence of motor block ( Khalil, 1999 ), is gaining wider use. In infants, the incidence of cardiac arrhythmias, systemic absorption, and serum-free fraction are all lower compared with bupivacaine ( Hansen et al., 2001 ; Karmakar et al., 2002 ). Hansen and others (2000) described a similar safety profile when ropivacaine was used in epidural infusions. These properties make ropivacaine the drug of choice when anticipating prolonged exposure in neonates or in patients with impaired metabolisms.

Other medications with analgesic properties, injected into the caudal space with and without local anesthetics, have been shown to be efficacious. Opioids, clonidine, and ketamine have been used with varying success and are discussed in greater detail in Chapters 13 and 14 (Pain Management and Pediatric Regional Anesthesia).

Urinary retention and the masking of essential diagnostic symptoms of surgical complications have been cited as postoperative concerns. Urinary retention occurs in approximately 10% of patients and is typically short lived ( Yaster and Maxwell, 1989 ). Postoperative emptying of the urinary bladder along with parental education and reassurance should minimize this problem. A report describing an unrecognized compartment syndrome in a patient who received epidural anesthesia for an orthopedic procedure has raised concerns ( Strecker et al., 1986 ). It was thought that the absence of pain prolonged the time to diagnosis. The administration of caudal anesthesia must be selective, but, more important, careful postoperative monitoring and nursing care should minimize the incidence of such complications.

Field and Nerve Blocks

Other regional and field block techniques have also been used as adjuncts to general anesthesia and to manage postoperative pain. Compared with caudal anesthesia, ilioinguinal-hypogastric nerve block, wound infiltration, local anesthesia “splash,” dorsal penile nerve block, and subcutaneous ring block have all been shown to be equally effective for the chosen surgical procedure ( Yeoman et al., 1983 ;Cross and Barrett, 1987 ; Hannallah et al., 1987 ; Fell et al., 1988 ; Casey et al., 1990 ). These techniques are applicable to orchiopexy, herniorrhaphy, hypospadias repair, and circumcision.

Peripheral nerve blocks can also supply analgesia for the upper and lower extremities. Axillary, interscalene, sciatic, and femoral nerve blocks have all been described. Recommended volumes appear inTable 11-6 . The blocks can often be easily performed in young children, who tend to have better defined anatomy and landmarks. In older children, the use of a nerve stimulator can be helpful ( Bosenberg et al., 2002 ). Toxic doses of local anesthetics can be avoided by using diluted solutions and solutions containing epinephrine ( Berde, 1989 ). Head and face nerve blocks can also reduce the need for opioid analgesia and so reduce the incidence of nausea and vomiting ( Suresh et al., 2002 ).

Epidural Anesthesia

Epidural block, by either a single injection, repeated injections, or continuous infusion via catheter, has been described in children ( Dalens et al., 1986 ; Desparmet et al., 1987 : Tusi et al., 2002 ). Bupivacaine (0.125% to 0.25%) and ropivacaine (0.2%) are recommended for both methods. A continuous infusion through a lumbar catheter at a rate of 0.3 mL/kg per hr maintains an analgesic level between T10 and L1. Although traditionally described from the lumbar approach, epidural analgesia can also be performed in children at the thoracic level ( Bosenberg et al., 1988 ). Needle placement at these locations tends to be technically more challenging, with an increased risk of complications in small infants. Because of these difficulties, thoracic epidural blocks should be performed only by anesthesiologists who are experienced in their use and reserved for children undergoing a surgical procedure in the thoracic area or upper abdominal area that is associated with considerable postoperative pain (see Chapter 14 , Regional Anesthesia).

Caudal catheters can be inserted with relative ease and minimal risk, similar to single-injection techniques previously described. A Touhy needle is inserted into the caudal space, and an appropriately sized catheter is advanced through it. The catheters are frequently styletted to facilitate direct advancement to higher levels with decreased risk of accidental placement in the nerve root sheath. The relatively short and straight path found in infants also minimizes complications. More rostral positioning of the catheter allows for improved postoperative pain management for upper abdominal procedures and thoracotomies.

Epidural Opioids

As described in adults, extremely effective analgesia can be achieved by injecting opioids into the epidural space ( Jensen, 1981 ; Shapiro et al., 1984 ; Attia et al., 1986 ; Rosen and Rosen, 1989 ). Activation of opioid receptors in the dorsal horn of the spinal cord produces regional analgesia without the discomfort or danger of sympathetic, sensory, or motor blockade. Respiratory depression is a major complication requiring careful dosing and observation. Other side effects, including pruritus, nausea, vomiting, and urinary retention, can be prevented by using smaller doses of opioids, and are relatively easily managed by a small dose (0.5 to 1.0 mcg/kg) of naloxone. Nalbuphine 50 mcg/kg or 60 mcg/kg per hr has been shown to be effective in treating epidural morphine side effects without attenuating analgesia ( Wang et al., 1998 ).

Various techniques, opioids, and opioid-local anesthetic combinations have been described. Preservative-free morphine (30 to 70 mcg/kg caudally and 50 mcg/kg epidurally) has resulted in effective and safe analgesia in children after various surgical procedures ( Jensen, 1981 ; Krane et al., 1989 ; Rosen and Rosen, 1989 ; Rash et al., 1990 ; Wolf et al., 1990 ; Irving et al., 1993 ). Morphine's hydrophilic nature reduces its absorption from the epidural space, resulting in delayed onset of effect, decreased systemic uptake, rostral spread, and prolonged duration of action. The delayed onset (20 to 40 minutes) and duration of analgesia (mean range of 15 to 20 hours) in children are similar to those in adults, although the plasma half-life is shorter in children ( Attia et al., 1986 ; Rash et al., 1990 ). Adequate monitoring of respiratory rate and depth and level of sedation is essential because serious respiratory depression has been reported in children with a higher dose (100 mcg/kg) of caudal morphine ( Krane, 1988 ). Even at a recommended lower dose (50 mcg/kg) without clinical respiratory depression or apnea, ventilatory response to carbon dioxide is reported to be depressed throughout the duration of analgesia, independent of plasma morphine levels ( Attia et al., 1986 ).

In contrast to morphine, fentanyl, sufentanil, and hydromorphone are lipophilic and have a more rapid onset, greater systemic absorption, shorter duration of action, and limited epidural redistribution (Dalens et al., 1986 ; Benlabed et al., 1987 ). These drugs are appropriate for rapid treatment of pain and are better suited for continuous infusions. Alone or in combination with diluted local anesthetics, their site of action is limited to the general location of the catheter tip placement.

Subarachnoid Opioids

Subarachnoid injection of morphine has also been studied ( Dalens and Tanguy, 1988 ). The efficacy, side effects, and duration of analgesia with this technique are similar to those of epidural instillation with doses of 10 to 20 mcg/kg ( Krechel and Helikson, 1993 ). Respiratory depression may be more severe. Intrathecal opioids are often restricted to intraoperative and postoperative management of patients undergoing extremely painful surgical procedures, such as scoliosis repair and open heart surgery. Delayed respiratory depression may occur, necessitating monitoring and observation in a more closely staffed setting ( Jones et al., 1984 ; Nichols et al., 1993 ).

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Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.

Copyright © 2005 Mosby, An Imprint of Elsevier

▪ EMERGENCE AND EXTUBATION

▪ EMERGENCE

Emergence from anesthesia begins as soon as the anesthesiologist stops the administration of anesthetic agents. In current practice, general anesthesia is often produced with a combination of inhaled or intravenous anesthetics, muscle relaxants, intravenous opioids and/or hypnotics, and, sometimes, regional nerve blocks. The presence of diverse agents makes the process of emergence more complex than after the use of a single agent. To facilitate prompt awakening and tracheal extubation, the anesthesiologist must anticipate, with reasonable accuracy, the conclusion of the surgical procedure. This allows for appropriate tapering of the concentration of inhaled anesthetics and decreasing or withholding intravenous agents, including muscle relaxants, before the procedure ends.

Normal recovery from anesthesia begins in the operating room with the reestablishment of adequate spontaneous breathing and extubation of the trachea. Discontinuation of the volatile agent, increasing the oxygen–nitrous oxide, oxygen, or oxygen-air mixture fresh gas flow, and moderately increasing the rate of manually controlled ventilation increase the pulmonary venous-to-alveolar concentration gradient of an inhaled anesthetic and facilitate the elimination of residual inhaled anesthetic, whereas excessive hyperventilation causes cerebral vasoconstriction and impedes the elimination of anesthetic from the brain. Furthermore, excessive hyperventilation depletes the carbon dioxide stores in the body tissues, delaying the onset of spontaneous breathing.

