Chapter 20. Evaluation of Children

1. Children have significantly different physiology and psychology and behavior to necessitate a comprehensive pediatric approach for the child and the family based on their requirements.

2. The percentage of total body composition that is water decreases with age; intracellular fluid increases, whereas extracellular fluid decreases.

3. Fat and muscle mass increase from 13% to 22% and 20% to 50%, respectively, with age.

4. The distribution of blood flow varies, with a decreased percentage of flow going to the vessel-rich groups with increased age.

5. Infants have a large tongue and relatively small jaw. Infants usually are described as having an anterior and cephalad displacement of the airway, with the narrowest segment at the level of the cricoid. The epiglottis generally is large and floppy compared with that of adults.

6. Younger children tend to experience airway closure and alveolar collapse with atelectasis because the end-expiratory lung volume from which tidal breathing occurs is close to closing capacity.

7. Although the functional residual capacity in milliliters per kilogram is smaller in infants compared with adults (30 vs 34), increased oxygen consumption is the major factor in the rapid desaturation of infants.

8. The perioperative risk of reversion to a transitional circulation is related to pulmonary hypertension triggered by hypoxemia, hypercarbia, hypothermia, acidosis, and increased catecholamines.

9. Cardiac output depends on heart rate in infants and young children. Infants have parasympathetic hypertonia, decreased sympathetic innervation, and a ventricle with less muscle and more noncontractile mass per unit volume. These all lead to a myocardium that is less able to generate adequate force than in adults.

10. A hematocrit nadir of approximately 35 at approximately age 3 months is the so-called physiologic anemia of infancy.

11. The glomerular filtration rate/1.73 m2 increases from 40 to 130 mL/min with age. Ability to concentrate urine is limited, and maximal osmolarity may be only 700 mOsm.

12. Slack lower esophageal sphincter tone with reflux is common in infants younger than 6 months, but the maintenance of low gastric volumes by nothing-by-mouth (NPO) regulations should be balanced by awareness of the risk of hypoglycemia.

13. The liver is functionally immature in children, affecting synthetic and metabolic function.

14. Defending the thermoneutrality of infants is a cornerstone of pediatric anesthesia.

15. Cold stress in neonates can increase oxygen consumption and decrease oxygen delivery, leading to increased hydrogen ion concentration and decreased glycogen and glucose. This may result in respiratory distress, disseminated intravascular coagulation, shock, and persistent fetal circulation.

16. The large surface-area-to-mass ratio in children and decreased subcutaneous tissue mass lead to increased heat loss via conduction, convection, radiation, and evaporation.

17. The large volume of distribution noted in neonates is related to decreased protein binding and a greater proportion of extracellular water.

18. In preoperative evaluation, the anesthesiologist should prepare himself or herself, the family, and the child for the procedure. The primary objective is to ensure that the child is in optimal condition. Developmental milestones and growth charts should be reviewed to assist in the general assessment of well-being. Optimal drug levels (eg, anticonvulsants and theophylline) should be ensured.

19. Many congenital anomalies are associated with airway and cardiac abnormalities.

20. In children with known cardiopulmonary disease, it is imperative that the anesthesiologist be completely familiar with the child's current status and be assured that therapy has been optimized preoperatively.

21. In infants, feeding is the major exercise, and failure to thrive may indicate compromised cardiovascular function.

22. The "runny nose" remains a controversial area, but whenever possible, surgery and anesthesia should be delayed at least 2 weeks when the child has a runny nose associated with lower respiratory or systemic symptoms.

23. Routine laboratory testing for healthy children remains controversial and should be dictated by clinical situation.

24. The trend of NPO status is toward a more liberal NPO restriction for clear liquids.

25. Rigorous, compulsive, and systematic evaluation of critically ill children is essential.

The preanesthetic evaluation of the child requires not only an understanding of the different surgical procedures children undergo, but also an understanding of the unique psychology, development, and physiology of children. There are many obvious differences between adults and children that affect anesthetic management. Apart from the differences of size, communication skills, and issues involving parents, there also are multiple, less obvious differences in the physiology, psychology, anatomy, and pharmacology of children. The most characteristic and important feature of childhood is development. Not only does children's responsiveness to other people follow recognized patterns of psychological development that require appropriate responses from the anesthesiologist, but virtually every organ system undergoes distinct, well-described development that is relevant to the anesthetic management of children. The key to understanding pediatric anesthesiology is to recognize the dynamic processes that occur at the various developmental stages of childhood. The mindset required is not that of understanding anesthesia that is appropriate for adult physiology and adapting this approach to children, but rather to flexibly approach the child as the child grows from fetus to adult. A specific anesthetic plan appropriate to developmental stages should be designed for each child. Because the developmental characteristics of children determine anesthetic management, this chapter focuses on those changes that occur after the neonatal period. Chapter 19 discusses neonatal physiology. This chapter familiarizes the anesthesiologist with the anesthetic implications of development from neonates to adults.

Growth is not solely a process of proportional enlargement. Total body composition, including proportional fluid content, the relationship of head-to-body size, and cardiorespiratory function, all change disproportionately during development. For example, the head becomes proportionately smaller, with relatively little change in the size of the cranial vault after 2 years of age. At the same time, major changes in facial configuration occur. Most striking is the development of the mandible, which develops from being small and obliquely set to the skull of infants to becoming proportionately larger, less obliquely set, and more mobile in adults.

The development of body composition is important because it is an essential determinant of developmental pharmacology. In the fetus, 90% of total body composition is water; at full term, 75% of total body composition is water, but by age 1 year, 60% of total body content is water.1 Adult water composition is attained by age 1 year. There is also a change in the relative proportion of extracellular water over the first years of life. Extracellular water volume demonstrates a greater decrease than intracellular volume, which undergoes a complementary increase. Intracellular fluid increases from approximately 20% in premature infants to 30% in term infants and to 40% in adults, whereas extracellular fluid falls from 60% in premature infants to 45% in term infants and 20% in adults.2 The percentage of body composition that is muscle in premature infants is less than 20% and increases to more than 20% at term, and attains 50% in adults.1 Fat likewise increases with age, from 13% in term infants to 22% of total body weight in adults.1 There also is an age-dependent change in the relative proportion of blood flow to the various organs. Distribution of blood flow to various organ groups defined by their vascularity (vessel-rich group [VRG], muscle group [MG], and vessel-poor group [VPG]) also demonstrates major developmental change (Table 20-1).3 For example, there is a decreased percentage of flow going to VRGs with increasing age. The VRG in neonates accounts for 22% of total body volume, whereas in adults, it only accounts for 10%. Thus an anesthetic caregiver would expect a smaller portion of blood flow to VPGs in infants and a more rapid attainment of the plateau phase of the alveolar end-tidal concentration (FA)-to-inspired concentration (FI) ratio with use of inhalational anesthetics. This has clear implications for the induction of inhalational anesthesia in children, and, not surprisingly, the uptake and distribution of inhalational anesthetics in children.3

Respiratory System

The major features of the respiratory system that undergo important developmental changes are (1) the upper airway, (2) airway caliber, (3) respiratory system (chest wall and lung) mechanics, (4) central control of breathing, and (5) respiratory muscle characteristics. Each is described in the following material.4

The upper airway undergoes major development (Fig. 20-1). The first developmental difference is that an infant's tongue is relatively large compared with the rest of the airway. Intubation may be hampered by the overlarge tongue situated in the relatively small jaw. Infants usually are described as having an anterior, cephalad-displaced glottis, with the airway forming an inverse cone (Fig. 20-2). The narrowest segment of the airway is at the cricoid cartilage and remains so until puberty. These factors are important for intubation. An endotracheal tube that will be admitted to the glottis may be too tight for the subglottic area. The presence of an air leak below 30 cm H2O airway pressure always should be ensured for routine anesthesia.

In infants, the glottis is located at C2, 2 to 3 vertebral bodies higher than in adults, in whom the glottis is located at C4-C5. The cricoid cartilage is found at C4 in children and at C6-C7 in adults. The obliquity of the vocal cords also changes with age. In infants, these are slanted down and anteriorly compared with adults. This makes the angle for intubation more acute and more difficult in children, and makes blind nasal intubation difficult. Another difference in the child's airway is the nature of the epiglottis. The epiglottis in small children is relatively larger, longer, more curved (omega [Ω] shaped), and floppy compared with that in adults. Maturation begins to occur at age 2 years, and the adult configuration is achieved sometime near puberty, when the epiglottis is shorter, smaller, blunter, and less curved rather than Ω shaped. These anatomic differences in the airway have a major effect on which intubation techniques will be useful in children. For example, a straight laryngoscope blade (eg, Miller blades) that can lift directly the epiglottis out of the larynx during glottic visualization is useful in children.

