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

PART TWO – General Approach to Pediatric Anesthesia

Chapter 10 – Induction of Anesthesia and Maintenance of the Airway in Infants and Children

Etsuro K. Motoyama,Brian J. Gronert,
Gavin F. Fine

  

 

Induction of General Anesthesia, 319

  

 

Psychological Consideration,319

  

 

Medical Considerations, 320

  

 

Preoperative Fasting, 321

  

 

Premedication, 321

  

 

Preanesthetic Preparations, 322

  

 

Methods of Induction, 324

  

 

Laryngeal Mask Airway, 330

  

 

Endotracheal Intubation, 331

  

 

Indications for Endotracheal Intubation, 331

  

 

Equipment, 332

  

 

Laryngoscopes and Blades, 332

  

 

Flexible (Fiberoptic) Bronchoscope,332

  

 

Bullard Laryngoscope, 333

  

 

Endotracheal Tubes, 334

  

 

Techniques for Endotracheal Intubation, 338

  

 

Oral Intubation Under General Anesthesia and Muscle Relaxants,338

  

 

Intubation Under General Anesthesia Alone, 341

  

 

Nasotracheal Intubation, 342

  

 

Intubation in a Child With a Full Stomach, 343

  

 

Intubation in an Awake Infant, 346

  

 

Difficult Airway and Intubation Techniques, 347

  

 

Intubation Using a Flexible Fiberoptic Bronchoscope,350

  

 

Intubation with a Lighted Stylet, 352

  

 

Intubation with the Retrograde Technique, 352

  

 

Summary, 353

▪ INDUCTION OF GENERAL ANESTHESIA

The induction of anesthesia is the most crucial and stressful period of general anesthesia for the young patient as well as for the anesthesiologist. The consequences of this stressful experience by a child become apparent in the immediate postanesthetic period and may persist for weeks or even longer ( Kain and Mayers, 1996 ; Kotiniemi et al., 1997; Kain et al., 1999 ; McCann and Kain, 2001 ). Regrettably, anesthesia is often induced with too little consideration for the child's anxiety, despite better awareness by anesthesiologists of preoperative stress experienced by the young patient and improved psychological preparations since the 1980s (see Chapter 7 , Psychological Aspects). This discrepancy continues in part because the anesthesiologist is preoccupied with the technical aspects of anesthetic induction and is naturally focused on the maintenance of cardiorespiratory stability, particularly when dealing with a poor-risk child, and pays too little attention to the child's psychological needs. In addition, in the era of managed care in the United States and elsewhere and with the economical pressure for efficiency and quick turnover between surgical cases, it has become increasingly difficult for the pediatric anesthesiologist to spend sufficient time with young patients and his or her parents preoperatively to get to know each other and earn the child's confidence. No matter how healthy the child or how minor the procedure, the experience of being placed on an operating table and forcefully put to sleep (a.k.a. “gorilla induction” or “brutaine”) can be a terrifying and never-to-be-forgotten horror. Consequently, children who must return for repeated anesthesia and surgery could be emotionally disturbed ( Dombro, 1970 ), although the adverse effects of the anesthetic experience are not easy to separate from the overall effects of hospitalization ( Myers and Muravchick, 1977) . It is the responsibility of the pediatric anesthesiologist to understand the emotional needs of young patients and to provide the optimal psychological preparation before and during the induction of anesthesia.

▪ PSYCHOLOGICAL CONSIDERATION

The psychological environment for hospitalized children has improved substantially since the 1980s, with organized preoperative hospital tours, audiovisual programs, and playrooms with trained child life specialists, who are trained to facilitate the child's coping with the perioperative environment and stress by providing play experiences using modeling techniques, particularly in the preoperative waiting area ( Melamed and Ridley-Johnson, 1988 ; Melamed, 1993 ). By the mid-1990s most major children's hospitals in the United States had developed the child life program for children and their parents (O';Bryrne et al., 1997). Unfortunately, while effective preparation programs to reduce the child's anxiety in the preoperative holding area are well established, progress in the effectiveness of reducing anxiety during the process of anesthetic induction has been limited ( Kain et al., 1996, 1998 ).

Stress and anxiety manifested in children before and during anesthetic induction result from the interaction between the child's personal predisposition (age, maturity, personality, and his or her past experiences in the hospital environment) and the environmental factors (unfamiliar environment, exposure to many strangers, the noise level, intensity of lights in the operating room, etc.). The child may look scared (e.g., clinging to his or her mother), may try to ignore or escape from the anesthesiologist, or may start to cry. During the preoperative examination, it is extremely important to identify the child who is likely to develop extreme fear and anxiety before the induction of anesthesia (see Chapter 7 , Psychological Aspects). Premedication with sedatives has been shown to be most effective, especially for those who are at high risk of developing extreme anxiety and distress, although some parents are reluctant to allow or even refuse premeditation altogether, against the anesthesiologist's advice.

▪ MEDICAL CONSIDERATIONS

Infants and children with preexisting medical conditions should be carefully examined, and, when a decision is made to go ahead with induction with known medical problems, appropriate measures, including medications, should be taken before or shortly after anesthetic induction. This issue has been detailed elsewhere ( Chapter 8 , Preoperative Preparation; Chapter 27 , Anesthesia for Same-Day Procedures; and Chapter 32 , Systemic Disorders). Some basic preparations before anesthetic induction are listed next.

Upper Respiratory Tract Infections

Upper respiratory tract infection (URI) is by far the most common problem the pediatric anesthesiologist has to deal with before the induction of anesthesia, especially in the same-day surgery setting. Although a recent history or the presence of URI per se may not necessarily increase the risk of long-term outcome beyond the immediate postoperative period, URI or lower respiratory tract infection and inflammation does increase the irritability and secretion of the respiratory tract and may increase the incidence of laryngospasm, bronchospasm, and perioperative hypoxemia ( DeSoto et al., 1988 ; Cohen and Cameron, 1991 ; Coté, 2001 ; Bordet et al., 2002 ; Elwood et al., 2003 ). Risk factors for respiratory complications include endotracheal intubation, history of prematurity (even in older children), reactive airway disease and passive smoking, nasal congestion and copious secretions, and airway surgery ( Tait et al., 2001 ).

It is also important to note that with viral lower respiratory infection clinically limited to upper airway symptoms, airway reactivity and hyperresponsiveness indistinguishable from bronchial asthma often develop, even in patients without a history of asthma ( de Kluijver et al., 2002 ). Increased airway reactivity with viral respiratory infection lasts as long as 6 to 8 weeks ( Empey et al., 1976 ). Special consideration should be made to provide a warmed humidified gas mixture during the induction and maintenance of anesthesia, because anesthetic dry gas mixture irritates already inflamed upper airways and may trigger coughs, laryngospasm, or bronchospasm. Prophylactic bronchodilator treatment should be given, as indicated, before the induction of anesthesia and/or before the emergence from anesthesia and extubation.

For children with a history of reactive airway disease, one has to make sure that each patient has received optimal treatment before reaching the operating room. Careful history taking is the single most important element of the preoperative evaluation of children with reactive airway disease. If a child has had symptoms of URI with episodes of wheezing requiring bronchodilator treatment in the previous weeks, the anesthesiologist should consider postponing elective surgery for at least 4 to 6 weeks after an episode of symptomatic asthma, although this is often not practical. The history of the child's steroid requirement over the past several months is important for determining if he or she should be given stress-dose steroid coverage (see Chapter 32 , Systemic Disorders).

For patients with recent episodes of wheezing and bronchodilator treatment but requiring surgery, preinduction treatment with a β2-agonist with or without corticosteroids is recommended to minimize respiratory complications, especially laryngospasm and bronchospasm. A study in adult patients with reactive airway disease showed significant decreases in bronchospasm after tracheal intubation (Silvanus et al., 2004 ).

The patient's history, physical examination, and laboratory tests are all helpful for determining if the patient's condition is adequately managed. A child with active wheezing at a preoperative physical examination, especially wheezing with symptoms of upper or lower respiratory infection, should not be operated on unless it is a dire emergency (see Chapter 32 , Systemic Disorders).

Children With Congenital Heart Disease

Many children with congenital heart lesions will require antibiotic prophylaxis preoperatively for the prevention of bacterial endocarditis. Recommendations by the American Heart Association (AHA) are listed in the inside cover of this publication ( Dajani et al., 1997 ). The recommendations can also be downloaded from the AHA website at http://www.americanheart.org. The consensus statement for the AHA subacute bacterial endocarditis (SEB) prophylaxis has been formulated by the writing group within AHA and has been reviewed by outside experts. It consists of five tables that are periodically updated:

  

   

Table 1: Cardiac conditions associated with endocarditis

  

   

Table 2: Dental procedures and endocarditis prophylaxis

  

   

Table 3: Other procedures and endocarditis prophylaxis

  

   

Table 4: Prophylactic regimens for dental, oral, respiratory tract, or esophageal procedures

  

   

Table 5: Prophylactic regimens for genitourinary/gastrointestinal (excluding esophageal) procedures

Amoxicillin, 50 mg/kg (with an addition of gentamicin, 1.5 mg/kg for genitourinary or gastrointestinal procedures), given intravenously or intramuscularly 30 minutes before the procedure, has been the standard prophylaxis. Alternative antibiotics for those who are allergic to penicillin are also listed (clindamycin, cephalexin, azithromycin, vancomycin, etc.).

For optimal effect, the intravenous antibiotics should be administered 30 minutes prior to the start of the surgical or endoscopic procedures. This procedure, however, can be problematic for infants and young children without an access to an intravenous route preoperatively, especially in same-day surgery settings. In case the preoperative establishment of intravenous access under sedation is not practical for any reason, it is often the practice in many centers to start the infusion of antibiotics during or right after inhalation induction of general anesthesia and intravenous access is established. The patient may be positioned and prepared for surgery, but the skin incision should be delayed at least for 20 minutes after the infusion of an antibiotic. In case preoperative antimicrobial prophylaxis was missed for any reason, an animal study indicates that the prophylaxis given within 2 hours (but not after 4 hours) following the procedure will still provide effective prophylaxis ( Dajani et al. ,1997 ; Berney and Francioli, 1990 ), although, for obvious reasons, no clinical studies have confirmed this finding.

Latex Allergy

Since the first report of intraoperative anaphylactic reaction due to latex allergy in the anesthesiology literature in 1989 (Gerber et al., 1989), latex allergy has increased at an alarming pace in the latter part of the twentieth century ( Murat, 2000 ) and is detailed elsewhere in this publication ( Chapter 32 , Systemic Disorders). Allergy to latex is the main cause of intraoperative anaphylaxis in children, whereas in adults, allergy to muscle relaxants is the main cause ( Murat, 1993 ). Children with congenital urogenital abnormalities, myelomeningocele, and hydrocephalus with ventriculoperitoneal shunts are among the high-risk groups (Dormans et al., 1994, 1997 [70] [71]). Repeated exposure to latex-containing products in the neonatal period and early childhood is the apparent cause of the development of a latex allergy. High-risk groups of children have been well defined ( Kwittken et al., 1995 ; Porri et al., 1997 ; Cremer et al., 1998 ). Fortunately, over the past decade, latex-containing products, including adhesive tapes, blood pressure cuffs, tourniquets, and surgical gloves, have largely been replaced by latex-free products in the United States and other industrialized countries. It has become much simpler to provide a latex-free environment for children with high risks during the early postnatal years. Anesthesiologists should remain vigilant, however, to protect their patients from inadvertent exposures to latex, especially with latex gloves used by the surgeons. The U.S. Food and Drug Administration (1991) recommended that all patients should be questioned preoperatively for latex hypersensitivity.

▪ PREOPERATIVE FASTING

The purpose of preoperative fasting is to allow sufficient time for gastric emptying of ingested food and liquid and, thus, to minimize the risk of aspiration of gastric contents into the lungs during anesthesia. For the preparation of infants and children for general anesthesia and surgery, it is extremely important to properly instruct the family in regard to preoperative food and fluid intake.

To decrease the incidence of aspiration, it was routine practice prior to the 1990s to keep all children NPO after midnight before surgery. This practice ignored both the differences in the rate of gastric emptying between ingested solid food and clear liquids and the differences in the scheduled times of surgery ( Welborn, 1993 ). A number of studies in the 1990s demonstrated that clear liquids with or without added sugar are rapidly cleared from the stomach and that the gastric fluid pH and volume are independent of the duration of fasting beyond 2 hours, provided that only clear liquids are given on the day of surgery ( Schreiner, 1990 ; Splinter and Schaefer, 1990 ; Litman et al., 1994 ). The liberalization of guidelines for preoperative fluid administration in the 1990s offers the benefit of improved patient comfort. It also means that fewer infants and children demonstrate signs of hypoglycemia or dehydration at the time of anesthetic induction ( Welborn et al., 1993 ). Over the last decade, most pediatric hospitals have altered and shortened the fasting period of clear liquids to 2 hours prior to induction of anesthesia for all ages ( Ferrari et al., 1999 ).

In 1999, Ferrari and coworkers reported the results of a survey of current practice of preoperative fasting in pediatric institutions in the United State and Canada. Of 51 institutions surveyed, 44 responded. The survey revealed that a “2-4-6-8 rule” represents the majority of institutions providing pediatric care in North America ( Ferrari et al., 1999 ). This rule restricts clear fluids for 2 hours. Infants less than 6 months of age on breast milk require 4 hours of fasting. Older infants over 6 months of age on milk or infant formula should be fasted for 6 hours; milk or infant formula should be considered as solid food because the fat is the main determinant delaying gastric emptying ( Litman et al., 1994 ). Children on solid food, including toast, cereal, and juice with pulp, such as orange juice, are usually fasted for 8 hours (or NPO after midnight) prior to induction of anesthesia.

▪ PREMEDICATION

The use of premedication is most effective for reducing preoperative anxiety for young patients and their parents. Preanesthetic medication is described in detail in Chapter 8 (Preoperative Preparation) and is discussed only briefly here. There has been progress in the effectiveness of premedication and preoperative sedation during the past 10 years. With the advent of newer anesthetic agents, especially sevoflurane for inhalation induction, the nature of premedication has also evolved. With less secretions and fewer cardiorespiratory side effects with sevoflurane compared with halothane, anticholinergic agents (atropine, glycopyrrolate) are rarely required before induction, perhaps with the exception of neonates and preterm infants. Furthermore, with few exceptions (such as intramuscular ketamine in agitated, uncontrollable children), intramuscular premedication is all but eliminated from routine pediatric anesthesia practice.

Hypnotics

The most common drug for premedication has been midazolam, a water-soluble benzodiazepine, in fruit-flavored syrup to mask its bitter taste (0.3 to 0.5 mg/kg given orally). It is effective within 10 to 15 minutes ( Kain et al., 2000 ). Even lesser doses of oral midazolam (0.25 mg/kg) have been reported to be effective, although it may take slightly longer than the larger dose to produce effective sedation (Coté et al., 2002 ). Midazolam has also been used less frequently via the nasal (0.2 to 0.3 mg/kg) or rectal (0.3 mg/kg) routes but with their own disadvantages. In 10 to 15 minutes of oral medication administration, most children become calm, euphoric, or drowsy and are unsteady walking, and they must be held carefully or placed in bed. There is minimal separation anxiety when taken away from parents toward the induction area. Prolonged recovery time with midazolam premedication had been a concern, especially for infants and children for same-day surgery, but the time of discharge from the hospital is not increased (Bevan et al., 1997, Viitanen et al., 1999 ).

Opioids

Opioid premedication is infrequently used in healthy children because of potential respiratory depression, especially in young infants less than 6 months of age. Oral transmucosal fentanyl citrate (OTFC) has the advantage of self-titration and has a relatively rapid onset without increases in gastric pH ( Nelson et al., 1989 ; Stanley et al., 1989 ). However, it causes more preoperative and postoperative side effects such as pruritus, vomiting, and hypoxemia ( Goldstein-Dresner et al., 1991 ; Ashburn et al., 1990, 1993 [7] [3]) (see Chapter 8 , Preoperative Preparation).

Ketamine

Intramuscular injection of ketamine in a relatively low dose (2 to 3 mg/kg, undiluted) is effective in uncooperative, combatant children as the last resort to avoid inhalation induction by force or for the insertion of an intravenous catheter. Ketamine may be combined with glycopyrrolate to reduce secretions. Hannallah and Patel (1989) reported that inhalation induction with halothane in uncooperative children with intramuscular ketamine took even less time than induction with cooperative children without premedication. Ketamine has also been given via the oral, nasal transmucosal, or rectal routes. Ketamine solution (6 mg/kg) diluted with fruit-flavored syrup and given orally produced effective sedation in 12 minutes ( Stewart et al., 1990 ; Gutstein et al., 1992 ). Ketamine mixed with midazolam was reported to produce a better anxiolysis than either drug alone ( Funk et al., 2000 ). Nasal transmucosal ketamine has also produced effective sedation ( Weksler et al., 1993 ).

Clonidine

An α2-adrenergic receptor agonist, clonidine has been shown to produce perioperative sedation and reduce the anesthetic requirement and postoperative analgesia (Ghinone et al., 1987). Clonidine has been used for premedication in children over the past decade, although it is most frequently used as an adjunct to caudal and epidural blocks (( Mikawa et al., 1993 ; Nishina and Mikawa, 2002 ). Oral clonidine (4 mcg/kg) provides satisfactory anxiolysis and sedation ( Nishina et al., 1999 ). A study compared the efficacy of premedication between clonidine (4 mcg/kg orally, given 60 minutes before induction) and midazolam (0.4 mg/kg rectally, given 30 minutes before induction) by means of clinical observation, and bispectral index (BIS). During rapid sevoflurane induction (8% in 50% N2O in O2), both agitation requiring restraint and hemodynamic responses were significantly less and shorter in duration with clonidine premedication than with midazolam premedication ( Constant et al., 2004 ). A major limitation of oral clonidine as a premedicant, especially in the same-day surgery setting, is that it must be given at least 60 minutes prior to induction.

A mail survey of randomly selected practicing anesthesiologists in the United States in 2002 (27% response, n = 1362) showed that a significantly larger proportion of young children undergoing surgery were reported to receive sedative premedication compared with a previous survey in 1995 (50% versus 30%, P = 0.001) and that midazolam was the predominant, if not exclusive, sedative for premedication ( Kain et al., 2004 ).

▪ PREANESTHETIC PREPARATIONS

It is essential for the anesthesiologist to try to gain the patient's confidence in the preoperative waiting area, especially when the child is not properly premedicated. Dressed in a strange operating room outfit and standing tall over the frightened child is not the way to initiate contact with a young patient. The anesthesiologist should sit close to the child or even down on the floor to be at the child's eye level before starting communication with the child. If a line of communication has been found through a child's toy, pet, or favorite television program, then focusing attention on this may help to gain the child's confidence and divert or reduce fear and anxiety. The game of “peek-a-boo” in infants and young children may calm them and even bring a smile to their faces. Infants less than 6 months of age may be less subject to anxiety and need gentle handling and a reassuring voice long before words can be understood. During the brief stay in the preanesthetic waiting area, a child is encouraged to be engaged in play, with a toy or a video game with or without the presence of parents ( Fig. 10-1A ); an infant can also be held in arms for comfort ( Fig. 10-1B ).

 
 

FIGURE 10-1  The preoperative waiting (play) area provides a last opportunity for the anesthesiologist to improve his or her communication with the child in a relaxed atmosphere.  (Photograph by Frank A. Leavens, Pittsburgh, PA.)

 



Most unpremedicated children can be well managed in this friendly environment. The anesthesia mask may be given to the child to play with in the waiting area before induction. Provide a sense of self-control by letting the child choose his or her favorite flavor (bubble gum, cherry, strawberry, etc.) to be added to the mask. The additional support of pacifiers, toys, and music boxes often is helpful. Children should keep the object of their choice brought from home, particularly a “security blanket,” during the induction of anesthesia. The short trip from waiting area to operating or induction room can be extremely important. The child is moved back onto a stretcher from the play area and wheeled to the operating room, or held in the arms of the anesthesiologist, taking the security blanket and/or best-loved toys with him or her. Some older unpremedicated children prefer to walk along with the anesthesiologist ( Fig 10-2 ). If the child proves actively resistant at this stage, he or she may be convinced by a parental presence at induction (see later), but if this also fails, then further sedation may be administered.