The less-soluble volatile anesthetics, such as desflurane and sevoflurane, may produce more rapid emergence, as discussed earlier, but with careful anticipation and appropriate timing, all patients anesthetized with various agents and techniques should emerge when planned. The timing for the discontinuation of intravenous medications must be determined by considering each agent's pharmacokinetics. Infants have longer elimination half-lives for many agents and thus require earlier termination of agents. Nitrous oxide (or, alternatively, sevoflurane or desflurane) is often continued during this period, to smooth the emergence from general anesthesia to wakefulness. Because of its low solubility and pleasant, minimal odor, nitrous oxide is an ideal transitional agent.

A smooth emergence is achieved by anticipating the patient's response to the pain caused by the surgical procedure and the disorientation caused by the anesthetic agents or the sudden wakefulness. The analgesic action of opioids and regional anesthesia and the sedative effects of opioids and hypnotics may help reduce agitation on emergence. If patient status or surgical procedure did not allow for the intraoperative use of these agents, they should be considered before emergence.

As the anesthetics are curtailed, the anesthesiologist observes the rate and pattern of spontaneous breathing. A rapid respiratory rate may be seen during stage 2 (the excitement phase) or in a patient with inadequate analgesia. Synchronous contraction of the intercostal muscles and diaphragm (that is, the upper part of the chest expands, as opposed to sinking paradoxically, during inspiration) is important because the intercostal muscles are more sensitive to inhaled anesthetics ( Tusiewicz et al., 1977 ; Nishino et al., 1984, 1985 [316] [317]; Ochiai et al., 1989 ). Paradoxical movement of the thorax and abdomen (thoracoabdominal asynchrony) may indicate incomplete recovery from general anesthesia or residual paralysis. The paradoxical breathing pattern may also indicate partial or complete upper airway obstruction as a result of relaxation of the upper airway muscles, which are most sensitive to the depressant effect of anesthetics and sedatives, especially in young infants (Ochiai et al., 1989, 1992 [319] [319]). Careful and continuous auscultation with a precordial stethoscope is extremely important during the period of emergence.

Recovery From Neuromuscular Blockade

Recovery from neuromuscular relaxation can be monitored by means of peripheral nerve stimulation. As newer intermediate-acting and short-acting nondepolarizing muscle relaxants have become available, anesthetic management is more easily controlled, especially for simple pediatric surgical procedures such as inguinal herniorrhaphy and tonsillectomy. The degree of neuromuscular blockade may change relatively quickly when short-acting or intermediate-acting muscle relaxants are used and can be monitored closely by observing the train-of-four and double burst nerve stimulations. If repeat dosing is needed, the drug dose is titrated to maintain twitch height at 10% to 25% of the control height, or one to two twitches on the train-of-four monitor.

Neuromuscular blockade is reversed with intravenous atropine (0.02 mg/kg) followed by neostigmine (0.06 mg/kg). In infants, a higher dose of atropine (0.03 mg/kg) is recommended to prevent bradycardia and hypersecretion. Glycopyrrolate (0.1 mg/kg) is as effective as atropine and may produce a more stable heart rate ( Cozanitis et al., 1980 ; Warran et al., 1981 ). Edrophonium (0.5 to 1.0 mg/kg) is faster acting (with shorter duration of action) and is as effective as neostigmine, but reversal with either drug is faster in children and infants than in adults ( Meakin et al., 1983 ). Recovery of the train-of-four (TOF) ratio over 0.70 had long been considered adequate recovery of neuromuscular function ( Ali and Kitz, 1973 ; Ali et al., 1975 ). This ratio is based on the observation that the diaphragm is more resistant to nondepolarizing muscle relaxants than skeletal muscles in adults ( Wymore and Eisele, 1978 ; Pansard et al., 1987 ) and in infants and children ( Laycock et al., 1988 ). In a more recent study, however, healthy young adult volunteers experienced considerable muscle weakness (diplopia, grip strength, and head lift) with TOF ratios between 0.70 and 0.90 after mivacurium infusion ( Kopman et al., 1997 ). These authors concluded that “adequate” recovery of neuromuscular function, especially in the same-day surgery settings, requires the return of the TOF value to at least over 0.90 and ideally to unity. A minimum of at least two strong twitches on the TOF monitor should be confirmed before the reversal with neostigmine (and a minimum of three strong twitches for edrophonium reversal) to ensure that adequate reversal of neuromuscular blockade can be achieved (B. Brandom, personal communication).

The criteria for adequate clinical recovery from nondepolarizing neuromuscular blockade in adults ( Ali and Miller, 1986 ) must be modified for use in infants and young children because of their inability to respond to verbal commands. Before tracheal extubation, the child should be able to do the following:

  

   

Maintain adequate, nonparadoxical breathing

  

   

Generate a negative inspiratory pressure against airway occlusion greater than 30 cm H2O

  

   

Sustain tetanic contraction at 50 Hz and strong double-burst contractions

  

   

Sustain hip flexion with leg elevation for 10 seconds

  

   

Lift the head and/or cough forcefully

When the child is awake, he or she should be able to perform the following:

  

   

Grimace using eyebrows and/or forehead

  

   

Spontaneously open the eyes

  

   

Perform purposeful movement, such as reaching for the ET tube

The anesthesiologist must make the final judgment on the adequacy of neuromuscular function and the readiness for tracheal extubation. Timing of extubation is based on careful clinical observation rather than solely on monitoring with a nerve stimulator or other instruments. Before the trachea is extubated, the child must be breathing normally and adequately, without paradoxical movements. In addition to inadequate neuromuscular function, paradoxical breathing can also suggest other complications, such as airway obstruction, pneumothorax, or phrenic nerve injury.

▪ EXTUBATION OF THE TRACHEA

Emptying of the Stomach

At the conclusion of surgery, while the child is still under general anesthesia, a suction catheter, lubricated with a surgical lubricant (or dipped in water), is gently passed into the stomach to remove gastric contents that accumulated or remained after suction at the beginning of the procedure. This practice reduces the risk of vomiting and aspiration during emergence. Gastric suctioning is especially important in patients thought to have a full stomach or an increased risk for gastroesophageal reflux. This practice is also indicated for patients who were mask ventilated during the procedure because it is helpful in removing any gases inadvertently introduced into the stomach with positive pressure ventilation. When the stomach contents are evacuated, the decrease in intra-abdominal pressure allows greater expansion of the lungs with manual expansions of the lungs, decreasing atelectasis at the base of the lungs and increasing the patient's functional residual capacity toward normal levels. For all patients, mucosal injury and bleeding from suctioning should be avoided. These preventable tissue injuries are usually sustained by forcing a dry catheter or by withdrawing the catheter with the suction generator attached.

Monitoring During Extubation

Once all anesthetics have been discontinued, muscle relaxation has been reversed, and vital signs are stabilized, the nerve stimulator, temperature probe, and blood pressure cuff may be removed. A precordial stethoscope should be applied, replacing an esophageal stethoscope if the latter was used intraoperatively. Electrocardiography should be continued at least until the trachea has been extubated, rhythmic breathing reestablished, and a stable sinus rhythm confirmed. Arterial saturation and heart rate should be continuously monitored by pulse oximetry throughout this period. Children are more likely to desaturate during emergence from anesthesia ( Motoyama et al., 1987 ), and pulse oximetry is a more sensitive indicator of hypoxia than are clinical signs and symptoms or capnography (Coté et al., 1988, 1991 [76] [77]).

Timing of Extubation

Extubation of the trachea must be performed with special care to avoid complications, such as laryngospasm or aspiration of gastric contents. Both of these complications can rapidly lead to severe hypoxia, cardiac depression, and significant patient compromise. Suzuki and Sasaki (1977) confirmed the age-old clinical impression by demonstrating in puppies that laryngospasm (defined as sustained adductor neural discharge after the cessation of a noxious stimulus) is worse during “light” general anesthesia than during wakefulness or deep anesthesia. The safest approach is to extubate the patient when he or she is either awake or well anesthetized.