Airway caliber undergoes continuous developmental change from the nares to the small airways. Although airway branching has been completed by birth, the caliber of the airways continues to increase. Airway resistance is inversely proportional to the fourth power of the radius, as seen in the Poiseuille equation:

where L is the airway length, n is the viscosity of the fluid, and r is the radius of the airway. It should be noted that total airway resistance is affected by consideration of caliber from the nares to the alveoli. Small airways have high resistance. The consideration of size also makes the seriousness of airway edema greater in younger children. A proportional increase in mucosal thickness in children increases resistance to a greater extent than it does in adults because equal mucosal thickening proportionately decreases caliber more in children. Airway resistance decreases approximately 15 times from infancy to adulthood, with a dramatic change occurring near age 8 years.5 This decrease in resistance with increasing age largely results from an increase in diameter of the small airways.6 Infants are obligate nose breathers, and nasal obstruction can cause severe respiratory embarrassment, which is more severe in premature infants.7

Respiratory mechanics change dramatically from birth to adulthood. These changes result from increased alveolarization, increased airway size, and changes in the chest wall. Only as the rib cage ossifies does its configuration change and become more rigid. In infants, the chest wall is soft and pliable because of its largely cartilaginous structure, which makes the chest wall highly compliant. This compliance promotes chest wall collapse when increased work of breathing requires more negative intrathoracic pressure. The clinical consequences associated with these chest wall factors are seen in infants with respiratory distress as marked sternal and subcostal retractions. In infants, the chest wall is at a mechanical disadvantage during breathing because greater pressure is required per unit of tidal volume moved. In addition to the compliance of the chest wall, there is also a decrease in elastic recoil of the total respiratory system and chest wall. This low elastic recoil tends to alter the relationship between closing volume, functional residual capacity (FRC), and residual volume.

The respiratory system undergoes significant and dramatic neuromuscular development. Central respiratory control, muscle fiber makeup (type I vs type II), and neural innervation of the chest wall show distinct developmental changes in infants and small children.8 The central respiratory control undergoes dramatic developmental changes. For example, full and preterm neonates demonstrate depression of the CO2 response curve and secondary apnea with hypoxia.9,10 This contrasts with the characteristic adult response, which is increased CO2 responsiveness in the presence of hypoxia, resulting in tachypnea. The impact of hypoxia in the presence of this paradoxic, immature response can be catastrophic in neonates.9 This infantile pattern of respiratory control is related to the risk of postanesthetic apnea in neonates.11 Anesthetic effects on the CO2 response curve are similar in infants and adults. The CO2 response curve undergoes depression by potent inhalational anesthetic agents and narcotics in children as it does in adults.12

Respiratory muscle type reaches the adult pattern of distribution at approximately age 2 years. This predisposes the infant to fatigue. Type II muscle fibers predominate and do not have the ability to perform repeated exercise against increased workloads as do type I fibers.8 Type I fibers become predominant at approximately age 2 years. Regarding neural innervation, reflex responses and spindle innervation of the thoracic cage also undergo developmental changes. For example, the Hering-Breuer response is accentuated in preterm infants compared with full-term infants and leads to apnea with lung inflation in preterm infants.13 These characteristics have a major impact on cyclic respiration, as can be seen from the immature respiratory pattern of periodic breathing. In addition, sleep state–dependent respiratory patterns show distinct developmental differences.14

These changes in chest wall recoil, elasticity, compliance, and neural control have a major effect on lung volumes (Fig. 20-3). One of the most important factors is the tendency in younger children for airway closure and alveolar collapse with atelectasis to occur. Children breathe from an end-expiratory lung volume (EELV) close to closing capacity (CC). Their FRC is actually below CC in premature infants and term neonates, increasing with age. Airway closure may occur even during normal tidal respiration in small infants.15 Induction of anesthesia is associated with decreased elastic recoil and airway tone and decreased respiratory muscle tone. Thus an expected lung volume decrease occurs with tidal respiration falling below closing volumes. These factors and those responsible for the decrease in EELV to less than FRC on induction of anesthesia in part account for the rapid occurrence of hypoxemia in apneic infants during induction of anesthesia. The other major factor related to the rapid occurrence of hypoxemia in apneic infants is their relatively increased oxygen consumption. In neonates, oxygen consumption is approximately 7 mL/kg/min.16 On a consumption-to-weight basis, this is approximately double that seen in adults, in whom oxygen consumption undergoes a gradual decrease with age. Although FRC/kg is less (30 vs 34 mL) in infants than adults, increased oxygen consumption is the major cause of the rapidity of desaturation in infants and small children who are apneic. Table 20-2 summarizes the developmental differences in respiratory physiology between infants and adults.

In addition to oxygenation issues, development of the respiratory system also affects ventilation. For example, VDS/VT, the ratio of dead space gas volume to tidal gas volume ventilation, is approximately 33% in neonates and adults.16 Thus an infant would be expected to have a 7-mL dead space gas volume with a 20-mL tidal gas volume. The addition of a few milliliters of dead space gas volume by the superimposition of anesthetic equipment may increase dead space gas volume from 7 to 12 mL and have a serious effect on VDS/VT and CO2 clearance in neonates. The dead space gas volume of all ventilatory equipment, endotracheal tubes, and especially face masks and anesthesia circuitry should be minimized.

Cardiovascular System

The cardiovascular system also undergoes dramatic developmental changes.17-19 The most obvious and dramatic changes occur perinatally, and these are detailed in the section on perinatal physiology. Even in full-term infants, there is a perioperative risk of complications related to the transitional circulation. Any factor that contributes to pulmonary hypertension (eg, infection, acidosis, hypoxia, hypercarbia, hypothermia, and aspiration) may lead to a serious decrease in cardiac output, hypoxemia, and hypotension. These factors should be avoided in the anesthetic plan for infants.

Multiple developmental changes occur in myocardial function. Changes in the proportion of muscle to connective tissue with development lead to an alteration in myocardial compliance.18 Developing left ventricular dominance also alters ventricular characteristics. Nearly every determinant of cardiac output (heart rate,19 contractility,20 afterload,21 and preload relationships22) undergoes distinct developmental changes (Fig. 20-4).17,23 Although myocardial ischemia only rarely plays a role in the anesthetic management of children, these factors and the varying responses to pharmacologic agents can lead to rapid, and occasionally catastrophic, hemodynamic decompensation in children undergoing anesthesia.23,24

In neonates and infants, heart rate is the predominant determinant of cardiac output.25 The infant's heart is able to sustain greater rates than that of the adult while maintaining preload, contractility, and myocardial oxygenation before there is a decrease in cardiac output (Fig. 20-5). Figure 20-6 shows the normal heart rates for infants and children. Bradycardia can drastically and seriously decrease the cardiac output in infants and children. Increasing cardiac output by increasing heart rate should be considered early in responding to intraoperative decreases in cardiac output as represented by hypotension. Bradycardia results from a predisposition to parasympathetic hypertonia, which is common in young children and can be induced by painful stimuli or hypoxia. Laryngoscopy, intubation, eye surgery, airway surgery, abdominal traction, and herniorrhaphy frequently are associated with marked increases in vagal tone and profound bradycardia. Under these circumstances, the cardiac output of the heart rate–dependent infant heart can decrease dramatically. That children adapt to changes in cardiac output by changes in heart rate accounts for the wide ranges in heart rate seen in healthy children. Anesthetic suppression of atrial conduction and loss of P waves on the electrocardiograph with nodal escape rhythms are seen in children during anesthesia, and the resultant bradycardia can be dramatic. Heart-rate depression during anesthesia is readily treated with atropine and is the reason many anesthesiologists make atropine part of any inhalational anesthetic plan in infants and small children. Sinus dysrhythmia, a variation in the heart rate with respirations, is so common in children that it is considered normal, although it can be confused with extra systoles or sinus arrest during anesthesia.

As Friedman originally reported in 1973, the myocardial length–tension relationships vary between the hearts of children and adults, and developmental differences in contractility are clearly seen.18 These differences are explained by changes in muscle mechanics, innervation, myocardial blood flow, and histologic structure, all of which have been implicated in children's relative inability to increase contractility. Fetal myocardial muscle sarcomeres are active and have about the same contractile power as the adult sarcomere.18 The fact that neonatal ventricular tissue contains less muscle mass and more noncontractile mass per unit volume than adult tissue accounts for the fact that the neonatal myocardium is less able than the adult myocardium to generate adequate force.26 The neonatal heart is only innervated partially by the autonomic nervous system (this innervation increases until mid childhood). Therefore, not only is the myocardium less able to develop inotropic force, but sympathetic innervation also is decreased. The Frank-Starling preload relationship also appears to be altered by differences in the fiber makeup of the infant myocardium and by the relationship of the right and left ventricles.18 These changes in compliance characteristics frequently make the infant heart preload insensitive. Volume load may generate higher filling pressures over a narrower proportional range in infants and small children than in adults.27 Normal adult contractility and compliance is reached between 1 and 2 years of age.

The final determinant of cardiac output—afterload—also changes with age. At birth, systemic resistance greatly increases with removal of the placenta, whereas afterload in the pulmonary circuit decreases dramatically.26,27 Adjustment to this massively increased afterload in the systemic circulation occurs rapidly, but further increases in afterload may be poorly tolerated in the first year of life. Right and left ventricular mass and wall thickness are relatively equal in neonates. During the next year or so of life, the left ventricle becomes markedly dominant. As a result of the factors mentioned previously, optimal cardiac output occurs at lower filling pressures in neonates compared with adults.27

All of these factors lead to optimal cardiovascular function at higher heart rates and lower blood pressures in infants than in adults (Fig. 20-5). Familiarity with the normal range of blood pressures (Table 20-3) is essential to guide appropriate intraoperative management.