 
 

FIGURE 10-2  Some children prefer to walk from the play area to the operating room with the anesthesiologist.  (Photograph by Frank A. Leavens, Pittsburgh, PA.)

 



Sedation at this point can be in the form of intranasal midazolam, 0.2 to 0.3 mg/kg, undiluted (5 mg/mL) to minimize the volume ( Wilton et al., 1988 ). Mixing with 1% to 2% lidocaine decreases the stinging discomfort to the nasal mucosa. For a larger combative child, intramuscular ketamine (2 to 3 mg/kg) can be used effectively as the last resort (see earlier). In the case of an older resistant child for an elective procedure, consideration should also be given to postponing the procedure until the child is properly prepared. One is rarely justified in bringing a screaming and resisting child into an operating room.

Parental Presence During Induction

A parental presence is desirable because it may reduce the need for preoperative sedatives and decrease the level of preoperative anxiety, especially upon separation to the operating room ( Berry, 1986 ) (see Chapter 7 , Psychological Aspects). A parental presence results in a significant decrease in the number of very upset children during induction in unpremedicated children ( Hannallah and Rosales, 1983). The disadvantages of a parental presence in the operating room include delays in the operative schedule, crowding of limited operating room space, and possible adverse effects on the parent during the induction process, especially if something goes wrong during induction.

If a separate induction room equipped with all the essential monitors and an anesthesia machine is not available, a parent, masked and gowned, may be allowed to enter the operating room and sit on a stool right next to the operating table, holding the child's hands during the induction. The induction process should be explained in layman's terms to the parent and he or she should be prewarned of possible excitement and upper airway obstruction (“loud snoring”) as part of a possible occurrence during induction. And the parents should be assured that they need not be concerned. The parent should be escorted out of the operating room by an operating room nurse as soon as the child loses consciousness.

In a 2002 national survey via mail with questionnaires sent to randomly selected anesthesiologists in the United States, Kain and others (2004) found that the practice of having a parental presence during induction of anesthesia (PPIA) has increased significantly, compared with a similar survey in 1995, and that regional differences in this practice have decreased. Overall, 10% of respondents allow parental presence during induction in more than 75% of the time, whereas 27% reported PPIA in less than 25% of all cases. Approximately 50% of all respondents never allowed parental presence during induction of anesthesia when anesthetizing children ( Kain et al., 2004 ). The frequency of practicing PPIA in the United States, however, remains far less than that in the United Kingdom.

Preparation for Induction

Before the induction of anesthesia, the temperature of the operating room should be properly adjusted and warming devices (warming blanket, radiant heat lamp) should be turned on, particularly for young infants ( Box 10-1 ). The anesthetic and monitoring equipment must be properly set up and ready before the child enters the room. The preinduction checklist should include gas pressures of accessory oxygen and nitrous oxide cylinders, gas tightness of the anesthesia circuit, and the necessary small equipment and supplies. These include a properly sized face mask, oral and nasal airways, a tongue depressor, three sizes of endotracheal tubes (the expected size plus one size larger and one size smaller), and a stylet; all must be available regardless of whether endotracheal intubation is planned. A laryngeal mask airway (LMA) appropriate for the patient's age should also be available if it is to be used. A suction apparatus with a Yankauer tonsil suction tip or a 14F oral suction catheter must be turned on, and additional sterile endotracheal suction catheters (6F to 10F, depending on the patient's age) and nasogastric tubes (10F to 18F) must be available. Adhesive tape, torn and ready for use, and a padded or foam rubber head ring or a small pillow should also be at hand.

BOX 10-1 

Preanesthetic Preparation

Operating Room Preparation

Warm operating room

Turn on warming devices (e.g., warming blanket, intravenous line warmer, radiant light heat source)

Anesthesia Equipment

Anesthesia machine checkout

Monitoring equipment (pulse oximeter, capnograph, anesthetic gas monitor) turned on and checked

Precordial stethoscope with double-stick adhesive

Proper-size blood pressure cuff, pulse oximeter probe, temperature probe

Proper-size facemask

Oral and nasal airways

Tongue depressor

Laryngeal mask airway (LMA) if planned

Laryngoscope handle and at least two blades

Three sizes of endotracheal tubes

Stylet

Suction turned on with Yankauer suction tip or suction catheter

Adhesive tape torn and ready for use

Intravenous fluid bag connected to appropriate tubings and injection ports

Intravenous catheters

Drugs

Intravenous drugs drawn up

  

   

Propofal and/or thiopental

  

   

Atropine, succinylcholine, nondepolarizing muscle relaxant

  

   

Reversal drugs (neostigmine, edrophonium, glycopyrrolate)

  

   

Opioids (morphine, fentanyl, or remifentanil on infusion pump)

Monitoring devices such as an in-flow oxygen analyzer, an automatic blood pressure measuring apparatus, an electrocardiograph (ECG), a pulse oximeter, an anesthetic gas monitor, and capnographic equipment should be turned on. In addition to intravenous drugs that are to be used in anesthetic management, atropine and succinylcholine should always be drawn into syringes and clearly labeled just in case of severe laryngospasm.

Monitoring During Induction

Because vital signs can vary markedly during the induction of anesthesia, it is important to attach a basic monitoring device to the patient before induction. Most children will accept a precordial stethoscope when it is warmed properly and quietly applied, and a pulse oximeter probe on a fingertip or a toe. If the child is anxious, it is unwise to further upset him or her by placing ECG leads and a blood pressure cuff before induction. They can be applied soon after the patient loses consciousness. On the other hand, particularly in a small and sick infant, it is important to place all of the monitors before induction and to obtain a baseline blood pressure measurement, which may be unexpectedly low. After the induction, the same blood pressure could be mistaken as a sign of anesthesia-induced hypotension and trigger unnecessary treatment such as fluid resuscitation or vasoactive drugs. Monitoring the child continuously with a pulse oximeter and capnograph is extremely important and is part of the American Society of Anesthesiologists (ASA) monitoring standards for patient safety ( 1986 ).

▪ METHODS OF INDUCTION

There are a number of techniques for safely inducing general anesthesia in children. The particular technique chosen varies with the age of the child, underlying illness, surgical procedure, and the skill and preference of the anesthesiologist. The induction techniques vary from inhalational, intravenous, and intramuscular, to rectal administration of anesthetics, although the latter is rarely used today.

Inhalation Induction

Inhalation induction by mask is the most commonly used technique in pediatric anesthesia in the United States because it can be achieved relatively easily and rapidly in most children and is less objectionable to most children than the insertion of an intravenous catheter. The pediatric anesthesiologist must be flexible and able to suit the child's need by varying his or her method of induction.

If a child has dozed off while awaiting induction or is well sedated with premedication, anesthesia can be induced by the “steal technique,” with the child on the stretcher as originally described by Guedel in 1921 (Calverley, 1986). This can be achieved by blowing a high flow of 70% nitrous oxide in oxygen into the anesthesia mask while it is held closely over the face, without touching the skin at first, and then placed gently on the face for a few minutes while increasing the concentration of sevoflurane up to 2 MAC (minimum anesthetic concentration) before the child is moved to the operating table. Minimal monitoring is used to avoid awakening the child, but adequate monitoring must be established as soon as the patient is sufficiently asleep to tolerate this without causing excitement phase reflexes. Monitoring devices, particularly a precordial stethoscope and a pulse oximeter probe, should be attached as soon as possible before transferring the child to the operating table.

Once in the operating room, the average child is cooperative but may be frightened by noisy personnel and strange sights. The conversation and communication between the child and the anesthesiologist should not be interrupted throughout the transition from the preanesthetic holding area through the transport and onto the operating table. The child needs repeated reassurance that he or she is doing fine and that no one is going to hurt him or her. An assistant (an operating room nurse, nurse anesthetist, attending anesthesiologist, etc.) should help position the child on the operating table and stand by. It is usually best if the anesthesiologist alone does the talking; and the talking should be continual. Surgeons and nurses are reminded to be quiet immediately before and during the induction or are asked to stay out of the operating room if they need to carry on a conversation.

The procedure should be smooth and continuous and unbroken by the last-minute preparation of equipment. The two most important pieces of monitoring equipment during an inhalation induction are a precordial stethoscope and a pulse oximeter. The stethoscope should be positioned over the left sternal border at the second to fourth intercostal space (not below the nipple line) with a double stick adhesive so that both the breath and heart sounds will be heard clearly ( Fig 10-3 ). A layer of blanket or a pajama top over the stethoscope and ECG pads will help divert the child's attention away from the strange objects on the chest wall.

 
 

FIGURE 10-3  Precordial stethoscopes with double-stick adhesive.  (Courtesy 3M Company, St. Paul, MN.)

 



Frequently a small child is content to sit up and play but has no intention of lying down on the operating table. In such cases, it is much better to proceed with induction with the child sitting up near the upper edge of the operating table and his or her back leaning against the anesthesiologist's chest or the child on the anesthesiologist's lap ( Fig 10-4 ).

 
 

FIGURE 10-4  Children who refuse to lie down on the operating table often have little objection to a “sitting up” induction with minimal monitoring, usually with a precordial stethoscope and a pulse oximeter probe.

 

 

Some children may object strenuously to both the sight and smell of the mask, even before the gas flow is started. Varied approaches may be used to temper these emotional reactions. Fruit-scented lipsticks have been successful in hiding the smell of inhaled anesthetics from a reluctant child. Bubble gum flavor seems to be the favorite scent of most children. A regular disposable clear plastic mask with an inflatable cuff around the rim is acceptable to children. One should never begin the induction by putting a mask on the child's face abruptly and without warning. The mask, detached from the anesthesia circuit and scented with a fruit flavor of choice, should be shown to the child, even if he or she has seen it previously. Let your assistant (nurse or attending anesthesiologist) or the parent (most often the mother), if he or she is present at the bedside, try the mask first and let approve the sweet flavor before applying it to the child's face to assure the child that it is harmless. The anesthetic circuit is then connected and started with N2O and O2 (2:1).

At the outset, the child may be responsive, apprehensive, resistant, or alert; the approach must be suited to the child's mood. It is best to rely on the establishment of communication and especially on the building of self-confidence. One can pretend to need a child's help by having him or her hold the mask on his or her face by himself or herself ( Fig 10-5 ). If the child objects to the smell of the inhaled anesthetic, he or she should be told to breathe through the mouth because this reduces the smell. A child's imagination may be used to alleviate anxiety. Unlike adult patients, it is not useful to ask a child to take a deep breath because he or she may not respond to the command or may become apneic after deep breaths and disrupt smooth induction with a steady increase in inhaled anesthetic concentrations. One does not stimulate a quiet child by asking questions and prodding him or her awake. It is better to discourage activity by suggesting more and more soporific themes. Some degree of hypnosis is involved in most inhalation inductions.

 
 

FIGURE 10-5  The child may hold the mask himself.

 

 

As the child goes to sleep, he or she may close the eyes and not move but may lose consciousness slowly and continue to hear very accurately, especially when halothane is used for induction. Apprehension may increase as the child becomes dizzy and disoriented and may feel that he or she is floating off in space, completely helpless and abandoned. To prevent these sensations, the anesthesiologist must be sure to maintain contact with the child, continually reassuring him or her by touching him or her lightly. The assistant stands quietly beside the patient. Most children, and many teenagers and adults, appreciate having a hand to hold as they begin to lose control of things.

It is extremely important to know the signs of early induction and to check them before disturbing the child. The first sign of anesthetic induction usually is the appearance of nystagmus; then the eyes usually close, respiration becomes slower, regular, and deeper, then shallower and more rapid, and the child becomes still. For some time after that the child may be only half asleep and responds to verbal command. Until he or she no longer reacts to one's voice and the eyelash reflex in gone, nothing should be done to move or stimulate the patient, unless airway obstruction or a similar need arises. Nurses and surgeons should know not to touch the patient without getting a nod to go ahead from the anesthesiologist. As soon as anesthesia is induced and the patient can tolerate moderately painful stimuli, an intravenous infusion can be started. An intravenous dose of atropine (0.01 to 0.02 mg/kg) may be given to infants to prevent bradycardia and hypotension caused by inhaled anesthetics, especially with halothane.

An effective and safe method of inhalation induction for children is to run a high flow of nitrous oxide and oxygen, 2:1, over the mouth and nose as one slowly lowers the mask onto the face as oxygen saturation (usually 100%) is continuously monitored. The patient will get the full effect of nitrous oxide within 1 to 2 minutes, as evidenced by the appearance of nystagmus and a regular and slower respiratory pattern of breathing. Then sevoflurane is added. Except for young infants less than 3 to 6 months of age, the concentration of sevoflurane can be increased rapidly to 6% to 8% in otherwise healthy patients without causing significant hypotension or bradycardia. DuBois and others (1999) compare the three techniques of sevoflurane induction: incremental increases in sevoflurane (2%, 4%, 6%, and 8%) in 100% oxygen, a high concentration of sevoflurane (8%) in O2, and a high concentration of sevoflurane in the 1:1 mixture of N2O and O2. There were minimal differences among the three approaches. An addition of N2O with a high concentration of sevoflurane decreased the time to eyelash reflex and tended to decrease the incidence of excitement during the induction.

Halothane is a potent, relatively nonirritant, volatile anesthetic with a sweet odor that was introduced for clinical use in 1956 in the United Kingdom (1958 in the United States). It soon displaced all existing volatile agents for pediatric use ( Wark, 1997 ). Fulminant hepatitis associated with halothane anesthesia (halothane hepatitis) eventually eliminated its use in adults, and it was replaced by isoflurane in the early 1980s. Until recently, halothane enjoyed the role of the sole agent for inhalation induction, mostly because there was no alternative to halothane and the incidence of halothane hepatitis in children has been reported to be relatively low, estimated as less than 1:80,000 to 1:500,000; it has not been a major concern for clinical use ( Wark, 2001 ).

When halothane is used for induction, the concentration must be increased by 0.5% increments every 2 or 3 breathes. Concentrations of 3.5% to 4.0% halothane are considered proper limits for induction and should be reduced to 1.0% to 1.5% once anesthesia is established. For practitioners who are not familiar with halothane, inhalation induction with halothane should be discouraged, especially for infants, without proper supervision, because, in comparison with sevoflurane, halothane causes more myocardial depression, hypotension, and arrhythmias (Holzman et al., 1996; Blayney et al., 1999 ). The Pediatric Perioperative Cardiac Arrest (POCA) Registry reports that cardiac arrest related to medication is the most common cause (37% of total), of which 66% were associated with halothane (versus 4% with sevoflurane) ( Morray et al., 2000 ).

Soon after the approval of sevoflurane for clinical use in the mid 1990s in North America and in Europe (since 1993 in Japan), it rapidly replaced halothane as the primary (if not the sole) inhalation induction agent. Sevoflurane has a low blood-gas partition coefficient of 0.6 ( Wallin et al., 1975 ) and is well tolerated by infants and children for inhalation induction ( Naito et al., 1991 ; Sarner et al., 1995 ). Children anesthetized with sevoflurane exhibited more rapid emergence and a significantly shorter postoperative recovery time compared with those receiving halothane ( Naito et al., 1991 ).

There are several potential problems with the clinical use of sevoflurane: its degradation in CO2 absorbers ( Morio et al., 1992 ), the production of carbon monoxide and excessive heat, and biodegradation to inorganic fluoride ion ( Frink et al., 1992 ).

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 ).

A breakdown product, fluoromethyl-2-2-difluoro-1-(trifluoromethyl) vinyl ether (compound A), is formed by the reaction of sevoflurane with CO2 absorber (there is more breakdown with barium hydroxide lime [Baralyme] than with sodium hydroxide base [soda lime]). The formation of compound A increases with decreasing gas flow, with increasing sevoflurane concentrations, with increasing CO2production and temperature, and with the drying of the absorbent ( Biebuyck and Eger, 1994 ; Steffey et al., 1997 ; Meakin, 1999 ). However, the degradation of sevoflurane to compound A in CO2absorbents is not a clinical issue if a minimum of 2 L/min fresh gas flow is maintained for a circle system or, alternatively, Mapleson D circuits (such as Bain circuit) are used on the anesthesia machine and the biotransformation does not seem to be associated with renal toxicity ( Frink et al., 1996 ; Mazze and Jamison, 1997 ).

The degradation of sevoflurane with the presence of CO2 absorbents has led to several new products that absorb CO2 but without reacting with sevoflurane ( Lerman, 2004 ). Amsorb and Dragersorb-Free are such “inert” CO2 absorbers ( Kharasch et al., 2002 ; Kobayashi et al., 2003 ). The degradation of inhaled anesthetics is virtually eliminated by excluding the sodium and potassium bases from these products. Amsorb contains only calcium hydroxide ( Kharasch et al., 2002 ; Kobayashi et al., 2003 ). With the advent of the new class of CO2 absorbers, it is likely that low-flow sevoflurane anesthesia with semiclosed or even closed circle ventilation will become a reality in the near future ( Peters et al., 1998 ; Meakin, 1999 ).

Another problem with sevoflurane is its exothermic reaction with desiccated CO2 absorber, especially with barium hydroxide lime (Baralyme), producing carbon monoxide (CO) and/or excessive heat. The reaction with desflurane produces more CO, whereas sevoflurane is associated with the most heat production compared with all other inhaled anesthetics ( Wissing et al., 2001 ). Excessive overheating and melting of CO2 canisters and spontaneous ignition and explosions within anesthesia circle systems have been reported. These accidents were associated with a combined use of sevoflurane and desiccated Baralyme (resulting from high fresh gas flow) ( Castro et al., 2004 ; Wu et al., 2004 ); the data also included a case report of a serious injury (acute respiratory distress syndrome [ARDS]) to the patient (Fatheree and Leighton, 2004 ). In order to prevent excessive dehydration or desiccation of CO2 absorbents, it is recommended that the common practice of running oxygen through the anesthesia circuit overnight and weekend be discontinued, especially in the remote and infrequently used anesthetizing locations ( Woehlck, 2004 ). Routine monitoring of CO2 canister temperature using a skin temperature probe may be an easy addition to the circle system for detecting the overheating of CO2 absorbent during sevoflurane anesthesia ( Woehlck, 2004 ). The new class of calcium hydroxide-based CO2absorbents appears to be safe against exothermic reactions in part because calcium hydroxide is hydrophilic and prevents excessive dehydration.

Whether there still is a place for halothane in pediatric anesthesia has been actively debated in the literature ( Wark, 1997 , 2001; Holzki and Kretz, 1999 ; Murat, 1998 , 2001b). The relatively high blood-gas partition coefficient of halothane and its slower emergence and analgesic effects in comparison to sevoflurane could be advantages for certain cases for different reasons (e.g., bronchoscopy, myringotomy) (see Chapter 11 , Intraoperative and Postoperative Management). In addition, sevoflurane is 20 times more expensive than halothane, one major reason why halothane is still used for the maintenance of pediatric anesthesia in the cost-conscious managed care environments of the United States and Australia ( Wark, 2001 ). With the advent of a new class of “inert” CO2 absorbents that do not degrade inhaled anesthetics (see earlier), low-flow circle absorber techniques in the future would decrease the cost of sevoflurane anesthesia. Sevoflurane, even with the advantage of a low blood-gas solubility coefficient, is not the ideal inhaled anesthetic, having its own drawbacks, like postoperative agitation that especially occurs after short surgical procedures. In addition, there have been reports of QT prolongation associated with sevoflurane anesthesia ( Kleinsasser et al., 2001 ; Maier et al., 2002 ). Yet, with the cardiovascular stability and the lack of airway irritation that sevoflurane provides, the risk/benefit ratio of sevoflurane is much better than that of halothane ( Murat, 2001b ) (also see Chapter 6 , Pharmacology).

Desflurane is not recommended for inhalation induction due to a high incidence of coughing not altered by premedication (58%) and frequent and severe laryngospasm (49%) with significant hemoglobin desaturation ( Zwass et al., 1992 ).