One method of extubating older infants and children takes place while they are still anesthetized with sufficient inhaled or intravenous anesthetics (a minimum of 2 MACs by briefly increasing sevoflurane or desflurane concentration) to avoid coughing or laryngospasm. This technique (the deep extubation) is especially useful for patients with a history of reactive airway disease, such as asthma or bronchopulmonary dysplasia. Before considering this method, however, the anesthesiologist should know that the patient's airway had been well maintained by mask ventilation during induction of anesthesia. A prophylactic bronchodilator treatment (such as albuterol with a metered-dose inhaler) should be given to patients with a history of reactive airway disease (see later). An oropharyngeal airway should be placed to avoid upper airway obstruction caused by the collapse of velopharynx or the tongue falling back against the posterior pharyngeal wall after extubation (see Chapter 2 , Respiratory Physiology). If airway patency was satisfactory before intubation, the return to spontaneous breathing is not a prerequisite for extubation in deeply anesthetized patients. Deep extubation can be performed safely when using sevoflurane or desflurane and awakening the patient expediently shortly after extubation ( Valley et al., 2003 ). Airway problems may be more frequent with desflurane, and maintaining a higher concentration at extubation is recommended ( Cranfield and Bromely, 1997 ).

The child suspected of having a full stomach should be awake and have complete return of protective laryngeal reflexes before extubation. Other conditions that require awakening before extubation include wiring of the jaw or a surgical intervention with a danger of airway obstruction. In such patients without a full stomach, intravenous lidocaine (1.0 to 1.5 mg/kg), given 2 to 3 minutes before extubation, helps decrease laryngeal responses to the ET tube. However, intravenous lidocaine tends to sedate and prolong the recovery from anesthesia, particularly in infants. A child with a history of reactive airway disease may also be safely extubated awake after pretreatment with a nebulized bronchodilator, such as albuterol. The patient is given two puffs of bronchodilator in a metered-dose inhaler into a mixing chamber, inserted between the anesthesia circuit and ET tube, followed immediately by slow and deep inspiration by gently squeezing the anesthesia bag to a static end-inspiratory pressure (>30 cm H2O) for several seconds. This maneuver is repeated once more to conclude the pretreatment.

Before awake extubation, young children, particularly infants in the early months, may respond to laryngeal stimulation by breath-holding, bronchospasm, chest wall rigidity, marked cyanosis, and oxygen desaturation. The oxygen saturation on a pulse oximeter often drops suddenly to 70% or lower and continues to nose-dive even when both lungs are well ventilated manually with 100% oxygen. This phenomenon is impressive and frightening for a pediatric anesthesiologist; it resembles the cyanotic spells that occur in infants with tetralogy of Fallot. It has been observed mostly in young infants but occasionally in children up to 4 years of age (E. K. Motoyama, unpublished observation). In one case report, echocardiography showed a transient right-to-left shunt through a reopened foramen ovale (Moorthy et al., 1987 ), presumably as the result of a sudden increase in pulmonary vascular resistance, right ventricular afterload, and a shift in the right–to–left atrial pressure gradient and shunt. Fortunately, these episodes are self-limiting, provided that alveolar ventilation is maintained. Older children show less tendency toward sudden desaturation, but greater laryngeal response and irritation that produce forceful “bucking” (coughing with an ET tube in place) when extubation is delayed. This may lead to a greater incidence of postintubation croup ( Koka et al., 1977 ). Thus, older children should be extubated as soon as protective reflexes return.

Technique of Extubation

Removal of the ET tube must be carried out with as much attention to detail as was needed for its insertion. As the child awakens, any stimulation may cause tightening of the jaw, occlusion of the teeth on the ET tube, and compromise of the airway. Severe or complete occlusion of the ET tube or the upper airways associated with marked inspiratory effort and intrathoracic negative pressure can result in postobstructive pulmonary edema (POPE) and hypoxemia ( Galvis et al., 1980 ; Sofer et al., 1984 ). These children require supplemental oxygen, diuretics, and possible reintubation to provide continuous positive airway pressure (see later). This condition usually is resolved within 24 to 48 hours. Placement of an oral airway or a bite block before awakening can greatly reduce the risk of this occurring. Soft bite blocks made of rolled gauze and tape can reduce the incidence of soft tissue damage to the gums, palate, and lips associated with plastic airways. Oropharyngeal airways are preferred in patients whose airway patency was less than satisfactory during anesthetic induction. An oral airway does not stimulate laryngeal reflexes in most patients as long as it is inserted when the patient is still anesthetized and is left undisturbed. The oropharynx is then suctioned and, if indicated, the ET tube is suctioned of any secretions by passing a sterile suction catheter that takes up no more than half the internal diameter of the ET tube, to avoid the strong negative pressure collapsing the alveolar gas.

Until recently, it has been a standard practice before extubation to “preoxygenate” the patient with increased flow of 100% oxygen for several minutes, to wash out residual anesthetics and nitrous oxide, and to replace them with oxygen. Studies, however, have convincingly demonstrated that the age-old practice of preoxygenation must be modified and that the patient must be breathed with an oxygen-air mixture, rather than 100% oxygen, before extubation to minimize airway closure and atelectasis.

The reason for this maneuver is based on the fact that general anesthesia always produces significant reductions in resting lung volume (FRC), due to relaxation of the thoracic inspiratory muscles, especially in infants and young children (see Chapter 2 , Respiratory Physiology). Reductions in FRC, in turn, result in small airway closure and considerable atelectasis, as oxygen and nitrous oxide in the trapped airways are absorbed into the pulmonary circulation ( Serafini et al., 1999 ; Benoit et al., 2002 ). To eliminate the atelectasis developed during general anesthesia, the lungs must be reinflated with several vital capacity maneuvers (sustained airway pressure of 40 cm H2O for several seconds) with a 30% to 70% oxygen and air mixture and an additional PEEP of 5 cm H2O immediately thereafter, in both adults and children ( Benoit et al., 2002 ; Lindahl and Mure, 2002 ; Tusman et al., 2003 ). Administering 100% oxygen before extubation worsens the gas exchange and increases atelectasis, even when the lungs have been sighed with vital capacity maneuvers ( Loeckinger et al., 2002 ).

Based on these findings, it is now recommended, instead of the traditional preoxygenation with 100% oxygen, that the patient be ventilated with an oxygen and air mixture between the ratio of 1:1 and 2:1 (FIO2, 0.6 to 0.73), to wash out residual anesthetics and nitrous oxide, and that the lungs be gently inflated by a sustained peak pressure between 30 and 40 cm H2O for 3 to 5 seconds. This maneuver should be repeated several times to reexpand the lungs and eliminate atelectasis, and then PEEP of 5 to 6 cm H2O be added thereafter to sustain FRC before extubation. Before extubation, the lungs are inflatedsynchronously with the child's inspiration by gently squeezing the anesthesia bag. The bag is then held momentarily at end-inspiration with a positive pressure of 15 to 20 cm H2O to maintain a high lung volume as the ET tube is gently pulled out. This last maneuver serves three functions: (1) it inflates the lungs with an oxygen-rich gas mixture and provides an increased oxygen reservoir that may be needed if breath-holding or laryngospasm occurs ( Motoyama et al., 1987 ); (2) the positive pressure (or stretching the airway walls) decreases the incidence and intensity of laryngospasm ( Suzuki and Sasaki, 1977; Sasaki, 1979 ); and (3) the patient's first response after extubation will be a forceful exhalation or coughing, expelling any secretions trapped between the ET tube and the laryngeal wall, thus minimizing the laryngeal reflex to secretions and laryngospasm.

The initial moments after extubation are critical. The larynx is suctioned quickly to remove the secretions brought up from the upper trachea by the ET tube and then a facemask is applied to reestablish the breathing circuit and CPAP. The patency of the airway is maintained by lifting the mandible forward (the jaw-thrust position) and administering an oxygen mixture by a facemask. Unless laryngospasm develops, spontaneous ventilation resumes promptly. If laryngospasm does occur, oxygen can be forced past the vocal cords using a bag and mask in most patients, if a proper approach is used. Even during severe laryngospasm, there often is a pattern of rhythmicity in the child's respiratory movement. This is characterized by a period of stiffness or bearing down (“expiratory” phase), followed by a transient period of relative relaxation of the larynx (“inspiratory” phase). To oxygenate the child in laryngospasm, the anesthesiologist applies a tightly fitting facemask and maintains no more than 20 cm H2O of CPAP. He or she then watches the patient's breathing pattern very closely and, during the brief moment of laryngeal relaxation, gives a firm squeeze on the anesthesia bag. In most cases, this maneuver delivers enough oxygen through the vocal cords to avoid severe hypoxemia and cardiac depression until laryngospasm resolves. Indiscriminate use of high positive pressure, regardless of the pattern or phase of laryngospasm, often makes matters worse.

