Chapter 31 Pediatrics
Developmental physiology
1. How does the oxygen consumption of a neonate compare with that of an adult?
2. How does the cardiac output of a neonate compare with that of an adult?
3. Are changes in the cardiac output of a neonate more dependent on changes in the heart rate or stroke volume?
4. How does the position of the oxyhemoglobin dissociation curve in a neonate compare with that of an adult? Describe how this affects the affinity of oxygen for hemoglobin. At what age does the curve approximate that of an adult?
5. How does the hemoglobin level of a neonate compare with that of an adult? How does the hemoglobin level change as the infant progresses to 2 years old?
6. What hemoglobin level is worrisome in the newborn? What hemoglobin level is worrisome in infants older than 6 months of age?
7. At what age does the foramen ovale close? What percent of adults have a probe patent foramen ovale?
8. How well do neonates reflexively respond to hemorrhage as compared with adults?
9. How does alveolar ventilation in neonates compare with that of adults?
10. How does the tidal volume per weight in neonates compare with that of adults?
11. How does the respiratory rate in neonates compare with that of adults?
12. How does carbon dioxide production in neonates compare with that of adults? How does the PaCO2 in neonates compare with that of adults?
13. How does the PaO2 change in the first few days of life?
14. How predictable is the neonate’s response to hypoxia?
15. What percent body weight in neonates is contributed by the extracellular fluid volume? How does this compare with an adult?
16. What are some ways in which infants and children maintain normal body temperature? Why is maintenance of normal body temperature more difficult in neonates and children than in an adult?
17. How effective is kidney function at birth? When does kidney function become approximately equivalent to that of an adult?
18. After fluid restriction, what is the maximum urine osmolarity possible for term neonates at birth? At what age are adult levels of urine concentrating abilities achieved?
Pharmacologic differences
19. What are some physiologic characteristics of neonates that explain the pharmacologic differences between pediatric and adult responses to drugs?
20. How is the uptake and distribution of inhaled anesthetics different in neonates and infants when compared with adults?
21. How does the minimum alveolar concentration (MAC) of inhaled anesthetics change from birth to puberty?
22. What is the effect of intracardiac shunting on the rapidity of anesthesia induction with halogenated anesthetic gases?
23. What physiologic factors increase the sensitivity of neonates to the effects of intravenous anesthetics?
24. How does the dose of thiopental change between neonates and adults?
25. How does the rate of plasma clearance of opioids differ between neonates and adults?
26. Are neonates more or less sensitive to nondepolarizing neuromuscular blocking drugs than adults? How does the initial drug dose differ between these two groups?
27. How does the duration of action of nondepolarizing neuromuscular blocking drugs differ between neonates and adults?
28. How does the dose of neostigmine necessary to antagonize neuromuscular blockade in the neonate compare with the dose necessary in the adult? How does this affect clinical practice?
29. How does the dose of succinylcholine necessary to produce neuromuscular blockade in the infant and neonate compare with the dose necessary in the adult?
Fluids and electrolytes
30. What is the recommendation for fluid maintenance and replacement in the pediatric population?
31. What is the goal for urine output when monitoring the intraoperative volume status of the pediatric patient?
32. When should glucose administration be considered in the pediatric population?
33. What is the preferred crystalloid fluid to replace intraoperative losses and compensate for any preoperative fluid deficit?
34. What is a reasonable approach to replace preoperative fluid deficits in pediatric patients?
35. How are third-space losses and fluid replacement estimated according to the degree of invasiveness of the surgery? How does this contribute to an overall fluid management strategy for pediatric patients?
Transfusion therapy
36. What formula can be used to help guide the anesthesiologist with blood loss replacement?
37. What is the transfusion threshold for packed red blood cells (PRBC) in pediatric patients? What is the expected hemoglobin increase with PRBC transfusion? What special precautions are needed for PRBC transfusion in neonates and young infants?
38. What is the indication for a platelet transfusion in pediatric patients, and what is the expected response to platelet transfusion?
39. What is the usual indication for transfusion of fresh frozen plasma (FFP) in pediatric patients? What is the expected response to FFP administration?
40. What is the usual indication for administration of cryoprecipitate in pediatric patients? What is the expected response to cryoprecipitate administration?
41. What are some other pharmacologic agents that will either reduce blood loss or help achieve hemostasis with major blood loss surgery in pediatric patients?
Preanesthetic evaluation and preparation
44. What history should be obtained from a preoperative evaluation of a pediatric patient? What are some considerations that are specific to the pediatric population with regard to the history and physical examination?
45. What preoperative laboratory data may be important in the pediatric population?
46. What are the recommendations for the preoperative ingestion of solids and clear liquids for pediatric patients?
47. What are some considerations regarding the choice of premedicant in the pediatric patient? What are some drugs and their routes of administration for preoperative medication in the pediatric population?
Induction and maintenance of anesthesia
48. How can the induction of anesthesia be achieved in pediatric patients without an intravenous catheter in place?
49. What are some risks of an inhaled induction of anesthesia?
50. What is the indication for the placement of an intravenous catheter in the pediatric patient undergoing a surgical procedure?
51. How can the anesthesiologist regulate the intravenous fluids to be administered in the pediatric patient?
52. How can the induction of anesthesia be achieved in pediatric patients with an intravenous catheter in place?
53. How can the induction of anesthesia be achieved in pediatric patients without an intravenous catheter in place and in whom an inhalation induction is not possible?
54. What is the concern regarding the use of succinylcholine in pediatric patients? What are some alternatives that may be used?
55. Under what circumstances is succinylcholine accepted for use for neuromuscular blockade in the pediatric population?
56. What are some physiologic characteristics of the pediatric airway that differ from the adult airway?
57. Why has the classic teaching that uncuffed endotracheal tubes should be used for intubating the trachea of pediatric patients under the age of 8 years changed?
58. What is the benefit of the administration of heated and humidified gases or using a condenser humidifier in children undergoing prolonged operations?
59. What are some signs the clinician may use to determine the adequacy of the depth of anesthesia for surgery in the pediatric population?
60. When hypotension accompanies the administration of volatile anesthetics to neonates, what is it likely to be indicative of?
61. How does intraoperative monitoring in the pediatric population differ from intraoperative monitoring in the adult population?
62. What problem may be encountered with the monitoring of end-tidal carbon dioxide concentrations in pediatric patients?
63. How should the size of a blood pressure cuff be selected? What errors in blood pressure measurement may be encountered with an erroneously sized cuff?
64. What veins may be used to monitor the central venous pressure in the neonate? In infants? In children?
65. What are some regional anesthetic blocks that can be administered in the pediatric population?
66. What local anesthetic and what dose is commonly used in a caudal anesthetic? What is the approximate duration of the postoperative pain relief obtained from this caudal anesthetic? How is the length of the dural sac different in children and adults?
The postanesthesia care unit
67. Are most pediatric patients extubated “awake” or “deep”? What are some of the clinical implications of awake and deep extubation techniques?
68. What is emergence delirium?
69. How can pain be assessed in pediatric patients in the postanesthesia care unit?
70. What are some risk factors for postoperative nausea and vomiting in the pediatric population?
Medical and surgical diseases that affect pediatric patients
71. What is respiratory distress syndrome?
72. What are some physiologic complications that result from respiratory distress syndrome?
73. How should neonates with respiratory distress syndrome be managed intraoperatively?
74. What is bronchopulmonary dysplasia? What are some characteristic findings in these patients?
75. What is retinopathy of prematurity? What is another name for this pathologic finding?
76. What is a risk factor for retinopathy of prematurity? At what age does the risk of retinopathy of prematurity become negligible?
77. What PaO2 should be maintained during anesthesia in the premature neonate to minimize the risk of retinopathy of prematurity?
