Handbook of Clinical Anesthesia
The provision of safe anesthesia for pediatric patients requires a clear understanding of the psychological, physiologic, and pharmacologic differences between patients in different age groups from newborn to adolescent (Cravero JP, Kain ZN: Pediatric anesthesia. In Clinical Anesthesia. Edited by Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC. Philadelphia: Lippincott Williams & Wilkins, 2009, pp 1206–1220. Numerous specific anatomic, physiologic, and psychological issues should be understood before anesthetizing pediatric patients (Table 45-1).
- The Preoperative Evaluation (Table 45-2)
- Coexisting Health Conditions
- Upper Respiratory Infection (URI)
- A child with an URI or who is recovering from an URI is at increased risk of developing laryngospasm, bronchospasm, oxygen desaturation, and postoperative atelectasis and croup.
- It is unclear how long surgery should be delayed after an URI; however, bronchial hyperreactivity may exist for up to 7 weeks after an URI.
- The final decision should take into account the risk-to-benefit ratio of the surgical procedure.
- Mask anesthesia, but not a laryngeal mask airway (LMA), has been clearly shown to be associated with a significantly lower rate of perioperative complications compared with use of an endotracheal tube and thus should be used whenever possible with these children.
- Obstructive Sleep Apnea (OSA)
- Severe adenotonsillar hypertrophy with OSA is a frequent indication for children to undergo tonsillectomy and adenoidectomy.
Table 45-1 Anatomical and Physiologic Distinctions Between Adult and Pediatric Patients
- Children with OSA may experience obstruction with the use of preoperative sedative medication and during the induction process, so muscle relaxants should be used carefully in these patients.
Table 45-2 Preoperative Evaluation and Preparation of Children for Surgery
- Postoperatively, patients (especially children younger than 3 years of age) with severe OSA may exhibit worsening of their obstructive symptoms secondary to tissue edema, altered response to carbon dioxide, and residual anesthetic and analgesic agents.
- Children with severe OSA may require postoperative observation in the hospital.
- Obesity often accompanies OSA. (All patients with markedly increased body mass index should be questioned about sleep apnea symptoms.) Obese children have an increased incidence of difficult airway, upper airway obstruction, extended stays in the postanesthesia care unit, and postoperative nausea and vomiting.
- Asthma.Children with asthma should be under optimal medical care before undergoing general anesthesia and surgery. All oral and inhaled medications, such corticosteroids and β-agonists, should be continued up to and including the day of surgery.
- Former Preterm Infants
- Three frequent problems in former preterm infants are the impact that bronchopulmonary dysplasia might have on the patient's perioperative course, the presence of anemia, and the possibility of postoperative apnea.
- The risk of postoperative apnea is inversely related to postconceptual age, and infants with a history of apnea and bradycardia, respiratory distress, and mechanical ventilation may be at increased risk.
- Overnight hospital monitoring should be made for any child considered to be at significant risk for postoperative apnea.
- Laboratory Evaluation
- Healthy children undergoing elective minor surgery require no laboratory evaluation (including chest radiographs and urinalysis) and thus can be spared the anxiety and pain of blood drawing.
- Coagulation testing should only be considered in children in whom the history or medical condition suggests a possible hemostatic defect, in patients undergoing surgical procedures (cardiopulmonary bypass)
that might induce hemostatic disturbances, when the coagulation system is particularly needed for adequate hemostasis, and in patients for whom even minimal postoperative bleeding could be critical.
- Pregnancy screening (anesthetics may be teratogenic) of female patients of childbearing age before the administration of anesthesia is a matter of policy at individual facilities.
- Preoperative Fasting Period
- Solids are prohibited within 6 to 8 hours of surgery (generally after midnight), formula within 6 hours, breast milk within 4 hours of surgery, and clear liquids within 2 hours of surgery.
- Liquids such as apple juice and sugar water may be encouraged up to 2 hours before the induction of anesthesia.
- Hypoglycemia with prolonged intervals of fasting is a risk in young children with smaller glycogen stores.
- Preoperative Sedatives(Table 45-3). The primary goals of premedication in children are to facilitate a smooth and anxiety-free separation from the parents and induction of anesthesia.