Congenital heart defects can affect the determinants of cardiac output: heart rate, contractility, preload, afterload, and oxygenation. Left-to-right intracardiac shunting alters preload, potentially alters contractility, and even alters right ventricular afterload as pulmonary vascular resistance increases. Right-to-left shunting affects systemic oxygenation. Valvular disease can increase preload (regurgitant lesions), decrease preload (mitral and tricuspid stenosis), or increase afterload (aortic and pulmonic stenosis). Congenital and surgically acquired lesions can alter conduction and give rise to cardiac dysrhythmias. Thus careful evaluation of all aspects of cardiac function is necessary in assessing children with congenital heart disease. The specific anatomic diagnosis, the presence of intracardiac shunts, and myocardial function all have a bearing on the conduct of the anesthetic in children.

Hemoglobin content and oxygen affinity also vary with age.28 In the infant born at term, the normal hemoglobin concentration falls dramatically during the first year of life, reaching a nadir at approximately age 2 to 3 months, the so-called physiologic anemia of infancy.28 Although a physiologic hematocrit at this age could dip below 29%, a hemoglobin of less than 10 g/dL is rare. In the preterm infant, the hemoglobin concentration may fall to between 6 and 8 g/dL within the first 6 to 8 weeks of life.29 Although not unusual, this should not be considered "physiologic," and the same concern regarding a hematocrit of less than 25% in older children is appropriate. The hematocrit slowly increases to adult levels after puberty. Knowledge of these normal levels is necessary to guide blood transfusion and the timing of elective surgery that may be associated with significant blood loss.

Circulating blood volume is greater in neonates than in adults on the basis of body weight. Intravascular volume for neonates generally is 80 to 90 mL/kg (Table 20-4). Understanding this relative change in total estimated blood volume (EBV) (body weight × estimated blood volume/kg) is necessary when determining allowable blood loss (ABL) in children. The following formula is useful for estimating how much blood children can lose before the hematocrit is unacceptably low (ABL):

where Hct1 is the starting hematocrit, Hct2 is the minimum desired or allowable hematocrit, and the mean hematocrit is the simple arithmetic mean of Hct1 – Hct2. Thus, in a 12-kg, 1-year-old child with an initial hematocrit of 37% in whom a final hematocrit of 25% is acceptable, the ABL is:

A comparison of the estimate of expected intraoperative loss with the estimate of allowable loss should be made before surgery. If possible, preoperative therapy should be designed to decrease the need for blood transfusion. Iron and nutritional supplements may be beneficial. Erythropoietin should be considered in some children to increase the preoperative hemoglobin concentration when the child is chronically anemic, where there are religious reasons to refuse transfusion, or if the child is erythropoietin deficient (eg, renal disease). Preoperative treatment with erythropoietin has been advocated to increase the hematocrit in children to facilitate autotransfusion, either in directed autotransfusion with preoperative blood collection, or to facilitate intraoperative autotransfusion.30

Renal Function

Renal function changes dramatically with age.31 For example, glomerular filtration rate (GFR)/1.73 m2 changes from less than 40 mL/min at birth to 100 mL/min in the first year of life, which compares with 130 mL/min in adults (Table 20-5). These changes in renal function and GFR are accompanied by changes in the ability to regulate salt and water metabolism and by responses to changes in antidiuretic hormone (ADH) that occur during anesthesia.32 Although the factors regulating neonatal kidney function are complex in the transitional phase, the net result is that water is excreted in excess of sodium. The neonatal kidney wastes sodium, and there is a tendency toward hyponatremia in the premature and full-term neonate.33 The kidney of the full-term infant is able to conserve sodium.33,34 The ability of the kidney to concentrate urine is limited, and maximal osmolarity may be only 700 mOsm/L in infants.31,32 Thus infants are less able to defend intravascular volume against water deprivation.

Complete maturation of renal function usually occurs by approximately age 2 years. These developmental aspects of renal function have an effect on pharmacology. The effects of these changes are most prominent in the first few months of life and require careful fluid management in neonates and attention to sodium and potassium balance.34 Blood pressure regulation and the characteristics of hypertensive renal disease also show distinct differences in children.35 In children with renal disease, hypertension should be looked for because intraoperative blood pressure regulation may be difficult.

Dentition

Although teeth occasionally are present at birth, they may not erupt until nearly 1 year of age. The mean age for the development of the first tooth, usually a lower incisor, is around 6 months. By 1 year, children usually have upper and lower teeth present. By age 6 years, permanent teeth begin to appear, and the average 6-year-old has an intubation gap between the front incisors. The importance of deciduous teeth is that they fall out, and they should not fall out during anesthesia. Children younger than 12 years of age, especially those with loose incisors at around age 6 years, should be questioned and examined for the presence of loose teeth. Loose and carious teeth are at increased risk for dislodgment by the placement of oral airways, laryngoscope blades, and endotracheal tubes. A history of endotracheal intubation in the neonatal period is associated with subsequent development of abnormal dentition in neonates.36 Whether this is a result of direct trauma from the laryngoscope or from long-term placement of an endotracheal tube is not clear.37 Attention to children's oropharynx and condition of dentition is an essential part of the anesthetic evaluation.

Gastrointestinal System

Developmental changes in the gastrointestinal (GI) tract also have important anesthetic implications. At birth, gastric pH is alkalotic; however, by the second day of life, the normal physiologic range of gastric pH is achieved. The secretion and amount of gastric contents in full-term infants is similar to that of adults. Although fasting gastric contents and pH in children are similar to those in adults, the reflex coordination of swallowing and lower esophageal sphincter (LES) function is not fully mature until age 6 months.38-40 Slack LES tone with reflux is common in this age group. This is relevant to the question of preoperative fasting. The maintenance of low residual gastric volumes by nothing-by-mouth (NPO) regulations (a questionable assumption) should be balanced against the propensity of fasting children to develop hypoglycemia.38,39 This especially is true if the infants or children are born prematurely, small for gestational age (SGA), nutritionally deprived, or with increased metabolic needs because of conditions such as fever, sepsis, increased respiratory effort, or the condition that requires surgery. To ensure a suitable period of fasting, especially in small, ill children, preoperative intravenous (IV) supplementation with dextrose-containing solutions is indicated.

Development of the GI tract generally is complete at birth. Problems caused by congenital malformations or developmental anomalies generally are obvious within the first few days after birth.38 Upper GI obstruction (eg, duodenal atresia, malrotation) is indicated by bilious vomiting and regurgitation within the first few days of life. Lower intestinal anomalies (eg, volvulus or atresia of the small or large bowel) are manifested by failure to pass stools and by abdominal distension. Pyloric stenosis, another major cause of GI dysfunction in the first year of life, usually presents between ages 3 and 6 weeks. Its major symptoms are failure to gain weight and projectile vomiting.

The liver in neonates and young infants is functionally immature. This functional immaturity generally is a result of 2 main causes: (1) the development and growth of enzyme systems that, although present at birth, are not fully induced, and (2) relatively decreased hepatic blood flow.41 The ability of the liver to conjugate and catabolize circulating substrate and pharmacologic substances is diminished at birth. For this reason, drugs tend to have longer half-lives in neonates compared with older children. This functional immaturity of the liver is reflected by decreased concentrations of products of hepatic synthesis, such as albumin, in neonates.42 These decreased concentrations lead to decreased protein binding of many pharmacologic agents, which alters pharmacokinetics and pharmacodynamics.43,44 Hepatic function usually reaches adult levels within the first few months of life.

Thermoregulation

Perhaps no area is of greater concern to the pediatric anesthesiologist than the need to maintain normal body temperature perioperatively. The need for thermoregulatory control is underemphasized in adults but is critical in the treatment of children. Defending the thermoneutrality of infants has been a cornerstone of pediatrics since the 19th century. In 1900, Pierre-Constant Boudin demonstrated that there were striking differences in the survival of infants weighing less than 2000 g that depended solely on their rectal temperatures.45 The mortality rate for infants with core temperatures less than 95°F (35°C) was greater than 90% and for those with temperatures greater than 95°F (35°C) was only 23%. Boudin designed an incubator that provided heated air and humidity and then conclusively demonstrated that its use could dramatically improve the survival of neonates.45 This observation found its way to Julius Hays Hess, who is considered the founder of premature care in North America.46 He recognized the importance of these observations and, in 1922, opened the first premature infant center at the Michael Reese Hospital in Chicago.