78. Patients of what age are at risk of apnea spells in the postoperative period? What is the recommendation for these patients in the postoperative period?
79. Which pediatric patients are at risk of hypoglycemia?
80. What are some manifestations of hypoglycemia in this population? How do these manifestations change with general anesthesia? What is the immediate treatment of hypoglycemia in these patients?
81. Which pediatric patients are at risk of hypocalcemia?
82. When might hypocalcemia occur intraoperatively? How might intraoperative hypocalcemia manifest?
83. What is the incidence of malignant hyperthermia in the pediatric population? What is the incidence in the adult population?
84. What is the association between malignant hyperthermia and the calcium ion channel?
85. What are some anesthetic triggering drugs for malignant hyperthermia?
86. What are some clinical signs of malignant hyperthermia?
87. What is the treatment of malignant hyperthermia?
88. How can the patient at risk for malignant hyperthermia be identified preoperatively?
89. Which anesthetic regimen is reliably safe for patients susceptible to malignant hyperthermia? Name some drugs used in anesthesia that have not been shown to trigger malignant hyperthermia.
90. What preparations must take place before the administration of anesthesia to patients susceptible to malignant hyperthermia?
91. Is regional anesthesia considered safe for patients at risk for malignant hyperthermia?
92. What is a congenital diaphragmatic hernia? How is a congenital diaphragmatic hernia manifest in the neonate at birth?
93. What are some comorbid conditions associated with congenital diaphragmatic hernias?
94. How is the diagnosis of a congenital diaphragmatic hernia made?
95. What is the immediate treatment for the neonate with a congenital diaphragmatic hernia? What is the risk of hand ventilation with bag and mask in these neonates?
96. What is the risk of positive pressure ventilation of the lungs of the neonate with a congenital diaphragmatic hernia?
97. What inhaled anesthetics should be avoided in neonates with a congenital diaphragmatic hernia?
98. What clinical circumstance leads to suspicion of a tracheoesophageal fistula in a neonate?
99. What are some other congenital anomalies associated with a tracheoesophageal fistula?
100. How should neonates with a tracheoesophageal fistula be managed?
101. What is pyloric stenosis? What is the incidence of pyloric stenosis per live birth?
102. How does the neonate with pyloric stenosis typically present?
103. What electrolyte imbalances are seen in infants with pyloric stenosis?
104. Is the surgical correction of pyloric stenosis in infants an elective or emergent procedure?
105. How should the induction of anesthesia in infants with pyloric stenosis proceed?
106. What is necrotizing enterocolitis, and which patients are at risk?
107. How is necrotizing enterocolitis treated, and what are some of the anesthetic considerations for this disease?
108. What are gastroschisis and omphalocele? What are the similarities and differences between these conditions?
109. How are gastroschisis and omphalocele treated surgically in the modern era? What are some of the anesthetic considerations for these conditions?
110. What is the significance of a patent ductus arteriosus (PDA) in the premature infant? What are the medical and surgical approaches to treatment?
111. What are some anesthetic considerations and pitfalls for PDA closure in the premature neonate?
112. What is myelomeningocele, and how is it managed surgically? What are some of the anesthetic considerations?
Special anesthetic considerations
113. In what remote locations are pediatric anesthetics commonly performed? Are the requirements for preanesthetic evaluation, monitoring, and recovery the same for these anesthetics?
114. What is the ex utero intrapartum therapy (EXIT) procedure, and what are the indications for its use? What are some of the anesthetic considerations?
115. What are some indications for fetal surgery, and what are some anesthetic considerations?
116. What anesthetic and sedative agents have been implicated in developmental neurotoxicity in animal models? Is there clinical evidence to change the practice of pediatric anesthesia?
117. What is a major consideration for former premature infants who present for surgery? How should these infants be managed postoperatively?
Answers*
Developmental physiology
1. The oxygen consumption of a neonate is about twice that of an adult. In neonates the oxygen consumption increases from 5 mL/kg per minute at birth to about 7 mL/kg per minute at 10 days of life and 8 mL/kg per minute at 4 weeks of life. Oxygen consumption gradually declines over the subsequent months. (548, Table 34-1)
2. The cardiac output of a neonate is 30% to 60% higher than that of adults. This helps to meet the increase in oxygen demand neonates have as compared with adults. (549)
3. Changes in the cardiac output of a neonate or infant are dependent on changes in the heart rate, because stroke volume is relatively fixed by the lack of distensibility of the left ventricle in this age group. The neonate’s myocardium depends heavily on the concentration of ionized calcium, such that hypocalcemia can significantly depress myocardial function. (549)
4. In neonates, the oxyhemoglobin dissociation curve is shifted to the left. This reflects a P50 lower than 26 mm Hg, meaning that less of a PaO2 is required for a 50% saturation of hemoglobin. Conversely, the oxygen is more tightly bound to hemoglobin in neonates, necessitating a lower PaO2 for release of oxygen to the tissues. This occurs as a result of fetal hemoglobin. The position of the oxyhemoglobin dissociation curve becomes equal to that of adults by 4 to 6 months of age. (550)
5. The hemoglobin level of a neonate is approximately 17 g/dL. This, along with the increase in cardiac output, helps to offset the increase in oxygen requirements characteristic of neonates. At 2 to 3 months of age the hemoglobin of infants decreases to about 11 g/dL during the time period when fetal hemoglobin is being replaced by adult hemoglobin. This is termed the physiologic anemia of infancy, which may persist for a few months. During the remainder of the first year of life the hemoglobin level gradually increases and continues to do so until puberty, when hemoglobin levels approach adult hemoglobin levels. (550)
6. A hemoglobin level of 13 g/dL or less is worrisome in the newborn. In infants older than 6 months of age, a hemoglobin level less than 10 g/dL is worrisome. (550)
7. The foramen ovale closes between 3 and 12 months of age. Twenty to thirty percent of adults have a probe patent foramen ovale. (549)
8. Because of the decreased ability of neonates to vasoconstrict in response to hypovolemia, neonates are less able to tolerate hemorrhage with vasoconstrictive responses. (549)
9. Alveolar ventilation in neonates is 4 to 5 times higher than that of adults. (547, Table 34-1)
10. Tidal volume per weight in neonates is similar to that of adults. (547, Table 34-1)
11. The respiratory rate in neonates is three to four times higher than that of adults. (547, Table 34-1)
12. Carbon dioxide production in neonates is higher than that of adults. The PaCO2 in neonates is similar to that of adults, despite the increase in production. This is due to the increase in alveolar ventilation in neonates when compared with adults. (547, Table 34-1)
13. The PaO2 in the first few days after birth increases rapidly. The initially low PaO2 is due to a decrease in the functional residual capacity and to the perfusion of alveoli filled with fluid. The functional residual capacity of neonates increases over the first few days of life until it reaches adult levels at about 4 days of age. (547, Table 34-1)
14. The neonate’s response to hypoxia is somewhat unpredictable, owing to the immaturity of the central nervous system’s regulatory centers for ventilation in this age group. Neonates have decreased ventilatory responses to hypoxemia and hypercarbia. (547)
15. Extracellular fluid volume accounts for approximately 40% of the body weight of the neonate at birth. This compares with approximately 20% of body weight in adults being accounted for by extracellular fluid volume. The proportion of extracellular fluid volume to body weight in neonates approaches the adult proportion by 18 to 24 months of age. (552)
16. Some ways in which infants and children maintain normal body temperature include the metabolism of brown fat, crying, and vigorous movements. The metabolism of brown fat is stimulated by circulating norepinephrine. Children and infants, unlike adults, do not shiver to maintain their body temperature. Maintenance of normal body temperature is more difficult in neonates and infants than in adults because of their larger body surface area-to-volume ratio, as well as the relative lack of fat for insulation. (556)