Laryngospasm often results from overstimulation of the laryngeal reflexes by regurgitation or retained secretions. Under these circumstances the pharynx and larynx must be cleared of secretions swiftly, even during laryngospasm, to prevent further stimulation of the superior laryngeal nerve. Throughout laryngospasm, oxygen saturation, heart rate, and heart rhythm are continuously monitored with a pulse oximeter, precordial stethoscope, and electrocardiograph.

In the most severe episodes of laryngospasm, when all maneuvers seem ineffective, intravenous atropine (0.02 mg/kg) and succinylcholine (2 to 3 mg/kg) can be given for immediate relief. If an intravenous route is not available, succinylcholine (4 to 5 mg/kg) can be given as a sublingual injection for rapid results ( Smith, 1980 ).

Once alveolar ventilation is reestablished, the patient is carefully examined for gastric distension, airway secretions, foreign body aspiration, and pneumothorax. Even if the stomach was suctioned previously, the child may still retch and vomit enough to cause laryngospasm and aspiration. Suction equipment must be immediately available and used with care and efficiency. If vomiting occurs, it is often sufficient to turn the child's head to the side to allow secretions to fall into the cheek for removal or to roll the child on to the side. Tipping of the head of the table is not necessarily helpful.

▪ TRANSPORT TO THE POSTANESTHETIC CARE UNIT

When ventilation is satisfactory, the patient is transported to the postanesthetic care unit (PACU, or recovery room) in the lateral position with supplemental oxygen via mask, keeping the airway clear of the tongue and secretions and protecting against aspiration ( Fig. 11-3 ). During transport to the PACU, the guardrails should be up and the safety straps securely fastened. If the patient were to become agitated during transport, this simple restraint could prevent serious injury. Patients should be covered with warmed blankets to reduce heat loss during transport. Monitoring during transport should include clinical observation of chest movement, color, and gas exchange in awake and active patients and heart and breath sounds with a precordial stethoscope in sleeping patients. A portable pulse oximeter should be used during the transport for the patients with cardiorespiratory problems.

 
 

FIGURE 11-3  The infant is transported to the PACU in the lateral position.

 

 

Smith (1959) advocated the lateral position for transport nearly half a century ago, based on his clinical experience. A study by Isono and others in 2002, using flexible laryngoscopy, clearly corroborated the assertion by Smith that the lateral head position best maintains the upper airway patency by decreasing the collapsibility of the pharynx. By holding the chin up and extending the neck, the anesthesiologist can further ensure a patent airway and feel the warm breaths, indicating gas exchange.

The newer (Masimo SET) pulse oximeter can be used as a convenient transport monitor, as its monitoring head is battery operated and it can easily be detached from the main monitoring console and placed onto the stretcher without being disconnected from the patient or the sensor. More extensive monitoring, including continuous pulse oximetry, electrocardiography, and invasive blood pressure measurements, should be maintained for critically ill patients or those undergoing extensive surgical procedures and who are being transported to the intensive care unit. These patients, whether intubated or not, must have a self-inflating resuscitation bag or a Mapleson D circuit connected to an oxygen cylinder with a flow rate set to maintain adequate alveolar ventilation and oxygenation. Appropriately sized ET tubes, a laryngoscope, and medications for intubation and resuscitation should also accompany the patient.

Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com

Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.

Copyright © 2005 Mosby, An Imprint of Elsevier

▪ POSTANESTHETIC RECOVERY

The postanesthetic recovery period is a time of high risk for pediatric patients.

A large percentage (20-40%) of otherwise healthy infants and children develop oxygen desaturation (SpO2 ≥ 94%) during transport and upon arrival at the PACU ( Motoyama and Glazner, 1986 ; Pullertis et al., 1987; Patel et al., 1988 ). Oxygen desaturation occurs sooner, is more pronounced, and has a longer duration in infants than in children and in children than in adults ( Xue et al., 1996 ). All children, therefore, should be given oxygen supplementation during their transport from the operating room and upon arrival at the PACU, until he/she can maintain satisfactory oxygen saturation by pulse oximeter without supplemental oxygen.

One should also be aware that the Nelcor pulse oximeter is artificially preset to read SpO2, 2% to 3%, higher than real values and, consequently, gives a false sense of security about the patient's oxygenation (see previous discussion).

The cause of postoperative hypoxemia is most likely due to atelectasis secondary to a reduction in FRC and resultant small airway closure under general anesthesia, as mentioned above ( Motoyama and Glazener, 1986 ; also see Chapter 2 ). Children are more likely than adults to have airway problems, with an occurrence rate of 4% to 5% ( Cohen et al., 1990 ). Upper airway obstruction, postextubation croup, and apnea account for the majority of untoward events. Nearly 50% of all perioperative cardiac arrests caused by respiratory problems occurred during the recovery period ( Salem et al., 1975 ). Dysrhythmias and hypotension occur less frequently in children than adults but require quick and appropriate treatment when they do occur. Nausea, vomiting, temperature instability, and postoperative pain also require prompt and effective treatment to ensure patient comfort and efficient discharge timing.

▪ RECOVERY IN THE POSTANESTHETIC CARE UNIT (PACU)

The PACU should be situated adjacent to the operating rooms to facilitate rapid and safe patient transport and to allow the anesthesiologist ready access in case of an emergency. The number of beds depends on hospital size, caseload, and average length of stay. Each bed space should have an oxygen supply with humidification, a self-inflating resuscitation bag, suction apparatus, pulse oximeter, electrocardiographic monitor, and automated blood pressure apparatus. Other supplies and frequently used medications should be readily available ( Box 11-2 ). In addition, the PACU should be equipped to handle any emergency that may arise when caring for infants and children (Boxes 11-3 and 11-4 [3] [4]). The number of nursing personnel required depends on case type and load. Pediatric patients typically require closer observation, and 1:1 or 1:2 nurse-to-patient care ratio is recommended.

BOX 11-2 

Bedside Equipment and Supplies in PACU

Oxygen, flow meter, humidifier, facemask, and tent

Resuscitation bag with oxygen and anesthesia masks

Oral and nasal airways and lidocaine jelly

Suction apparatus, catheters, and tonsil suction tips

Nasogastric tubes and lubricant

Cups and water for clearing suction catheter

Blood pressure manometer and cuffs

Thermometer

Intravenous fluids, tubing, and three-way and T-connectors

Intravenous catheters, syringes, alcohol, and povidone-iodine (Betadine) wipes

Adhesive tape and tincture of benzoin

BOX 11-3 

Emergency Cart Equipment and Supplies in PACU

Cardiac defibrillator

Two laryngoscope handles and a variety of blades

Endotracheal tubes (2.5- to 7.5-mm inner diameter), stylets, tape, benzoin, and syringes for cuff

Resuscitation bags, oral airways, and bite blocks

Cutdown and tracheostomy sets

Sterile gloves, drapes, gowns, towels, and masks

Intravenous solutions, tubing, catheters, and syringes

Central venous catheter sets

Foley catheter

Bedboard for cardiopulmonary resuscitation

BOX 11-4 

PACU Emergency Cart Medications

α-Adrenergic agonist (phenylephrine)

Aminophylline

Antihypertensives (sodium nitropruside, labetalol)

Atropine

β-Adrenergic blocker (propranolol)

Calcium chloride

Catecholamines (epinephrine, norepinephrine, dopamine, dobutamine, isoproterenol)

Dextrose (50%)

Diuretics (furosemide, mannitol)

Heparin

Lidocaine (intravenous)

Naloxone

Phenytoin (Dilantin)

Racemic epinephrine and nebulizer

Steroids (cortisol, dexamethasone, methylprednisolone)

Succinylcholine

Additional features needed for PACUs are an isolation room for either infectious or immunosuppressed patients and the ability to function as a critical care unit with additional mechanical ventilatory and invasive monitoring capabilities. Ready access to portable radiography service and equipment and personnel for measuring blood gas tensions, pH, hemoglobin, and electrolyte analysis is important.

Initial Care

On arrival at the PACU, the anesthesiologist confirms the patency of the patient's airway, assesses the adequacy of ventilation, and ensures the supply of humidified oxygen. The anesthesiologist records the heart rate, respiratory rate, blood pressure, SpO2, and temperature, which are reported by the nurse. The anesthesiologist then gives a report to the nurse concerning the child's condition, special problems related to any underlying illnesses, the events of surgery, anesthetic technique, and medications given. The anesthesiologist should remain at the bedside until the child is in a reasonably stable condition and is well attended. PACU staff must be competent in recognizing and initiating the treatment of commonly encountered problems, including inadequate ventilation, agitation, pain, vomiting, temperature instability, and delayed awakening. Before leaving the PACU, the anesthesiologist writes a summary note in the chart and verifies that suitable postoperative orders have been written or entered into the computer.