Table 45-3 Preoperative Sedatives in Children
- Anesthetic Agents
- Potent Inhalation Agents
- Mask Induction Pharmacology.The incidences of bradycardia, hypotension, and cardiac arrest during inhalation induction are higher in infants younger than 1 year of age, reflecting rapid uptake of inhalation agents and high inspired concentrations used early in induction.
- The minimal alveolar concentration (MAC)of anesthetic required in pediatric patients differs with age. (There are small increases in MAC between birth and 2 to 3 months; after that time, MAC slowly decreases with age.)
- Intracardiac Shunts.Although intracardiac shunts can, in theory, alter the uptake of anesthetic agents and affect the speed of induction, this is rarely clinically evident.
- Inhaled Agents for Induction of Anesthesia.Sevoflurane is the only potent inhalation agent available for inhalation induction. The safety and efficacy of sevoflurane for maintenance of anesthesia in children has been established in hundreds of studies. Although emergence from anesthesia is more rapid with sevoflurane than with more soluble agents such as halothane or isoflurane, a growing literature supports the fact that agitation behaviors in children on emergence are more common with this agent.
III. Intravenous Agents
- Sedative hypnoticsmay be used after inhaled induction of anesthesia or as primary induction and maintenance agents in children who have intravenous lines in place.
- Doses of IV agents used in infants and toddlers often need to be increased by 25% to 40% to obtain the same level of sedation/anesthesia in children compared with adults.
- Propofol induction doses range from 3 to 4 mg/kg for children younger than 2 years of age to approximately 2.5 to 3.0 mg/kg for older children. Maintenance of anesthesia requires 200 to 300 µg/kg/min.
- Emergence from deep sedation/anesthesia is faster than that from most other sedative agents and most inhaled agents, especially after prolonged administration.
- Emergence from propofol is associated with less nausea and vomiting and is accompanied by less emergence agitation, so readiness for discharge is at least as rapid.
- Ketamine offers both hypnosis and analgesia, preserves airway reflexes, maintains respiratory drive, increases endogenous catecholamine release, and results in bronchodilation and pulmonary vasodilation.
- Induction doses of 1 mg/kg IV yield effective analgesia and sedation with rapid onset.
- Intramuscular doses of 3 to 4 mg/kg result in a similar state with significant analgesia that is appropriate for minor procedures such as IV starts or fracture manipulation.
- Simultaneous administration of an anticholinergic minimizes oral secretions.
- Emergence may be marked by diplopia, occasional disturbing dreams, and nausea or vomiting, although these are less common in children than adults.
- Note on Toxicity of Anesthetic Agents.Animal studies involving inhalation and IV anesthetic agents (drugs that act at NMDA [N-methyl-D-aspartic acid] receptors and γ-aminobutyric acid receptors) suggest that neurodegeneration with possible cognitive sequelae is a potential long-term risk of anesthetics. At present, insufficient data suggest that operative anesthesia is harmful in humans.
- Opioidsare important elements of balanced anesthesia and sedation in children.
- Use of opioids for surgical anesthesia decreases the MAC of inhaled agents, smooths hemodynamics during airway management or stimulating procedures, and provides postoperative analgesia.
- Opioids depress central respiratory effort, and newborns and infants younger than 6 months of age are particularly susceptible to this effect because of the immature blood–brain barrier and increased levels of free drug.
Table 45-4 Contraindications to Administration of Succinylcholine to Children
- Muscle Relaxants
- Succinylcholine (Sch) (1.5–2.0 mg/kg IV) produces excellent intubating conditions in 60 seconds with recovery in 6 to 7 minutes.
- Sch can also be given intramuscularly (IM) (4 mg/kg) in emergencies when IV access is not available.
- Sch is contraindicated in a variety of patients (Table 45-4).
- Sch is only recommended in situations in which ultra-rapid onset and short duration of action are of paramount importance (laryngospasm), when relaxation is required, or when IV access is not available and IM administration is required.
- All nondepolarizing muscle relaxants used in adults are also effective for pediatric patients (Table 45-5).
- Neonates and infants have a larger percentage of total body water and larger extracellular fluid (ECF) volume and thus a larger volume of distribution for these hydrophilic drugs than older children and adults. On the other hand, neonates and infants are slightly more sensitive to these drugs.