17. Kidney function at birth is immature. There is a decreased glomerular filtration rate, decreased sodium excretion, and decreased concentrating ability relative to that of an adult. Kidney function progressively matures over the first 2 years of life. Initially, in the first 3 months of life, kidney function increases rapidly to double or triple the glomerular filtration rate possible at birth. Kidney function then matures more slowly from 3 months to 24 months, when adult levels of kidney function are reached. (550)
18. After fluid restriction, the term neonate at birth can only concentrate urine to a maximum osmolarity of about 525 mOsm/kg. After 15 to 30 days of age, neonates are able to concentrate their urine to a maximum osmolarity of about 950 mOsm/kg. Adult levels of urine concentrating ability are achieved by 6 to 12 months of age. (550)
Pharmacologic differences
19. Some physiologic characteristics of neonates that explain the pharmacologic differences between pediatric and adult responses to drugs include an increased extracellular fluid volume, increased metabolic rate, decreased renal function, and decreased receptor maturity. (550, 551)
20. The uptake and distribution of inhaled anesthetics is more rapid in neonates than in adults. This is most likely due to a smaller functional residual capacity per body weight in neonates, as well as to greater tissue blood flow to the vessel-rich group. The vessel-rich group of tissues includes the brain, heart, kidneys, and liver. This group comprises approximately 22% of total body volume in neonates, as compared with the 10% of total body volume in adults. (551)
21. The minimum alveolar concentration (MAC) of inhaled anesthetics changes from birth to puberty. Preterm neonates have a lower MAC than term neonates, whose MAC is approximately 0.87% that of adults. The MAC of inhaled anesthetic agents is highest in infants 1 to 6 months old. The MAC is 30% less in full-term neonates for isoflurane and desflurane. Sevoflurane MAC at term is the same as at age 1 month. (551)
22. Patients with right-to-left intracardiac shunting have a slower inhaled induction of anesthesia, due to the volume of blood bypassing the lungs and not increasing its anesthetic level. This results in a slower rise in the arterial level of the anesthetic and a slower induction. This effect is most pronounced with less-soluble agents, such as desflurane and sevoflurane, and less pronounced with more-soluble agents, such as halothane and isoflurane. Left-to-right intracardiac shunts have little or no effect on the rapidity of induction. (551)
23. Physiologic factors that make neonates more sensitive to the effects of intravenous anesthetics include an immature blood-brain barrier and a decreased ability to metabolize drugs. They are more sensitive to highly protein-bound drugs because of the lower serum albumin and protein concentrations in neonates. In many cases the increased extracellular fluid volume and volume of distribution present in neonates offsets the increased sensitivity to intravenous drugs when compared with adults, thereby approximately equalizing the dose of initial intravenous injection of drug to achieve a given result. (550-551)
24. The dose of thiopental required to produce loss of lid reflex is similar in neonates, children, and adults. (551)
25. The rate of plasma clearance of opioids is decreased in neonates when compared with adults. (551)
26. Neonates are more sensitive than adults to nondepolarizing neuromuscular blocking drugs. This means that a lower plasma concentration of drug is required to produce similar pharmacologic results. Because of an increased extracellular fluid volume and increased volume of distribution in neonates when compared with adults, the initial dose of nondepolarizing neuromuscular blocking drug in these two age groups is similar. This is true despite the increased sensitivity to the drug for neonates. (551)
27. The duration of action of nondepolarizing neuromuscular blocking drugs in neonates may be prolonged while the mechanisms for clearance are still immature in the neonate. For example, the clearance of d-tubocurarine parallels the glomerular filtration rate at various ages. There exists a great deal of variability among pediatric patients with regard to the duration of effect of nondepolarizing neuromuscular blocking drugs. Monitoring of the neuromuscular junction with a peripheral nerve stimulator is recommended when nondepolarizing neuromuscular blocking drugs are administered to this population. (551)
28. The dose of neostigmine necessary to antagonize neuromuscular blocking drugs in the neonate is less than that of adults, although clinically the same dose may be used. (551)
29. The dose of succinylcholine per body weight necessary to produce neuromuscular blockade in the neonate and infant is increased from the adult dose. This is presumed to be due to the increase in extracellular fluid volume and increase in volume of distribution in neonates and infants. (551)
Fluids and electrolytes
30. Fluid maintenance and replacement in the pediatric population is based on the patient’s age and metabolic rate, underlying disease process, type and extent of surgery, and anticipated fluid translocation. The maintenance rate of pediatric patients is related to their metabolic demand, which in turn is related to the ratio of body surface to weight. Hourly fluid requirements are estimated to be 4 mL/kg for children up to 10 kg, an additional 2 mL/kg for each kilogram of body weight between 10 kg and 20 kg, and an additional 1 mL/kg for each kilogram of body weight above 20 kg. Additional fluid replacement may be required for the patient’s initial fluid deficit, third-space losses, or other losses. Fluid replacement can be guided by the patient’s systemic blood pressure, tissue perfusion, and urine output. (552, Table 34-3)
31. A goal for urine output when monitoring the intraoperative volume status in the pediatric patient is 0.5 to 1 mL/kg/hr. (552)
32. Glucose administration in the pediatric patient can be considered in patients who are at a high risk for hypoglycemia. Pediatric patients at a high risk for hypoglycemia include newborns of diabetic mothers or neonates whose hyperalimentation has been discontinued. Maintenance fluids of 5% dextrose in 0.45 normal saline can be administered to these patients intraoperatively as a piggy-back infusion by pump with care not to bolus glucose-containing solutions. (552-553)
33. Nonglucose containing isotonic fluids are most appropriate to replace losses. These include lactated Ringer solution and Plasma-lyte A, which both contain physiologic levels of sodium and potassium. Normal saline can be used, but with supraphysiologic levels of sodium and chloride, a hyperchloremic, hypernatremic, metabolic acidosis can occur with the administration of large volumes. (552)
34. Preoperative fluid deficits in the pediatric patient can be estimated by multiplying the number of hours the patient has been NPO by the hourly maintenance fluid requirement based on the 4-2-1 rule. Replace 50% of this deficit in the first hour, and the remaining 50% in the second hour. Minimizing preoperative fluid deficits by allowing clear liquids to be ingested orally up to 2 hours before surgery is an effective strategy to minimize preoperative deficits. (552)
35. For minimally invasive surgery, third-space losses are estimated to be 0 to 2 mL/kg/hr. This includes superficial surgery such as strabismus repair. For mildly invasive surgery such as ureteral reimplantation, these losses are estimated at 2 to 4 mL/kg/hr. For moderately invasive surgery such as elective bowel reanastomosis, fluid losses are estimated at 4 to 8 mL/kg/hr; and for maximally invasive surgery such as bowel resection for necrotizing enterocolitis, fluid losses are estimated to be 8 to 10 mL/kg/hr or greater. To this hourly fluid administration is added the maintenance fluid requirement according to the 4-2-1 rule, the preoperative fluid deficit as noted previously, and replacement for blood loss. The latter is replaced with 3 mL of isotonic crystalloid for each milliliter of estimated blood loss, or 1 mL of colloid such as 5% albumin for each milliliter blood loss, or milliliter for milliliter of blood product such as packed red blood cells. (552-553, Table 34-3)
Transfusion therapy
36. A formula that may be used by the anesthesiologist to help guide blood loss replacement is:
37. The pediatric patient’s transfusion threshold varies greatly according to the patient’s underlying physiology, age, nature of the surgery, and anticipated ongoing blood loss, and must be individualized. For patients with cyanotic heart disease, a hemoglobin threshold of 12 to 13 g/dL is often used. For otherwise healthy acyanotic patients, a lower threshold of 7 to 8 g/dL is often used; 10-15 mL/kg of PRBC should increase hemoglobin by 2 to 3 g/dL. Leukocyte reduction and irradiation of PRBCs minimizes the risk of cytomegalovirus transmission, graft versus host reaction, and HLA allosensitization. These procedures are used for infants less than 4 months, immunocompromised patients, and transplant or potential transplant recipients. (553)