Maintenance of the Upper Airway During Induction

The pharyngeal airway is composed of collapsible soft tissues surrounded by bony structures (the mandible anteriorly and spinal column posteriorly). In the awake state, the pharyngeal airway is kept open by tonic and phasic contractions of pharyngeal dilator muscles contracting synchronously with contractions of the diaphragm with inspiration (see Chapter 2 , Respiratory Physiology). During induction of anesthesia, airway obstruction frequently occurs as the pharyngeal and laryngeal muscles are preferentially relaxed ( Nishino et al., 1984 ; Ochiai et al., 1989 ). In order to maintain the airway patent, the neck must be extended, the jaw thrust forward in a sniffing position, and the mouth open in case of nasal obstruction (the triple airway maneuver), with a moderate continuous positive airway pressure (CPAP; 10 to 15 cm H2O). It is therefore essential to establish an airtight system with the bag and mask and maintain CPAP to resist the collapsing force of relaxed upper airway structures ( Motoyama, 1997 ; Hammer et al., 2001 ) until the patient is sufficiently anesthetized to tolerate the insertion of an oral airway without developing laryngospasm (Guedel's Stage 3, including the loss of intercostal muscle activities) (see Chapter 2 , Respiratory Physiology). Once the steady state of surgical anesthesia is achieved, CPAP of 5 to 10 cm H2O appears sufficient to maintain upper airway patency in spontaneously breathing children ( Reber et al., 2001 ).

Major causes of airway obstruction during induction of anesthesia are (1) preexistent nasal obstruction when the mouth is closed by the anesthesiologist; (2) obstruction of the oropharynx and/or nasopharynx (velopharynx) by the relaxation of upper airway dilator muscles, and resultant collapse of velopharynx and/or posterior displacement of the tongue ( Ochiai et al., 1989 ; Motoyama, 1997 ;Hammer et al., 2001 ); and (3) laryngospasm. Insertion of an oropharyngeal or nasopharyngeal airway usually solves the first and second problems, provided that the anesthesia is sufficiently deep to prevent pharyngeal reflex. During sevoflurane anesthesia, an oropharyngeal airway is tolerated relatively early during induction compared with halothane. Laryngospasm is common with isoflurane anesthesia and more frequent and severe with desflurane anesthesia ( Zwass et al., 1992 ). A nasopharyngeal airway is better tolerated even when the anesthesia is too light for insertion of an oropharyngeal airway; it should be well lubricated and inserted very gently to prevent mucosal injury and epistaxis.

The oropharyngeal airway should be large enough to extend the tip behind the base of the tongue. The proper length can be estimated by holding the airway over the side of the child's face; the tip should be at or near the angle of the mandible. In children, the oral airway should always be inserted with the aid of a tongue depressor to pull the tongue forward. One should avoid the method of inserting the airway upside down to get it past the front teeth and then swinging it around into place. This practice, although used commonly and successfully in adult patients, tends to push the tongue posteriorly and obstruct the pharyngeal airway, particularly in infants; it also easily twists out loose front teeth in children ( Smith, 1980a ).

If the insertion of an airway does not relieve the obstruction, the patient may have laryngospasm due to mucosal irritation often initiated by the aspiration of saliva; the presence of oral airways may make matters worse. If the vocal cords are tightly closed, the use of continuous high pressure, pushing the secretions down into the larynx, simply intensifies the spasm and may also inflate the stomach, further interfering with pulmonary gas exchange and increasing the chance of regurgitation and aspiration of gastric contents. A normal child can tolerate a few moments of laryngospasm. By using 100% oxygen and a high intermittent positive pressure (40 to 60 mm Hg), one can usually squeeze enough oxygen through the child's glottis to avoid serious hypoxemia. One successful approach is to maintain moderate continuous positive pressure with an air-tight mask and to add a firm, intermittent squeeze to the bag synchronous with the end of each “expiratory” phase (or the “bearing-down” phase of the laryngospasm cycle) when the glottis relaxes momentarily, with or without evidence of inspiratory effort against the closed glottis. However, if the child begins to show bradycardia with rapid oxygen desaturation, one should not delay any longer and should administer succinylcholine (2 mg/kg) and atropine (0.02 mg/kg) intravenously or 5 mg/kg of succinylcholine intramuscularly ( Liu et al., 1981 ; Hannallah et al., 1986 ) and reestablish the airway patency without delay, with or without tracheal intubation.

Intravenous Induction

In children, as well as in adults, induction via the intravenous route has the advantage of speed plus elimination of the mask and its unpleasant odors. The major disadvantage is the child's exaggerated fear of the needle and the difficulty of venipuncture. EMLA (eutectic mixture of local anesthetics 2.5% lidocaine and 2.5% prilocaine) cream seems to help alleviate this problem ( Ehrenstrom et al., 1982 ;Maunuksela and Korpela, 1986 ; Freeman et al., 1993 ). Children under 6 to 7 years of age, however, have shown less overall benefit than older children in the use of EMLA for venous cannulation. This is probably due to the fact that the young child still sees the intravenous needle and fears that the cannulation will be painful. EMLA cream must be applied at least 1 hour prior to intravenous cannulation to provide sufficient dermal analgesia compared with placebo. The EMLA cream is placed on intact skin over a promising vein with an occlusive dressing applied over the cream. Two potential sites of venous cannulation should be prepared with EMLA cream, usually on opposite hands. EMLA sometimes causes vasoconstriction and makes the insertion of a cannula more difficult. Removing the EMLA patch 10 to 15 minutes before venipuncture and warming the site causes vasodilation and eases the cannulation. EMLA should not be used in infants under 12 months of age with glucose-6-phosphate deficiency or other children more susceptible to methemoglobinemia ( Frayling et al., 1990 ). Children 8 to 10 years of age and older may prefer an intravenous induction to a mask, often because they have some fear of the mask from a previous unpleasant experience.

The dorsum of the hand, the radial vein, and the saphenous and other veins of the foot are examined as preferential sites for venipuncture. The volar aspect of the wrist has small visible veins that are inviting but are difficult to maintain in an awake child unless the wrist is immobilized and fixed in an extended position beforehand. Furthermore, venipuncture here is extremely painful. Likewise, venipuncture on the scalp is exceptionally painful and should be done only when peripheral veins appropriate for venipuncture are not found elsewhere.

To avoid frightening a child, one should hold the needle out of sight, avoid use of the word “needle,” and divert attention. If EMLA cream has been applied, the occlusive dressing is removed and the cream is wiped off. The skin should be allowed to dry after wiping with alcohol lest the venipuncture be unnecessarily painful. The assistant should hold the extremity gently but firmly to avoid jerky movement. In order to fixate the veins in the dorsum of the hand, the skin is pulled down toward the fingers. If EMLA has not been used, intradermal injection of approximately 0.1 mL of 1% lidocaine is made with a 25-gauge (or smaller) needle, particularly when larger than a 20-gauge catheter is used. One should give a warning like “here comes a little pinch” and command “take a deep breath” at the time of inserting a needle to divert attention. Subsequent intravenous insertion of a larger needle through the skin wheal is painless and more often successful.

Unless excessive fluid and blood losses are anticipated, a 22-gauge catheter in young children and a 20-gauge catheter in older children undergoing an elective surgical procedure are sufficient for the need for fluid replacement. For a small infant, a 24-gauge catheter usually is sufficient for fluid replacement, and a 22-gauge catheter can be used for blood transfusion. Before the infusion of propofol or sodium thiopental, the anesthesiologist should make sure that there is a free flow of intravenous fluid in order to avoid an inadvertent, painful subcutaneous infusion.

The patient is oxygenated just before the induction of anesthesia. If the child objects to a facemask, oxygen can be delivered by holding the right-angle connector, without the mask, between the fingers of a cupped hand and insufflating oxygen without touching the patient's face. The effect of oxygen insufflation should be immediately apparent as the pulse oximeter reading rises from the high 90's to 100%.

Propofol

An intravenous induction dose of propofol in healthy unpremedicated children 3 to 12 years of age with a smooth transition to inhalation anesthesia (ED95) usually requires 2.5 to 3.0 mg/kg ( Manschot et al., 1992 ). Children younger than 2 years required a significantly larger dose (2.6 to 3.4 mg/kg) ( Aun et al., 1992 ), whereas older children needed less ( Manschot et al., 1992 ). Induction with propofol in children causes significant decreases in blood pressure and heart rate, similar to those observed after thiopental ( Mirakhur, 1988 ; Hannallah et al., 1991 ; Manschot et al., 1992 ). Propofol has antiemetic properties and causes less laryngospasm than thiopental ( Borgeat et al., 1990 ). Propofol, however, has some undesirable properties, such as pain on injection, allergic reactions, and rapid microbial growth ( Eyres, 2004 ). The pain on injection is troublesome and often causes erythema near the site of injection ( Manschot et al., 1992 ). Pain is less frequent if a large antecubital vein is used or lidocaine is administered into the intravenous catheter prior to the injection of propofol ( Hannallah et al., 1991 ). Alternatively, a mixture of 9 mL of propofol (1%) with 1 mL (25 mg) of thiopental reduces injection pain considerably (Fine GF, personal communication). The duration of propofol anesthesia is largely due to its redistribution rather than to metabolism and elimination from the body. Because larger induction doses are needed in infants and children, the recovery time from propofol is more prolonged in children than in adults ( McFarlan et al., 1999 ; Eyres, 2004 ).

Thiopental

An intravenous dose of thiopental in healthy children is 5 to 6 mg/kg ( Coté et al., 1981 ). In infants 1 to 6 months of age, the median effective dose (ED50) is reported to be 6.8 mg/kg; in infants less than 2 weeks of age, it is 3.4 mg/kg ( Jonmarker et al., 1987 ). In a well-premedicated child or when the intravenous injection of opioids (such as 1 to 2 mcg/kg of fentanyl or 0.1 mg/kg of morphine) is given as basal anesthesia preceding thiopental, 2 to 4 mg/kg of thiopental usually is sufficient for a modified inhalation induction with nitrous oxide and sevoflurane or halothane.

A reasonable and safer approach to intravenous induction and intubation, particularly in infants, is a “modified inhalation induction” in which the child is given a sedative intravenous dose of opioids (e.g., fentanyl 1 to 2 mcg/kg) or benzodiazepine (e.g., midazolam 0.1 to 0.2 mg/kg, unless the patient is already well premedicated), followed by propofol or thiopental. As soon as the patient loses consciousness, mask induction is initiated with 2 to 3 MAC of an inhaled anesthetic (sevoflurane or halothane) until anesthesia is induced and ventilation is assisted or controlled.

Ketamine

Ketamine may be chosen for intravenous induction in specific situations, especially in high-risk patients with cardiovascular instability. Ketamine increases airway secretions; atropine (0.01 to 0.02 mg/kg) or glycopyrrolate, half the dose of atropine, should be given to counteract this effect. In these patients, one should try to maintain the airway through the careful positioning of the head rather than with insertion of an oral airway, to avoid laryngospasm. With a dose of 2 mg/kg, a child usually assumes a catatonic condition and is “asleep” within 1 to 2 minutes.

Intramuscular Induction

Low-dose intramuscular ketamine (2 to 3 mg/kg) is also useful to facilitate inhaled induction of anesthesia in those children who are uncooperative ( Hannallah and Patel, 1989 ). Although it is preferable to avoid intramuscular injections, children who are unhappy despite parents being present and do not permit oral or transmucosal premedication are better served with an expeditious ketamine intramuscular injection. Inhalation induction or the insertion of intravenous cannula is easily performed 2 to 3 minutes after intramuscular ketamine.

Rectal Administration of Anesthetic

For the anxious child who is deathly afraid of a mask as well as a needle stick, inducing anesthesia via the rectum is probably the least disturbing method. This method is particularly appropriate when the parents are present during induction. Thiopental sodium and methohexital sodium have been used successfully for rectal administration. Both agents induce drowsiness and sleep rapidly and effectively (seeChapter 6 , Pharmacology). For practical purposes, the standard 2.5% intravenous solution often is most convenient, although 5% and 10% solutions are also used. The usual dose of thiopental for children who have had no other sedation is 30 to 40 mg/kg ( Kaufman, 1973 ). If thiopental is given as a supplement to previous but inadequate sedation, 20 mg/kg is advised.

Methohexital is reputed to produce more rapid induction than thiopental, but this is of little clinical significance when it is given rectally. Rectal methohexital should always be regarded as an agent to induce anesthesia rather than as a premedication. Airway irritability and hiccoughs, frequently observed during intravenous use, do not usually occur with rectal administration. Hypersensitivity reactions to methohexital have been reported but are rare ( Driggs and O'Day, 1972 ; Wyatt and Watkin, 1975 ; Liu et al., 1984 ). Apnea after rectal methohexital has been reported in children with meningomyeloceles and should be used with caution in these children ( Yemen et al., 1991 ).

With either thiopental or methohexital, the exact dose of thiopental and an additional 5 mL or so of air is aspirated in a 10- to 20-mL syringe, depending on the age of the child. The syringe is then connected to a 8F to 12F feeding tube, which is lubricated with surgical lubricant. The child is placed on the stretcher or held by the mother in the lateral or supine position with hips and knees flexed. The catheter filled to the tip with the barbiturate solution is inserted rectally. The syringe containing the medication and air is held vertically and the contents injected with a single gentle downward push of the plunger into the rectum. The syringe and the catheter should be removed as a unit. With this technique, the solution is pulsed by air and the catheter should be clear of solution when it is removed. Children often feel as though they need to have a bowel movement after the drug is administered ( Berry, 1986 ). The buttocks must be held together firmly with the hands to avoid the loss or evacuation of the barbiturate solution. It is effective in 95% of children within 5 to 10 minutes; waiting longer than 10 minutes will not increase the incidence of success. Without additional sedative/hypnotics, the child awakens in about 20 to 60 minutes.

Induction by rectal thiopental is suitable for administration in the child's bed or the child held by a parent. It is useful for resistant children, especially the developmentally delayed or those who, for any reason, comprehend poorly. Rectal induction is less desirable in children older than 4 years or with a weight greater than 20 kg because it becomes an issue of the volume of drug to be instilled, as well as it being somewhat socially unacceptable. Because of the rapid onset and profound sedation, an anesthesiologist should remain with the child from the time of its administration until the end of surgery and anesthesia. This adds considerably to total anesthesia time and is a major deterrent to the widespread use of rectal methohexital. Midazolam has also been used rectally ( Spear et al., 1991 ). A dose of 1.0 mg/kg (0.2% solution or, if volume exceeded 10 mL, undiluted 0.5% is used) is effective for preinduction of anesthesia and does not delay discharge from the postanesthesia care unit. It produces enough sedation for easy acceptance of the anesthesia mask, although loss of consciousness does not occur.

Combinations of rectally administered midazolam (0.5 mg/kg), ketamine (3 mg/kg), and atropine (0.02 mg/kg) are effective in facilitating separation of children aged 8 months to 7 years from their parents or intravenous cannulation ( Beebe et al., 1992 ). The addition of ketamine to midazolam caused more children to be asleep when separating from parents.

Indications for Altered Induction Techniques

Many patients in the pediatric age group have various pathophysiologic conditions requiring special methods of anesthetic induction. Those with obstructive respiratory disorders at different airway levels, including “tonsil bleeders”; those with cardiac or renal disorders, increased intracranial pressure, open eye injury, or a full stomach; and those with many other conditions involve special considerations. Each of these situations is discussed in a section in different chapters devoted to the field involved.

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

▪ LARYNGEAL MASK AIRWAY

The laryngeal mask airway (LMA) is a device that is being used increasingly since the early 1990s, both in children and in adults for general anesthesia where mask ventilation is appropriate but the procedure is long enough that endotracheal intubation would be used. The original LMA is constructed of reusable soft medical-grade silicone rubber. It does not contain latex and will withstand repeated autoclaving. Disposable LMAs are available and are made of soft plastic. There are six sizes of LMA ( Table 10-1 , Fig. 10-6 ), with the appropriate size based on the patient's weight. Studies by Voyagis and others (1996) and Loh and others (2002), however, have suggested that larger than previously suggested sizes may be needed for young children of between 10 and 20 kg body weight. For older adolescents, the gender should also be considered, with size 5 for males and size 4 for females ( Voyagis et al., 1996 ). Flexible LMAs are also available in all six sizes and are advantageous for certain types of procedures, such as tonsillectomy. The Fastrach LMAs for blind oral intubation are available only in three large sizes (3, 4, and 5).

TABLE 10-1   -- Laryngeal mask airway sizes[*]

Mask Size

Patient Weight (kg)

Internal Diameter (cm)

Length (cm)

Maximum Cuff Volume Air (mL)

Largest ETT[†] (ID, mm)

1

<5

5.25

11.5

4

3.5

1.5

5 to 10

6.1

13.5

7

4.0

2

10 to 20

7.0

15.5

10

4.5

20 to 30

8.4

17.5

14

5.0

3

30 to 50

10

22

20

6.0 Cuffed

4

50 to 70

10

22

30

6.5 Cuffed

5

Adult, 70 to 100

11.5

23.5

40

7.0 Cuffed

6

Large adult >100

11.5

23.5

50

7.0 Cuffed

*

From LMATM Instructional Manual, Revised 2003, LMA North America, Inc., San Diego, CA. (Courtesy of LMA North America, Inc.)

ETT, endotracheal tube. This is the largest ETT that will pass inside the LMATM for endotracheal intubation after the LMATM is properly placed.

 

 
 

FIGURE 10-6  The original laryngeal mask airways (LMA Classic). From the top to bottom: sizes 1, 1.5, 2.0, 2.5, 3, 4, 5, and 6.  (Courtesy of LMA North America, Inc, San Diego, CA, with permission.)

 



The LMA ProSeal is a new LMA with a rear cuff and a drainage tube that allows the insertion of a gastric tube and the evacuation of gastric gas and liquid. Pediatric-size LMA ProSeals (sizes 1.5 and up) without a rear cuff have become available. Insertion of a ProSeal LMA is as easy as insertion of the classic LMA ( Shimbori et al., 2004 ). Before use, the LMA cuff is checked for leaks by inflating air into the cuff, as done with cuffed endotracheal tubes.

There are several methods of LMA insertion. The classic insertion, as originally described by Brain (1983) , is to aspirate the air from the cuff of the LMA, making sure that the cuff deflates flat by placing it on a flat surface as it is deflated. The LMA is inserted blindly into the pharynx, forming a low-pressure seal around the laryngeal inlet in a spontaneously breathing patient ( Haynes and Morton, 1993 ;Pennant and White, 1993 ). The sniffing position is recommended for insertion of the LMA, as with endotracheal intubations. With the patient's mouth open, the distal aperture of the LMA facing anteriorly, the tip of the cuff is slid down as it is firmly and continuously pressed against the hard palate using the index finger of the right hand to guide the tube over the back of the tongue. The tube is then advanced in one smooth movement until a characteristic resistance is felt as the upper esophageal sphincter is engaged ( Pennant and White, 1993 ). The reverse technique has also become a common practice: inserting the LMA with the aperture facing the palate and, when the resistance is felt, the tube is then rotated 180 degrees to cover the laryngeal inlet. There is no statistical difference between the two methods regarding successful insertion ( Soh and Ng, 2001 ), and when one method is not working, it may be possible to change to the other. Alternatively, insertion of the LMA partially inflated in children requires less time and is associated with a higher success rate ( O'Neill et al., 1994) .

Once the LMA has been inserted, it is then inflated with 5 to 30 mL of air (depending on the size as recommended (see Table 10-1 ). A slight and outward movement of the LMA usually follows this maneuver by 1 to 2 cm. Any further movement is usually indicative of incorrect placement and the LMA should be deflated, removed, and reinserted. After the LMA is positioned in the midline, stabilized with bite blocks in both sides of the LMA, and taped across the upper lip (as with the endotracheal tube), the 15-mm proximal connector is attached to the anesthesia circuit and the patient may breath either spontaneously or through controlled ventilation with a low peak pressure (<15 cm H2O).

When correctly placed, a seal pressure of 20 cm H2O is usually adequate and may predict correct placement. Inagawa and others (2002), however, found little correlation between seal and positioning of the LMA. Several studies have looked into the placement of the LMA both fiberoptically ( Rowbottom et al., 1991 ; Dubreuil et al., 1993 ) and radiologically (Goudsouzian et al., 1992) and found that clinically functioning LMAs were not necessarily in the correct position. Keidan and others (2000), however, reported a significant correlation between the inspiratory work of breathing and percent of airway obliteration by the epiglottis examined fiberoptically through the LMA. Movement of the head from the neutral position may easily dislodge the LMA and could have a profound effect on the LMA position and the ability to ventilate the patient ( Okuda et al., 2001 ). When general anesthesia under a caudal block and spontaneous breathing is planned for urogenital or other procedures, the anesthesiologist should induce the patient via mask and bag, insert an oral airway, and turn the patient to the lateral position to perform the caudal block; the patient is then turned back to the supine position, the stomach is emptied, and the LMA is inserted in order to avoid its dislodgment.