Awakening Responses

With most currently used general anesthetic techniques, awakening occurs within a few minutes of the conclusion of surgery. Many children wake up quietly, without excitement, nausea, vomiting, or other obvious disturbances, when an opioid-based technique ( Chinyanga et al., 1984 ) or propofol infusion ( Hannallah et al., 1994 ) is used. Unfortunately, no one technique guarantees a smooth emergence, and agitation may occur in the early recovery period ( Downs and Nicodemus, 1969 ). Agitation may be caused by numerous factors, including emergence delirium from anesthetic agents, especially with a newer inhaled anesthetic with low blood-gas solubility (sevoflurane or desflurane); pain; metabolic disturbances (hypothermia, hyperthermia, hypoglycemia, hyponatremia); neurologic disturbances; a behavioral response to sudden awakening in a strange environment; separation anxiety; airway obstruction with resultant hypoventilation and hypoxia; and combinations of these factors.

As discussed at the beginning of this chapter, a pediatric anesthesiologist should plan the general anesthetic approach to minimize or avoid many of these factors. Emergence delirium should be avoided with an opioid or benzodiazepine. Pain can be prevented in these patients by judicious use of analgesics or regional techniques intraoperatively. Monitoring and maintenance of metabolic homeostasis are essential aspects of all general anesthetics. Any disturbances should be quickly recognized and treated swiftly and appropriately. Adequate preoperative preparation for the recovery period can help minimize postoperative anxiety in children developmentally capable of understanding ( Peterson and Toler, 1986 ).

Alternative measures, other than the use of pharmacologic agents, can often be effective in calming the awakening pediatric patient. Some patients simply need reassurance or the comfort of being touched or held to alleviate anxiety. Parental presence has been shown to reduce the incidence of fear, crying, anger, and clinging during hospitalization ( Fiorentini, 1993 ; Fina et al., 1997 ; Patel et al., 2001 ). Both parents and PACU staff have reported beneficial results from parental involvement. Once the infant or child has documented stable vital signs, a parent should be present.

Last but not least, the importance of detecting airway obstruction, inadequate ventilation, hypercarbia, and/or hypoxemia as causes of agitation cannot be overemphasized. Misdiagnosis can lead to inappropriate use of opioids and sedatives. Delayed and erroneous treatment of these problems can have serious consequences, including respiratory and cardiac arrests. The etiology and treatment of these phenomena are discussed next.

▪ COMMON PROBLEMS IN THE POSTANESTHETIC CARE UNIT

Airway Obstruction

Although patients should be able to maintain airway patency before leaving the operating room, it is not uncommon for an infant or a child to have obstruction after the stimulation of extubation and transportation has subsided. The anesthesiologist must be acutely aware of any changes in the breathing pattern at this time because hypoventilation can lead to a reaccumulation of volatile agents in the alveoli that can further blunt the respiratory drive. Hypercarbia may result in dysrhythmias and hypertension, and hypoxemia in infants may lead to further suppression of breathing ( Knill and Gelb, 1978 ;Knill and Clement, 1984 ; Motoyama and Glazner, 1986 ). Neck extension, mouth opening, and jaw lift alone or together may be enough to correct the problem. Nasopharyngeal airways, if necessary, are better tolerated than oropharyngeal airway in this setting. If obstruction continues, reassessment of anesthetic and neuromuscular blockade reversal should be conducted and possible reintubation may be considered.

Other causes of respiratory distress may be present in a way similar to upper airway obstruction. Pneumothorax, silent aspiration, and pulmonary edema should be considered and investigated if the patient continues to exhibit respiratory compromise.

Apnea of Prematurity

Apnea may be central (no respiratory effort), obstructive (respiratory effort without gas flow), or mixed (both central and obstructive) ( Rigatto, 1986 ). Clinically, apnea is defined as cessation of breathing for longer than 15 seconds or for less than 15 seconds associated with bradycardia, cyanosis, or pallor ( Nelson et al., 1978 ; Thatch, 1985 ). Repetitive pauses of breathing, lasting 5 to 10 seconds and not associated with other changes in infants, are termed periodic breathing. These abnormal respiratory patterns, which are observed commonly in neonates and preterm infants ( Rigatto, 1986 ), can appear or worsen in preterm infants after exposure to anesthetic agents. This is particularly true for prematurely born infants with a previous history of apnea ( Liu et al., 1983 ) and those younger than 44 weeks postconceptional age (PCA) after simple surgical procedures such as inguinal herniorrhaphy ( Gregory and Steward, 1983 ). It had been recommended that former preterm infants less than 44 to 46 weeks PCA should be carefully observed postoperatively for at least 18 to 24 hours ( Gregory and Steward, 1983 ; Liu et al., 1983 ).

Kurth and others (1987) , meanwhile, reported prolonged apneic spells among preterm infants up to 55 weeks PCA in 18 of 49 occasions (37%) following inguinal herniorrhaphy as well as laparotomies and ventriculoperitoneal shunts. They proposed that all ex-premature infants less than 60 weeks PCA (adding 2 SDs to their data) were at high risk for postoperative apnea and should be monitored continuously for at least 12 hours. Malviya and others (1993) subsequently reported that the incidence of postoperative apnea following inguinal herniorrhaphy in ex-premature infants is different depending on their PCA. They reported a high incidence of postoperative apnea (26%) in infants less than 44 weeks PCA, whereas the incidence of apnea in those more than 44 weeks PCA was only 3%.

Subsequently, Coté and others (1995) performed a meta-analysis of the data from eight previously published studies of postoperative apnea involving 384 ex-premature infants following inguinal hernia repairs. In this report, they found that postoperative apnea was (1) strongly and inversely correlated to both gestational age and PCA; (2) associated with a previous history of apnea; (3) not associated with small-for-gestational age infants; they were somewhat protected from postoperative apnea; and (4) associated with anemia (hematocrit <30) as a significant risk factor, regardless of gestational age or PCA.Coté and others (1995) concluded that the probability of developing apnea in nonanemic infants free of the history of apnea is not insignificant (<5% with 95% confidence limits) until PCA was 48 weeks and gestational age of 35 weeks. The risk of apnea is not less than 1% until PCA was 54 to 56 weeks with gestational age of 32 weeks. They further concluded that older infants with apnea in the PACU and those with anemia should be admitted and monitored overnight ( Coté et al., 1995 ). Because of these findings, it is generally recommended that preterm infants less than 44 to 46 weeks PCA be admitted for monitoring following general anesthesia ( Gregory and Steward, 1983 ; Coté et al., 1995 ). Welborn and others (1988) found caffeine (10 mg/kg) to be effective in treating apnea in premature infants undergoing elective surgery. These patients, however, are still routinely admitted for observation and treatment.

Obstructive Sleep Apnea

Another group of patients predisposed to postoperative apnea consists of those with chronic obstructive sleep apnea syndrome (OSAS). OSAS is a disorder of breathing during sleep that is characterized by prolonged partial upper airway obstruction with or without intermittent complete obstruction and cessation of airflow that disrupts normal sleep time breathing and normal sleep patterns ( American Thoracic Society, 1996 ). Although OSAS in adults is common among obese middle-aged men and women, it is commonly associated with enlarged tonsils and adenoids in children ( Young et al., 1993 ). Surgical removal of enlarged adenoids and tonsils often markedly improves upper airway patency ( Schechter et al., 2002 ). OSAS also occurs in children with a narrowing of upper airways secondary to craniofacial abnormalities, muscular dystrophy, cerebral palsy, and Down syndrome (trisomy 21), which may worsen during the postoperative period ( Clark, 1980 ; Marcus, 2001 ). Some children with OSAS but without adenotonsillar hypertrophy may have abnormal neural control of upper airway muscles ( Marcus et al., 1994 ). The risk of postobstructive pulmonary edema is expected to be high in patients with OSAS (see later).