38. The usual indication for platelet transfusion in a pediatric patient is a platelet count below 50,000 to 100,000/dL, accompanied by surgical bleeding; 5 to 10 mL/kg of platelet concentrate transfusion should increase platelet count by 50,000 to 100,000/dL. (553)
39. Indications for FFP administration in pediatric patients include massive transfusion resulting in markedly reduced levels of coagulation proteins and hemodilution from cardiopulmonary bypass in small infants. Ten to fifteen milliliters per kilogram of FFP will increase most coagulation factors by 15% to 20%, which is often sufficient to improve hemostasis. (553)
40. Indications for cryoprecipitate administration in pediatric patients most often are low fibrinogen concentrations from massive hemorrhage or dilution from cardiopulmonary bypass. One unit of cryoprecipitate administered per 5 kg of patient weight is normally sufficient to restore adequate fibrinogen levels. (553)
41. The lysine analogs ε-aminocaproic acid and tranexamic acid reduce fibrinolysis by inhibiting plasmin. Recombinant factor VIIa is used for patients with factor VII deficiency or hemophiliacs with inhibitors to factors VIII and IX. It is also used in cases of massive hemorrhage such as cardiac surgery or trauma, as a life-saving measure to reduce bleeding. This agent causes a “thrombin burst” when exposed to tissue factor, resulting in massive activation of the coagulation cascade. Thrombotic complications have been reported with recombinant factor VIIa. (553)
The pediatric airway
42. Micrognathia is the single most common cause of difficult mask ventilation and tracheal intubation in young pediatric patients. The preoperative airway assessment in children should involve visual inspection for micrognathia, as well as midface hypoplasia or other cranio-facial abnormalities. Pierre-Robin sequence, Goldenhar, and Treacher-Collins syndromes are the most commonly encountered conditions resulting in micrognathia. (554)
43. The approach to the difficult pediatric and adult airway is generally similar: maintain spontaneous respiration; use adjuncts such as the laryngeal mask airway, videolaryngoscope, or fiber-optic bronchoscope to secure the airway; awaken the patient if possible if the airway cannot be secured; avoid neuromuscular blockade until the airway is secured; and have surgical backup for emergency tracheostomy for particularly difficult cases. The major difference between managing the pediatric versus adult airway is that young pediatric patients will not tolerate an “awake” intubation with topical anesthesia of the airway; they must have some level of moderate to deep sedation or general anesthesia. Also, cricothyrotomy is technically difficult in small patients and ventilation via this method ineffective. Thus, this method cannot be used in young pediatric patients. (554)
Preanesthetic EVALUATION AND PREPARATION
44. The preoperative history in the pediatric patient often comes from a parent. The history obtained should include such things as congenital anomalies, allergies, bleeding tendencies, and any recent exposure to communicable diseases. A special consideration for the pediatric population is whether the patient has had any recent upper respiratory tract infection, which makes it more likely that the patient will have increased secretions and airway hyperreactivity with anesthesia. Elective surgeries may be delayed in the presence of an upper airway infection. With regard to the airway examination, the presence of loose teeth should be evaluated, and removal of the loose tooth or teeth before airway manipulation should be considered. (555)
45. Laboratory data are typically unnecessary in the routine pediatric patient. Laboratory data should be ordered based on abnormalities in the history and physical examination. Urine pregnancy testing is practiced for menstruating females in many institutions. (555)
46. The recommendations for the preoperative consumption of solids and clear liquids are now standardized. Clear liquids are generally allowed up to 2 hours before induction of anesthesia, breast milk up to 4 hours before induction, and milk or formula allowed up to 6 hours before induction. Solid foods should not be ingested sooner than 6 to 8 hours before anesthesia. These guidelines apply to all ages of pediatric patients. (555-556)
47. Premedication of the pediatric patient should take into consideration the age of the patient, the patient’s underlying medical condition, the length of surgery, the mode of induction of anesthesia, and whether the patient will be staying in the hospital after the procedure. Infants younger than 6 months old typically do not require premedication, whereas patients between 9 months and 5 or 6 years old may benefit from premedication before separation from their parents. Premedicants may be administered orally, intravenously, intramuscularly, rectally, sublingually, transmucosally, or intranasally; however, the oral route is strongly preferred. One drug available and commonly used for premedication in the pediatric population is oral midazolam. (556)
Induction and maintenance of anesthesia
48. In the pediatric patient without an intravenous catheter, anesthesia can be induced via inhalation. An inhalation induction can be achieved by initially having the child breathe 70% nitrous oxide and 30% oxygen, followed by incremental increases in the concentration of a volatile anesthetic. The only volatile anesthetic available for inhalation induction in the United States is sevoflurane, because it is much less pungent than the other volatile anesthetics. Other adjuncts that may be used to decrease patient anxiety and facilitate the induction of anesthesia under these circumstances include having the parents present during the time of induction, flavoring the anesthesia mask with pleasant scents, and maintaining a constant monotone conversation with the patient. A story can be told by the anesthesiologist to distract the patient during induction. (557)
49. An inhaled induction of anesthesia has some inherent risks. First, while the pediatric patient is being induced, the anesthesiologist often increases concentrations of the volatile anesthetic to dangerous inspired concentrations of volatile anesthetic if maintained. Once anesthesia is induced it is important to reduce the inspired concentrations of volatile anesthetic to routine maintenance levels. This is especially true just before intubating the trachea, because connection of the circuit and ventilating the intubated patient with high inspired concentrations of volatile anesthetic while potentially distracted with endotracheal tube positioning is a risk. High inspired concentrations of volatile anesthetic, if continued, can lead to myocardial depression that is difficult to reverse. Another risk of an inhaled induction of anesthesia is that of laryngospasm. Laryngospasm, along with coughing, vomiting, and involuntary movement, can occur in stage 2 (the excitement phase) of induction of anesthesia. Laryngospasm is accompanied by a rocking-boat motion of the chest and abdomen as the patient attempts to inspire against a closed glottis. Laryngospasm should be treated by closing the pop-off valve and creating positive-pressure of about 10 cm H2O against the glottis. If necessary, positive pressure ventilation can be attempted. In most circumstances these will reverse the laryngospasm and the patient will spontaneously ventilate. Should these two interventions not reverse the laryngospasm, succinylcholine can be administered intravenously or intramuscularly. Succinylcholine is the neuromuscular blocking drug of choice under these circumstances. (557)
50. The placement of an intravenous catheter should be done in every pediatric patient undergoing a surgical procedure other than for very short surgical procedures. (557)
51. The administration of intravenous fluids in pediatric patients can be regulated by the use of a calibrated drip chamber yielding 60 drops/mL, and filled with only 50 to 100 mL of IV fluid, so as to minimize the risk that excessive amounts of fluid are accidentally administered. (552)
52. In the pediatric patient with an intravenous catheter, the induction of anesthesia can be achieved by the intravenous administration of an induction agent such as thiopental or propofol. This is the induction method of choice in patients at risk for the aspiration of gastric contents. (557)
53. Another method of induction in the pediatric patient without an intravenous catheter and in whom an inhalation induction is not possible is by the intramuscular administration of ketamine. This method of induction is used most commonly in developmentally delayed or severely uncooperative children. (557)