The LMA is more difficult to use in children than in adults and is associated with a higher incidence of misplacement ( Rowbottom et al., 1991 ; Dubreuil et al., 1992 ). The smaller the child, the more difficult is the placement of the LMA in the correct position ( Park et al., 2001 ). This is due to the fact that pediatric LMAs are miniaturized adult-sized LMAs and have a smaller margin of error in positioning the device; it thus can be more easily dislodged.

Problems of LMA insertion are often related to inadequate depth of anesthesia. The LMA may be inserted immediately after an adequate dose of an intravenous induction agent ( Allsop et al., 1995 ) or administration of a volatile anesthetic agent, although the depth of anesthesia for LMA insertion is less than that required for endotracheal intubation ( Aantaa et al., 2001 ). The depth of anesthesia for placing an LMA, however, is greater than when an oral airway is placed. Complications relating to poor positioning are airway obstruction, higher ventilatory pressures in patients on intermittent positive pressure ventilation or controlled ventilation, larger inspiratory leakage, more gastric insufflation, and other related complications that occur more frequently with younger than with older children. A study by Verghese and Brimacombe (1996) has shown the LMA to be safe and effective with a less-than-0.15% complication rate. The LMA is relatively contraindicated in patients who are obese or at risk for aspiration.

The LMA has been used in both conventional and nonconventional ways. Properly inserted LMA with the cuff inflated provides a low-pressure seal around the larynx, enabling positive pressure ventilation. The new LMA with the suction channel (LMA ProSeal) has a definite advantage over the classic LMA for positive pressure ventilation because the pediatric ProSeal LMA allows the passage of a 10F suction catheter more than 90% of the time ( Shimbori et al., 2004 ) and, at the same cuff inflation pressure, air leak pressure around the cuff is much higher than with the classic LMA (30 versus 20 cm H2O) ( Gaitini et al., 2004 ). Both pressure-controlled and volume-controlled ventilation have been used without the major problems of inflating the stomach. However, one is able to ventilate the patient more effectively with lower pressures using the pressure control mode ( Keidan et al., 2001 ). In patients with marked craniofacial abnormalities whose vocal cords cannot be visualized with conventional laryngoscopy for intubation, the LMA has a unique advantage and may be inserted with the patient awake, allowing for spontaneous inhalation induction and airway maintenance ( Markakis et al., 1992 ;Carenzi et al., 2001 ).

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

Copyright © 2005 Mosby, An Imprint of Elsevier

▪ ENDOTRACHEAL INTUBATION

The indications for endotracheal intubation in children are similar to those in adults, with small, but important, differences, particularly in infants. These differences are due to the altered respiratory mechanics in infants and children compared with adults and to the fact that infants are more prone to upper airway obstruction and gastric distention with positive-pressure ventilation under general anesthesia. Potential disadvantages of endotracheal intubation include increased airway resistance when the patient is breathing spontaneously; trauma of intubation to larynx and subglottis; possible laryngospasm during both intubation and extubation; damaged or dislodged teeth; and laceration of soft tissues and hemorrhage, especially with nasotracheal intubation, esophageal intubation, and endobronchial intubation.

▪ INDICATIONS FOR ENDOTRACHEAL INTUBATION

In general, intubation is indicated in most infants less than 6 months of age. The benefit of preventing potential difficulties in maintaining upper airway patency and the likelihood of distending the stomach by anesthetic gases with manual ventilation outweigh the potential complications of carefully executed intubation.

In infants and children between 6 and 12 months of age undergoing simple elective surgical procedures such as inguinal herniorrhaphy, intubation is optional, depending on the experience and choice of the anesthesiologist and the patency of upper airways under general anesthesia. Orthopedic or plastic procedures in children involving the extremities and lasting longer than 1 to 2 hours may be a relative indication for intubation for the purpose of safety, but more often in such cases it is used for the anesthesiologist's convenience.

Elective procedures in children older than 1 year that seldom justify intubation include short orthopedic procedures (wire removal, cast change), perineal and urologic procedures (inguinal hernia repairs, circumcision, cystoscopy), minor surgery on body or limbs, extraction of three or four deciduous teeth, probing and irrigation of lacrimal ducts, and myringotomy and tube insertion.

Needless to say, endotracheal intubation is as mandatory in children as in adults for intrathoracic, upper abdominal, and head and neck surgery and for laparoscopic procedures, as well as for procedures requiring prone, lateral, and sitting positions. In addition, intubation is necessary in patients with a full stomach or intestinal obstruction.

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

▪ EQUIPMENT

▪ LARYNGOSCOPES AND BLADES

Laryngoscope handles of standard length are suitable for pediatric use, although those of smaller diameter are easier to manipulate and are recommended, particularly for infants and small children. In the evaluation of laryngoscope blades, the length is of obvious importance, but additional features to note are the width and shape of the tip, the bore, and the curvature.

The use of a straight blade requires slightly more relaxation than use of a curved blade, but a straight blade gives better exposure in children. The curved tip of the Phillips blade makes it possible to retract the epiglottis, as with a Macintosh blade, without actually picking it up and lifting it directly ( Fig 10-7 ). In infants, the wider bore of the Wis-Hipple and Flagg blades enables one to see and to pass a tube more easily than does the flattened aperture of the Miller blade. For older children, the flatter, No. 2 Miller blade becomes more advantageous, because it is less likely to chip large new incisors. The blade designed by Phillips and Duerkson (1973) , with a more pronounced terminal curve, has been particularly useful in a situation where the exposure of the larynx is more difficult ( Fig 10-8 ).

 
 

FIGURE 10-7  Standard laryngoscope blades commonly used in pediatric anesthesia. Left (top to bottom), Miller 1 and 2, Macintosh 1 and 2, Bradshaw 1 and 2. Center, Flagg 1 and 2, Wis-Hipple 1 and 1.5, and Phillips 1. Right, Pediatric and standard laryngoscope handles.

 

 

 
 

FIGURE 10-8  Infant laryngoscope blades with different curvatures and light bulb positions (left to right): Wis-Hipple 1, Miller 1, and Phillips 1.

 

 

The Macintosh curved blade allows more room to pass the bulky cuffed endotracheal tube but may require a stylet unless the tube is properly curved. The small curved blade (No. 2 Macintosh) occasionally is useful in special situations, as in a small child with an ankylosed jaw or contractures of the neck secondary to burns.

The light bulb deserves special attention. For small patients, it is important to have the bulb near the tip of the blade. One finds considerable variation in this feature (see Fig. 10-8 ). If the bulb is far recessed from the tip, such as in the No. 1 Miller blade, the soft tissues of the infant's pharynx close around it and obstruct the light.

When testing a laryngoscope, one should be sure that the light is bright and of high intensity. A dim yellow light of low intensity denotes a failing battery and may prove inadequate. It is also important to confirm proper electrical conduction between the laryngoscope handle and blade by engaging the blade in position and observing a steady bright light before its use. It is advisable to have laryngoscope blades of several different shapes and sizes available before beginning induction and intubation.

The newer fiberoptic laryngoscopes have certain advantages. A high-intensity bulb housed in the handle, not on the blade itself, emits cool, high-intensity light through the glass fiber rod, eliminating the usual electrical problems associated with ordinary laryngoscopes. The blade is easier to clean; there is no bulb to change. One possible disadvantage may be that the sight of laryngeal structures can be blocked by the glare of bright, focused light reflecting from intervening soft tissues when exposure is inadequate.

▪ FLEXIBLE (FIBEROPTIC) BRONCHOSCOPE

Technological advances in flexible fiberoptic bronchoscopy enable one to intubate patients with difficult airways ( Patil et al., 1983 ) (see Chapter 9 , Anesthetic Equipment and Monitoring). The smallest fiberoptic bronchoscope with flexible control of the tip has an outer diameter (OD) of 1.8 mm (Olympus Corporation of America, New Hyde Park, NY) and can easily accommodate an endotracheal tube 2.5 mm in inner diameter (ID) without the connector ( Fig. 10-9 ) ( Finer et al., 1992 ). The smallest bronchoscope with a suction channel that can be used to instill topical anesthetic or to insufflate oxygen has an OD of 2.8 mm (ID = 1.2 mm) and accommodates an endotracheal tube with an ID of 3.5 mm. With advanced digital camera technology, the quality of video images has improved markedly. A major disadvantage of this instrument and technology, however, is that its proper use requires considerable practice and experience. In addition, the optic fibers are extremely delicate and are easily broken, leaving black dots on the image; and the instrument is too expensive for casual use.

 
 

FIGURE 10-9  A small Olympus pediatric fiberoptic bronchoscope (2.7 mm OD) with a flexible tip accommodates a 3-mm ID Shiley nasal tube (right) for intubation.

 

 

▪ BULLARD LARYNGOSCOPE

The Bullard laryngoscope, a fiberoptic and mirror combination instrument, deserves mention ( Fig. 10-10 ) (also see Chapter 9 , Anesthesia Equipment and Monitoring). The Bullard laryngoscope can be attached to a regular laryngoscope handle, it facilitates indirect oral laryngoscopy and endotracheal intubation with minimal practice; and it is particularly useful for difficult airways ( Borland, 1988 ). To insert the Bullard laryngoscope, the mouth is opened manually and the blade is inserted while the shaft of the scope (and the laryngoscope handle) is kept horizontally ( Fig. 10-10A ). The laryngoscope handle is then rotated from the horizontal to vertical position so that the tip of the blade can be slid around the tongue ( Fig. 10-10B and C ). The blade is then elevated beyond the epiglottis and lies against the dorsal surface of the tongue ( Fig. 10-10C ) ( Borland, 1988 ). It can also be attached to a video camera, and the enlarged image can be viewed on a video screen by multiple observers.

 
 

FIGURE 10-10  Sequence of placement of Bullard laryngoscope (lateral view). The mouth is opened manually, and the laryngoscope handle is rotated from the horizontal to vertical position, so that the blade can be slid around the tongue (A and B). The blade is then elevated to lie against the tongue's dorsal surface (C).  (From Borland LM: Int Anesthesiol Clin 26:27, 1988.)

 

 

 

▪ ENDOTRACHEAL TUBES

Since the early 1980s, disposable, sterile endotracheal tubes have been used in the United States and elsewhere. They are made of biologically inert, implant-tested (bearing the mark Z-79) polyvinyl chloride (PCV) in order to prevent chemical irritation to the upper airways. These disposable tubes are packaged with a suitable plastic, thin-walled adapter that minimally affects the internal diameter of the tube. PCV tubes are flammable and should not be used for laser surgery involving the airways. Under these circumstances, one should use nonflammable or laser resistant tubes specifically manufactured for this purpose (see Chapter 23 , Anesthesia for Otorhinolaryngology Surgery).

Most endotracheal tubes for infants and small children today have length markers from the tip, printed at 1-cm intervals, to aid the anesthesiologist in securing the tube at the proper depth ( Fig 10-11 ). The Magill-type oral endotracheal tubes are relatively short and are exclusively for oral intubation, although endobronchial intubation can still occur if the tube is advanced indiscriminately, particularly in infants and young children. The tube has a black band or bold black line around the wall 2.0 to 5.0 cm from the tip (the distance varies according to the size as well as by the manufacturer) that should be situated at the vocal cords when the tube is at the proper depth in infants and children of normal anatomy. Variations in the depth mark among different manufacturers are considerable ( Goel and Lim, 2003; Wallace and Bell, 2004 ), and reliance upon these markers (especially the black band) is potentially hazardous with endobronchial intubation or accidental extubation ( Munro et al., 1995 ; Molendijk, 2001). Sound clinical judgment is essential for optimal tube placement, especially with premature infants and those with abnormal facial and airway anatomy.

 
 

FIGURE 10-11  Endotracheal tubes used in pediatric anesthesia (left to right): Magill oral tube, Shiley nasal tube, nasal and oral RAE tubes, Sheridan tube with a gas sampling port, and armored tube tied in knot.

 

 

The Shiley nasotracheal tube (see Fig 10-11 ) is a soft, flexible tube used primarily for nasal intubation. It can be cut to suit individual needs and preferences and can be used orally or through a tracheostomy stoma under special circumstances. This and many other tubes have single, double, and triple circumferential line markers about 1 cm apart, starting 2.0 to 2.5 cm from the tip. The distance of the middle (double) line from the tip usually is the proper depth for the glottis.

Armored or anode endotracheal tubes (see Fig. 10-11 ), consisting of thin silicon rubber (Silastic) reinforced by coiled wire, have the advantage of tolerating extreme flexion without kinking. In limited situations they prove valuable. Although Silastic anode tubes have improved considerably from older versions made of latex, their wall is still much thicker than that of the PVC tube, and there is a tendency for the tip of the tube to flip out of the trachea even when the tube is properly secured at the mouth ( Cohen and Dilon, 1972) . For this reason some pediatric anesthesiologists prefer Magill or preformed, acute-angled (RAE) tubes for neurosurgical procedures, reserving the anode tube for exceptional surgical procedures about the face.

The preformed, acute angle oral and nasal endotracheal tubes developed by Ring, Adair, and Elwyn in 1975 (RAE tubes) (see Fig. 10-11 ) are particularly useful for oral surgery as well as for certain neurosurgical procedures. There are other preformed orotracheal tubes not commonly used in the United States ( Lindholm, 1973 ; Morgan and Steward, 1982b ).

The oral RAE tube is bent sharply at the lower incisors and can be fixed over the mandibular midline for surgery involving the oral cavity, such as adenotonsillectomy or cleft palate repair. The nasal RAE tubes are about 1 inch longer, and the preformed acute bend is opposite to that of the oral RAE tube. The bend is directed over the patient's forehead yet eliminates pressure on the naris. A potential problem of this otherwise excellent innovation is that the length of the oral RAE tube to the acute angle, particularly in smaller oral RAE tubes, is slightly too long in some children, so that one must be careful to avoid endobronchial intubation. The uncuffed nasal RAE tubes (Mallinckrodt), on the other hand, tend to be a little too short and may cause accidental extubation, whereas the cuffed nasal RAE tubes of the same internal diameters are about 1 inch longer than the uncuffed nasal RAE tube.

Cuffed Endotracheal Tubes

Until the mid-1990s, the routine use of cuffed endotracheal tubes was not recommended in children younger that 8 to 10 years ( Fisher, 1989 ; Coté and Todres, 1993 ; Wood, 1986 ), although the recommended age for cuffed tubes varied among the authors of pediatric textbooks ( Uejima, 1989 ). Literature, however, suggests that the recommendation for the use of uncuffed endotracheal tubes in children may be outdated ( Khine et al., 1997 ; Fine et al., 2000 ; James, 2001 ; Fine and Borland, 2004 ).

The use of uncuffed tubes had been an important consideration through the 1960s, when most young patients breathed spontaneously under diethyl ether anesthesia. The primary reason for not using a cuffed endotracheal tube had been that one must choose a cuffed tube one or two sizes (0.5 to 1.0 mm ID) smaller than the uncuffed tube to accommodate the bulk of the cuff through the subglottis, the narrowest portion of the upper airway ( Eckenhoff, 1951 ). An endotracheal tube with a smaller diameter would markedly increase flow resistance (as much as fourth power of the diameter) and result in increases in work of breathing (see Chapter 2 , Respiratory Physiology).

Another major argument against cuffed endotracheal tubes had been based on early experiences relating to laryngeal damage caused by overinflated, high-pressure/low-volume cuffed tubes for prolonged periods of time ( Hawkins, 1977 ; Honig, 1979 ). Laryngeal damage should not occur from inflated endotracheal cuffs of limited duration intraoperatively if care is taken to make sure that the cuff is properly placed in the mid trachea, rather than straddling in the larynx ( James, 2001 ). Okuyama and others (1995) determined the proper positioning of the cuff in small children by palpating the cuff externally between the cricoid and sternal notch. There were no complications attributable to the use of small (3.5 to 5.0 mm ID) cuffed tubes in children ( Okuyama et al., 1995 ). Studies using low pressure-high volume cuffs have shown no difference in the rate of complications between cuffed and uncuffed endotracheal tubes in terms of long-term complications, such as subglottic stenosis ( Deakers et al., 1994 ).

Care must be taken not to inflate the cuff greater than 25 cm H2O to remain below the capillary perfusion pressure (20 to 25 mm Hg) of the laryngotracheal mucosa and to avoid pressure-induced mucosal ischemia and scarring ( Tonnenson et al., 1981 ; Seegobin et al., 1984 ; James, 2001 ). During general anesthesia, nitrous oxide increases cuff pressure in a time-dependent fashion ( Mehta, 1981 ); as high as six times the initial pressure can be reached and could cause laryngeal and tracheal mucosal ischemia ( Patel et al., 1984 ). Alternatively, Patel and others (1984) recommend using saline, instead of air, to inflate the cuff. Inflating the cuff with the same gas mixture of nitrous oxide and oxygen should also protect the cuff from hyperinflation. In 174 children under general anesthesia with nitrous oxide using cuffed tubes inflated with room air, the cuff pressure was noted to increase variably, with increased cuff pressure occurring in 39% of cases. Numerous gas removals were required to maintain the cuff pressure less than 25 cm H2O, especially during the first hour of anesthesia, independent of the tube sizes (Felten et al., 2003). For prolonged endotracheal anesthetics with nitrous oxide, a manometer should be attached to the cuff to monitor cuff pressures and prevent mucosal injury to the upper airways.

With a cuffed endotracheal tube, there is rarely a need for repeated laryngoscopic procedures because an endotracheal tube 0.5 to 1.0 mm (ID) smaller than the uncuffed tube is always selected and the leak around the tube is sealed by inflating the cuff (to 20 to 25 cm H2O), thus avoiding multiple intubation attempts, important risk factors for trauma to the larynx and trachea ( Khine et al., 1997 ). Choosing the correctly sized uncuffed endotracheal tube based on formulas tends to be extremely difficult ( King et al., 1993 ). Additionally, the leak test (listening for leakage of air around the endotracheal tube) is unreliable, with large interobserver variations ( Schwartz et al., 1993 ). Choosing cuffed endotracheal tubes solves all of these problems.

Finally, the use of cuffed endotracheal tubes is more economical than using uncuffed tubes. With cuffed tubes, a lower fresh gas flow can be used. Maintenance of inhalation anesthesia with low gas flow is not possible with uncuffed tubes with large leaks, and consumption of anesthetic agents increases as fresh gas flow is increased. Khine and others (1997) have shown that increased gas leak around the tube into the operating room environment importantly contributes to air pollution of the operating room, increasing anesthetic gases above the safe levels recommended by the National Institute of Occupational Safety and Health (NIOSH) (1997) (see www.osha.gov). Increased pollution of the operating room with anesthetic gases (particularly nitrous oxide) has been causatively linked to an increased incidence of miscarriages among female anesthesia providers exposed to anesthesia (Rowland et al., 1992, 1995 [268] [267]).

In 1995, Okuyama and others in Japan reported a routine use of cuffed endotracheal tubes in small children without complications associated with this practice. At Hopital d—enfants Armand Trousseau in Paris, all children requiring mechanical ventilation intraoperatively have been intubated with cuffed endotracheal tubes since 1997 ( Murat, 2001a ). Of 3434 children under 8 years of age, 904 were infants (<1 year old). Of 55 respiratory complications reported, none were attributable to intubation and no subglottic stenosis was reported. The atmospheric level of nitrous oxide measured at the level of the anesthesia provider decreased from 48.1 ppm to 0.3 ppm after the institution wide adoption of the cuffed tube and closed circle system ( Murat, 2001a ).

One potential problem of using cuffed pediatric endotracheal tubes may be the inconsistency of existing cuffed tubes produced by different manufacturers, in terms of outer diameter for the same size (ID) tubes, different depth markings, and cuff length. There is the potential of cuffs inflating within the larynx or endobronchial intubation even when the cuff is properly positioned in the mid trachea ( Weiss et al., 2004 ).

Stylets

Intubation in normal children rarely calls for the use of a stylet, particularly as a straight laryngoscope blade is used routinely. A stylet is likely to complicate the procedure, because its extraction after passage of the tube sometimes is difficult (it should be lubricated when used), inviting laryngospasm and hypoxia. The presence of a stiff, pointed object always adds potential trauma. A stylet, however, may help when patients have anatomic abnormalities and they should be kept available. The stylet of silicone-coated soft wire, manufactured for this use, is preferable; three different sizes are usually available to accommodate various tube sizes. Except for the most difficult intubation, the tip of a stylet should be recessed at least 1.5 to 2 cm from the tip of the endotracheal tube to keep the tip of the tube flexible and less traumatic, and the tube should be stoppered by a silicon rubber cork, or the stylet should be bent at the endotracheal tube adaptor to prevent accidental forward displacement of the stylet.