Thermoregulation is a complex process involving peripheral and central thermoreceptors, the central nervous system (CNS), and hypothalamic integration with central thermoreceptors.47 A complex integration of responses leads to alterations in cutaneous blood flow and thermogenesis from shivering and nonshivering sources.48 This complex system is necessary to maintain mammalian core temperature within a normal range. Sources of heat production include basal metabolism, movement, shivering thermogenesis, and nonshivering thermogenesis. Basal metabolism is responsible for the greatest amount of baseline heat production. Shivering thermogenesis is the uncontrolled, rapid contraction of skeletal muscles and is common on emergence from anesthesia in older patients. Nonshivering thermogenesis is under direct control of the autonomic nervous system and produces heat by mobilizing fat from muscles, liver, and brain.49 Although neonates metabolize both white and brown fat, brown fat is used by neonates to a greater extent than by adults. This is important because neonates cannot respond to cold stress with shivering thermogenesis until age 6 months to 1 year. Brown fat is distributed around the back of the neck, mediastinum, and interscapular regions, and around the kidneys and adrenals. Brown fat owes its color to a high content of mitochondria and rich blood supply, which mirror its metabolic capability. Brown fat metabolism increases heat production when stimulated by autonomic catecholamine release.49 Cold stress also leads to norepinephrine secretion, which causes adipocytes to release glycerol and fatty acids from brown fat depots. Brown fat metabolism provides the only possibility of increasing body temperature in the immobile, anesthetized infant with decreased metabolic rate. Cardiac output is diverted from other organs to brown fat depots. Vasoconstriction of the systemic and pulmonary circulations occurs as a result of norepinephrine release. Consequently, cold stress can lead to peripheral vasoconstriction, pulmonary vasoconstriction, decreased cardiac output, and shunting of cardiac output away from other organ systems to brown fat depots, all of which may pose a serious threat to neonates. Importantly, inhalational anesthetics inhibit brown fat-dependent thermogenesis, which explains the propensity of neonates to become hypothermic during inhalational anesthesia.50 This complex system can compensate for heat loss, but at a high cost. Avoiding cold stress is preferred.

During anesthesia, environmental challenges to thermal integrity should be minimized, especially as inhalational anesthetics inhibit brown fat thermogenesis.50 Hypothermia increases cardiorespiratory demand because of increased oxygen demand and the need for thermogenesis and alters every basic enzyme system. Environmental cold stress in neonates leads to increased oxygen consumption, hypoxia, acidosis, respiratory distress, depletion of glycogen stores, hypoglycemia, pulmonary vasoconstriction, pulmonary hypertension with persistence of the fetal circulation, shock, and even disseminated intravascular coagulation. Altered drug metabolism, delayed emergence, prolongation of the effects of neuromuscular blocking agents, and other pharmacologic effects accent the need for intraoperative thermoregulatory control in children.46

Heat loss occurs through 4 basic mechanisms: conduction, convection, radiation, and evaporation. Each of these, under certain circumstances, can be the major cause of heat loss. Conductive heat losses can be eliminated by minimizing the direct contact of children with surfaces colder than themselves. The use of a warming pad or heating blanket in the operating room can eliminate heat loss to the cold operating room table. Warming of the operating room greatly reduces conductive heat loss. Convective heat losses can be further limited by the use of an incubator, by surgical drapes, and warm blankets for the child. Radiant heat losses also should be minimized. Heat is radiated to objects of lower temperature. Warming objects in the patient's environment will lead to decreased radiant losses. This is the principle that underlies "radiant" neonatal warmers.51 The use of double-walled incubators decreases radiant losses. Transportation of neonates to the operating room in double-walled isolettes probably is optimal, but the use of radiant warmers that minimize convective loss also is acceptable. Finally, evaporative losses intraoperatively should be curtailed to minimize heat loss.

The use of warmed solutions for skin preparation and irrigation is important. The use of heated humidified air for ventilation also contributes to the thermoregulatory control of children. It is the Children's Hospital of Los Angeles' routine practice to use humidifiers in all pediatric circuits, maintain warm operating rooms with a high humidity, and use heating pads for all children who are anesthetized. For newborns and small neonates, the operating room should be maintained at 80°F (26.7°C), for infants ages 0 to 6 months at 78°F (25.6°C), and for children age 6 months to 2 years at 76°F (24.4°C), always maintaining a minimum of 80% humidity. Warming of intravascular fluids and rapidly transfused blood also is necessary. Factors that contribute to infants becoming cold are basically related to their large surface-area-to-mass ratio. In addition, areas richly supplied with blood, such as the head and cranial vault, are proportionally larger in infants, giving rise to heat loss. In premature neonates, this situation is aggravated by their decreased subcutaneous tissue. Some method should be used to eliminate heat loss from the skin surface, especially the head, such as the use of plastic wraps and blankets. Convective warming with forced warm air devices is probably more effective than conductive (heat pad) warming and appears to decrease postoperative thermal stress when used in the recovery area.52,53

The developmental differences among neonates, infants, and adults impact pediatric pharmacology. Until recently, our understanding of pediatric pharmacology was at best sketchy and at worst incorrect. Pharmacokinetic principles that govern the distribution and metabolism of anesthetic agents in adults are not directly applicable to children. Pediatric drug dosages initially were determined by calculating the proportionate amount of an adult dose on a weight basis. Some assumptions about converting adult dosages to children's dosages on a per kilogram, surface area, or age basis have been proven incorrect.43 Perhaps no other area demonstrates more clearly that children are not small adults. There are many reasons why merely scaling down dosages on a per-kilogram basis does not yield equivalent drug concentrations or pharmacologic effects. During the development from fetus to adult, factors that affect drug uptake, distribution, metabolism, and sensitivity to drugs change. Volume of distribution, elimination half-lives, drug sensitivity, side effects, organ function, protein binding, and clearance undergo major changes with age.

Complex issues of clinical investigation contribute to the poor knowledge of pharmacokinetics in children. Medicolegal and ethical issues affect the ability to obtain data directly applicable to children. These factors have resulted in a largely empiric approach to pediatric anesthesia. This empiricism is yielding to better-designed, better-informed studies in small children, aided by the advent of microassay techniques that require smaller volumes of blood sampling. There are now several excellent studies of the pharmacokinetics of many agents, including local anesthetics, narcotics, and sedatives, and of the uptake and distribution of inhalational agents in children.

Drug Administration

Anesthetic agents may be delivered orally, rectally, transnasally, percutaneously, conjunctivally, intramuscularly, intravenously, or by inhalation. Administration of drugs across mucous membranes requires passive diffusion, which depends on the concentration and the chemical properties of the agents used and on the amount of surface area exposed. The fact that agents are absorbed across the mucous membrane in the rectum has made this route of administration popular for numerous sedatives and induction agents, such as fentanyl, methohexital, midazolam, thiopental, and ketamine.54 Because the degree of ionization generally depends on pH and surface area, formulation is particularly important. Rectal absorption is generally slow and uneven, but can be enhanced by large volumes of dilute solutions, which come in contact with a greater surface area.55 Analgesic agents also can be administered by this route, allowing mild analgesia without the need for oral administration perioperatively. This route is acceptable for most children younger than 5 years old.

Intranasal and transconjunctival administration of benzodiazepines, ketamine, and narcotics has been reported.56–58 Formulation, solubility characteristics, desired end points, and concentration affect the rapidity, duration, and depth of sedation and define an agent's suitability to induce anesthesia. Novel formulations, such as oral transmucosal fentanyl citrate, have yet to find a place in routine clinical practice.54,59

Intramuscular administration is not recommended in children because of pain on injection and pain after injection, which may last for several days.60 Induction, neuromuscular blocking, and analgesic agents may be administered intramuscularly. When no other route of administration of an induction agent is possible, intramuscular ketamine (5-10 mg/kg) might achieve anesthetic induction in agitated, uncooperative children within 5 to 7 minutes. Although intramuscular administration of narcotics is time-honored, it is generally avoided. Administration of diazepam is associated with burning and muscle pain; however, water-soluble midazolam appears to be less irritating. Pain on injection and its variable duration make intramuscular administration rarely used in children.60

The distribution of drugs administered intravenously depends on many factors, most of which are affected by developmental changes. Degree of binding to circulating blood elements, such as proteins and erythrocytes, blood–tissue partition coefficients, distribution of blood flow to various tissue beds, and changes in tissue volumes, affect the distribution of intravenously administered agents.