54. There are multiple concerns regarding the use of succinylcholine in pediatric patients. First, the administration of succinylcholine can result in cardiac arrhythmias, including bradycardia and, rarely, cardiac sinus arrest. The pretreatment of pediatric patients with atropine may reduce succinylcholine-induced bradycardia. Second, it is believed that in patients who have been administered succinylcholine and have subsequent masseter muscle rigidity, there may be impending malignant hyperthermia. Finally, there have been reports of pediatric patients who were otherwise healthy and went into irreversible cardiac arrest after the administration of succinylcholine. Many of these patients had hyperkalemia, rhabdomyolysis, and acidosis. It is postulated that these pediatric patients may have had undiagnosed myopathies. Postmortem muscle biopsies have shown many of them to have muscular dystrophy. The group at highest risk of this catastrophic event are males 8 years of age or younger. Because of these concerns, there is now a “black box warning” by the U.S. Food and Drug Administration prohibiting routine use of succinylcholine in pediatric patients. It is only indicated for airway emergencies, such as laryngospasm or rapid sequence induction. Some alternatives that may be used are the nondepolarizing neuromuscular blocking drugs, such as larger doses of vecuronium or rocuronium. (557)
55. Succinylcholine is accepted for use for rapid onset neuromuscular blockade in pediatric patients for the treatment of laryngospasm and in patients at high risk for aspiration of gastric contents in whom rapid sequence induction/intubation is indicated. (557)
56. There are multiple physiologic differences between the pediatric airway and the adult airway. Pediatric patients tend to have a larger tongue relative to the size of their mouths. Particularly true in neonates is that the occiput is larger, so that placing the head in the neutral position naturally places the head in a position favorable for direct laryngoscopy. Extending the head can make direct laryngoscopy difficult. The larynx is more cephalad in pediatric patients, with the cricoid cartilage opposing the C4 vertebra rather than the C6 vertebra as in adults. The larynx is also more anterior. The epiglottis is longer, stiffer, and U shaped and has more of a horizontal lie. The narrowest point of the airway is at the level of the cricoid cartilage in the presence of neuromuscular blockade. These differences between the pediatric airway and the adult airway are present until about the age of 8 years, after which the difference between the pediatric airway and the adult airway is mainly just a difference in size. (554)
57. Because the narrowest point of the pediatric airway is at the level of the cricoid cartilage, it was believed that an endotracheal tube that passes easily through the larynx may cause ischemia or damage to the trachea distally. However, recent imaging studies challenge this notion, and the difference in diameter between the larynx and subglottis in younger children is minimal. Historically, uncuffed tubes were the standard of care in children younger than 8 years of age owing to concerns about subglottic stenosis and postextubation stridor. However, with the introduction of tubes with high volume–low pressure cuffs, recent studies suggest that there is no increased risk of airway edema with cuffed endotracheal tubes and that the use of cuffed endotracheal tubes may decrease the number of laryngoscopies and intubations due to inappropriate tube size. The risk of postintubation tracheal edema is greatest in children between 1 and 4 years of age, whether a cuffed or uncuffed ETT is used. Postintubation tracheal edema/croup can be treated with humidified gases and aerosolized racemic epinephrine. Dexamethasone has also been administered intravenously for the treatment of postintubation tracheal edema. (554)
58. Because of their larger surface area to weight ratio, infants tend lose body heat much more rapidly than adults. This is particularly true in a cold operating room environment. The administration of heated and humidified gases or use of a condenser humidifier in children undergoing prolonged operations is useful in decreasing intraoperative heat loss and in avoiding decreases in body temperature. Warming the operating room, the use of radiant warmers, and warmed intravenous fluids are other methods of maintaining normothermia. (554)
59. Signs for the adequacy of depth of anesthesia for surgery are the same for neonates, infants, and children as they are in adults. Those signs include blood pressure, heart rate, and skeletal muscle movement. Processed electroencephalographic technologies may be used as in the adult population, but are less reliable in younger children. (556)
60. Hypotension in the neonate that accompanies the administration of volatile anesthetics is likely to be indicative of hypovolemia. (552)
61. Intraoperative monitoring in the pediatric population is not any different from intraoperative monitoring in the adult population undergoing comparable surgical procedures. Routine monitors should include blood pressure, heart rate, electrocardiogram, peripheral oxygen saturation, capnography, anesthetic gas concentration, and temperature monitoring. (556)
62. The monitoring of end-tidal carbon dioxide concentrations in small children, infants, and neonates may be complicated by large dead space introduced between the CO2 sampling line and the trachea by endotracheal tube connectors, condenser humidifiers, and elbow connectors at the end of the Y-piece of the anesthesia circuit. The small tidal volumes of these patients exacerbate the problem and can result in falsely low end-tidal CO2 readings. In addition, congenital heart disease patients with right-to-left shunting will have a falsely low end-tidal CO2 due to the blood bypassing the lungs. (556)
63. An appropriately sized blood pressure cuff is one that is greater than one third of the circumference of the limb. A blood pressure cuff that is too small will result in artificially high blood pressures. The opposite is also true, that a blood pressure cuff that is too large will result in artificially low blood pressures. (556)
64. Central venous pressure can be monitored in the neonate via an umbilical vein catheter. The internal jugular vein, femoral vein, or subclavian vein can be used for central venous pressure monitoring in neonates, infants, and children. (549)
65. There are several procedures in which regional anesthetic techniques can be considered in the pediatric population. For circumcision or hypospadias repair, a penile block may be used. For inguinal hernia repair an ilioinguinal and iliohypogastric block may be used. For femur surgery, a fascia iliaca compartment block may be used. For arm and wrist surgery a brachial plexus block may be used. Intravenous regional anesthesia may also be used in the pediatric patient for tendon laceration repairs or extremity fractures. Caudal anesthesia is a common form of anesthesia and is used for postoperative pain relief in the pediatric population in whom the surgical site is below the level of the diaphragm. Conversely, a lumbar epidural anesthetic may also be used in the pediatric patient. (557, 558)
66. For caudal epidural anesthesia, the local anesthetic most commonly used is bupivacaine at a concentration of 0.125% to 0.25%, and ropivacaine at 0.1% to 0.2%. The volume is 0.5 to 1 mL/kg, up to a maximum of 20 mL. The duration of pain relief provided by this dose of local anesthetic in the caudal epidural space is 4 to 6 hours, therefore possibly providing some postoperative pain relief. The dural sac extends more caudad in children than in adults, making inadvertent intrathecal injection a possibility. The risks of caudal epidural anesthesia are minimal. (557)
The postanesthesia care unit
67. It is common practice in pediatric anesthesia to extubate the trachea of the patient during deep anesthesia. The advantage of extubating the trachea during deep extubation is that emergence from anesthesia without a tracheal tube in place avoids coughing and straining on surgical suture lines, as removal of the endotracheal tube is prior to the return of airway reactivity. The decision of when to extubate the trachea is made on a case-by-case basis, however. In some cases airway reflexes are preferred to have returned prior to tracheal extubation, as in patients at risk for the aspiration of gastric contents or with blood and secretions in the airway. (557)
68. Emergence delirium refers to a dissociated state of consciousness that occurs while waking from anesthesia. It occurs more frequently in the pediatric population after anesthesia with sevoflurane or desflurane. During this time the pediatric patient is inconsolable, irritable, incoherent, and/or uncooperative. The patient may be crying, moaning, kicking, and restless. During this time there may be accidental removal of intravenous catheters, surgical bandages, and drains. During emergence delirium, children usually do not recognize or identify familiar and known objects or people. Emergence delirium is generally self-limiting, and typically lasts only about 5 to 15 minutes. (558)
69. The assessment of pain in postoperative pediatric patients can be particularly difficult as these patients may be nonverbal. There are several scales for assessing pain, including scales that monitor for facial expressions, movement, crying, and consolability. (558)