Guidelines for Endotracheal Tube Size and Depth

Various methods have been devised for choosing the correct diameter of endotracheal tubes in infants and children. Several formulas have been suggested and proved to be useful. These formulas should be used only as a general guide, however, because of the great variations in laryngeal size in relation to age, weight, or body length, revealed in data obtained at postmortem dissection ( Engel, 1962 ; Butz, 1968 ), in living subjects using graduated bougies ( Chodoff and Helrich, 1967 ; Keep and Manford, 1974 ; Mostafa, 1976 ), and by radiographic examination ( Wittenborg et al., 1967 ). The formula most frequently used is that of Cole (1957) :

Or its modification ( Morgan and Steward, 1982 ):

Both versions are applicable in children older than 2 years.

Penlington's formula (1974) is based on analysis of the data of Keep and Manford (1974) and gives a tube size similar to that derived with the Cole formula.

For children less than 6½ years of age:

For children 6½ years and older:

Another clinically useful yet scientifically untested method used by some anesthesiologists is to compare the outer diameter of the tube with that of the child's small (fifth) finger. Again, these formulas are useful as general guides, but the airway size varies greatly from one child to the next, necessitating a leak test after every intubation to confirm that the tube size is adequate. The leak test is accomplished by gently squeezing the anesthesia bag or by closing the pop-off valve of the anesthesia circuit and letting the airway pressure rise slowly; the airway pressure at which audible gas leak occurs around the tube is detected with a stethoscope. The leak pressure should be between 15 and 25 cm H2O. When a cuffed endotracheal tube is used, the selection of the tube size is less important, because an endotracheal tube one or two sizes (0.5 to 1.0 mm ID) smaller than the uncuffed tube normally used is selected and the gas leak around the tube is accommodated by inflating the cuff.

In the classic retrospective study by Koka and others (1977) , postoperative laryngotracheitis (postintubation croup) was associated with excessive endotracheal tube size (no leak at 40 cm H2O) more than any other factor. Furthermore, the use of an oversized tube has a greater effect on the incidence of postintubation croup in children with a history of infectious or postintubation croup compared with those without a similar history ( Lee et al., 1980 ). Khalil and others (1998) did not find a similar correlation between the leakage of airway gas mixture around the tube and the incidence of postoperative croup among 159 healthy outpatient children undergoing strabismus correction. They, however, did find a positive correlation between the duration of surgery (>2 hours) and the incidence and severity of postoperative croup. This difference in the postintubation croup may be related in part to the difference in the materials of the endotracheal tube'sterile, implant-tested tubes versus the older-type tubes used in the earlier study, which were not sterilized. Indeed, Litman and Keon (1991) found far less incidence of postintubation croup (0.1%) among 5589 healthy children compared with the incidence of 1% among the 7875 children reported in the original study by Koka and others (1977) . Nevertheless, oversized endotracheal tubes are clearly associated with subglottic injury, and the air leakage around the endotracheal tube should be kept between 15 and 25 cm H2O for both cuffed and uncuffed tubes to prevent ischemia of mucosa around the endotracheal tube. This also ensures adequate tidal ventilation.

A report with an editorial in Anesthesiology has raised renewed awareness of laryngeal trauma from routine endotracheal intubation. Tanaka and others (2003) studied laryngeal resistance under general anesthesia in adult patients before and after clinically atraumatic intubations lasting 1 to 4 hours. After extubation they found that airway resistance (pressure drop across the larynx) increased significantly from preintubation values, whereas there was no change in laryngeal resistance postoperatively in the control group of patients anesthetized with LMA. Furthermore, flexible laryngoscopy revealed considerable laryngeal swelling and narrowing of the vocal cord angle only in the postextubation group ( Tanaka et al., 2003 ). This study raises a great deal of concern about safety, regarding whether routine endotracheal intubation is as safe as one assumes (or wishes) ( Maktabi et al., 2003 ). This concern is especially valid with pediatric anesthesiologists, because the effect of upper airway swelling on airway resistance would be far greater in infants and young children with smaller airways sized in absolute terms (see Chapter 2 , Respiratory Physiology).

Table 10-2 is a general guide for the choice of tube diameter related to age, as recommended by Smith (1980b) and Davenport (1973) , with modifications. One takes the endotracheal tube size indicated as most suitable as indicated in the table, as well as the next larger and next smaller sizes. Of these three, one should be the correct size. The tube diameters listed should allow some leakage around the tube at 20 to 25 cm H2O of airway pressure if the size is adequate yet not excessive.


TABLE 10-2   -- Endotracheal tube size[*]

Age

Weight (kg)

ID (mm)

Length (OT) (cm)

Length (NT) (cm)

Suction Catheter (F)

Premie

0.7 to 1.0

2.5

7 to 8

9

5

Premie

1.0 to 2.5

3.0

8 to 9

9 to 10

5

Newborn

2.5 to 3.5

3.5

9 to 10

11 to 12

6

3 mo

3.5 to 5.0

3.5

10 to 11

12

6

3 to 9 mo

5.0 to 8.0

3.5 to 4.0

11 to 12

13 to 14

6

9 to 18 mo

8.0 to 11.0

4.0 to 4.5

12 to 13

14 to 15

8

1.5 to 3 yr

11.0 to 15.0

4.5 to 5.0

12 to 14

16 to 17

8

4 to 5 yr

15.0 to 18.0

5.0 to 5.5

14 to 16

18 to 19

10

6 to 7 yr

19.0 to 23.0

5.5 to 6.0

16 to 18

19 to 20

10

8 to 10 yr

24.0 to 30.0

6.0 to 6.5

20 to 22

21 to 23

10

10 to 11 yr

30.0 to 35.0

6.0 to 6.5[†]

20 to 22

22 to 24

12

12 to 13 yr

35.0 to 40.0

6.5 to 7.0[*]

20 to 22

23 to 25

12

14 to 16 yr

45.0 to 55.0

7.0 to 7.5[*]

20 to 22

24 to 25

12

Data modified from Smith RM: Anesthesia for infants and children. CV Mosby, 1980, St. Louis; Davenport HT: Paediatric anaesthesia. Year Book Medical Publishers, 1973, Chicago.

ID, inner diameter; OT, orotracheal tube; NT, nasotracheal tube; F, French size (number is approximately equal to ID × 4).

 

*

The endotracheal tube should fit so as to allow full normal expansion of both lungs with positive airway pressure but to permit a gas leak about the tube at 20 to 25 cm H2O.

Cuffed tube.

 

 

Should the child be reintubated if there is no gas leakage around the endotracheal tube (>30 cm H2O) after the initial intubation? A practical guideline would be to consider changing the tube to the next smaller (i.e., 0.5 mm less ID) size, if the surgical procedure is expected to take longer than 2 hours ( Khalil et al., 1998 ). If the passage of the endotracheal tube was smooth without resistance and the case is expected to be relatively short (i.e., <1 hour), the tube may be kept in place, considering the fact that each attempt for intubation would add an additional chance of causing more mucosal damage to the larynx ( Tanaka et al., 2003 ). In either case, the patient should be pretreated with dexamethasone (0.4 to 0.5 mg/kg) to prevent mucosal swelling and postoperative croup. If one plans to use a cuffed endotracheal tube, the tube size should be 0.5 to 1.0 mm ID smaller than the uncuffed tube, to accommodate the easy passage of the cuff through the subglottic space.

Endotracheal Tube Length

Much concern has also been shown for establishing the proper lengths for oral and nasal endotracheal tubes at different ages ( Shellinger, 1964 ; Fearson and Whalen, 1967 ; Coldiron, 1968 ; Mattila et al., 1971 ; Morgan and Steward, 1982a, 1982b [216] [215]). In most full-term newborn infants, the proper distance is 9 to 10 cm at the incisor; it is considerably less in the premature infant. At 1 year of age, the length increases to about 12 cm ( Davenport, 1973 ), and at 3 years, it increases to 14 cm ( Morgan and Steward, 1982b ). Beyond this age, Morgan and Steward (1982a) found remarkably good correlations between airway length (incisors to midarea of trachea) and age, height, or weight. Their formula, based on regression equations for age (>3 years), can be approximated by the following simplified formula:

which closely resembles that of Cole (1957) (age/2 + 12). Airway length also can be estimated by the following equations by Morgan and Steward (1982a) :

As with tube diameter, however, the variations prove too great to allow a reliance on any predetermined reference scale. The correct length, therefore, must be determined individually at the time of intubation. The tip of the endotracheal tube should be advanced under direct vision, not more than 2.5 cm in newborn infants, because the distance between the glottis and the carina is only 4 to 5 cm and is even shorter in premature neonates ( Fearson and Whalen, 1967 ). In older children, a cuffed endotracheal tube is advanced not more than 1 cm beyond the upper end of the cuff, to disappear through the glottis. The desired length of a nasotracheal tube may be considered to be 20% more than that of an orotracheal tube for practical use ( Smith, 1980b ).

Yates and others (1987) derived a simple formula for estimating the nasotracheal tube length in infants and children, based on the tube size S (ID) chosen by the formula of Morgan and Steward (1982b) :

The length of the nasotracheal tube (L) is:

The practical formula is simplified as follows:

Table 10-3 is a comparison of the estimated nasotracheal tube length with this formula and two previously published formulas (Rees, 1966; Steward, 1979 ).


TABLE 10-3   -- Recommended nasotracheal tube dimensions

 

TUBE LENGTH (L) (cm)

Age (yr)

Tube Size (S) (ID, mm)

Yates et al. (1987)

Rees (1966)

Steward (1979)

0 to 3 mo

2.5 to 3.0

9.5 to 11.0

11.8

13.5

4 to 7 mo

3.5 to 4.0

12.5 to 14.0

13.6

 

1

4.0

14.0

14.5

15.0

2

4.5

15.5

15.2

16.0

3

4.5 to 5.0

15.5 to 17.0

15.6

 

4

5.0

17.0

16.5

17.0

5

5.0 to 5.5

17.0 to 18.5

16.8

 

6

5.5

18.5

17.1

19.0

7

5.5 to 6.0

18.5 to 20.0

17.8

 

8

6.0

20.0

18.3

21.0

9

6.0 to 6.5

20.0 to 21.5

18.8

 

10

6.5

21.0

19.1

22.0

11

6.5 to 7.0

21.5 to 23.0

19.1

 

12

7.0

23.0

 

22.0

 

 

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

▪ TECHNIQUES FOR ENDOTRACHEAL INTUBATION

▪ ORAL INTUBATION UNDER GENERAL ANESTHESIA AND MUSCLE RELAXANTS

Once anesthesia has been induced and an intravenous route established, an intravenous bolus of atropine (0.01 to 0.02 mg/kg) is recommended for neonates and young infants, especially when the patient is bradycardic (<100/min) or hypotensive, because compliance of ventricles is low and cardiac output is rate dependent in this age group (see Chapter 3 , Cardiovascular Physiology). Until recently, atropine or glycopyrrolate (half the dose of atropine) was given routinely to children for halothane induction to prevent bradycardia and hypotension. With sevoflurane induction, the use of vagolytic agents is optional in older infants and children because, with careful induction, marked myocardial depression and bradycardia are not commonly encountered. If the procedure dictates muscle relaxation, a nondepolarizing muscle relaxant is usually administered next, to facilitate endotracheal intubation. Intermediate-acting nondepolarizing relaxants, such as cisatracurium (0.2 mg/kg) and vecuronium (0.1 mg/kg), are most commonly used for endotracheal intubation ( Brandom et al., 1984 ; Meakin et al., 1988 ; Meretoja, 1989 ; Sloan et al., 1991 ; Kenaan et al., 2000 ; Taivanien et al., 2000 ). Intubating doses of muscle relaxants are shown in Table 10-4 .

TABLE 10-4   -- Intravenous doses of muscle relaxants for intubation

Drug

Dose (mg/kg)

Succinylcholine

 Infants

3.0 ( Meakin et al., 1989 )

 Children

2.0

 Adolescents/adults

1.0

Pancuronium

0.1 to 0.15 ( Cunliffe et al., 1986 )

Vecuronium

0.1 to 0.15 ( Meretoja, 1989 )

Cisatracurium

0.15 to 0.2 ( Taivanien et al., 2000 )

Mivacurium

0.2 to 0.3 ( Gronert et al., 1994 )

Rocuronium

0.6 to 0.8 ( O'Kelly et al., 1991)

 

 

Intravenous succinylcholine, the only depolarizing muscle relaxant in use, has the fastest onset of action and shortest duration of action of all muscle relaxants ( Brandom et al., 1989 ; Gronert et al., 1993a, 1993b [124] [123]) and is especially useful in patients with a full stomach, in whom a rapid sequence induction with propofol or thiopental is required. The routine use of succinylcholine in children under 10 years of age is not recommended, due to the small chance that the child may have an unrecognized muscle disease (e.g., Duchenne's) that may result in hyperkalemia and cardiac arrest ( Delphin et al., 1987 ; Rosenberg and Gronert, 1992 ). Under these circumstances, as many as 60% of afflicted children could not be resuscitated. This finding is coupled with the fact that there are many good alternative nondepolarizing muscle relaxants to succinylcholine, even for short pediatric surgical cases. However, in infants and children with a full stomach requiring emergency surgery, succinylcholine provides the fastest onset of muscle relaxation and spontaneous recovery.

Rocuronium and vecuronium, nondepolarizing muscle relaxants, offer a possible alternative to succinylcholine for rapid sequence intubation. Bolus intravenous administration of 0.6 mg/kg of rocuronium produces complete neuromuscular blockade of the adductor pollicis in infants and children in an average of 49 and 80 seconds, respectively ( Woelfel et al., 1994 ). Increasing the dose to 0.8 mg/kg in children shortens this time to an average of 28 seconds ( O'Kelly et al., 1991) . Spontaneous recovery of T1 (the first of the train-of-four twitches) to 25% of control requires 26.7 minutes and 45.1 minutes in infants and children, respectively, with 0.6 mg/kg of rocuronium. If the dose of vecuronium in children is increased from 0.1 mg/kg to 0.4 mg/kg, the time to paralysis of the thumb (to 95% depression of twitch response) shortens from an average of 83 seconds to 39 seconds ( Sloan et al., 1991 ). With this increased dose of vecuronium, however, the duration of action of vecuronium approaches that of pancuronium.

When the patient is adequately anesthetized, the anesthetic concentration is reduced to a maintenance level, nitrous oxide is turned off, and the patient is preoxygenated with increased ventilation briefly with 100% oxygen in preparation for endotracheal intubation. Alternatively, in most children a 50% nitrous oxide-oxygen mixture may be used safely before intubation while oxygen saturation of hemoglobin is monitored continuously with a pulse oximeter. The time for achieving FIO2 of greater than 0.9, after nitrous oxide is turned off and 100% oxygen is turned on, was reported to be less than 60 seconds (mean, 36 seconds) in spontaneously breathing infants. In older children, the time for achieving FIO2 of greater than 0.9 was within an average of 40 to 70 seconds ( Morrison et al., 1998 ). The time for achieving FIO2 sufficient for intubation would be substantially shorter were the patient manually hyperventilated. Intubation normally is relatively easy to perform in children, but it may prove rather difficult in young infants.

The anatomic drawing in Figure 10-12 illustrates the dimensional relations of the glottis, trachea, and supporting cartilages with the head of an infant properly positioned for laryngoscopy and intubation. The large tongue relative to small mandible, large head, and short neck is obvious, as is the high (cephalad) location of the epiglottis. In infants at or younger than 4 months, the epiglottis is at or above the level of the first cervical vertebra overlapping with the soft palate ( Fig 10-13 ) ( Sasaki et al., 1977 ). By 6 months of age, the epiglottis has moved down to the level of the third cervical vertebra and separated from the soft palate ( Fig 10-14 ) ( Sasaki et al., 1977 ), probably making oral breathing more feasible. Unlike in adults, the epiglottis in infants and young children is hard and narrow, folded into an omega or “U” shape ( Fig 10-15 ), and is often difficult to lift with the tip of a laryngoscope blade. Until adolescence, the shape of a child's larynx is that of an inverted cone, with the circular cricoid cartilage at its narrowest (lowest) point; the shape of the adult larynx is more cylindrical ( Eckenhoff, 1951 ; Coté and Todres, 1993 ).

 
 

FIGURE 10-12  Anatomic drawing of neonatal airway with actual relations of the larynx, trachea, and supporting cartilages.

 

 

 
 

FIGURE 10-13  Lateral neck radiograph in the neonatal period indicates epiglottis at level of first cervical vertebra. Epiglottis (E) engages posterior surface of soft palate (P) during tidal respiration.  (From Sasaki CT, Levine PA, Laitman JT, et al.: Arch Otolaryngol103:169, 1977. Copyright 1977, American Medical Association.)

 

 

 

 
 

FIGURE 10-14  Lateral neck radiograph at age 18 months. Epiglottis (E) remains at level of third cervical vertebra. P, soft palate.  (From Sasaki CT, Levine PA, Laitman JT, et al.: Arch Otolaryngol 103:169, 1977. Copyright 1977, American Medical Association.)

 

 

 

 
 

FIGURE 10-15  A, Infant glottis. B, Adult glottis. Note the soft, edematous appearance of infant tissue and folded, omega (ω) or “U” shape of the infant glottis  (Courtesy Dr. Hollinger, Chicago.)

 



Before intubation is attempted, the anesthesiologist is seated comfortably or standing at the proper height in relation to the operating table, with eye level about 1 foot above the patient's head. This positioning provides the proper angle and distance for visualization. The child's neck is moderately extended beyond a neutral position or “sniffing” position to align the oral, pharyngeal, and laryngeal axes ( Stoelting, 1986 ). A soft head ring may be used to help stabilize the head. In infants, it is not necessary to elevate the head by placing pads under the occiput to align the upper airway axes because the infant's head is disproportionately large.

For laryngoscopy a straight blade is most commonly used. The mask is lifted and the oral airway, if used, is removed. The blade held by the left hand is moistened and inserted through the right corner of the mouth while the head is held in the extended position by the right hand. Opening the mouth by crossing or scissoring the right index finger and the thumb at the right corner of the mouth, the technique commonly practiced for the adult patient, should not be used in infants and young children because the small mouth opening prevents the practitioner from properly inserting the laryngoscope blade at the right corner of the mouth and swinging the tongue to the left.

The laryngoscope blade is now moved gently toward the midline to displace the tongue to the left. It is then advanced further toward the epiglottis at about a 45-degree angle to the horizontal plane, and the laryngoscope handle is gently lifted forward and upward along its axis. The larynx is now exposed, and the posterior portion of the vocal cords should be visible below or behind the epiglottis.

In an anesthetized, relaxed child, the blade should barely touch the upper teeth and lip. Needless to say, one should never use the upper teeth as a lever to pivot the laryngoscope blade; such a motion would easily result in the damage to or loss of teeth and bleeding. One should also be careful not to pinch the upper or lower lip between the teeth and the laryngoscope blade.

In older children, the distal end of the straight blade is further advanced beneath the lower (laryngeal) surface of the epiglottis, and the laryngoscope handle is lifted upward along the axis of the handle to achieve full exposure of the glottis. In infants, however, because the epiglottis is hard and omega shaped (see Fig. 10-15 ), it may be difficult to pick up with the blade. In this situation, the straight blade is simply advanced into the pharyngeal base of the epiglottis or the vallecula, and the laryngoscope handle is lifted upward and slightly forward, as with a Macintosh blade, to expose the glottis. A straight blade with a curved tip, such as a No. 1 Phillips blade, is especially useful under these circumstances.

The endotracheal tube, held lightly with the right thumb and index finger and supported by the middle finger, is inserted along the right side of the blade but not through the straight part of the blade, so as to maintain an unobstructed view as the tip of the tube slips through the glottic opening. The tube is further advanced to the black marker on the tube or about 2.5 cm (more in older children) from the tip, halfway between the glottis and the carina in newborn infants. When a cuffed endotracheal tube is used, one should make sure that the upper end of the cuff disappears out of sight and the tube advanced an additional centimeter or two. One eye should be kept on the glottis throughout the process of intubation. The tube is then held tightly against the child's upper teeth or lip as the laryngoscope blade is withdrawn gently and a distance number, or any symbol on the tube wall at the lip, is noted as the proper depth marker.