Hypoxemia

Supplemental oxygen should be administered to all children on arrival in the PACU. Pulmonary gas exchange deteriorates during general anesthesia primarily because of a reduction of FRC and resultant airway closure and atelectasis ( Westbrook et al., 1973 ; Motoyama and Glazener, 1986 ; Motoyama, 1996 ; Serafini et al., 1999 ). Infants and children, being even more susceptible to reductions in FRC and to atelectasis, demonstrate frequent (28% to 43%) and marked oxygen desaturations (SpO2 ≥94%, estimated PaO2 <67 mm Hg) if allowed to breathe room air immediately after general anesthesia (Motoyama and Glazner, 1986 ). Infants, especially those younger than 6 months ( Kataria et al., 1988 ; Xue et al., 1996 ) and those with upper respiratory infection ( DeSoto et al., 1988 ), are at increased risk. Humidified oxygen should be delivered by “blow-by” or with a funnel-shaped facemask (face tent). Termination of oxygen therapy is determined by normal and stable pulse oximeter readings at or above preoperative levels with the patient breathing room air. Clinical signs of wakefulness and a high score on the modified Aldrete scale have been shown to be unreliable indicators ( Soliman et al., 1988).

Postobstructive Pulmonary Edema

Pulmonary edema developing shortly after the relief of upper airway obstruction is known as postobstructive pulmonary edema (POPE). POPE was first described in 1977 following difficult intubation in children ( Travis et al., 1977 ). Subsequently, POPE was described following the relief of laryngospasm both in infants and children ( Galvis et al., 1980 ; Sofer et al., 1984 ). The first sign of POPE may occur immediately after the relief of upper airway obstruction. They are characterized by rales, wheezing, and hemoglobin desaturation with the appearance of copious, frothy, pink (pulmonary edema) fluid pouring out of the trachea. Although POPE can occur in patients without a history of intrinsic pulmonary or cardiac disease, patients with acute or chronic upper airway obstruction are more vulnerable to POPE. These conditions in children may include subglottic croup, acute supraglottitis, OSAS, laryngomalacia, tracheomalacia, craniofacial dysmorphology and soft tissue obstruction of different etiologies ( Tami et al., 1986 ; Oudjhane et al., 1992 ).

Among a number of factors associated with the development of pulmonary edema, increased interstitial negative pressure by forced inspiratory effort against the closed glottis (Mueller maneuver), which would increase transudation of fluid from pulmonary capillaries to interstitial space, and altered capillary permeability, due to acute hypoxia, may be the likely causative factors of POPE (Stalcup and Mellins, 1977; Smith-Erichsen and Bo, 1979; Palvin et al., 1981 ).

Once upper airway obstruction is cleared, the patient with POPE should receive CPAP by mask (5 to 10 cm H2O) with a high concentration of oxygen with an air mix to maintain oxygen saturation by pulse oximeter. Diuretics should be considered along with intravenous fluid restriction. If hypoxemia (SpO2 <95%) persists the patient may require ET intubation and ventilation with a moderate PEEP (10 cm H2O) under sedation, often with morphine or other opioids, until pulmonary edema is dissolved. In most cases of POPE, pulmonary wedge pressure remains within normal range and pulmonary arterial pressure is also normal or only slightly increased ( Willms and Shure, 1988 ).

Postintubation Croup

The incidence of postintubation croup was reported to be about 1% ( Koka et al., 1977 ). The most common cause is a tight-fitting ET tube without an air leak at 30 to 40 cm H2O with positive airway pressure ( Koka et al., 1977 ). Patients less than 4 years of age seem to be more susceptible to croup, probably because of their small laryngeal lumen, which is more readily obstructed with mucosal edema. Other factors associated with postintubation croup may include traumatic or repeated intubation, “bucking” or coughing with the ET tube in place, changing the head position ( Koka et al., 1977 ), duration of surgery, and neck surgery. An increased incidence is also seen in children with trisomy 21 ( Sherry, 1983 ). Additional factors that may contribute to the incidence of postintubation croup include the use of analgesic jelly for lubricating the ET tube ( Loeser et al., 1980 ), insufficient intraoperative anesthetic gas humidification, and the presence of upper respiratory infection.

The incidence of postintubation croup seems to have decreased with or without a leak around the ET tube at or above 20 to 25 cm H2O positive airway pressure ( Khalil et al., 1998 ). Whether this trend is due to less irritating ET tube material (implant tested versus red rubber ET tubes), more liberal use of corticosteroids for laryngeal surgery or other factors needs to be explored. In addition, the trend of using the cuffed ET tube in infants and young children (Khine et al., 1997; Fine et al., 2000 ; Fine and Borland, 2004 ) would theoretically reduce the incidence of postintubation croup, by choosing an ET tube that is one to two sizes (0.5 to 1.0 mm OD) smaller to accommodate the cuff and thereby avoid having the ET tube tightly fitting the subglottis and decreasing attempts for reintubation due to a tube that is either too tight or too small in diameter (with excessive gas leakage around the tube). At Hopital d'Enfants Armand Trousseau in Paris, all children requiring mechanical ventilation intraoperatively have been intubated exclusively with cuffed ET tubes since 1997 ( Murat, 2001 ). Of more than 15,000 children intubated with cuffed ET tubes in the 4-year period, there were no increases in respiratory complications. In a prospective study between 2000 and 2001, 55 respiratory complications were reported in the recovery room out of 3434 children less than 8 years of age but none of them were attributable to ET intubation ( Murat, 2001 ).

The croup scoring system by Downs and Raphaely (1975) objectively quantifies the severity of the condition and its use can be helpful in treatment decisions ( Table 11-7 ). Cool humidified mist administered after extubation may be helpful in mild cases of croup. Racemic epinephrine (0.5 mL of 2.25% solution), diluted in 3 to 5 mL of normal saline solution and administered by nebulizer for 5 to 10 minutes, assists patients with progressively worsening symptoms and stridor by producing mucosal vasoconstriction, resulting in a shrinking of swollen airway mucosa. Jordan and others (1970) found that only the L-isomer of epinephrine is pharmacologically active, so the reduced incidence of dysrhythmias may be a dilutional effect. The “rebound effect” and reoccurrence of symptoms are well described and necessitate observing the patient up to 4 hours after treatment.

TABLE 11-7   -- Croup score

 

SCORE

Criteria

0

1

2

3

Stridor

None

Only with agitation

Mild at rest

Severe at rest

Retractions

None

Mild

Moderate

Severe

Air entry

Normal

Mild decrease

Moderate decrease

Severe decrease

Color

Normal

N/A

N/A

Cyanotic

Level of consciousness

Normal

Restless when disturbed

Restless when undisturbed

Lethargic

Total Score

Degree

Management

≤4

Mild

Outpatient; given mist therapy

5 to 6

Mild to moderate

Outpatient if child improves in emergency room after mist, is greater than 6 months old, and has a reliable family

7 to 8

Moderate

Admitted; given racemic epinephrine

>8

Severe

Admitted; given racemic epinephrine, oxygen, and intensive care therapy

From Downes JJ and Raphaely RC: Pediatric intensive care. Anesthesiol 43:238, 1975.

 

 

 

The efficacy of corticosteroids on postintubation croup has been controversial ( Koren et al., 1983 ; Kuusela and Vesikari, 1988 ). However, Anene and others (1996) , in a prospective, double-blind, placebo-controlled study, found that dexamethasone is effective in reducing the incidence of postintubation croup in children intubated for longer than 48 hours.

Cardiovascular Instability

Cardiac rhythm disturbances and blood pressure fluctuations tend to be less problematic in infants and children recovering from general anesthesia than in adults ( Fogliani et al., 1982 ). Electrocardiographic monitoring is not routinely performed in pediatric PACUs because abnormalities, such as ST-segment and T-wave changes, are extremely rare. Bradycardia is typically a response to medications such as neuromuscular blockade reversing agents or fentanyl, or a normal variant that should be treated only if associated with hypotension. Tachycardia may be secondary to hypovolemia, inadequately treated pain, or anticholinergic medications. Careful assessment and appropriate therapy should be instituted to correct volume deficit or the need for analgesia. Hypertension may also reflect inadequate analgesia, an anticholinergic effect, or excessive hydration, or it may be an artifact caused by the use of an inappropriately small blood pressure cuff. Hypotension is more unusual and is most often caused by hypovolemia secondary to inadequate fluid replacement or ongoing blood loss. Appropriate fluid resuscitation should be instituted.

Nausea and Vomiting

Postoperative nausea and vomiting (PONV) is a relatively frequent and unpleasant complication of anesthesia in infants and children and a major cause of delayed discharge from the PACU or unscheduled admission for same-day or outpatient surgery patients ( Patel and Hannallah, 1988 ). Although rarely life threatening in the PACU, vomiting has the potential for causing aspiration, hypovolemia, and/or hypernatremia. The average incidence of postoperative vomiting in children above 3 years of age has been reported to be 40% or greater ( Lerman, 1992 ). The risk of PONV is higher after certain types of surgery, such as strabismus repair, adenotonsillectomy, and orchiopexy. Other factors affecting the incidence of nausea and vomiting can include age, gender, history of motion sickness, anesthetic techniques (inhaled anesthetics, nitrous oxide versus intravenous anesthetic with propofol), inadequate analgesia, gastric distention, and the skill of the anesthesiologist. Intraoperative use of opioids without antiemetics may also precipitate postoperative vomiting. Early ambulation and offering clear liquids, in an attempt to meet the discharge criteria in the short-stay surgery settings, may precipitate vomiting, particularly in susceptible patients ( Schreiner et al., 1992 ).