70. Risk factors for postoperative nausea and vomiting in the pediatric patient population include age 3 years or older, strabismus surgery, duration of surgery, and previous history of postoperative nausea and vomiting in the patient or in a parent or sibling. (558)
Medical and surgical diseases that affect pediatric patients
71. Respiratory distress syndrome, also referred to as hyaline membrane disease, is a syndrome affecting preterm neonates who at birth have a deficiency of surfactant. Surfactant is necessary to maintain alveolar stability, so that without it alveoli collapse. Surfactant is a surface active phospholipid in the alveoli that can now be administered into the lungs of neonates for the treatment or prevention of respiratory distress syndrome. The compliance of the lung and arterial oxygenation often improve rapidly after its administration. The administration of surfactant has decreased the morbidity and mortality resulting from this syndrome. (563-565)
72. With the alveolar collapse associated with respiratory distress syndrome, there is resultant right-to-left intrapulmonary shunting, arterial hypoxemia, and metabolic acidosis. (563-565)
73. Neonates with respiratory distress syndrome should have their arterial oxygenation closely monitored intraoperatively. The PaO2 the anesthesiologist should try to maintain in these patients is the PaO2 level the patient had before surgery. This may require high inspired concentrations of oxygen and positive end-expiratory pressure. The PaO2 should ideally be monitored from a preductal artery. If the surgical procedure is short and intraarterial monitoring is not feasible, oxygenation may be monitored by pulse oximetry. These neonates are at an increased risk for pneumothorax with positive-pressure ventilation. Neonates with respiratory distress syndrome should be well hydrated. It may be prudent to maintain the hematocrit near 40% to optimize the delivery of oxygen to the tissues. (564)
74. Bronchopulmonary dysplasia is a chronic pulmonary disorder in infants and children who had prolonged respiratory disease at birth, defined as the need for supplemental oxygen beyond 30 days of life after a diagnosis of respiratory distress syndrome. It is thought to result from the required high inspired concentrations of oxygen and mechanical ventilation with high peak airway pressures for a prolonged period of time as treatment for the respiratory disease. Some characteristic findings in patients with bronchopulmonary dysplasia are increased airway resistance, increased airway reactivity, decreased arterial oxygenation due to ventilation-to-perfusion mismatch, and recurrent pulmonary infections. A chest radiograph in these patients may show large lung volumes, fibrosis, and atelectasis. These patients may have chronic hypercarbia as well. The incidence of bronchopulmonary dysplasia has decreased since the advent of surfactant therapy in neonates at risk. (565)
75. Retinopathy of prematurity, also referred to as retrolental fibroplasia, is a condition in which the retinal vasculature becomes neovascularized and scarred. Permanent visual impairment can result. (564)
76. A risk factor for retinopathy of prematurity is a PaO2 greater than 80 mm Hg or an oxygen saturation greater than 94% in the presence of prematurity. Retinopathy of prematurity has occurred in neonates whose PaO2 was maintained at about 150 mm Hg for 2 to 4 hours. Neonates whose birth weights are lower than 1500 g are especially at risk. The risk of retinopathy of prematurity becomes negligible 44 weeks after conception. (564)
77. A PaO2 between 50 and 70 mm Hg or an oxygen saturation between 88% and 93% should be maintained during anesthesia in the premature neonate to minimize the risk of retinopathy of prematurity. (564)
78. Apnea spells that result in the cessation of breathing for 20 seconds or longer can lead to cyanosis and bradycardia. Especially at risk are preterm infants younger than 50 weeks postconception. It is estimated that 20% to 30% of preterm infants have apnea spells during their first month of life. Apnea spells may be increased in the neonate in the postoperative period secondary to the residual effects of inhaled and injected anesthetics that affect the control of breathing. The recommendation for these patients is that apnea and bradycardia monitors be used after surgery that will sound an alarm if apnea or bradycardia is detected in the patient. These patients are not candidates for outpatient surgery because of the risk of apnea occurring at home where health care providers are not available to respond. An alternative is to postpone nonessential surgery until infants are older than 50 weeks postconception. Treating anemia and administering a single dose of IV caffeine citrate will reduce the incidence and severity of postanesthetic apnea in this population. (565)
79. Neonates are at risk of developing hypoglycemia, particularly neonates of diabetic mothers. Hypoglycemia is defined by a plasma glucose concentration less than 40 mg/dL in the preterm neonate, less than 50 mg/dL for the term neonate younger than 3 days old, and less than 60 mg/dL in the term neonate older than 3 days of age. Neonates are at risk of hypoglycemia secondary to their poorly developed system for the maintenance of adequate plasma glucose concentrations. In addition, patients receiving total parenteral nutrition with high dextrose concentrations are at risk for hypoglycemia if the infusion is interrupted. Also, patients with poor nutritional status or liver disease often have inadequate hepatic glycogen stores and are also at risk. (552-553)
80. Manifestations of hypoglycemia in neonates include irritability, seizures, bradycardia, hypotension, and apnea. These clinical manifestations may be masked by general anesthesia, making perioperative vigilance very important; frequent analysis of blood glucose is important in patients at risk. The immediate treatment of hypoglycemia in neonates is the intravenous administration of 0.5 to 1 g/kg of glucose. (552-553)
81. Preterm neonates are at risk of developing hypocalcemia. Hypocalcemia in the neonate is defined by a plasma ionized calcium concentration less than about 1.1 mEq/dL. Fetuses develop their calcium stores during the third trimester, so that the preterm neonate has inadequate calcium stores at birth. (549)
82. Hypocalcemia might occur intraoperatively as a result of citrated blood transfusions or during an exchange transfusion. The rapid infusion of citrate that occurs with citrated blood or fresh frozen plasma transfusions can result in hypotension secondary to hypocalcemia. The hypotension can be minimized by the administration of calcium gluconate, 1 to 2 mg intravenously for every 1 mL of blood transfused. (553)
83. The incidence of malignant hyperthermia in the pediatric population has been reported to be as high as 1 in 12,000 pediatric anesthetics. However, with the virtual disappearance of the use of two of the most potent triggering agents, halothane and succinylcholine, in the pediatric population, this incidence is now believed to be significantly lower. The incidence of malignant hyperthermia in the adult population is approximately 1 in 40,000 adult anesthetics. (555)
84. The calcium channel is important in the pathophysiology of malignant hyperthermia. There is a defect in the calcium release channel in the sarcoplasmic reticulum of the skeletal muscle, specifically the ryanodine receptor (RYR1 gene mutation is the leading cause). This defect allows for higher concentrations of calcium to be sustained in the myoplasm, resulting in persistent skeletal muscle contractions when a patient at risk for developing malignant hyperthermia is exposed to inciting anesthetic agents or drugs. The genetic coding site for malignant hyperthermia is the ryanodine receptor. (555)
85. Anesthetic triggering drugs for malignant hyperthermia include succinylcholine and volatile anesthetics, halothane being by far the most potent agent. (555)
86. Clinical signs of malignant hyperthermia are related to some of the consequences of sustained skeletal muscle contraction. These include tachycardia, arterial hypoxemia, metabolic acidosis, respiratory acidosis, and increases in body temperature. Early signs of malignant hyperthermia include tachycardia and an increase in the exhaled concentration of carbon dioxide that are otherwise unexplained. A late sign of malignant hyperthermia is the increase in body temperature. (555)
87. The primary treatment for malignant hyperthermia is dantrolene. Dantrolene inhibits the release of calcium from the sarcoplasmic reticulum. The dose of dantrolene to be administered is 2 to 3 mg/kg intravenously and repeated every 5 to 10 minutes until the symptoms are controlled. Other treatment interventions for malignant hyperthermia are directed toward supportive management. First, the inhaled anesthetic being administered should be immediately discontinued. The lungs should be hyperventilated with oxygen. For the hyperthermia, active cooling should be initiated. Active cooling may include cold saline, 15 mL/kg intravenously every 10 minutes. Gastric lavage with cold saline and surface cooling may also be used. For the severely acidotic patient, sodium bicarbonate may be administered at a dose of 1 to 2 mEq/kg intravenously, and guided by arterial pH. Diuresis of the patient should also be considered, either by hydration, mannitol, or furosemide. (555)