- The result is a pharmacokinetic and pharmacodynamic profile in which the recommended doses of these agents are identical for children and adults, but the duration of action tends to be slightly longer.
- Rocuronium has the fastest onset of action in this class (60–90 seconds for a 1-mg/kg dose) and is generally the choice for rapid sequence intubation.
- Muscle twitch should be monitored and reversal agents (0.05 mg/kg of neostigmine with 0.015 mg/kg
of atropine or 0.01 mg/kg of glycopyrrolate) administered if residual weakness is detected.
Table 45-5 Comparative Pharmacology of Nondepolarizing Neuromuscular Blocking Agents in Children
- Postoperative nausea and vomiting (PONV) is among the most common causes of prolonged recovery stays and unanticipated hospitalization in children.
- Ondansetron (0.05–0.15 mg/kg) is effective in tonsillectomy and strabismus models, but its effectiveness as a “rescue” medication has not been proven.
- Dexamethasone (0.15–1.0 mg/kg) appears to be effective in limiting PONV after oral pharyngeal surgery (tonsillectomy).
- Droperidol is effective in children as an antiemetic, but concerns regarding prolonged QT syndrome and possible torsades de pointes with its use have impacted the frequency of administration of this drug.
- The practice of requiring patients to eat or drink before discharge increases PONV.
- The use of pain control modalities in lieu of opioids (acetaminophen or nonsteriodal anti-inflammatory drugs [NSAIDs] and regional anesthesia) likely decreases the overall risk of PONV.
- Fluid and Blood Product Management
- Perioperative fluid and blood product management for pediatric patients must take into account fluid deficits (calculated maintenance requirement times number of hours NPO), translocation of fluids and blood loss during surgery, and maintenance fluid requirements (Table 45-6).
Table 45-6 Maintenance Fluid Requirements for Pediatric Patients
- Immediate intravascular volume expansion may be accomplished with a 10-mL/kg bolus of isotonic fluid. The balance of the calculated fluid deficit can be given over 1 or 2 hours and is often provided in the form isotonic fluid or a 5% dextrose solution in 0.9% normal saline.
- Liberalized recommendations for intake of clear fluids (generally up to 2 hours before surgery) mean that hypoglycemia is unlikely in children because of fasting before surgery.
- Administration of 5% dextrose solutions to replace deficits or fluid losses intraoperatively may result in hyperglycemia, which is problematic for patients with intracranial injury.
- Intraoperative monitoring of blood glucose is appropriate for newborns, former premature infants, and all high-risk pediatric patients.
- Surgical manipulation is associated with the isotonic transfer of fluids from the ECF compartment to the nonfunctional interstitial compartment (third-space loss).
- Estimated third-space loss during intra-abdominal surgery varies from 6 to 15 mL/kg/hr. In intrathoracic surgery, it is less (4–7 mL/kg/hr), and during intracranial or cutaneous surgery, it is negligible (1–2 mL/kg/hr).
- These third-space losses should be estimated and replaced on an hourly basis.
- These losses are derived from ECF, and it is important to replace them with a balanced salt solution to avoid hyponatremia that would result from using hypotonic replacement.
- Lactated Ringer's solution is frequently used because normal saline contains an excessive chloride and acid load for infants.
- Indications for blood or blood component therapy in pediatric patients are based on considerations of the patient's blood volume, preoperative hematocrit, general medical condition, and ability to provide oxygen to tissues, as well as the nature of the surgical procedure and the risks versus benefits of transfusion.
- All blood loss should be measured as accurately as possible and accounted for with some form of volume replacement to maintain intravascular volume and perfusion.
- If an isotonic solution is chosen to replace some element of blood loss, it should be given in a ratio of 3:1 (crystalloid:blood lost).
- The concept of the maximum allowable blood loss takes into account the patient's total blood volume, starting hematocrit, and estimated “target” hematocrit (lowest acceptable hematocrit for the patient considering his or her age and comorbid conditions).
- In general, blood volume is estimated at 100 mL/kg for preterm infants, 90 mL/kg for term infants, 80 mg/kg for children 3 to 12 months old, and 70 mg/kg for patients older than 1 year of age.