For PONV prophylaxis, intravenous serotonin (5-HT3) receptor antagonist, such as ondansetron (0.1 to 0.15 mg/kg) and granisetron (0.04 mg/kg) given intraoperatively 30 minutes before the emergence, has been shown to be highly effective in preventing PONV with rare side effects ( Patel et al., 1997 ; Fujii et al., 2002 ). A small dose of dexamethasone (0.2 to 0.5 mg/kg), with or without ondansetron, is also effective ( Aouad et al., 2001 ). Gan and others (2003) published guidelines for preventing and treating PONV and recommend prophylaxis only in patients with moderate to high risk. In untreated or pretreated patients who develop PONV in the PACU, a repeated dose of ondansetron or granisetron should be considered. For those patients for whom prophylaxis fails, antiemetic drugs that work via other mechanisms, such as dexamethasone (0.5 mg/kg) ( Aouad et al., 2001 ), diphenhydramine (0.5 mg/kg) ( Kranke et al., 2002 ), or perphenazine (70 mcg/kg) ( Splinter et al., 1998 ), are suggested.

Temperature Instability

Even with the most careful attention to maintaining normothermia, patients frequently arrive in the PACU with lowered body temperature. Usually covering the patient with warm blankets is sufficient, but radiant warming lamps and conductive warming blankets should be used in extreme cases. Hyperthermia that develops in the PACU may indicate the onset of an infectious process and should be watched closely. Malignant hyperthermia may be seen initially during the postanesthetic period. If malignant hyperthermia is suspected, appropriate investigation and therapy should be instituted without delay (seeChapters 6 and 31 , Pharmacology of Pediatric Anesthesia and Malignant Hyperthermia).

Emergence Agitation

The increased use of short-acting opioids, sedatives, and regional techniques has significantly reduced the incidence of this problem. With the introduction of desflurane and sevoflurane, however, emergence delirium and agitation have reappeared, particularly in children ( Davis et al., 1994 ; Aono et al., 1997 ; Walker et al., 1997 ; Grundmann et al., 1998 ). Because it is not feasible to fully evaluate a young child's psychological state during emergence, the term delirium is often replaced with the descriptive terms agitation or excitation. Proposed theoretical explanations for this occurrence have included increased pain sensation, rapid emergence to a strange environment, variable recovery resulting in a dissociative state, and a yet-to-be-defined psychomotor side effect.

Inadequately treated pain has been proposed to be a major contributor to this phenomenon. Studies, though, have demonstrated a high incidence of emergence agitation in presumably pain-free patients; those who received desflurane for genitourinary surgery with adequate caudal blocks and those who received sevoflurane for noninvasive procedures and magnetic resonance imaging ( Wells et al., 1999 ;Uezono et al., 2000 ). Davis and others (1999) demonstrated that in children undergoing bilateral myringotomies and tube insertions with a brief exposure to sevoflurane, incidence of emergence agitation was minimal when analgesia was achieved with ketorolac (0.5 mg/kg). Finkel and others (2001) reported similar results using intranasal fentanyl 0.1 mcg/kg. Cohen and others (2001) found in children undergoing adenodectomy that an intraoperative dose of fentanyl (2.5 mcg/kg) was effective in reducing the incidence of emergence agitation but that pain scores were similar between treated and control groups. Postoperative analgesics and sedatives have also been shown to be effective but prolong recovery and time to discharge from the PACU.

Pain and Discomfort

All pediatric patients, including neonates and premature infants, experience pain if untreated (see Chapter 13 , Pain Management in Infants and Children). Differentiating between pain, anxiety, and other causes of stress in this age group is still an unresolved challenge. Each age group and each patient has a different behavioral manifestation and communication ability regarding pain. The selection of the appropriate pain assessment tool, from the multitude available, is crucial. Many of these tools are not designed for patients recovering from surgery and general anesthesia. Disorientation, fear, and regression may alter communication and behavior, causing misinterpretation. Some pain scales have a limited application in the clinical setting.

As with pain assessment, selection of a pain management technique must be individualized for the patient, the surgical procedure, and the hospital setting. Selection must also be made with a good understanding of each technique's advantages and shortcomings. For these techniques to be successful, conscientious postoperative care must be given.

Pain Measurement and Assessment

Most techniques measure the intensity of pain by assigning incremental values. The most common technique, self-reporting, depends on verbal, cognitive, and developmental skills. Adapting adult patient surveying tools such as the McGill Pain Questionnaire ( Melzack, 1975 ), researchers have developed scales using verbal description and graphic rating. Such tools are modified for age, culture, and cognitive ability ( McGrath et al., 1985 ; Varni et al., 1987 ). Word lists and questioning techniques have been developed ( Abu-Saad et al., 1990 ; Wilkie et al., 1990 ).

Graphic or symbolic representations of pain intensity also require modification. The visual analog pain scale, initially developed for adult pain measurement, is typically a 10-cm horizontal line defined by “no pain” on the left end and “severe pain” on the right. In older children and adolescents, this instrument has been used with success ( Abu-Saad, 1984 ; McGrath et al., 1985 ). In younger children, replacing the definers with different words, such as “no hurt”/“most hurt,” numbers, or happy/sad faces has also been tested ( Broadman et al., 1988 ; Savedra and Tesler, 1989 ). For younger children, with preoperational reasoning, less abstract quantitative measurements, including counting poker chips ( Hester, 1979 ), selecting color scales ( Eland and Anderson, 1977 ), and marking graduate thermometers (Jeans and Johnston, 1985 ), are more easily understood and used. Further variations include a progression of happy to crying faces either illustrated, as in McGrath's Facial Affective Scale ( McGrath et al., 1985 ), or photographed, as in Beyer's Oucher Scale ( Beyer and Aradine, 1988 ). Numerical values are assigned in each of these methods for progressive levels of pain intensity.

In infants and preverbal children, observational pain scales must be implemented. For the evaluation of postoperative pain, the Children's Hospital of Eastern Ontario Pain Scale (CHEOPS) ( McGrath et al., 1985 ) and the Objective Pain Scale ( Hannallah et al., 1987 ) grade behavioral manifestations of pain. The CHEOPS assesses six categories: cry, facial expression, verbal response, torso position, leg activity, and arm movement in relationship to the surgical wound. The Objective Pain Scale contains physiologic and behavioral changes associated with pain. These scales were designed for research purposes and are specific for age. Neonatal and premature infant pain scales have been created and verified; these include the Neonatal Infant Pain Scale (NIPS), the CRIES (Crying Requires oxygen Increased vital signs Expression Sleep) scale, and the Premature Infant Pain Profile.

Physiologic alterations, such as changes in heart rate, blood pressure, respiration, transcutaneous oxygen saturation, and sweating caused by pain, can be observed and easily measured ( Holve et al., 1983 ;Williamson and Williamson, 1983 ; Owens and Todt, 1984 ). Using changes in vital signs removes the subjectivity of behavioral pain scoring methods, but these parameters may reflect change for reasons other than pain. To assess pain accurately in children, location, duration, frequency, historical precedent, and present setting must be assessed, as well as intensity of pain. In addition, the child's developmental level, coping style, and motivation must be considered. In older children and adolescents, verbal responses are the most accurate. The Vami/Thompson Questionnaire and The Children's Comprehensive Pain Questionnaire, as well as less-structured interview techniques, can elicit accurate and detailed descriptions of pain ( McGrath and Unruh, 1987 ). How the questions are phrased, who asks them, and what the child expects all affect the response.

Observational pain assessment techniques are also fraught with variability. Studies have demonstrated that scoring by parents, nurses, and physicians can be unreliable when assessing pain by cry, behavior, and constructed pain scales ( Wasz-Hocket et al., 1985 ; Beyer et al., 1990 ; Favaloro and Toozel, 1990 ; Watt-Watson et al., 1990 ). As with older children, previous experience, emotional and medical status, and clinician interaction can affect the response.