88. The patient at risk for malignant hyperthermia may be identified preoperatively by a detailed preoperative medical history and by a family history that especially notes any problems with anesthesia. Preoperative testing of the level of creatinine kinase is not always useful, because only about 70% of patients who are susceptible to malignant hyperthermia have increased resting levels of creatinine kinase. The definitive diagnosis of a patient’s susceptibility to malignant hyperthermia requires a skeletal muscle biopsy. The skeletal muscle is then tested in vitro for isometric contracture in response to exposure to caffeine or halothane or both. This test has the highest sensitivity and specificity for MH. Recently, genetic testing for the ryanodine receptor abnormality (RYR1 mutation) has become available. This test is not as sensitive as the contracture test but is highly specific. (555)
89. No anesthetic regimen is known to be reliably safe for administration to patients who are susceptible to malignant hyperthermia. Some drugs that are used in anesthesia that have not been shown to trigger malignant hyperthermia include barbiturates, opioids, benzodiazepines, propofol, etomidate, nitrous oxide, local anesthetics, and nondepolarizing neuromuscular blocking drugs. (555)
90. It is now the consensus of many that preoperative dantrolene is not necessary in susceptible patients because general anesthesia with nontriggering agents has proven to be mostly uneventful. There are multiple preparations for the operating room before anesthetizing a patient at risk for malignant hyperthermia. The vaporizers may be removed or sealed. The soda lime should be changed, and the fresh gas outlet hose may be changed. High fresh gas flows should be maintained for at least 20 minutes prior to the induction of anesthesia, and an expired gas analyzer should be used to confirm that traces of anesthetic gases have been purged. (555)
91. Regional anesthesia is considered safe for patients at risk for malignant hyperthermia. (555)
92. A congenital diaphragmatic hernia is a congenital defect in the diaphragm that results in the herniation of abdominal viscera into the chest. Almost all the abdominal viscera can be in the chest, including the liver and spleen. It results from the incomplete closure of the diaphragm in an embryologic stage of development of the fetus. The defect in the diaphragm is usually on the left through the foramen of Bochdalek. In the presence of a congenital diaphragmatic hernia, there is an associated hypoplasia of the lung on the ipsilateral side. The degree of hypoplasia depends on the gestational age at which the herniation occurred. Manifestations at birth include a scaphoid abdomen, respiratory distress, acidosis, and profound arterial hypoxemia. The incidence of congenital diaphragmatic hernia is about 1 in every 5000 live births. (562-563)
93. Some comorbid conditions associated with congenital diaphragmatic hernia include polyhydramnios, congenital heart disease, and pulmonary hypertension. (562-563)
94. The diagnosis of a congenital diaphragmatic hernia can be made in utero during ultrasonography of the fetus. The diagnosis at birth is confirmed by the clinical manifestations of the anomaly, by auscultation of intestines and decreased breath sounds over the affected lung area, and by chest radiograph. On the chest radiograph, loops of intestine are seen in the affected thorax, as well as a shift of the mediastinum to the opposite side. (562-563)
95. The immediate treatment of a congenital diaphragmatic hernia in a neonate involves decompression of the stomach with a nasogastric tube, endotracheal intubation minimizing hand ventilation of the lungs, and the administration of oxygen. Positive pressure when ventilating by hand with bag and mask can increase the volume of the gastrointestinal tract with air, further compromising pulmonary function by direct mechanical compression. This can lead to hypotension as well as worsening hypoxemia. The lungs should be ventilated with small tidal volumes at a rate of 60 to 150 breaths/min. Hyperventilation of the lungs with oxygen can improve pulmonary blood flow by reversing the hypoxia and acidosis. High frequency oscillatory ventilation and inhaled nitric oxide are frequently used to improve gas exchange and reduce pulmonary artery pressures. The neonate with a congenital diaphragmatic hernia in whom arterial oxygenation is difficult may require extracorporeal membrane oxygenation (ECMO) for stabilization before surgical intervention. ECMO support of these neonates has led to a decrease in the mortality of neonates with congenital diaphragmatic hernia. Surgery is often delayed in the critically ill neonate with a congenital diaphragmatic hernia while the pulmonary vascular resistance decreases. Surgery may be accomplished while on ECMO or on high-frequency oscillatory ventilation. (562-563)
96. Positive-pressure ventilation of the lungs of a neonate with a congenital diaphragmatic hernia can result in a pneumothorax on the contralateral side of the affected lung if peak airway pressures exceed 25 to 30 cm H2O. Expansion of the hypoplastic lung after surgical correction of the congenital diaphragmatic hernia should not be attempted because of the risk of pneumothorax or other damage to the normal lung. (562-563)
97. The anesthetic management of neonates with a congenital diaphragmatic hernia undergoing a surgical procedure should include monitoring of arterial oxygenation and the avoidance of nitrous oxide. Nitrous oxide should be avoided because it can diffuse into the loops of intestine in the chest and expand the intestines further, leading to more pulmonary compromise. (562-563)
98. A tracheoesophageal fistula should be suspected when soon after birth a neonate develops cyanosis and coughing during oral feedings. The clinician should also suspect the presence of a tracheoesophageal fistula when an oral catheter cannot be passed into the stomach. The severity of illness in these patients can range from mild to severe. (561)
99. Thirty to forty percent of neonates with a tracheoesophageal fistula have associated congenital heart disease, including ventricular septal defect, tetralogy of Fallot, and coarctation of the aorta. Tracheoesophageal fistula is also a component of the VACTERL association (V for vertebral defects; A for imperforate anus, C for cardiac defects, TE for TE fistula, R for renal anomalies, and L for limb anomalies). Prematurity accompanies tracheoesophageal fistulas about 40% of the time. (561)
100. Neonates with a tracheoesophageal fistula are at risk for pulmonary aspiration, gastric distention, and difficulty with ventilation. These neonates should have a catheter placed in the esophagus to drain secretions and prevent the accumulation of fluids in the esophageal pouch. Manual positive-pressure ventilation of the lungs with a mask should be kept at a minimum to lessen the risk of gastric distention and pulmonary aspiration. When intubating the trachea of an infant with a tracheoesophageal fistula, the anesthesiologist must be careful to place the endotracheal tube distal to the level of the fistula. This can be confirmed through the auscultation of decreased breath sounds over the stomach. Some surgeons or anesthesiologists will perform a rigid or flexible bronchoscopy to diagnose the location of the fistula to aid in endotracheal tube placement. Care should be taken to avoid endobronchial intubation as well. Attention to breath sounds, chest movement with ventilation, peak inspiratory pressures, and oxygen saturation should continue throughout the surgical procedure because small movements in the endotracheal tube can lead to its malposition. (562)
101. Pyloric stenosis occurs as a result of hypertrophy of the pyloric smooth muscle. This muscle hypertrophy, in combination with edema of the pyloric mucosa, results in progressive obstruction of the pylorus. The incidence of pyloric stenosis is 1 in every 500 live births. (564)
102. The usual clinical scenario of an infant with pyloric stenosis is one of persistent vomiting in a male infant at 2 to 8 weeks of age. (564)
103. The electrolyte imbalances that are commonly seen in infants with pyloric stenosis occur as a result of the loss of hydrogen ions that is associated with persistent vomiting. These electrolyte imbalances include hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis. There is often a compensatory respiratory acidosis. (564)