- These estimates of blood volume may be used in calculating the individual patient's blood volume by multiplying the child's weight by the estimated blood volume per kilogram.
- The end point of fluid and blood therapy is adequate blood pressure, tissue perfusion, and urine volume (0.5–1 mL/kg/hour).
- Airway Management
The choice of airway should depend on the age of the child, the time since last oral intake, coexisting illness, and the procedure to be performed.
- Endotracheal tubes are preferred for premature infants and most neonates because of the greater difficulty of providing effective face mask ventilation under appropriate levels of anesthesia and the risk of filling the stomach with air while providing mask ventilation.
- LMAs come in a range of sizes and half sizes and can be used in infants, toddlers, and older children for almost any procedure that does not involve opening the abdomen or thoracic cavity.
- Because the narrowest portion of the pediatric airway is at the level of the cricoid cartilage, uncuffed tubes can be used and create a functional seal when appropriately sized. Air should leak out at no higher than 20 to 25 cm H2O to minimize the risk of postextubation croup.
- Intubation in children can be safely accomplished after inhaled induction with or without the use of muscle relaxant.
VII. Pediatric Breathing Circuits
Non-rebreathing circuits minimize the work of breathing because they have no valves to be opened by the patient's respiratory effort. A number of combinations of the simple T-piece tubing, reservoir bag, and sites of fresh gas entry and overflow are possible. Circle breathing systems can also be used very effectively in infants and children.
Pediatric patients should be monitored continuously with a precordial or esophageal stethoscope. Pulse oximetry, capnography, blood pressure (measured with appropriately sized cuffs), temperature, and the electrocardiogram should also be monitored routinely in children as in adults. Low tidal volumes, rapid respiratory rates, and changing intrapulmonary shunts make ETCO2 measurements inaccurate for infants and premature neonates with respiratory distress syndrome.
- Awareness and Level of Consciousness Monitoring.Monitors of depth of anesthesia that have been validated in children (bispectral index, spectral entropy, narcotrend index) track the level of sedation/anesthesia in children as they do in adults. (These monitors are not reliable in infants and neonates.) No monitors have been evaluated in term of their ability to decrease awareness in children.
- Pain Management and Regional Anesthesia
Children experience pain, just like adults, regardless of their age. Younger children experience more distress and pain from procedures than older children.
- Pharmacologic Treatment of Pain
- The most common oral analgesic used in children is acetaminophen (10–15 mg/kg orally every 4 hours). The rectal route of administration can be particularly effective for children with no IV access.
- Ketorolac (0.75 mg/kg IM) is effective but has the disadvantage of prolonging bleeding time because of its effect on platelet aggregation.
- Ibuprofen (10 mg/kg) is the most popular NSAID given orally to children.
- Regional Anesthesia
- The ilioinguinal–iliohypogastric nerve block, ring block of the penis, or caudal block can be very useful for common pediatric surgical procedures.
- Use of ultrasound localization allows a lower dose or volume of local anesthetic to be used, which is particularly important in infants and children in whom total dose is limited by weight-based dosing. Strict attention must be paid to the dose of local anesthetic, dose of epinephrine, and technique of administration.
- Caudal blockis the most commonly used form of regional anesthesia in children. This technique can provide postoperative analgesia after a wide variety of lower abdominal and genitourinary surgical procedures. Bupivacaine or ropivacaine produce postoperative analgesia that typically lasts 4 to 6 hours, and at concentrations used (about 0.175%), it is not associated with motor paralysis.
- Spinal anesthesiamay be used for procedures involving surgical dermatomes below T6.
- It is important to note that the dural sac migrates cephalad during the first year of life. In neonates, it is at S3, but in children older than age 1 year, it is at the S1 level.
- Spinal anesthesia is an option for premature infants who undergo surgery because the incidence of postoperative apnea is reduced in these infants with the use of this technique.
- Postanesthesia Care
Table 45-7 Challenges During Recovery of Young Children in the Postanesthesia Care Unit
Editors: Barash, Paul G.; Cullen, Bruce F.; Stoelting, Robert K.; Cahalan, Michael K.; Stock, M. Christine
Title: Handbook of Clinical Anesthesia, 6th Edition
Copyright ©2009 Lippincott Williams & Wilkins
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