Because no single technique or approach is ideal, medical personnel assessing pain in children must be well versed and flexible. Verbal, graphic, behavioral, and physiologic measures have been examined and tested, but further work on psychology and emotional interplay is needed. Although cognitive development is well understood, a hospitalized child often regresses, and expected and previously observed abilities may be lost. Much progress has been made in acknowledging that infants and children experience pain, but a great deal of work is still needed to fully reveal the degree and manner of their experience.

Pain Management

The intraoperative use of opioids and regional anesthesia for preventing postoperative pain has been discussed. Even with the best planning, patients may still experience pain in the PACU. Although most pain and discomfort originate from surgical incision and tissue irritation, other causes, including tight bandages or casts, distended bladders, and corneal abrasions, should not be overlooked. Each of these problems requires immediate attention from the appropriate medical personnel. Foley catheters and nasogastric tubes may also be causes for distress. Preoperatively, patients should be prepared to expect these catheters, which will reduce anxiety during recovery.

Treatment of pain in the PACU depends on the patient's medical condition, the surgical procedure, and discharge disposition. Oral acetaminophen (10 to 15 mg/kg) is useful in patients without intravenous access who have had minor surgical procedures. Rectal acetaminophen (30 to 40 mg/kg) may take up to 2 hours to achieve a therapeutic level and so is not effective for treating acute pain in the PACU. NSAIDs can play an important role in pain management for patients with compromised airways and respiratory function and can serve as adjuncts to opioid techniques, including neuraxial and patient-controlled analgesia use. Ketorolac should be avoided in patients with an increased risk for bleeding and those post bone-grafting procedures.

Morphine (0.025 to 0.05 mg/kg) or fentanyl (0.5 to 1.0 mcg/kg), given in incremental doses, can be used to achieve an analgesic state in patients recovering from a general anesthetic. If hospital admission overnight or longer is planned, then morphine use is preferable because of its longer duration of action. For patients undergoing extensive surgical procedures with moderate to severe pain anticipated, continuous infusion of an opioid should be considered. Hendrickson and others (1990) demonstrated better analgesia and greater patient satisfaction with continuous infusion compared with intermittent dosing. Continuous infusion can create consistent analgesic blood levels of morphine and remove the need for children to communicate their pain ( Berde, 1989 ; Esmail et al., 1999 ).

Patient-controlled analgesia (PCA) allows the patient to self-administer small incremental doses of a local anesthetic and an opioid. PCA has been extensively studied in children, and studies support its efficacy and safety ( Gaukroger et al., 1989 ; Lawrie et al., 1990 ; Tyler, 1990 ; Berde et al., 1991 ). In younger children and infants, nurse-assisted PCA is a useful alternative ( Monitto et al., 2000 ). It is most effective if patients are selected, evaluated, and instructed before surgery. Side effects of opioid use, including nausea, vomiting, pruritus, and urinary retention, should be anticipated and treated when they occur.

Placement of indwelling catheters in the epidural space, body cavities, and nerve sheaths allows for continued use of local anesthetics and opioids for several days after surgery. In older children, patient-controlled epidural anesthesia (PCEA) has been shown to be safe and effective ( Birmingham et al., 2003 ). Careful dosing and monitoring for side effects, including oversedation, respiratory arrest, and toxicity of local anesthetics, are essential. The advantages, limitations, and possible dangers of these techniques are discussed more fully elsewhere (see Chapter 13 , Pain Management in Infants and Children and Chapter 14 , Pediatric Regional Anesthesia).

▪ DISCHARGE FROM THE POSTANESTHETIC CARE UNIT

With more rapid recovery from general anesthesia and a greater variety of surgical cases being scheduled on an outpatient basis, strict time criteria for discharge from the PACU are becoming less useful. The Modified Aldrete Score ( Soliman et al., 1988 ) ( Table 11-8 ) examines the following five criteria: motor activity, respiration, blood pressure, consciousness, and color. The Simplified Postanesthetic Recovery Score ( Steward, 1975 ) assesses three criteria: consciousness, airway, and movement. Both scores can be helpful as guidelines in determining when a patient is ready for discharge. Inclusion of oxygen saturation by pulse oximetry is indicated. Before a child can be safely discharged from the PACU, a careful examination should be conducted to ensure safety on the patient floor, with its reduced nursing care and observation. The following criteria must be met:

  

1.   

The child is fully awake or easily aroused when called.

  

2.   

The airway is maintained and protective reflexes are present.

  

3.   

Oxygen saturation is maintained above 95% on room air or stable at the preoperative level with or without oxygen.

  

4.   

Hypothermia is absent, and hyperthermia is controlled.

  

5.   

Pain and nausea/vomiting are controlled.

  

6.   

There is no active bleeding.

  

7.   

Vital signs are stable.


TABLE 11-8   -- The Aldrete score

Able to move 4 extremities voluntarily or on command

2

 

Able to move 2 extremities voluntarily or on command

1

Activity

Unable to move extremities voluntarily or on command

0

 

Able to breathe deeply and cough freely

2

 

Dyspnea or limited breathing

1

Respiration

Apneic

0

 

BP ± 20% of preanesthetic level

2

 

BP ± 20–49% of preanesthetic level

1

Circulation

BP ± 50% of preanesthetic level

0

 

Fully awake

2

 

Arousable on calling

1

Consciousness

Not responding

0

 

Able to maintain O2 saturation > 92% on room air

2

 

Needs O2 inhalation to maintain O2 saturation >90%

1

O2 Saturation

O2 saturation < 90% even with O2 supplement

0

 

Modified from Aldrete JA, Kroulik D: A post-anesthetic recovery score. Anesth Analg 9:924–928, 1970. In Aldrete JA: The post-anesthesia recovery score revisited (Letters to the editor). J Clin Anesth 7:89, 1995.

 

 

 

From the PACU, patients can be admitted to a short-stay recovery unit or to a hospital ward. Regardless of the patient's disposition, the anesthesiologist is responsible for the follow-up, to ensure that no anesthetic complications occur and to continue treatment for those patients receiving special pain management techniques. For ambulatory patients, a single visit is usually all that is needed, whereas for patients with complicated medical conditions and/or extensive surgery, visits should continue until the patient is stable. Postanesthetic notes should be written in the patient's chart to communicate any findings or suggestions that may assist in the patient's recovery.

▪ SHORT-STAY RECOVERY UNIT

Patients undergoing outpatient procedures continue to recover in an ambulatory or a short-stay recovery unit (SSRU) (also see Chapter 27 , Anesthesia for Pediatric Same-Day Surgical Procedures). Complications seen in the PACU can also occur here. The most frequent causes for unplanned hospital admission from the SSRU are vomiting, croup, fever, and family request ( Patel and Hannallah, 1988).

Patel and Rice (1991) set forth the following criteria for discharge to home:

  

   

Vital signs are stable.

  

   

Intact gag reflex, swallowing, and cough allow for oral intake.

  

   

Ambulation or movements are appropriate for developmental level. (Patients who received regional analgesia must demonstrate returning motor function.)

  

   

Nausea and vomiting should be minimal, allowing for retaining of ingested fluids.

  

   

No signs of respiratory distress such as stridor retractions, nasal flaring, “barking” cough, wheezing, cyanosis, or dyspnea.

  

   

Patient is oriented to person, place, and time as appropriate for age.

Voiding is not necessary, but if present, it is helpful to assess fluid status and residual regional anesthesia.

When discharged to home, the patient's family should be instructed concerning fluid intake, pain control, nausea and vomiting, and any special directives concerning the surgical procedure. In addition, a telephone number where someone will be available 24 hours a day should be supplied.

Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com

Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.

Copyright © 2005 Mosby, An Imprint of Elsevier

▪ SUMMARY

Maintenance of anesthesia, emergence, and postoperative care are parts of the continuous perioperative care of a patient. With improved technology in intraoperative monitoring under the guidelines for standards of monitoring and vigilance, anesthetic management of infants and children has become much safer in recent years. Yet the understanding of the young patient's special needs in terms of equipment, fluid requirement, airway management, and altered pharmacokinetics is essential. Newer anesthetic agents and adjuvant drugs, together with progress in regional analgesic techniques in infants and children, allow pediatric anesthesiologists to combine conduction analgesia with various general anesthetics for prompt and smooth emergence with appropriate postoperative analgesia. The great variety in patient age, size, and physiology necessitates planning and execution of postoperative management to be patient specific.

Copyright © 2008 Elsevier Inc. All rights reserved. - www.mdconsult.com

Motoyama & Davis: Smith's Anesthesia for Infants and Children, 7th ed.

Copyright © 2005 Mosby, An Imprint of Elsevier

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