104. Concerns for the anesthesiologist caring for the patient with pyloric stenosis include the metabolic abnormalities, severe dehydration, and full stomach, often with barium after a radiologic study. These all place the infant at an increased risk for morbidity perioperatively. Although pyloric stenosis is a medical emergency, surgical correction of pyloric stenosis is an elective procedure. The corrective procedure for these infants can be done after 24 to 48 hours of intravenous fluid rehydration, the correction of their electrolyte abnormalities, and suctioning on a catheter placed in the stomach. (565)
105. The induction of anesthesia in infants with pyloric stenosis should be preceded by the emptying of stomach contents with a catheter to minimize the risk of the pulmonary aspiration of gastric contents. Induction should then be done in a rapid sequence fashion with cricoid pressure. Alternatively, an awake intubation may be performed, although this is rarely practiced in the modern era. Extubation of the trachea after the procedure should only be performed when the infant is awake and vigorous because postoperative depression of ventilation is frequently seen in these infants. This may be partially due to an increase cerebrospinal fluid pH which decreases the respiratory drive. In fact, these patients should be monitored for 12 to 24 hours postoperatively for apnea. (565)
106. Necrotizing enterocolitis is a common surgical emergency in the neonate, primarily in premature newborns. It is an intestinal mucosal ischemic injury sometimes resulting in bowel necrosis. It is seen in premature infants, with incidence inversely proportional to gestational age. Reduced mesenteric blood flow from a patent ductus arteriosus, bacterial infection, and the institution of enteral feeding all have a role in the etiology of necrotizing enterocolitis. (559)
107. Medical treatment of necrotizing enterocolitis includes bowel rest, antibiotics, and serial abdominal examinations and radiographs. Surgical treatment may be emergent, laparotomy, with drainage, bowel resection, and reanastomosis or creation of ostomies. Patients are often unstable and critically ill with sepsis, acidosis, coagulopathy, and pulmonary morbidity. Availability of colloids and blood products, invasive monitoring, inotropic agents, and frequent measurement of blood gases, electrolytes, ionized calcium, glucose, lactate, and hemoglobin are important anesthetic considerations in managing patients with necrotizing enterocolitis. (559-560)
108. Gastroschisis and omphalocele are both abdominal wall defects usually diagnosed in utero by ultrasound, requiring treatment in the neonatal period. Gastroschisis is a defect where the intestines usually protrude to the right of the umbilicus and do not have a covering peritoneal sac. Infants with gastroschisis usually do not have additional associated anomalies. Omphalocele is a midline defect covered by the peritoneal sac with the umbilical cord incorporated into the defect. Patients with omphalocele often have other associated anomalies. (560)
109. Large or giant defects are now managed with a staged approach, whereby the intestines are partially reduced into the peritoneal cavity, and the edges of the defect are sutured to a synthetic “silo.” The intestines are then reduced into the peritoneal cavity in several steps over days to weeks. This is followed by final surgical closure of the defect. The former approach of one stage repair has been abandoned because of the high incidence of intestinal ischemia and respiratory morbidity associated with this strategy. Anesthetic considerations include awareness of associated defects with omphalocele patients, especially congenital heart disease. Covering the defect with moist gauze, administering adequate intravenous fluid to account for very large third-space losses with exposed viscera, providing appropriate muscle relaxation, and careful attention to ventilator status as the intestines are reduced are important anesthetic considerations. (560)
110. A patent ductus arteriosus (PDA) is most often seen in premature infants, and can result in pulmonary edema, which complicates respiratory distress syndrome and prevents weaning from mechanical ventilator support. It also may “steal” systemic blood flow resulting in mesenteric ischemia and increasing the risk for necrotizing enterocolitis, hypotension, and cardiac failure from the large left-to-right shunt. Indomethacin treatment is often attempted, but this may result in platelet and renal dysfunction. (563)
111. PDA ligation is often performed at the bedside in the neonatal intensive care unit, and full monitoring including capnography must be provided. Transport to a distant operating room has a significant risk for cardiopulmonary instability. Anesthesia is usually provided with fentanyl, 25 to 50 μg/kg, with an intravenous amnestic agent or low-dose volatile anesthetic. Because the PDA is so large, it can be mistaken for the descending thoracic aorta, and the aorta may be inadvertently ligated. The anesthesiologist must monitor lower extremity perfusion, most commonly via pulse oximeter on the foot, to detect this problem. (563)
112. Myelomeningocele is a defect in the development of the neural tube, resulting in an open neural placode covered only by a thin membrane and cerebrospinal fluid. It is diagnosed in utero with ultrasound, and ranges from small lumbosacral defects with minimal neurologic sequelae, to large thoracolumbar defects with high paraplegia. After birth, the infant is managed prone so as not to rupture the sac. Anesthesia induction involves either intubation in the lateral decubitus position or brief supine positioning on a padded gel doughnut to protect the sac. A nonlatex environment, including surgical gloves, is crucial to avoid latex sensitization. Muscle relaxants are avoided so the surgeon can evaluate motor function during the repair. The patient is managed prone during the initial days after surgery. (564)
Special anesthetic considerations
113. Anesthesia and sedation are delivered in the cardiac catheterization laboratories, magnetic resonance imaging and computed tomography scanners, gastrointestinal and pulmonary procedure suites, interventional radiology, radiation therapy, dental clinics, and many other locations. Magnetic resonance image (MRI) scanning in particular has undergone explosive growth and greatly increased the need for remote sedation and anesthesia services. Requirements for preanesthetic evaluation, monitoring, and recovery are identical to those for operating room surgical anesthesia. MRI-compatible anesthesia machines and monitors are available and full monitoring must be used. In particular, capnography for nonintubated, sedated patients via divided nasal cannula should be used for all sedation cases. (565)
114. The ex utero intrapartum therapy (EXIT) procedure involves partial delivery of the head, chest, and arms of the fetus to manage a severe airway or pulmonary anomaly. The fetus remains connected to the placental circulation to provide oxygenation and carbon dioxide removal during the procedure to secure the airway or manage the airway or lung mass. Indications include large airway, neck, or chest masses such as cystic hygroma, teratoma, and congenital adenomatoid malformation. Two anesthesiologists are required, one for the mother and one for the fetus. The mother requires deep inhalational general anesthesia to reduce uterine tone during the fetal procedure to prevent placental separation. The fetus receives intravenous or intramuscular fentanyl or morphine for analgesia. Resection of the mass or securing the airway by rigid bronchoscopy or tracheostomy is the primary goal. Then, the fetus is delivered. (565-566)
115. Multiple trials of open fetal surgery have been attempted, including congenital diaphragmatic hernia, posterior urethral valves, lung masses, and myelomeningocele. In open fetal surgery mother and fetus are anesthetized, a hysterotomy is done, the fetus exteriorized, the surgery done, and then the fetus returned to the uterus to be delivered as close to term as possible. Two anesthesiologists are required, one for the mother and one for the fetus. Most trials of fetal surgery have not resulted in improved outcomes. However, meningomyelocele repair in utero results in better overall functional outcomes, and so is likely to be increasingly performed. (566)
116. In animal models, agents that bind to γ-aminobutyric acid (GABA) receptors as agonists and to N-methyl-D-aspartate (NMDA) receptors as antagonists, have been implicated in neuronal cell death caused by apoptosis. GABA agonists include volatile anesthetics, propofol, and benzodiazepines. NMDA antagonists include ketamine. Most experts agree that there are not sufficient clinical data as of this writing to change clinical practice. (566)
117. Former premature infants who present for surgery are at an increased risk for postanesthetic apnea. This risk increases with increased prematurity at birth and younger age at the time of the anesthetic. The current recommendation is that former premature infants should have their elective surgery delayed until 50 weeks postconceptual age or greater to minimize this risk. Prior to this, and in a case-by-case basis, infants may need to be admitted postoperatively for 24 hours of apnea monitoring. (565)