If the tube meets resistance at the cords, the fingers holding the tube should rotate the tip of the tube slightly and gently. If resistance beyond the vocal cords cannot be cleared by this maneuver, the tube should be withdrawn, remembering that the narrowest diameter of the upper airway system is at the cricoid cartilage rather than at the glottis ( Eckenhoff, 1951 ). After reoxygenation, laryngoscopy is repeated with a smaller endotracheal tube.

Correct positioning of the endotracheal tube is confirmed by symmetric ventilatory movements of both hemithoraces with manual positive pressure ventilation, by equal and satisfactory breath sounds bilaterally in the upper aspect of the chest, and by the presence of an end-tidal carbon dioxide waveform on a capnograph. It is important to listen to the right upper aspect of the chest because ventilation of the right upper lobe is most vulnerable in cases of endobronchial intubation, especially if the tube is without a Murphy eye. Occasionally, the right upper lobe originates from an anomalous tracheal bronchus above the carina, which is easily blocked if the tip of the tube is close to the carina ( Vredevoe et al., 1981 ). Once the correct position has been verified, and the depth marker on the tube that is aligned with the lip or incisors has been reconfirmed, the endotracheal tube is fixed with adhesive tape.

Induction of anesthesia and intubation may be achieved by means of intravenous atropine, propofol or thiopental, and succinylcholine, followed by intubation, fixation of the tube, and establishment of controlled ventilation with high concentrations of inhalation anesthesia in healthy, well-prepared children and adolescents, as in healthy adults. This technique is not suitable in infants and young children, however, because their cardiovascular system is exceptionally sensitive to a sudden increase in anesthetic concentration after the administration of propofol or thiopental. In the presence of airway problems, such as in patients with upper airway obstruction or difficult anatomy, one should never induce apnea with muscle relaxants unless it is certain that manual ventilation can be maintained.

▪ INTUBATION UNDER GENERAL ANESTHESIA ALONE

In infants and children with intact cardiovascular function, endotracheal intubation can be accomplished safely under deep inhalation anesthesia without muscle relaxants. Once anesthesia has been induced by mask with a volatile anesthetic and intravenous access is established, the patient is deepened with a high concentration of sevoflurane (6% to 8%) in oxygen with controlled ventilation for a few minutes while the heart rate and tone are continuously monitored through a precordial stethoscope and blood pressure watched to avoid excessive myocardial depression. Intravenous atropine may be given as indicated. After the child has become motionless and apneic, with fixed pupils, vocal cords are sprayed with 1% to 2% lidocaine (1 mg/kg) under direct vision with a laryngoscope. Lidocaine spray can be accomplished with a metal or plastic atomizer tip attached to a 3-mL syringe. Alternatively, a 20- or 22-gauge plastic intravenous catheter with the needle removed can be used for the same purpose if an appropriate atomizer is not readily available. The child's lungs are manually ventilated for an additional 6 to 12 breaths with sevoflurane in oxygen to give enough time for topical anesthetic to take effect before laryngoscopy and endotracheal intubation. With this technique, laryngospasm is avoided even when the patient becomes too light or if intubation is not swiftly accomplished. Alternatively, a dose of intravenous propofol (1 to 2 mg/kg) is given once the patient is sufficiently deepened for laryngoscopy and intubation. In most children undergoing relatively short surgical procedures requiring endotracheal tubes for airway protection, such as adenotonsillectomies, endotracheal intubation can be achieved without muscle relaxants, the potential side effects of these drugs thus being avoided.

The depth of anesthesia is often difficult to judge. The most reliable signs of adequate depth for intubation are centrally fixed pupils, flaccidity of arms and hands, jaw relaxation, apnea, and blood pressure lower than the preinduction level. Because infants and young children have relatively high MAC and increased myocardial sensitivity to inhaled anesthetics, intubation under deep inhaled anesthetics should be performed with the utmost care, with continuous attention to the quality of heart tone, by means of a precordial stethoscope, in addition to standard monitoring. In healthy children, 1 to 12 years old, deep sevoflurane provides satisfactory anesthetic induction and intubating conditions and more rapid emergence than provided by halothane ( Sarner et al., 1995 ). Heart rate and systolic blood pressure were better maintained during the anesthetic induction period with sevoflurane than with halothane.

Position, Size, and Fixation of Endotracheal Tube

Numerous complications are caused by the incorrect placement of endotracheal tubes and their dislodgment after intubation. Accidental intubation of the esophagus may occur and may be difficult to immediately recognize. For this reason, auscultation with a stethoscope over both sides of the chest and confirmation of CO2 waveforms with capnography are essential. Endobronchial intubation is a relatively common occurrence. As stated earlier, the endotracheal tube should be advanced under direct vision just beyond the vocal cords, that is, 2 to 2.5 cm in newborn infants and not more than 3 to 4 cm in older children. Unfortunately, this approach is not always possible, especially when unusual anatomy makes it difficult to visualize the larynx. Alternatively, the endotracheal tube may be advanced until the breath sounds in one lung (usually left side) start to diminish; the tube is then pulled back by 2 to 4 cm and taped securely.

After intubating the child, the anesthesiologist should keep the patient's head in the intended position for surgery when confirming breath sounds because flexion and extension of the head can cause considerable movement of the tube ( Bosman and Foster, 1977 ). Continuous auscultation with a precordial stethoscope over the left sternal border is a reliable method for detecting endobronchial intubation ( Smith, 1975 ). In this situation auscultation is better than pulse oximeter because breath sounds diminish or disappear over the left chest long before oxygen desaturation is noticed on pulse oximetry. When intubation is intended for prolonged ventilatory support, as in the intensive care unit, radiographic confirmation of its position is essential at the outset and at subsequent intervals as indicated.

To securely fix the endotracheal tube, common cloth-backed adhesive tape usually serves well. Both the tube and skin surface over and under the lips should be clean and dry. Nearly every pediatric anesthesiologist has his or her own “right” way of taping the endotracheal tube. One method is to use two strips of 1-inch-wide tape that are long enough to extend halfway to the ear on each side of the mouth. Each tape is split halfway longitudinally. The intact half of the first tape is applied to the right cheek. The upper half of the split strip is taped across the mouth between the nose and upper lip to the left cheek, while the lower half of the strip is wrapped spirally toward the proximal end of the tube, which is usually situated at the right corner of the mouth. The second tape is again applied on the right cheek. The lower half of the split strip is taped across the mouth below the lower lip toward the left cheek, while the upper half of the strip is wrapped spirally around the endotracheal tube as with the first tape. Tincture of benzoin seldom is needed for the average procedure in children, although it should be used before prolonged procedures, particularly for craniotomies and posterior spinal fusions, in which the patient is in the prone position or the endotracheal tube is out of sight or reach of the anesthesiologist.

When the maintenance of patent airway is difficult, requiring oropharyngeal airway during the induction of anesthesia, the airway should be reinserted before extubation at the conclusion of surgery and anesthesia to make sure that an adequate airway is maintained during emergence from anesthesia after extubation. During the maintenance of anesthesia, a soft bite block commonly made of rolled and taped 4 ×4-inch gauze sponges suffices to keep the patient from clamping down on the tube. If the head is moved either laterally or vertically, the anesthesiologist should hold both the head and tube together so that there is no change in relative position. If the child's body is to be moved or the operating table turned, the tube is disconnected from the anesthesia breathing apparatus until the new position has been reestablished.

▪ NASOTRACHEAL INTUBATION

Nasotracheal intubation is indicated for a number of surgical procedures involving the mouth and face. In addition, nasal tubes are preferred when patients are expected to require postoperative ventilatory care, because the nasal tube can be fixed more securely, is less irritating to the patient, and cannot be bitten. Nasal intubation is more difficult and time consuming to perform compared with oral intubation and can start profuse hemorrhage from the nose or pharynx. Furthermore, pieces of adenoidal tissues can be torn away, and these and other scrapings may be carried into the trachea, increasing the danger of lower airway obstruction and pulmonary infection ( Berry et al., 1973 ).

Before starting anesthesia, one should check the patency of the nares by having the child breathe through the nose with the mouth closed while each nostril is blocked in turn ( Block and Brechner, 1973 ). Frequently, air moves better through one nostril than the other, making it the better one to use for intubation. The application of a nasal decongestant (such as 0.05% oxymetazoline) is recommended to vasoconstrict the nasal mucosa and to minimize hemorrhage, especially when the turbinate appears swollen. If phenylephrine (0.25%) is used instead, the dose should be limited to 20 mcg/kg to prevent possible systemic side effects.

In preadolescent children, one may expect to use uncuffed nasotracheal tubes of the same size that is required for oral intubation ( Yates et al., 1987 ). Older children may require a nasal tube that is two or three sizes (1.0 to 1.5 mm OD) smaller with a cuff. The length of a nasal tube at the nostril should be approximately 20% longer than that of an oral tube at the incisors (see Table 10-3 ).

Nasal intubation may be expected to take longer and thus requires a well-established depth of anesthesia and/or muscle relaxation. In addition to the use of a lubricant on the endotracheal tube and a nasal decongestant, a topical spray of a local anesthetic (1% to 4% lidocaine) applied to the nostrils, pharynx, and glottis reduces the chance of inducing laryngeal responses in patients who are not given muscle relaxants. One must be careful, however, not to overdose the child with local anesthetic (one squeeze of the atomizer equals approximately 0.1 mL, or 4 mg of lidocaine, if a 4% solution is used), because topical anesthetics are absorbed rapidly from the mucosal surface. In addition, if the atomizer is not held upright during spraying, a large unknown quantity of local anesthetic can be deposited inadvertently on the mucosal surface and can cause a circulatory catastrophe. It is therefore imperative to preset the total dose of lidocaine (not more than 5 to 6 mg/kg) in an atomizer or a disposable cannula-syringe set (LTA set; Abbott Laboratories, North Chicago, Ill.). Alternatively, intravenous lidocaine (1.5 mg/kg) may be used. With rapid onset of action, it seems to be as effective as topical anesthesia in the adult (Hamill et al., 1981 ).

When the child is suitably prepared, the head is slightly elevated and the neck extended as with oral intubation. A well-lubricated nasotracheal tube is inserted through a nostril and advanced gently as the remaining body of the tube is pushing down against the upper rim of the nostril. If the tip of the tube is pointed straight downward or toward the base of the skull, as frequently happens when inserted by the inexperienced, the tube would gouge its way through the turbinate, causing bleeding. When properly directed, the tube may meet mild resistance, which may be overcome by pulling the tube back slightly and rotating it before it is again gently advanced. If one encounters a solid obstruction, the attempt should be halted, the tube withdrawn, and the opposite naris tried.

As noted previously, there is a definite danger of shearing off adenoidal tissues in children, with bothersome bleeding and the additional risk that pieces of adenoid may either be carried into the trachea or remain as obstructing plugs in the tube. To prevent this from occurring, a suction catheter can be inserted through the endotracheal tube with its tip protruding beyond the tip of the tube, thus acting as a probe as the tube is advanced. The nasotracheal tube that is hung up in the nasopharynx can also be redirected safely by inserting a gloved finger through the mouth (provided the child is well anesthetized or paralyzed) and gently lifting the tip of the tube off the posterior pharyngeal wall as it is advanced.

When the tube has reached the pharynx, the child can be ventilated manually through the tube as a nasopharyngeal airway by connecting the anesthesia circuit to it while the opposite nostril and the mouth are occluded by the left hand. With this maneuver, the patient can be adequately ventilated without removing and reinserting the nasotracheal tube through the nasopharynx, especially when intubation is difficult or prolonged.

A laryngoscope is then passed to visualize the tube and glottis. It may be possible to maneuver the glottis into position by flexing or extending the neck and inserting the tube under direct vision. If the tube is too straight, the neck should be extended. If the tube is too sharply curved, the head must be lifted and the neck flexed. Frequently, the Magill forceps are needed to direct the tube into the glottic opening, with an assistant ready to advance the tube when it is properly positioned. If the tube is too straight, its tip is grasped with the Magill forceps and redirected downward or posteriorly as the assistant advances the tube. If a cuffed endotracheal tube is being used, it is imperative to position the Magill forceps either proximal or distal to the cuff when directing the endotracheal tube advancement, because grasping the cuff portion of the tube often damages the cuff.

In taping the nasotracheal tube in place, it is extremely important to avoid creating pressure of the tube against the edge of the nostril. This could easily traumatize the soft tissue and, if prolonged, would produce ulceration followed by nasal scarring and obvious facial distortion ( Fig 10-16 ). The tube should be taped so that the entire upper rim of the nostril is visible and can be observed throughout the surgery and during postoperative intensive care, should this be necessary.

 
 

FIGURE 10-16  Nasal ulceration caused by pressure of nasotracheal tube during critical neonatal illness.

 

 

Blind nasotracheal intubation in children, particularly in infants, is rather difficult and is not recommended because the glottis is situated more cephalad and the tubes are less adaptable, increasing the likelihood of trauma and hemorrhage. With the advent of ultrathin fiberoptic bronchoscopy, allowing atraumatic intubation in infants and small children with difficult airways ( Patil et al., 1983 ), there is no justification for blind nasotracheal intubation ( Berry, 1984 , 1986).

▪ INTUBATION IN A CHILD WITH A FULL STOMACH

Overview

One of the most dangerous and challenging situations in anesthetizing all age groups is the patient whose stomach is filled with solid food or distended by intestinal obstruction. Mendelson (1946) reported 66 cases of fulminating chemical pneumonitis (Mendelson syndrome) occurring in pregnant women following pulmonary aspiration of gastric contents during obstetric anesthesia. The report drew attention to the danger of a full stomach and aspiration during general anesthesia, although the incidence of aspiration in this report was relatively low and only two patients died of causes not directly associated with anesthesia. Additional early studies, however, reported high morbidity and mortality, especially among infants and children associated with gastric aspiration ( Smith, 1956 ; Graff et al., 1964 ).

These reports of high mortality associated with perioperative aspiration alerted the emerging specialty of anesthesiology to the problem and have resulted in numerous experimental and clinical studies during the ensuing half century, attempting to minimize the risk of perianesthetic gastric aspiration and its associated complications. Prophylaxes of gastric aspiration included rapid sequence intubation with a cuffed endotracheal tube; cricoid pressure ( Sellick, 1961 ); attempts to reduce gastric acidity with sodium citrate ( Henderson et al., 1987 ) and H2 blockers ( Goudsouzian et al., 1981 ; Goudsouzian and Young, 1987 ); and attempts to reduce gastric fluid volume with glycopyrrolate (Salem et al., 1976) and metoclopramide ( Lerman et al., 1988 ).

A large-scale epidemiologic study from Sweden in the mid-1980s involving more than 185,000 general anesthetics revealed quite a different story. Although the radiographic evidence of pneumonia (or atelectasis) was confirmed in 47% of cases, the mortality rate in children was relatively low (0.2:10,000). The incidence of aspiration of gastric contents in children, however, was significantly higher than that in the adult population (8.6 versus 4.5:10,000) ( Olsson et al., 1986 ). Risk factors for perianesthetic aspiration included the skill and experience of anesthetists; a number of coexisting diseases and ASA physical status (PS) 3 to 5; emergency surgery, especially at night; and neurologic or esophagogastric abnormality ( Olsson et al., 1986 ). Other high-risk categories included children with intestinal obstruction, increased intracranial pressure, and increased abdominal pressure and obesity. Incidence of gastric aspiration was even lower in studies from the French-speaking countries (1.0:10,000) ( Tiret et al., 1988 ) and from Norway (2.9:10,000) (Mellin-Olsen et al., 1988) in the 1980s.

The first study from the United States came from Children's Hospital of Pittsburgh and reported an incidence of aspiration of gastric contents of 4.9:10,000 based on 50,880 anesthetic procedures ( Borland et al., 1998 ). In this institution, pulmonary aspiration of gastric contents was treated aggressively with flexible bronchoscopy and removal of solid food particles, if any were present, followed by reexpansion of the lungs and the maintenance of CPAP. Twenty-nine percent of these children were kept intubated in the postanesthetic care unit (PACU) and only 23% of these patients stayed overnight. None of these children developed clinically significant pneumonia, and there were no deaths ( Borland et al., 1998 ). Similarly, a study from the Mayo Clinic reported the incidence of aspiration being low (3.8:10,000) and similar to that of adults (3.1:10,000) with no serious respiratory morbidity and no associated deaths ( Warner et al., 1999 ). These epidemiologic studies suggest that the incidence of gastric aspiration and associated morbidity and mortality in both adults and children has declined considerably. The risk of aspiration, however, remains higher in infants and children than in adults ( Olsson et al., 1986 ; Tiret et al., 1988 ; Weaver, 1993 ).

Based on these findings of reduced incidence, morbidity, and mortality associated with aspiration of gastric contents in children, the routine use of preoperative antacid or H2 blocker may not be justified (Weaver, 1993 ; Borland et al., 1998 ). In children, the majority of gastric aspiration occurs during inhalation induction without muscle relaxants ( Warner et al., 1999 ) or during intravenous induction (Borland et al., 1998 ). About 30% of aspiration took place during emergence and extubation.

These reports are encouraging and are no doubt the results of improved training in pediatric anesthesia and sophisticated and vigilant clinical practice. One should be aware, however, that a combination of factors makes infants and young children potentially more susceptible to regurgitation and aspiration. These factors include excessive swallowing of air during crying, strenuous diaphragmatic breathing, possible relaxation of the gastroesophageal sphincter, a shorter esophagus and smaller hydrostatic pressure gradient between the stomach and larynx in the sitting position, and, most important, the tendency in infants and children for upper airway obstruction ( Salem et al., 1973 ). Furthermore, in pediatric anesthesia, patients are less adaptable to alternatives such as local and regional anesthesia and intubation while awake. Children also give less reliable information about when, what, and how much they have ingested ( Splinter et al., 1990 ). When gastric pH and residual volume have been measured in fasted normal children, nearly all have gastric pH less than 2.5 as well as a residual volume greater than 0.4 mL/kg ( Coté et al., 1982 ).

Preparation and Management

Although there has been some disagreement about the right approach to take for this problem, the following essential safety factors are generally accepted for the management of children with a full stomach:

  

1.   

Avoidance or delay of general anesthesia, if possible; consideration of regional block with minimal sedation

  

2.   

Careful preparation if anesthesia is required

  

3.   

Preanesthetic relief of gastric distention, if present

  

4.   

Rapid and smooth induction and cricoid pressure until intubation is completed successfully

Delaying anesthesia is an important consideration, although it is well known that food may lie in the stomach undigested for many hours or even overnight when an accident occurs shortly after a meal or when the patient is in pain. The anesthetic management of children considered at high risk for aspiration is controversial. If the surgical procedure is emergent, H2 receptor antagonists ( Goudsouzian et al., 1981 ) (e.g., cimetidine, ranitidine), nonparticulate antacids ( Taylor and Pryse-Davies, 1966 ) (e.g., sodium citrate), or agents to stimulate gastric emptying (e.g., metoclopramide) are effective in decreasing the pH of gastric fluid, or gastric volume. A reduction in gastric fluid pH or volume, however, does not prevent aspiration of gastric contents per se, which can still be life threatening.

In healthy children without known causes of delayed gastric emptying, “preoperative fasting” guidelines have been liberalized. Drinking clear liquids up to 2 hours prior to induction of anesthesia for elective surgical procedures does not substantially affect the volume of gastric fluid contents or the percentage of patients with a gastric fluid pH less than 2.5 ( Schreiner et al., 1990 ; Nicolson et al., 1992 ). In addition, parents report less difficulty adhering to the preoperative feeding instructions, rated their children as less irritable, and rated the overall preoperative experience more positively ( Schreiner et al., 1990 ). While human milk has been shown to leave the stomach more rapidly than formula in both preterm and full-term infants (Cavall, 1979, 1981 [45] [44]), there is controversy as to whether this should be considered a clear liquid preoperative. A clear glucose-containing fluid should be used for feeding infants 2 to 3 hours before an elective surgical procedure (see Chapter 8 , Preoperative Preparation).