Drug Distribution

The existence of the free, nonbound, water-soluble moiety in the circulation is required for a drug to cross the endothelium and other cell membranes (where its effect is achieved) and for plasma clearance. The bulk of protein binding is by albumin; however, α1-acid glycoprotein also is a significant circulating protein to which drugs bind. The concentration of the latter and its contribution to protein binding appear to be greater in older children than in adults. In contrast, infants have low concentrations of α1-acid glycoprotein, therefore, they may have a larger, unbound, circulating concentration of certain drugs.61 Curare, metocurine, propranolol, lidocaine, bupivacaine, digoxin, barbiturates, and narcotics demonstrate protein binding. Their protein affinities have a major effect on the pharmacokinetics of drugs in infants and children. Because the protein-bound fraction acts as a reservoir for the drug to maintain tissue and plasma concentrations, concomitant presence of substances that displace drugs from binding sites, such as bilirubin in the neonate, will alter the pharmacology of highly protein-bound agents. Substances that reduce protein binding include free fatty acids, maternal steroids, and sulfonamides. Protein binding affects a drug's volume of distribution. Agents that are poorly protein bound have a larger apparent volume of distribution because the free drug penetrates tissues more easily. Thus a reduction in plasma protein binding causes an increase in the apparent volume of distribution, which partially explains the large volume of distribution frequently found in neonates. Nearly twice as much barbiturate and morphine is bound in the neonatal CNS as compared with what is bound in adults and older children, at least partly as a result of reduced plasma protein binding in neonates.62 Plasma protein binding also may have a major effect on determination of blood–gas and blood–tissue partition coefficients and leads to developmental differences in uptake and distribution of anesthetics.63

The developmental changes of blood flow to various tissue compartments and body fluid composition cause differences in drug distribution with increasing age.43 Distribution is altered by the relatively small muscle mass and fat stores in neonates, which results in greater flow to the central organs, such as the liver, brain, blood, heart, and kidneys. A water-soluble drug may require a larger initial dosage to achieve a desired blood level. This is relevant for most antibiotics and, most notably, for succinylcholine. The increased volume of distribution also has an effect on clearance, causing delayed excretion and metabolism and prolonged half-lives. A further effect of change in body composition is seen with fat-soluble drugs. Drugs that rely on redistribution into fat for the termination of their therapeutic effects, such as thiopental, may have a more prolonged clinical effect in younger children. Those that redistribute into muscle, such as narcotics, also have a prolonged effect.64

Other factors may alter the uptake and distribution of anesthetic agents. First is the change in the blood–brain barrier that occurs perinatally.15,43 The integrity of the blood–brain barrier is immature at birth. Because many anesthetic drugs are lipid-soluble, this leads to a more rapid uptake of anesthetic agents by the neonatal CNS than occurs in adults. The proportion of blood flow to the brain is higher in neonates than in adults, and for highly lipid-soluble drugs, diffusion across the blood–brain barrier leads to higher brain concentrations and a larger apparent volume of distribution in neonates compared with adults. A second factor that may affect uptake of anesthetic agents arises from differences in dose–response relationships, which may result from receptor affinities, changes in receptor density, or sensitivity with age. With uptake and distribution considered, the minimum alveolar concentration (MAC) of inhalational anesthetics, the hypnotic dose of thiopental, and the sensitivity to succinylcholine have age-related differences that can be explained by potential differences in receptor sensitivity to these agents.

The termination of a drug's effect depends on distribution, metabolism, and excretion. Distribution, as shown previously, varies dramatically with age. Drug metabolism and the enzyme systems responsible, especially cytochrome P450 and hepatic conjugation, also undergo distinct developmental changes.15,62 Finally, the developmental differences in renal function also have an effect on the clearance and termination of drug effects.

Myriad developmental differences and multiple factors varying dramatically with age determine the uptake, distribution, metabolism, and excretion of anesthetic agents. Thus it is not surprising that there is no simple relationship between age and a dosage calculated on a milligrams per kilogram basis.

Examining and preparing children for anesthesia and surgery require a specialized approach because of the unique physiologic and psychological needs of children and their families. The same basic goals of preoperative examination that should be achieved in adults also are applicable to children, but in addition, the emotional and psychological needs of not only the child but the child's family should be addressed. Familiarity with the specific perioperative needs of children and their families is necessary for the anesthesiologist to obtain an appropriate history, physical examination, and thorough preoperative evaluation from a wailing infant, a hyperactive child, or a shy, frightened 5-year-old, without undue trauma for all concerned. In these situations, although it may be difficult, it is necessary to thoroughly examine children. Understanding the physiology and psychology of children is necessary.65,66

Purpose

The two goals of preoperative evaluation are (1) for the anesthesiologist to obtain, through interview history and physical examination of the patient, information pertinent to the child's physiologic and emotional preparedness for surgery; and (2) for the patient, to allay the anxieties of the child and parent and prepare them for surgery. Both of these goals are important and should be viewed as necessarily compatible in the anesthetic treatment of children. From the outset, both goals should be constantly kept in mind (Box 20-1).

The anesthesiologist's first contact with the child and family necessarily sets the stage for the remainder of the anesthesia management. The information obtained and the interactions that occur during the preoperative evaluation will determine the quality of the intraoperative management and the postoperative recovery. Although this is obvious when examining the physiologic status of the child, which is used to guide the choice of preoperative medication, induction agent, and anesthetic maintenance, as well as the postoperative requirements, it likewise is true for addressing the emotional and psychological needs of the child and family. Not only should the preoperative evaluation familiarize the anesthesiologist with the child and the parents, it also should provide an excellent and critical opportunity for the child and family to become comfortable with the anesthesiologist and to understand the anesthesiologist's responsibilities. The preconceived notions of children and their families about the events that will occur in the perioperative period and the personnel with whom they will interact form the background for the preoperative interview. The skilled and experienced anesthesiologist is aware of these preconceptions and addresses them whether or not they are mentioned by the child or the family. This anticipatory approach to the child's needs frequently smoothes the path for induction and emergence from anesthesia for the child, the family, and, not unimportantly, the anesthesiologist.

The key to smooth anesthetic management is not only the complete familiarity of the anesthesiologist with the child's medical and psycho-emotional background, but also of the child's and family's understanding of the procedures associated with anesthesia and surgery. A comfortable and competent anesthesiologist, familiar with all aspects of the perioperative course of surgery in children, is able to optimize this experience for all concerned. This approach applies to infants or older children, as well as to inpatients and outpatients. The exact setting and the child's unique characteristics determine the specific technique for dealing with each circumstance. Whereas it may be necessary in one case to separate the child from the family early and use preoperative sedation, in another case, parental presence during induction and emergence may be the optimal approach. The knowledge and experience of the anesthesiologist are important in determining which approach is best for which child.

The first objective of preoperative examination and preparation is to ensure that the child is in his or her optimal status for the procedure planned. The question of whether or not the child can tolerate the anesthetic and surgery is less relevant than in the past. Pediatric anesthesiologists are capable of providing the most advanced physiologic support for children who require complex surgery. It almost always is possible to provide monitored critical care and analgesia for any surgical procedure. What does vary from patient to patient is not the ability of the anesthesiologist to deliver anesthesia care and ensure survival, but the risk to the child for each set of circumstances. The all-important question of whether the anesthetic and surgical risk to the child is greater than the benefits of the procedure should be addressed. Concerns of survival largely are replaced by a precise, accurate, and clear evaluation of the risks of anesthesia for each child, which then can be realistically compared with the child's surgical needs. The underlying goal is that for each child, given the circumstances, the best possible preoperative status will be attained for the procedure. This varies tremendously if the child is undergoing decompression of an epidural hematoma after a traffic accident in which the child has sustained bilateral femoral fractures, a ruptured spleen, pulmonary contusion, and intracranial injury with little time for preoperative assessment compared with myringotomy in a child with Down syndrome and a recently diagnosed atrioventricular canal defect who also happens to be wheezing. Both of these children can be anesthetized and are likely to survive the anesthetic; however, the wisdom of immediately proceeding varies considerably based on the results of an analysis of the specific risk-to-benefit relationship.

It is the anesthesiologist's responsibility to ensure that an accurate assessment of the risks and benefits of the anesthetic is as clear as possible to the child, the parents, the surgeon, where necessary the operating room (OR) team, and the pediatrician. Careful attention to these details is essential in evaluating and preparing children for anesthesia. Questions of preoperative preparation, timing of surgery, specific surgical procedure, and anesthetic plan are within the anesthesiologist's purview. These should be addressed by the anesthesiologist in the preoperative evaluation. A thorough and adequate examination of the child is essential for identifying and predicting physiologic as well as psychological and emotional problems that the child might encounter intraoperatively and postoperatively.65,67 The anesthesiologist, armed with this extensive background information, can provide the best intraoperative care and advise on postoperative treatment (Box 20-2).

General Approach

Preconceptions

It is essential to understand some of the preconceived notions that the child and family may have acquired from society and the surgeon. Most parents think that anesthesia is a source of some risk to their child; the spectrum may vary from fear of postoperative nausea, vomiting, headaches, and behavioral disturbances, to fear of a serious threat to the child's life. It is important to recognize, inquire about, and address these issues because these preconceptions frequently differ from the anesthesiologist's view.

Whereas the anesthesiologist may view a child whose American Society of Anesthesiologists physical status (ASA PS) score is P1 for a unilateral myringotomy as being at extremely low risk and very low on the anxiety scale, parents do not necessarily always appreciate this (Box 20-3). They frequently may demonstrate a parental "Moro response" to any perceived threat to their child, no matter how trivial the threat. Any threat to their child naturally may trigger defensive and protective responses, as well as high levels of anxiety in families. The underlying concerns and anxieties experienced by parents of children undergoing what to anesthesia caregivers may be a routine procedure frequently do not qualitatively differ from those of parents whose children have been admitted to the pediatric intensive care unit. For parents of former premature infants and critically ill children, the perception of vulnerability, not surprisingly, heightens anxiety.68 Although anesthesia caregivers may consider this parental response inappropriate, it is important to recognize that the parents of a child undergoing a routine procedure may be terribly concerned for their child's well-being. A sympathetic and understanding approach to this parental response is a crucial ingredient of expert management. Ensuring calm, informed, confident parents is frequently the most essential aspect of ensuring calm, cooperative children. Terrified, nervous, defensive, angry, ill-informed parents are incapable of allaying their child's anxieties for the upcoming procedure.69 Time taken to explain, answer questions, anticipate and allay anxieties, and demonstrate care and concern for the child is time well spent.

Areas of Childhood Anxiety

Childhood anxieties in the perioperative period center on 5 areas (Box 20-4).66 The first, fear of injury is universal; fear of death (even for minor procedures) often is present. Fear of pain and the potential for resulting body disfigurement is common. Second, fear of parental separation (separation anxiety) is common in children age 6 months or older and can be a concern in adolescents. Common sense dictates that the less time the conscious child is separated from the parents the better for all concerned. Apart from obvious humanitarian concerns, a calm, comfortable, nonscreaming child is more aesthetic physiologically and is better able to tolerate anesthesia and surgery than a distraught child.69 The third area of anxiety that correlates with the developmental stage of separation—individuation—concerns fears centered on the loss of individuality and autonomy, which may be a source of considerable stress in children. Taking a child who has spent several years learning to walk, who is comfortable away from his or her parents only for short times, and who has independent control of major functions, and suddenly reducing the child to lying on his or her back, surrounded by what appear to be giants, with no control of the situation, certainly provokes anxiety. Along with the loss of autonomy is the threatened loss of function and loss of control that were won so recently. Anything that can be done to encourage and enhance the child's autonomy and control of the situation, such as allowing choices (eg, position [sitting, lying, standing], method of induction, which stuffed animal to bring to the operating room, or color of gown) can help calm the child's fears.

The fourth issue is fear of the unknown. Children often are intimidated by the new. Most children will not have undergone either anesthesia or surgery in the past, and this generates anxiety. Recognition of this issue, followed by frank, honest, and as complete a disclosure as possible of the procedures and occurrences that the child will experience is necessary. The child's knowledge reduces the dark, mysterious areas of ignorance and uncertainty. The phrases "it won't hurt" or "you have nothing to worry about" can be some of the most anxiety-provoking words an anesthesiologist can utter. The child knows it is not true and suspects a coverup.

The fifth area, and perhaps the least obvious, is the child's fear of breaching behavioral standards and eliciting from authority figures, including parents, a reprimand. The fear of transgression and punishment is a characteristic underlying anxiety of childhood (and frequently extends into adulthood) and may be a major source of concern to the child. Explaining the permissibility of crying appropriately, of expressing anxiety and fear about the procedure, and of having a negative attitude toward the procedure, thus validating the child's emotions, decreases the anxiety associated with this childhood concern.

These areas should be always remembered and addressed consciously by the anesthesiologist in his or her approach to the child.65,66 Openness, honesty, and cheerful confidence are the main tools for allaying child and family anxieties and in producing a setting that is most conducive to obtaining information by history and by physical examination. Children are capable of seeing through fraud and spotting lack of confidence. Once their trust is lost, the ability to provide them with the best anesthesia care also is lost. Honestly telling a child that an IV start might be unsuccessful and will be painful is preferable to saying "it won't hurt" and then repeating this painful procedure unsuccessfully several times. Spending the extra time to gently talk a child through a mask inhalational induction frequently may be more rewarding (although more time consuming) for the child, the parent, and the anesthesiologist than walking into the room and, with little preparation, jabbing a needle in the child's thigh. Developing the skills necessary to approach children and their families increases the facility with which the anesthesiologist provides the best anesthesia care and increases the rewards of anesthesia practice.70,71

Developmental Stage

Just as an adult approach is inappropriate for the child, so is an approach that does not consider the developmental stage of the child. The anesthesiologist's approach to a 6-month-old infant is different from the approach taken with a 14-year-old pubertal adolescent. Developmental stage determines approach (Table 20-6).

Neonates and Infants Younger Than 6 Months

Probably because infants and neonates are unable to express themselves, it is assumed that the psychological ramifications of separation and surgery are minimal. This assumption may be as erroneous as the assumption by earlier medical practitioners that infants were unable to feel pain. Although infants do not have the apparent adverse responses to strangers that are seen in older children (older than 6 months of age) and can be comforted by a nurse or physician, they unquestionably recognize their mother and are comforted by her presence.72 Consequently, it is judicious to minimize the time children are separated from their parents. For this age group, although direct psychological preparation of children is not possible, parental preparation can form the basis of the approach to neonates and young infants. Experience indicates that fretful, anxious, uptight parents frequently convey this attitude to their young infants. Psychological preparation should be directed toward the child's family. Parents know that anesthesia and surgery present a threat to adults and reason that this threat is much greater for frail infants. Specifically addressing this frequent, although false, assumption and pointing out that a robust infant undergoing routine surgery is more likely to recover rapidly from the stress of surgery and anesthesia than a grandparent or a parent is important. Such information can alleviate anxiety and remarkably calm the parents, who, in turn, calm the infant.

Nine Months to 5 Years

Older infants and preschool children ages approximately 9 months to 5 years are in a difficult stage. They are aware of their environment and surroundings, are able to perceive a threat, and can remember painful experiences. Unfortunately, this is combined with an inability to reason and a poor perception of reality. Although these children are able to recognize stressful situations, they are unable to express their fears by modes of communication other than crying, regressive behaviors, sullen withdrawal, or other nonspecific responses to stressful situations.73 Even though it may not be possible to determine exactly what is most disturbing to a child, attention to the areas mentioned previously and a specific explanation can alleviate their concerns. There is value in explaining what is going to happen and in familiarizing the child with the procedure, even though the child might not appear to be receptive. If this has no benefit other than to demonstrate the anesthesiologist's concern for the child's well-being to the parents, it is worthwhile.

Five Years to Adolescence

This developmental stage of childhood is characterized by an increasing capability of expression and reasoning. Gaining control over behavioral and emotional responses is one of the major tasks of this period. The ability to understand and trust adults, even strangers, generally develops during this time. Disclosure of anesthetic procedures and careful, honest, and compassionate explanation of the events that surround surgery generally is rewarded in this age group. Explaining to the child and parents the anesthesiologist's role and what happens during the perioperative period decreases anxiety. In this age group, and throughout adolescence, children's imaginations are well developed. Frequently, this imagination, aided and abetted by exposure to the hyperkinetic modern media (eg, television), can lead to vivid and distorted anticipation of what actually goes on inside an operating room. As much realistic exposure to personnel, equipment, and methods of dress as possible before the procedure may drive some of these vivid, preconceived, and frequently terrifying notions from the child's (and parents') mind.66,70 It often is informative to ask the child what he or she anticipates, and, if one is fortunate to have a communicative child, this can be worthwhile and permit the practitioner to directly assess and address the child's concerns.

In older children and adolescents, an underlying fear is that of death. This fear may be reinforced by well-meaning parents, friends, and adults, as well as by medical personnel. Saying that the child "will be put to sleep" or the anesthesiologist's reference to "getting him down" may be counterproductive. Unfortunately, these statements may remind a child of what happened to a pet. In adolescents, the fear of death can be strong, and this, coupled with the loss of control and autonomy that accompanies anesthesia, frequently worries children and teenagers. Talking expectantly and openly about the postoperative period is worthwhile. Discussing how the child will feel and what steps will be taken to awaken him or her and to relieve pain will confidently lead the child away from any notion that he or she will not awaken after surgery.

A "macho" attitude in teenagers may lead them to be trapped in silence with their fears. In dealing with adolescents, it is worthwhile to specifically ask if they have any fears and specifically ask if there is concern about pain and dying. The frequency with which these questions are answered affirmatively is revealing. Understanding these underlying anxieties and specifically, honestly, and openly addressing them is valuable and certainly rewards the time required to do it. This is true even if the adolescent bravely denies such fears.

Preoperative Psychologic Preparation

Psychologic preoperative preparation begins for children before coming to the hospital. Informing the parents that they should explain openly and honestly to the child what is about to occur can begin the child's psychological preparation at home.74 Honesty and an open demeanor cannot be overemphasized as the cornerstones of this reassurance.69-71 Many hospitals have programs for inpatients and outpatients designed to introduce children and their families to the hospital and operative setting in an enjoyable manner. There are many alternatives for accomplishing these goals, including a preoperative film, a puppet show, a coloring book, a tour of the hospital, and a friendly meeting with doctors and nurses.71,72 Selecting from these options is not as important as implementing a program to ensure that the child's association with the hospital or surgical center begins on a positive note. This provides a major contribution to the preoperative preparation of children. Younger children, and occasionally older children, should be encouraged to bring familiar things to the hospital. They should bring their stuffed animals and their own pajamas, arrive in their own clothes, and be allowed to retain them as long as possible. Comforting, familiar books and toys certainly should be encouraged. Parents should be reminded of the importance of this. Encouraging older children to be involved in the planning of the surgery also can be beneficial. Allowing them to select the time of surgery and participate in the planning process can raise the young adult's spirits and reassure the child.