In addition to a full complement of airways, endotracheal tubes, laryngoscope and blades, emergency drugs, the usual monitoring devices, and two strong, functioning suction devices, also readily at hand should be several suction catheters small enough to pass easily through the endotracheal tube, larger suction catheters (14F) to clear the mouth and pharynx, rigid “tonsil” (Yankauer) suction tips, and large-bore nasogastric tubes. In addition, a large uncuffed endotracheal tube without the plastic connector and fitted with an adapter to the suction apparatus is useful for removal of solid vomitus from the mouth and pharynx should copious vomiting with solid food occur during induction or emergence from anesthesia. A bite block is useful for preventing the jaws from clamping together. Equipment for rigid bronchoscopy and tracheotomy should also be readily available.

Premedication may be given to alleviate fear and anxiety in the holding area or in the operating room before induction. Intravenous midazolam (0.05 to 0.1 mg/kg) in divided doses usually works well for this purpose. A dose of atropine (0.01 to 0.02 mg/kg) should be given in anticipation of administering succinylcholine. If gastric distention is present or suspected, the stomach should be decompressed before induction using a large-bore nasogastric tube, nasally or orally, although this is uncomfortable and may upset the child even with intravenous sedation.

The most common technique for induction and intubation in a healthy or hemodynamically stable child with a full stomach is a rapid sequence induction with intravenous propofol (3 to 4 mg/kg) or thiopental (4 to 6 mg/kg) followed by succinylcholine (1 to 2 mg/kg), while cricoid pressure is applied ( Sellick, 1961 ) to prevent regurgitation ( Salem et al., 1972b ). Atropine (0.01 to 0.02 mg/kg) should always be given prior to induction with succinylcholine. In older children, fasciculations and the incidence of postoperative myalgias can be decreased by pretreatment with approximately 10% of the paralyzing dose of a nondepolarizing muscle relaxant. Salem and others (1972a) , however, found in infants and children that succinylcholine caused much less fasciculation and actually decreased mean gastric pressure slightly. Alternatively, a modified rapid-sequence intubation can be achieved within 60 seconds with higher doses of vecuronium (0.4 mg/kg) or rocuronium (1.0 mg/kg), but the duration of neuromuscular blockade is prolonged (O'Kelly et al., 1991; Sloan et al., 1991 ). If a combination of thiopental and rocuronium is planned, thiopental must be cleared from the intravenous tubing before rocuronium is infused so as to avoid precipitation in the tubing. Rocuronium may be associated with some tachycardia ( O'Kelly et al., 1991) .

The Sellick maneuver has been shown to be effective in both adult and pediatric patients ( Salem et al., 1972b ). By obliterating the esophageal lumen, it prevents regurgitated material from reaching the pharynx ( Sellick, 1961 ; Salem et al., 1972b ). Before induction, an assistant palpates the cricoid ring lightly between the thumb and the middle finger; then, after the patient has lost consciousness, the pressure is steadily increased using the index finger while the neck is kept extended ( Salem et al., 1973 ). The pressure necessary for preventing gastric reflux is reported to be 30 to 40 Newtons (equivalent to 3 to 4 kg of force), which creates the pressure of about 50 cm H2O in the upper esophagus ( Vanner et al., 1992 ). Moynihan and others (1993) showed that the appropriate application of cricoid pressure in infants and young children was effective for preventing gastric insufflation during mask ventilation up to 40 cm H2O peak airway pressure ( Landsman, 2004 ). The Sellick maneuver also effectively seals the esophagus in the presence of a nasogastric tube. Nevertheless, removal of the nasogastric tube before intubation is recommended ( Salem et al., 1973 ). This provides a much better mask fit and glottic exposure to facilitate endotracheal intubation.

The efficacy of cricoid pressure to prevent gastric regurgitation has been questioned ( Brock-Utne, 2002 ); some clinicians believe the technique is ineffective and even unnecessary ( Brimacombe and Berry, 1997 ). Surveys among pediatric anesthetists in the United Kingdom indicate that cricoid pressure is used in only 40% to 50% of patients with a full stomach ( Stoddart et al., 1994 ; Engelhardt et al., 2001 ). Even when cricoid pressure is used, it is not certain whether and how often the maneuver is applied appropriately, that is, with the correct position and pressure in clinical settings ( Landsman, 2004).

A study by Smith and others (2003) further casts doubt about the efficacy of cricoid pressure for preventing gastric regurgitation. They studied the anatomical relationship between the upper esophagus and the cricoid cartilage in anesthetized spontaneously breathing adult volunteers in a supine position with the use of magnetic resonance imaging (MRI), with and without cricoid pressure. The study revealed that the esophagus was situated lateral to the cricoid cartilage in more than 50% of the patients without cricoid pressure; with cricoid pressure, the esophagus was laterally displaced more than 90% of the time. Cricoid pressure distorts the anatomy of the upper airways and makes laryngoscopy more difficult ( Mac et al., 2000 ); the pressure must be eased to improve the exposure of the larynx. Cricoid pressure is also associated with decreases in upper and lower esophageal sphincter tones ( Vanner et al., 1992 ; Tournadre et al., 1997 ). From the foregoing discussion, it appears rather difficult to apply cricoid pressure correctly to prevent gastric regurgitation. Nevertheless, properly applied cricoid pressure facilitates intubation with rapid sequence induction and mask ventilation. The safe and effective use of this maneuver requires a knowledge of neck anatomy and proper training or experience to know the appropriate technique and pressure to be applied ( Landsman, 2004 ).

The head-up tilt position has been proposed for reducing the danger of regurgitation in adults ( Snow and Nunn, 1959 ) as well as in children (Gregory, 1994), with the belief that the gastric pressure would be less than the hydrostatic pressure reaching the larynx. Gastric pressure in infants, however, can reach 18 cm H2O or more, much higher than the hydrostatic distance of the head-up tilt position in infants (7 to 8 cm) or even in adults (18 cm). The head-up tilt is of little value in preventing material from reaching the laryngeal level in pediatric patients ( Salem et al., 1973 ). Indeed, Roe (1962) showed that vomiting could easily overcome a head-up tilt, which would then increase the hazard of aspiration. On the other hand, the head-down position was proposed for reducing the danger of aspiration, because gastric contents would find their way into the oropharynx rather than flow against gravity into the larynx in case of regurgitation ( Inkster, 1963 ). It is obvious, however, that a head-down tilt also would increase the hazard of regurgitation. Consequently, most anesthesiologists believe that it is best for the patient to be level during induction with the head turned well to the side to enable secretions to flow into the cheek and escape.

Aspiration of Gastric Contents

Despite the best efforts of the anesthesiologist, aspiration of secretions, blood, or vomitus unfortunately occurs occasionally and may cause airway obstruction, bronchospasm, and/or hypoxia. Although aspiration occurs most commonly during the induction of anesthesia, it can also occur during maintenance of or emergence from anesthesia ( Borland et al., 1998 ). The first sign of aspiration is often laryngospasm with oxygen desaturation. Laryngospasm tends to be intense and sustained, especially if the patient is lightly anesthetized and not paralyzed. Localized rhonchi or rales on auscultation, especially over the lower dependent lung fields, after an episode of vomiting and laryngospasm, are the classic signs of aspiration. A definite diagnosis, however, is often difficult at the time of incidence, unless foodstuff or bile-stained liquid is recovered by tracheal suction or by flexible bronchoscopy through the endotracheal tube. A chest radiograph may or may not show changes for some time after aspiration. When in doubt, it is best to assume the worst, notify the surgeon and postpone the planned surgery if nonemergent, and start treatment without delay. Continuous monitoring with a pulse oximeter, along with a precordial stethoscope, is most useful for the evaluation and care of a patient after suspected pulmonary aspiration.

The management of pulmonary aspiration in children is essentially the same as in adults, as reviewed by Gibbs and Modell (1990) . The treatment should be aimed at restoring pulmonary function and gas exchange as soon as possible. After a minor incidence or questionable aspiration, the child may be observed and given supplemental oxygen via mask if satisfactory oxygen saturation (>96% in room air) and ventilation can be maintained. Otherwise, the trachea should be intubated and the patient given general anesthesia or additional sedation and muscle relaxants as indicated. The trachea and major bronchi may be examined with a small fiberoptic bronchoscope and any solid food particles, if present, removed, while ventilation is continued without interruption ( Borland et al., 1998 ). Aspirated food particles may be found in the midtrachea, between the tracheal wall and endotracheal tube, whereas the lower trachea and carina are free of aspirated material. In these circumstances, the endotracheal tube may be gently moved cephalad as the anesthesiologist suctions the aspirated particles and the trachea is reintubated; this procedure can be repeated to clear the trachea of food particles successfully without resorting to rigid bronchoscopy.

Lungs should be gently inflated fully to total lung capacity (i.e., end-inspiratory pressure of 40 cm H2O) and kept inflated for several seconds. This (vital capacity) maneuver is repeated several times; then continuous positive end-expiratory pressure (PEEP) is instituted and kept at the level that maintains the optimal oxygenation or compliance without interfering with circulation ( Suter et al., 1975 ). Inspiratory oxygen concentration is gradually lowered and kept at the lowest level necessary to maintain adequate oxygen saturation. With this aggressive management of gastric regurgitation and aspiration,Borland and others (1998) reported excellent outcome without serious pulmonary outcome among more than 50,000 pediatric general anesthetic procedures.

Pulmonary lavage with a bicarbonate solution is not helpful because mucosal damage by acidic gastric juice occurs within 20 seconds ( Hamelberg and Bosomworth, 1964 ; Gibbs and Modell, 1990 ) and may even be harmful by spreading vomitus farther down the tracheobronchial tree. Corticosteroid therapy is not recommended because it does not reduce the inflammatory process of aspiration pneumonitis and may interfere with healing ( Wynne et al., 1979 ). Antibiotics should not be used unless there is a known pathogen because they are not only ineffective but also their routine use would select out drug-resistant organisms.

▪ INTUBATION IN AN AWAKE INFANT

Intubation can be performed quickly and safely in an awake infant by a skillful pediatric anesthesiologist. Even in the hands of the inexperienced, this method may be relatively safe, as it is widely practiced by medical and paramedical personnel in neonatal intensive care settings. Nevertheless, it is rather cruel to the helpless, struggling infant, who can respond to noxious stimuli ( Anand and Hickey, 1987 ), and it may cause trauma to the mouth, larynx, and pharynx. Thus, its use has been declining over the years and should be limited to infants with severe airway obstruction (such as lymphangioma of the tongue) and intestinal obstruction (as in meconium ileus), and perhaps to very young, nonresistant infants (premature and newborns <1 week of age). When the infant is strong enough to resist vigorously, this approach should not be used.

Because intubation in an awake infant often provokes strong vagal stimulation and bradycardia, a vagolytic dose of atropine (0.03 mg/kg) is administered via the intravenous route shortly before the attempted intubation. If the condition permits, intravenous lidocaine (1.5 mg/kg) or a small dose of fentanyl (1 to 2 mcg/kg) may be considered. In addition, to reduce the infant's discomfort, it may help to expose the pharynx and apply topical anesthesia with 1 or 2 atomizer bursts of 1% to 2% lidocaine directed toward the base of the tongue and vocal cords. Oxygen is given for 1 additional minute while the anesthetic takes effect.

The patient should be monitored with an electrocardiograph, precordial stethoscope, and pulse oximeter and should be preoxygenated for 1 to 2 minutes, or until 100% saturation is observed on the pulse oximeter monitor, before intubation is attempted. An assistant, the key person for successful intubation, holds down the infant's shoulders and chest on the table and immobilizes the head in the “sniffing position.” The use of a modified Miller 0 blade with a port for oxygen running 1 to 3 L/min (Oxyscope; Foregger, Smithtown, NY) ( Fig 10-17 ) or its further modification ( Diaz, 1984 ) improves oxygenation during intubation in the awake neonate and is highly recommended ( Todres and Crone, 1981 ). The anesthesiologist chooses the most likely endotracheal tube size (usually 3.0 mm ID for a newborn infant weighing 2 to 4 kg) lightly coated with lubricant and keeps it in his or her right hand until the time for insertion, to avoid having to grope for the tube on the table after the glottis is exposed. The anesthesiologist dips the blade of the laryngoscope into warm water and then inserts the tip over the right edge of the infant's mouth, gently opening the mouth and sweeping the tongue to the left. The tips of the blade and tube are advanced side by side to bring the glottis into view, so that the infant continues to breathe. If the infant chokes or stops breathing, or pulse oximeter reading drops below 95%, the laryngoscope is withdrawn just enough to let the infant breathe briefly with oxygen insufflation, until saturation returns to 100% (or the highest level previously achieved for a given patient). When possible, the blade should not be completely withdrawn from the mouth, for then the entire process must be started again. The blade is advanced again, keeping the pressure on the tongue upward without touching the upper jaw with the blade. If the glottis appears too far “anterior,” the left little finger is used to apply a gentle pressure over the larynx to position and hold the glottis precisely as needed ( Fig 10-18 ).

 
 

FIGURE 10-17  Oxyscope (modified Miller 0 blade with oxygen delivery channel) with pediatric laryngoscope handle for intubation of the awake infant.

 

 

 
 

FIGURE 10-18  A diagram of intubating an infant showing the anesthesiologist's use of the left fifth finger to bring glottis into position and immobilize it before intubation.

 

 

At this point, the anesthesiologist waits with the tips of the blade and tube, side by side, within a centimeter above the glottis. As the infant takes the next deep breath, the glottic aperture widens momentarily, and the tube is advanced swiftly about 2 cm beyond the cords. The tube must be held firmly until its position is confirmed by visible motion of the chest, capnographic tracing, and auscultation. Then the tube is taped in place, and general anesthesia with intravenous injections of propofol, fentanyl, and a nondepolarizing muscle relaxant with or without an inhalation anesthetic follows immediately as cardiorespiratory stability is monitored continuously.

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

▪ DIFFICULT AIRWAY AND INTUBATION TECHNIQUES

In infants and children, a wide variety of difficult airways occur that can be extremely challenging as well as nerve-racking for the pediatric anesthesiologist. Some conditions, such as Pierre Robin association (syndrome) and large hemangioma of the tongue, are obvious and are likely to exhibit airway obstruction, whereas other conditions, such as Hurler's and Hunter's syndromes (mucopolysaccharidosis) and ankylosis of the jaw, usually are not associated with airway difficulty when the patient is awake and may escape recognition before the induction of anesthesia.

Nothing could be worse for the pediatric anesthesiologist than encountering severe airway obstruction after induction of anesthesia and paralysis in a child who could not be ventilated and whose jaw is found to be ankylosed. The best approach to the difficult airway problem is not to be caught by surprise. Careful history taking and physical examinations and making a rational plan (and alternative plans in case the first approach fails) to the problem are essential to prevent such a catastrophe.

A history of difficult intubation, particularly with the cancellation of planned surgery, should not be taken lightly, whether it is documented in the hospital record or at a different institution or recounted by a parent. One should always assume that the anesthesiologist previously involved was experienced and competent. Infants and young children with a history of prolonged intubation or of recurrent or severe croup are likely to have airway difficulties during the perioperative period.

The difficult airway algorithm for adult patients has been developed and recommended by the American Society of Anesthesiologists—Task Force on Airway Management ( Caplan et al., 1993 ) and has been updated with an addition of LMA in the algorithm ( Benumof, 1996 ). A difficult airway algorithm for children has been proposed ( Fig 10-19 ) ( Wheeler, 1998 ).

 
 

FIGURE 10-19  A difficult airway algorithm for the unexpected difficult airway in pediatric patients. LMA, laryngeal mask airway; OELM, optimal external laryngeal manipulation.  (From Wheeler M: Management strategies for the difficult pediatric airway. Anesth Clin North Am 16:759, 1998, Figure 1.)

 

 

 

During the preoperative visit, it is important to ask the child to open the mouth wide and to extend the neck, to rule out ankylosis of the jaw and cervical spine. An unstable cervical spine, congenital (Down's syndrome) or acquired, is noted. A high arched palate with a narrow mouth is often associated with difficult exposure of the larynx. One should examine the size and shape of the mandible in relation to that of the tongue. The distance between the lower edge of the mandible and the thyroid notch in the adult is about 6.5 cm and that between the mandible and the hyoid cartilage is 3 cm. The distance in the newborn is about one-half that in the adult ( Berry, 1986 ). A reduction in submandibular space (micrognathia) leaves too little room to displace the tongue and surrounding soft tissues for laryngoscopy and often is associated with difficult exposure and intubation ( Patil et al., 1983 ; Berry, 1986 ). The classification of difficult airway by the exposure of the larynx (Grades 1 to 4) proposed byMallampati and others (1985) can be useful in older and cooperative children but is not helpful in younger or frightened children who are not willing or capable of opening the mouth for examination.

If the child is already having difficulty breathing, the ventilation and degree of obstruction should be observed carefully. In case of acute upper airway obstruction such as supraglottitis, one should refrain from examining the pharynx, because immediate and severe airway occlusion may develop if the pharynx is manipulated. Other factors to be examined include the state of stomach emptying, adequacy of oxygen-carrying capacity, and presence of complicating lesions. Box 10-2 lists the diversity of conditions in which difficult airway and intubation problems may be encountered in pediatric anesthesia. The difficulties involved are quite varied, with the most hazardous being a child presenting with upper airway obstruction and/or in a critical hypoxic state, as with acute supraglottitis, when therapy must be immediate and involves great risk.

BOX 10-2 

Difficult Airways in Pediatric Anesthesia

Congenital Anomalies

Encephalocele

Double cleft lip and palate

Micrognathia, Pierre Robin syndrome (sequence)

Macroglossia (Beckwith-Wiedman syndrome, Down syndrome)

Craniofacial deformity (Crouzon's disease, Apert's syndrome)

Mandibular dysplasia, microsomia (Treacher Collins syndrome, Goldenhar's syndrome)

Mucopolysaccharidosis I, II (Hurler's syndrome, Hunter's syndrome)

Tumors

Cystic hygroma

Hemangioma of tongue, pharynx

Teratoma

Infection

Retropharyngeal abscess

Acute supraglottitis (epiglottitis)

Laryngotracheobronchitis (subglottic croup)

Ludwig's angina

Adenotonsillitis, abscess, hypertrophy (obstructive sleep apnea)

Musculoskeletal Problems

Ankylosis of jaw, cervical spine

Unstable or dislocated cervical vertebrae (Down syndrome, trauma)

Wired teeth, jaw

Cervical cord tumor

Halo traction apparatus

Trauma

Facial fractures, lacerations

Burns of mouth, airway

Foreign body aspiration

Several generalities apply to many situations. To avoid trouble, one must be prepared for trouble. General anesthesia in children with airway problems should be administered only by an experienced anesthesiologist (or under his or her close supervision) and should be performed in the area where personnel and equipment are available for bronchoscopy, tracheostomy, and resuscitation. The anesthesiologist should go into the procedure with a definite strategy, one best suited for the particular circumstances (Plan A), and with alternative courses of action in mind (Plans B and C) in case the intubation is not successful with Plan A. Parents, surgeons, and nurses should be forewarned of the possibility of prolonged time, the risk of manipulative trauma and the possible need for tracheostomy (with the consent signed), and the possible postponement of the planned surgery (Plan D).

When difficult intubation is anticipated, a difficult airway cart (stocked with added equipment necessary for difficult airway management) should be wheeled into the induction area. The difficult airway cart should include different types of laryngoscope blades; endotracheal tubes of various sizes, curves, and length (oral and nasal); stylets; forceps; bite blocks; local anesthesia equipment; Bullard laryngoscopes; lighted stylets; and apparatus for retrograde intubation ( Box 10-3 ). In addition, a setup for fiberoptic bronchoscopy, rigid bronchoscopy, as well as equipment for tracheostomy and resuscitation should be on hand.