During the preoperative evaluation, it should be remembered that the evaluation is a 2-way process. Not only does the medical establishment (whether it is a nurse, nurse practitioner, or anesthesiologist) gain information pertinent to the anesthetic management of the child, but also the child and family gain information that is useful for building confidence and anxiolysis about the anesthesiologist and hospital setting. It is useful to remember that throughout the interview with the family, the child is the center of attention.71 The battle may be lost with the parent and child if the anesthesiologist interacts only with the parent to obtain information about the child, tells the parent the procedure, and leaves the room. The initial contact should be made with the child with a cheerful greeting and an attempt made to win the child's confidence before beginning the medical interview. Assuring the child that the main intent is not to inflict injury but to get to know him or her is crucial. No one will appreciate this more than the parents. Making it clear to the child and family that the anesthesiologist takes the child's procedure as seriously as the child does and is there to help, not only during the painful times but also during the anxiety-provoking times, is beneficial. Explanations of how the child will awaken and what will be done to manage pain are worthwhile.

Many parents will expect to be with their child during the induction of anesthesia. This may frequently be a pleasant experience for the child, parent, and practitioner. The benefit for the child has been greatly debated recently.71 Parents seem to prefer to be present, whereas practitioners prefer they are not. The focus should be on the child and, after much study, parental presence does not appear to provide a significant benefit over preoperative medication. Clearly, tearing a terrified child away from the comforting arms of a parent is difficult for the child, the parent, and the caregivers. If this parental separation cannot be achieved comfortably with preoperative psychoprophylaxis and behavioral modification as described previously, or with pharmacologic means, such as preoperative medications including benzodiazepine and barbiturates, then there may be a need to defer parent–child separation until general anesthesia has been induced. Medicating the child preoperatively with an oral benzodiazepine more frequently provides smooth, calm conditions for induction than does parental presence without medication.65 A confident, competent anesthesia practitioner may be able to reduce the need for preoperative medication. Parental presence appears neither to decrease emergence phenomena nor the incidence of postoperative behavioral changes and does not add an advantage over that provided by preoperative sedative medication, such as oral midazolam.

Just as psycho-emotional preoperative preparation of the child should begin before the anesthesiologist meets the child, the anesthesiologist also should have prepared before the meeting. The anesthesiologist should be familiar with the surgery that the child requires, the surgeon's needs, and the anesthetic implications of the surgical procedure. The anesthesiologist should be as familiar as possible with the child's medical background as documented in the medical records. Communication with the pediatrician and surgeon before meeting the child and family will reveal areas of particular interest to the anesthesiologist before the interview.74 An anesthesiologist who is aware of the child's name, age, general background, medical problems, and surgical procedure and who has communicated with the child's pediatrician and surgeon is in a strong position to win the confidence of the child and family. When a child has an extensive previous medical history, it is worthwhile reviewing old records. Specific attention should be directed to the presence of congenital anomalies and pediatric syndromes that may be associated with anomalies that are unrelated to the surgery but that could complicate the anesthetic management. A review of the drug and allergy history may provide information critically important to the anesthetic management.

Finally, if there were any previous anesthetic procedures, careful review of these records may provide an opportunity to improve anesthetic management. Specifically noting whether premedication was necessary, its effect when given, the response to various anesthetic agents, airway management, and emergence particularly may be useful. There may be information in this record that the anesthesiologist wishes to have before speaking to the parents. If the child, after what appeared to be a minor procedure, was intubated and ventilated in the intensive care unit for 3 days, the parents would be, not surprisingly, somewhat skeptical should the anesthesiologist be unaware of this occurrence. In children who have had several operations, consideration of latex allergy is important. A review of the previous anesthetic records for unexplained hypotension or wheezing should raise the consideration of latex allergy and the need for latex precautions.75

It may be worthwhile to discuss areas of concern with the surgeon and the child's physicians before meeting the family so the family can have the most complete information possible at the preoperative assessment. When meeting with the family, the anesthesiologist can determine the child's general health, level of activity, interests, favorite toys, background, and mental and medical condition. Knowledge of the parents' nickname for the child might be useful during emergence. Finding out which fingers or thumb the child sucks as a guide to IV placement may make the difference between a calm patient and an inconsolable patient postoperatively.

A systems review of appropriate depth always is indicated. A history of current and recent drugs and a history of allergies should be completed in all patients. Specific questioning about previous anesthetics and any history of siblings or family members who have had prolonged awakening, canceled surgery while in the operating room, intraoperative cardiorespiratory catastrophes, or unexplained fevers specifically should be sought in each case. Frequently, no one else will have asked questions concerning potential drug allergies, malignant hyperthermia, or adverse anesthetic reactions.

Physical Examination

The examination of the child should begin as soon as the physician enters the room. During the time spent obtaining the history from the parents and, when appropriate, from the child, important observations can be made. This period is invaluable for establishing rapport with the child and family. Constant efforts to gain the child's confidence (eg, by getting down to the child's level [sitting down is necessary], offering a toy, or interacting with the child) are of tremendous help. While discussing the child with the family, attempting to interact with the child and desensitizing the child to the close presence of the anesthesiologist is critical. Briskly walking into the room, interrogating the mother or father, and turning to the child will not yield optimal information from the physical examination. Interacting with, humoring, reassuring, and playing with the child during the interview not only calms the child, but can also provide valuable information regarding the child's general health status, developmental status,76 respiratory condition, level of activity, state of hydration and perfusion, and level of anxiety concerning hospitalization.

The examination of the child falls into 3 areas: (1) general health and systems examination, (2) areas specifically related to the provision of anesthesia, and (3) areas related to surgery. The physical examination is guided by the findings in the history and interview and the needs of the surgical procedure. As mentioned previously, the examination begins when the anesthesiologist first meets the child. A great deal can be learned about the patient's perfusion, hemodynamic status, and respiratory status by general observation. Determining the child's growth and weight (eg, short stature, failure to thrive) is essential because they guide anesthetic management and may indicate the necessity for closer evaluation (Figs. 20-7, 20-8, 20-9, and 20-10).76

The airway can be assessed by observing phonation, inspiratory sounds, and respiratory rate; evidence of respiratory distress, such as retractions or tachypnea, are readily noted without interfering with the child. Coughs, runny noses, and upper respiratory tract infections can be detected without hands-on examination of the child. With specific regard to airway evaluation, determining the presence of airway anomalies, such as cleft lip or palate, large tonsils, the state of the child's dentition, loose teeth, or absent teeth is essential. A small jaw or a skeletal anomaly that may indicate a difficult intubation should be noted. It is possible to obtain a fairly comprehensive impression of the child's overall status without actually having to physically examine the child.

Familiarity with the surgical procedure also is necessary. The anesthesiologist should have a fair idea of how extensive the surgery is, whether it will affect airway management, what sort of blood loss to expect, and if there are any particular factors complicating anesthesia management. Concerns about positioning and duration of surgery should be addressed. The presence of a cystic hygroma, for example, should dictate meticulous examination of the airway, auscultation for upper airway sounds, and determination of whether any airway involvement may have occurred. Discovery of capillary hemangiomas also may indicate the need to rule out airway involvement.

Systems Review

Neuromuscular System

Much will be apparent about the developmental stage of the child's CNS during the initial contact. Conversely, assessment of anesthetically relevant neurologic conditions will depend on the child's age and developmental status. Familiarity with the development of children gives the anesthesiologist a background by which to assess the child (Fig. 20-11). A wide spectrum of neuromuscular disorders that are important to the anesthesiologist accompanies various childhood conditions. In all children, information concerning mental and developmental stage, gestational age, gross motor function, presence of a seizure disorder, and any preexisting neurologic sensory deficits should be sought.