BOX 10-3 

Equipment Included in the Difficult Airway Cart

Oral and nasal airways and lubricant

Intubating oral airways for fiberoptic bronchoscopic intubation

Airway endoscopy (Frei) mask

Laryngoscope handles, blades (various types and sizes)

Bullard laryngoscope

Endotracheal tubes and stylets

Laryngeal mask airway (all sizes)

Intubation (Frei) masks (all sizes)

Tracheal tube exchangers

Lighted stylets (with light source)

Retrograde intubation kits

Cricothyrotomy kit

Saunders jet ventilation stylets (with equipment available)

Additional equipment at hand with the difficult airway cart

  

   

Manual (Saunders) or high-frequency jet ventilator

  

   

Fiberoptic bronchoscopy setup including a video monitor

  

   

Rigid bronchoscopy setup

  

   

Tracheostomy setup

Premedication may be varied to suit the situation but, in general, should be given intravenously and be carefully titrated in a monitored situation. Atropine (0.01 to 0.02 mg/kg) or glycopyrrolate (0.005 to 0.01 mg/kg) is indicated for most situations for both vagolytic and antimuscarinic effects. No sedative should be given to the infant with upper airway obstruction who is to be intubated while awake or to the child with supraglottitis or subglottic croup (laryngotracheobronchitis). However, children who have airway problems but who are not in acute distress, such as those with facial deformities, may be given small divided doses of propofol to facilitate inhalation induction. With few exceptions, the presence of airway obstruction contraindicates the use of ketamine (see later). Muscle relaxants should not be used, at least until the airway is secured or an endotracheal tube is placed. When difficult intubation is anticipated, an intravenous dose of corticosteroid (dexamethasone 0.4 mg/kg) should be given as prophylaxis against edema formation ( Biller et al., 1970 ).

Sevoflurane with oxygen without nitrous oxide is most commonly used for inhalation induction. As the upper airway muscles start to relax with general anesthesia, especially with sevoflurane, one frequently encounters progressive airway obstruction. A combination of the head extension, the jaw thrust, and (especially if the nasal airway is compromised) the mouth kept open (the triple airway maneuver) should be used during induction. A well-lubricated nasopharyngeal airway often is helpful when the patient is too lightly anesthetized to accept an oral airway. It is advisable to use a nasal decongestant (0.05% oxymetazoline or 0.25% phenylephrine) before induction to prevent nasal bleeding, which could seriously compromise difficult intubation. A moderate (10 to 15 cm H2O) level of CPAP is also helpful for maintaining upper airway patency as described previously. If adequate ventilation can be maintained manually, ventilation may be gradually taken over and controlled while anesthesia is deepened. Sevoflurane may be switched to halothane or propofol infusion at this point to provide a steady level of anesthesia and allow the anesthesiologist more time for laryngoscopy. Intubation may be attempted after the use of topical lidocaine. Muscle relaxants should be avoided, so that in the event the patient cannot be intubated, mask ventilation or spontaneous ventilation can be maintained.

Alternatively, the patient with a potential difficult airway may be managed with intravenous induction. Propofol with divided doses, combined with topical anesthesia with lidocaine spray, may be used for intubation attempted while the patient is spontaneously breathing. Ketamine should be avoided for intubating patients with difficult airway because it maintains or exaggerates pharyngeal and laryngeal reflexes ( Green, 1990) . It also stimulates salivation and airway secretions, even with pretreatment by atropine or glycopyrrolate. The risk of cough and laryngospasm may be increased ( Faithful and Haider, 1971 ; Cook et al., 1996 ). Anecdotal accounts exist of severe laryngospasm with attempted intubation with ketamine. Such reports, however, have been scarce in the literature ( Sussman, 1974 ;Lassiter, 1982 ). Ketamine has been used successfully, however, as a bronchodilator for patients with status asthmaticus ( Strube and Hallam, 1986 ; L'Hommedieu and Arens, 1987) ; for the treatment of bronchospasm during mechanical ventilation ( Hemmingsen et al., 1994 ); and as an anesthetic in symptomatic and asymptomatic asthmatic patients ( Corssen et al., 1972 ). Furthermore, studies report the successful use of ketamine comparable with propofol and topical lidocaine for emergency procedures involving the insertion for laryngeal mask airway, with relatively low incidence of coughs (2%) and laryngospasms (1.5%) ( Gloor et al., 2001 ; Bahk et al., 2002 ).

Dexmedetomidine, an α2-adrenergic receptor agonist, has been used for its sedative and analgesic effects and as an adjunct to general anesthetics with circulatory stability in both adult and pediatric patients ( Tobias and Berkenbosch, 2002 ; Ard et al., 2003 ; Jorden et al., 2004 ). With an intravenous dose of 0.5 to 1.0 mcg/kg given slowly for induction followed by continuous infusion of dexmedetomidine (0.5 to 1.25 mcg/kg per hr), spontaneous breathing is well maintained. Ramsey and Luterman (2004) has reported the use of high-dose dexmedetomidine (10 mcg/kg per hr) as a total intravenous anesthetic in three adult patients with difficult airways while spontaneous breathing was well maintained in room air with satisfactory hemoglobin saturation on pulse oximetry. The patients tolerated fiberoptic bronchoscopy with the addition of topical lidocaine. Only one patient required a chin lift to maintain airway patency. End-tidal PCO2 was measured in one patient and was well within normal limits. In addition, dexmedetomidine is a potent bronchodilator antagonizing histamine challenge in the dog ( Groeben et al., 2004 ). Dexmedetomidine in lower clinical doses decreases systemic blood pressure, presumably due to central sympatholytic effect. At higher plasma levels, however, it may increase both pulmonary and systemic blood pressures due to peripheral α2-adrenergic receptor-mediated vasoconstriction ( Ebert and Maze, 2004 ). Although at the time of this writing the literature on the clinical experience with dexmedetomidine has been limited, procedural sedation or even total intravenous anesthesia with dexmedetomidine with or without topical lidocaine appears to provide an excellent condition for fiberoptic intubation while spontaneous breathing is well maintained ( Grant et al., 2004 ).

During attempts at intubating the patient with difficult airway, it is mandatory to monitor oxygen saturation by means of pulse oximetry with an audible pulse signal to warn of developing hypoxia. Attempts at intubation must be interrupted for frequent and sufficient periods of oxygenation and stabilization. During attempted intubation, one must not persist with a maneuver that is unsuccessful; every attempt increases the chance of injury. One should instead try various instruments, techniques, and approaches. For a difficult exposure, the infant Phillips blade with its sharply curved tip often is helpful. Mandibular advancement with both hands by an assistant may improve the exposure of the larynx with laryngoscopy, especially for inexperienced physicians ( Tamura et al., 2004 ).

When the problem of exposure is due to a large tongue combined with micrognathia, a paraglossal approach using a straight blade may be helpful for laryngeal exposure ( Henderson, 1997 ). With this approach, the head is slightly tilted to the left and the laryngoscope blade is inserted from the right corner of the mouth over the molars while the assistant retracts the right corner of the mouth with a small retractor and the tongue is pulled out to the opposite corner of the mouth with forceps (M. B. Borland, personal communication).

The Bullard laryngoscope is superior to conventional laryngoscopes for the exposure of difficult airways with limited mouth opening, micrognathia, and/or macroglossia, although this instrument, as with most other tools, requires prior experience ( Borland, 1988 ). The use of this instrument has been described earlier in this chapter (see Fig. 10-10 ) (also see Chapter 9 , Anesthetic Equipment and Monitoring).

▪ INTUBATION USING A FLEXIBLE FIBEROPTIC BRONCHOSCOPE

In experienced hands, endotracheal intubation with a flexible fiberoptic bronchoscope is usually successful, with minimal or no injury to the patient, even with the most difficult airway ( Ovassapian et al., 1983 ). The nasotracheal route is preferred with this technique, particularly in infants and children, because it is less traumatic and considerably easier than the oral approach for visualizing the glottis (Wood, 1985, 1988 [347] [346]).

The safest and most common approach for all ages is to have the patient well sedated and breathing spontaneously. A topical decongestant (0.05% oxymetazoline or 0.25% phenylephrine) should be given to prevent nasal bleeding, which would interfere with viewing through the fiberscope. A nasotracheal tube, one or two sizes smaller than that appropriate for the patient, with the connector removed, is threaded over the scope retrograde and is held at the upper end of the scope until it is ready to be lowered down into the trachea. A low-flow oxygen (<1 L/min) source may be attached to the suction port during flexible laryngoscopy to improve the patient's oxygenation during the procedure.

The tip of the flexible bronchoscope is introduced through the nostril and advanced through the center of the air passages without touching the nasal mucosa, toward the choana. It is then advanced into the nasopharynx by adjusting the vertically flexible tip with the lever situated near the eyepiece with the right thumb and by holding and rolling a portion of the scope above the nostril between the left thumb and index finger. The tip of the scope is farther advanced without touching the pharyngeal wall. Once the glottis is visualized, the bronchoscopist gives topical anesthesia by spraying the vocal cords and tracheal mucosa by pushing 1 mL of 2% lidocaine and air in a vertically held 5-mL non-Luer-Loc syringe through the suction port.

As the patient inhales and the glottic aperture widens, the tip of the fiberscope is swiftly advanced into the midtrachea. The tracheal rings, the carina, and the bronchial lumens beyond are now visible through the scope. The tip of the bronchoscope is steadied with the right hand of the operator with its tip in the mid trachea; the lubricated tip of the nasotracheal tube is slid down with the left thumb and index finger over the flexible scope through the nasal cavity and past the vocal cords into the mid trachea while the bronchoscope is held steadily without being advanced too far past the carina as the nasotracheal tube is advanced. The tip of the endotracheal tube is visualized above the carina through the scope as it is pulled back 1 to 2 cm to the mid trachea, and the tube is held firmly at the nostril, as the scope is completely withdrawn. Satisfactory and equal breath sounds on both sides of the chest are confirmed, and then the patient is anesthetized rapidly by intravenous injection of propofol or thiopental, an opioid, and a muscle relaxant of choice, with or without inhalation anesthesia as indicated.

Alternatively, fiberoptic intubation can be performed under general anesthesia. The patient may be anesthetized with sevoflurane and oxygen, switched over to propofol infusion with spontaneous breathing, as with rigid bronchoscopy, while intubation is attempted with a flexible bronchoscope as described earlier. In this case, however, extreme caution should be exercised and adequate topical anesthesia is used to prevent laryngospasm.

Fiberoptic bronchoscopy may also be performed orally on a patient whose ventilation is controlled under sevoflurane or halothane anesthesia with or without neuromuscular blockade. It is mandatory, however, to have a special intubation oral airway for bronchoscopic intubation. Its cross section is “C” shaped so that it can be removed once the tip of the bronchoscope is advanced into the tracheal lumen before the endotracheal tube is advanced over the bronchoscope (IMD Inc., Park City, UT). However, there are only three sizes available (infant, child, and adult), and these are often inadequate. When exposure of the oropharynx is difficult due to either relative macroglossia or micrognathia, it is helpful to have an assistant (a surgeon or an anesthesiologist) pull the tongue outward and downward over the lower incisors with a pair of forceps, towel clips, or a suture through the tongue to improve visualization.

Intubation With a Flexible Bronchoscope and an Endoscopy (Frei) Mask

Frei and others (1995) constructed a special endoscopy mask from a disposable clear plastic facemask. The original connector in the center of the mask was cut out to leave a large hole (40 mm in diameter) and was covered with a distensible silicon rubber (Silastic) membrane with a small hole off-center to accommodate a pediatric fiberoptic bronchoscope. An additional hole (10 mm in diameter) was cut over the lateral aspect of the mask, an airtight silicone rubber adapter was connected to a flexible extension tube, and a 15-mm adapter was inserted to serve as a connector to the anesthesia breathing circuit ( Fig. 10-20 ). A flexible, pediatric fiberoptic bronchoscope can be threaded through the tiny hole in the Silastic diaphragm and an uncuffed endotracheal tube (up to 7 mm ID) can be slid over the scope into the trachea, while the patient can be ventilated manually and continually uninterrupted with manual intermittent positive pressure ventilation ( Fig. 10-21 ). The same endoscopy mask can be used for either nasal or oral intubation by simply adjusting the position of the small hole in the Silastic diaphragm up or down, respectively. Frei and others reported nearly 100% success in fiberoptic intubation without hypoxemia (SPO2 <95%) or significant trauma or complications ( Frei and Ummerhofer, 1996 ; Erb et al., 1997 ).

 
 

FIGURE 10-20  The airway endoscopy mask assembly (Frei mask) for fiberoptic bronchoscopic intubation.  (Courtesy Dr. Franz Frei, Basel, Switzerland.)

 



 
 

FIGURE 10-21  A fiberoptic bronchoscope with an overriding endotracheal tube penetrating through an airway endoscopy mask.  (Courtesy Dr. Franz Frei, Basel, Switzerland.)

 



Intubation With a Flexible Bronchoscope and Laryngeal Mask Airway

The LMA has been exceptionally useful as an emergency airway in the patients whose lungs cannot be ventilated adequately with the conventional mask and bag and who cannot be intubated ( Benumof, 1992 ). Under these circumstances, an LMA in place can be used to ventilate the patient and as a conduit to place a flexible bronchoscope and facilitate endotracheal intubation in children ( Maekawa et al., 1991 ; Theroux et al., 1995 ; Walker et al., 1997 ), as well as in the neonate ( Tom et al., 1995 ). Using a long endotracheal tube, the LMA can be left in place after intubation facilitated by a flexible bronchoscope. If the LMA must be removed for any reason, an endotracheal tube exchanger, made of a long, stiff plastic catheter, exists for this purpose (Cook Airway Exchange Catheter; Cook Critical Care, Bloomington, IN). The endotracheal tube exchanger is inserted into the endotracheal tube before removing the LMA so that the endotracheal tube can be reinserted over the tube exchanger in case it is inadvertently pulled out with the LMA ( Thomas and Parry, 2001 ; Jöhr and Berger, 2004 ). Oxygen can be insufflated through the tube exchanger while the tube is being exchanged. The smallest tube exchanger accommodates an endotracheal tube with a 3-mm ID.

Alternatively, two endotracheal tubes are connected back to back, are loaded onto the flexible bronchoscope, and advanced into the trachea as described earlier. The flexible bronchoscope is withdrawn first and then the LMA is withdrawn. The proximal endotracheal tube is then detached; the tracheal tube connector is attached to the distal endotracheal tube before it is reconnected to the anesthesia circuit to resume assisted or controlled manual ventilation.

▪ INTUBATION WITH A LIGHTED STYLET

Stylets with a light at the tip (lighted stylets or light-wands) have been used successfully in patients for both oral and nasal intubations ( Ellis et al., 1986 ; Fox et al., 1987 ). Lighted stylets are advantageous for intubation in patients with difficult anatomy because the endotracheal tube can be guided by observing the movement of light under the skin. Fiberoptic lighted stylets consist of a reusable fiberoptic light guide, the distal portion of which is coated with annealed surgical stainless steel and covered with a sterile, disposable sheath. The fiberoptic light guide connects to most light sources for fiberoptic or rigid bronchoscopy. The lighted stylet is inserted through a properly sized endotracheal tube, making sure that the end does not protrude out of the tip of the endotracheal tube. Intubation with a lighted stylet is performed orally in an anesthetized patient with or without muscle paralysis. The stylet and endotracheal tube are sharply curved at the tip and are inserted into the mouth so that the end of the styletted tube is pointing in the midline toward the glottis.

In a darkened operating room, the light of the stylet can be seen through the skin over the anterior neck, especially in young children with fewer tissues for the light to penetrate through, and the styletted tube is manipulated so that the light is visible as the operator attempts to pass the tube down the trachea. When the styletted endotracheal tube is successfully introduced into the trachea beyond the larynx, the stylet is withdrawn as the endotracheal tube is advanced farther. Proper placement of the endotracheal tube must be confirmed by auscultation of both lung fields, chest movement, and the presence of end-tidal carbon dioxide waveforms on the capnograph. The lighted stylet appears to have a place in pediatric anesthesia as an additional device and technique for difficult intubation.

▪ INTUBATION WITH THE RETROGRADE TECHNIQUE

Endotracheal intubation can be accomplished using a retrograde guide through the cricothyroid membrane. This technique is not without the risks of airway obstruction and hemorrhage and other complications, and it should not be used casually ( Smith et al., 1975 ). In addition, in infants and young children less than 2 to 3 years, there is a potential for damage to the immature cartilages in the larynx, resulting in laryngeal obstruction and impairment in speech development ( Berry, 1986 ). Furthermore, with the availability of ultrathin, flexible, fiberoptic bronchoscopes and lighted stylets, as described earlier, the indications and justification for the retrograde technique have diminished considerably.

Retrograde intubation may be accomplished with the patient under sedation or under either inhalation or intravenous anesthesia and spontaneously breathing. The patient is premedicated with atropine to prevent vagal stimulation and to reduce secretions. In addition, a topical anesthetic is atomized in the pharynx and larynx to prevent laryngospasm. The neck is extended by placing pads under the shoulders. The cricothyroid membrane (very narrow in infants) is palpated and a local anesthetic (1% lidocaine) is injected intradermally. The needle is then advanced into the tracheal lumen, as confirmed by the aspiration of air into the syringe, and a transtracheal block is performed. A 20-gauge needle attached to a saline-filled syringe is introduced through the skin wheal and the cricothyroid membrane ( Powell and Ozdil, 1967 ). After confirming the intratracheal position with air aspiration into the syringe, a flexible-tip guide wire, used for central venous cannulation, is threaded cephalad via the needle through the larynx and is retrieved in the oropharynx with a Magill forceps ( Borland et al., 1981 ).

In case of nasotracheal intubation, a rubber catheter is passed through the naris into the oropharynx and is tied with the guide wire and retrieved through the nasal cavity. A well-lubricated endotracheal tube is then threaded over the guide wire while tension is maintained on the guide wire from both ends ( Borland et al., 1981 ).

Complications in Pediatric Patients with Difficult Airway

Complications from intubation attempts in patients with difficult airway can increase the risk of injury to the upper airways. The upper airways are lined with the mucosa supported by a rigid framework of cartilages, bone, and muscles. These structures with a relatively rigid external skeleton are predisposed to acute and chronic injuries from attempted intubation ( Loh and Irish, 2002 ).

Acute nasal mucosal injuries can occur as a result of nasotracheal intubation. The use of an inappropriately large tube for the nasal passages is the most common factor, particularly when the nasal mucosa is not adequately decongested and the tube is not sufficiently lubricated. A deviated nasal septum, nasal polyps, and enlarged adenoidal tissues can predispose the patient for nasal and nasopharyngeal injuries. The failure to direct the tip of the nasotracheal tube anteriorly at the site of the nasopharynx can lead to deep mucosal injury. Softening of the nasotracheal tube by immersion in warm water before intubation can reduce epistaxis and mucosal injury ( Kim et al., 2000 ).

Dental injury with partial or complete dental fracture and root avulsion may result during intubation with a difficult exposure of the larynx. When dental injuries occur, it is imperative to recover the loose tooth immediately to prevent aspiration. A dental consultation is required, especially when the permanent teeth are involved (see Chapter 24 , Anesthesia for Dentistry).

Mucosal laceration can occur at the lips, the tongue, and the pharyngeal mucosa as the result of trauma caused by a laryngoscope blade, by an endotracheal tube, and during fiberoptic bronchoscopy when the endotracheal tube is advanced inappropriately. Most lacerations are superficial, however, and heal without surgical intervention. The contributing factors to laryngotracheal mucosal injuries are similar to those of pharyngeal mucosa with difficult airways; and bleeding often complicates the exposure and the process of securing airway access. Most injuries are superficial but may require consultation with a laryngologist ( Weymuller, 1992 ; Loh and Irish, 2002 ).

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

Preparations for the induction of anesthesia in infants and children differ considerably from those for adult patients. Equipment and techniques must be adjusted to accommodate a wide range of sizes in patients, from a premature infant weighing less than 1 kg to an obese teenager weighing well over 100 kg. Psychological preparation for anesthesia induction is as important as clinical readiness. The approach must be adjusted according to the maturity of the child and his or her psychological needs and at times to the psychological needs of the parents as well. A variety of newer and safer drugs and techniques have become available for the preparation and induction of anesthesia for pediatric patients. The characteristics and uses of standard, as well as newer anesthetic and adjuvant agents, are discussed. Indications and techniques of endotracheal intubation and the use of LMAs are discussed in detail, although their indications vary, depending on different surgical procedures and durations as well as the use of regional anesthetic techniques, as detailed in subsequent chapters for specific surgical procedures. With the advent of newer anesthetic and adjuvant agents, standard induction agents have evolved from halothane to sevoflurane and from thiopental to propofol for inhalation and intravenous inductions, respectively. Standard and various approaches to the management of the difficult airway are also covered, including the use of fiberoptic bronchoscopy alone or together with the intubation mask or LMA. In addition, a technique of fiberoptic intubation in infants and children can be viewed with the audiovisual program attached to this chapter.

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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