Cerebral Palsy and Mental Retardation

A common problem in children who present for surgery for either multiple congenital anomalies or complications after prematurity is mental retardation or cerebral palsy. It should be stressed that not all children with cerebral palsy, even those with severe neuromuscular involvement, are mentally retarded. Incapacitating hypertonicity and spasticity, which may render a child unable to readily express himself or herself, do not necessarily interfere with the ability of the child to understand or the anesthesiologist's responsibility to inform the child about the course of the perioperative period. The anesthetic implications of mental retardation and cerebral palsy are legion. The response to a host of anesthetic drugs, including muscle relaxants, sedatives, analgesics, and hypnotics, varies and is less predictable in these children compared with healthy children. Older children with mental retardation and cerebral palsy also may have significant pulmonary complications that arise from musculoskeletal anomalies caused by imbalance of muscle groups, resulting in scoliosis and kyphosis and leading to restrictive lung pathology. Pharyngeal discoordination, difficulty with handling secretions, and the not infrequent association of gastroesophageal reflux in children with mental retardation and cerebral palsy can lead to recurrent, chronic, pulmonary parenchymal injury, which may complicate the anesthetic management. The presence of gastroesophageal reflux should be sought because it is frequent in this patient population. This may have particular relevance to NPO precautions and may indicate the need for histamine receptor (H2) antagonism, antacids, agents that hasten gastric emptying, and rapid sequence intubation. Specific questioning about gastroesophageal reflux, recurrent aspiration, recurrent pneumonias, and wheezing should be directed toward the parents, and the anesthetic should be altered accordingly.40

Seizure Disorders

Children with a history of epilepsy or seizure disorders also are of concern perioperatively. In the past, problems have resulted from a failure to maintain adequate anticonvulsant levels perioperatively. Most oral anticonvulsants can be given on the morning of surgery and have a sufficiently long half-life to ensure adequate levels intraoperatively. Sodium valproate and carbamazepine may be exceptions. The anesthesiologist should ensure that the optimal serum levels of anticonvulsants are achieved preoperatively and that these are maintained perioperatively. If a prolonged NPO status postoperatively is anticipated, alteration of anticonvulsant therapy preoperatively may be indicated to include agents that can be given parenterally. A consultation with the child's pediatrician or pediatric neurologist may be required. Preoperative awareness of the child's epilepsy should lead to avoiding epileptogenic anesthetic agents, such as methohexital and possibly etomidate.

Intracranial Hypertension

The management of anesthesia for children with intracranial hypertension requires special care. Recognition of the classic triad of hypertension, bradycardia, and apnea in children who may require neurosurgical procedures, or ventricular peritoneal shunts, or who have suffered acute head injury is crucial in determining the anesthetic management of these children. In younger children with chronically elevated intracranial hypertension, the need for perioperative management of intracranial pressure is indicated by complaints of nausea, vomiting, headache, irritability, lethargy, and finding on physical examination of the sunsetting sign. Careful questioning for an acute change in the child's status may indicate the need preoperatively for measures directed at decreasing intracranial pressure, such as diuresis and osmolar therapy. Intraoperative provision of deep anesthesia and controlled ventilation to maintain normocapnia would be wise.

If the child has an existing decompressive shunt, the anesthesiologist should be aware of it. If it contains a valve and pump mechanism, its function should be evaluated. Perioperative fluid shifts may alter cerebrospinal fluid (CSF) function and upset the balance of CSF production and drainage, leading to elevated intracranial pressure and perioperative catastrophe, especially in the anesthetized child. Assurance of shunt patency and functional history is necessary.

Muscular Dystrophy

Congenital neuromuscular disease, such as muscular dystrophy, myotonic dystrophy, and acquired diseases, such as myositis, dermatomyositis, and collagen vascular diseases, raise questions concerning the use of muscle relaxants. In patients with myotonic dystrophy, the use of succinylcholine should be avoided.77 Although this is less clear in patients with some of the muscular dystrophies, the occurrence of rhabdomyolysis and the suspicion of an increased incidence of malignant hyperthermia in patients with Duchenne muscular dystrophy suggests caution in the use of depolarizing muscle relaxants and inhalational anesthetics.78 The use of nondepolarizing muscle relaxants in children who have muscle weakness and neuromuscular impairment should be guided by meticulous perioperative monitoring and perhaps are best avoided when possible (Box 20-5).

The majority of neurologic deficits and impairments will be obvious from a review of the patient's records, the parents' interview, and observation of the child. If detailed neurologic examination and documentation are required, or if the presence of serious CNS disease is suspected, a pediatric neurologist should be consulted. With the increasing use of regional anesthesia, it is wise for the anesthesiologist to search for and document existing neurologic deficits before performing nerve blocks.

Respiratory System

A host of illnesses and congenital abnormalities affect respiratory function in children. Many congenital anomalies are associated with small, difficult-to-visualize airways, upper airway obstruction, and difficult intubation. All of these conditions should specifically be sought and investigated whenever the suspicion arises (Table 20-7). The relatively small diameter of a child's airway, a child's different anatomic makeup, and high oxygen consumption relative to FRC put children at increased risk for developing hypoxia, decreasing the margin for error.

Specific questioning about airway obstruction (eg, snoring), recurring episodes of croup, tonsil or adenoid hypertrophy, and any history of apnea is part of routine history taking in pediatric anesthesia. Noticing characteristic facies, such as those associated with Treacher Collins syndrome, Pierre Robin syndrome, or Hunter and Hurler mucopolysaccharidosis, is an essential skill of the pediatric anesthesiologist in detecting the potential for difficulty with intubation and upper airway obstruction perioperatively. Careful examination of the nares, of the oropharynx for loose teeth, and for the presence of respiratory distress indicating airway obstruction should be part of every examination. Routine attention to these airway issues may prevent potentially lethal complications in the operating room.

Assessment of children with chronic respiratory disease also is necessary. The high frequency of chronic lung disease (bronchopulmonary dysplasia [BPD]) in former premature infants who required ventilatory support in the neonatal period should be remembered.79 Evidence should be sought for this in the patient's record and by questioning the parents. BPD may range from mild recurrent wheezing to a chronic oxygen requirement—even mechanical ventilation at home. In children with BPD and asthma, the anesthesiologist should be completely familiar with the child's respiratory status and ensure that therapy has been optimized preoperatively. The child's exact therapy should be ascertained, and when possible, an effort should be made to ensure that appropriate doses of bronchodilator therapy have been achieved. A history of recent steroid use should be sought, and consideration should be given to initiating steroid therapy preoperatively.

Particular attention should be directed to the history of exercise tolerance in children with or suspected of having chronic lung disease. In patients with musculoskeletal disease, especially kyphosis or scoliosis, one should seek evidence of restrictive lung abnormalities. Preoperative investigations in children with chronic lung disease may include determination of blood gases and pulmonary function tests. A cardiac examination with electrocardiography and possibly echocardiography may be necessary to discover and define the severity of pulmonary hypertension and cor pulmonale.

Acute lung disease is an indication for canceling elective surgery. Pneumonia, croup, and acute asthma pose serious perioperative threats, both acutely as well as after apparent resolution. Airway reactivity is increased for several weeks after an acute asthmatic attack.80,81 Deteriorating pulmonary status caused by viral or bacterial infection, superimposed on BPD, cystic fibrosis, or asthma may cause serious intraoperative hypoxia, increased secretions with the risk of endotracheal tube obstruction, and difficulty in maintaining airway patency. Postoperative atelectasis and pneumonia can be serious complications after surgery. Specific questioning about episodes of apnea should be included because these may be associated with fatal postoperative respiratory difficulties.82

Runny Nose Problem

Frequently, the problem of the child with a runny nose arises. Rhinorrhea can be caused by an acute viral or bacterial upper respiratory tract infection (URI), allergic rhinitis, or foreign object. There is evidence that recent URIs increase airway hyperreactivity for 6 to 8 weeks after infection.80 Anecdotally, most anesthesiologists believe that URIs are associated with increased secretions, incidence of laryngospasm and bronchospasm, endotracheal tube obstruction, and intraoperative respiratory difficulties.83 An increased incidence of postintubation stridor and other postoperative respiratory complications also has been reported.84 Experience in recent years has failed to substantiate an increased risk of complications in patients with simple URIs.

When is it appropriate to cancel elective surgery on the basis of rhinorrhea? The patient should be in optimal condition before induction of anesthesia. The recent onset of mucopurulent rhinorrhea, especially if accompanied by pharyngitis and fever, is an indication for cancellation of elective surgery. The child who always has clear rhinorrhea on the basis of allergic rhinitis probably is at no increased anesthetic risk. Multiple considerations, such as the inconvenience to the family because of long travel or arranged time off work, the potential of complications from delaying surgery, and the risks of proceeding, need to be weighed when deciding whether to proceed. With healthy children who are afebrile and have clear rhinorrhea, we proceed with elective surgery. Anesthesia caregivers are more cautious with other respiratory diseases, especially asthma and BPD.80,81 Although this topic remains controversial, whenever possible, surgery and anesthesia should be delayed for at least 2 weeks.85

Cardiovascular System

Because of the multiple cardiovascular effects of anesthetics in children and the frequency with which cardiac anomalies accompany other congenital malformations, particular attention to the cardiovascular system is necessary (Table 20-8). Recognition of the setting in which congenital heart disease may occur, coupled with careful attention to the previous history and questioning of the family, help define the type and severity of the defect. Examination of the child may lead to discovery of hitherto undiagnosed cardiac defects or to the presence of a cardiac murmur and demonstrate the need to alter the anesthetic plan and perhaps to seek further pediatric cardiology consultation. The cardiovascular system undergoes significant developmental changes, and reference to normal age-related values is essential in assessing children (see Figs. 20-4, 20-5, and 20-6).86,87

Poor exercise tolerance, as in adults, is a hallmark of inadequate cardiovascular function. Children who tire easily, become tachypneic, have dyspnea on exertion, or have orthopnea must be evaluated carefully. In infants, the major exercise is feeding. An irritable child with a history of poor feeding accompanied by diaphoresis and tachypnea may have borderline cardiac function. Failure to thrive may indicate compromised cardiac function. In younger infants, clubbing is never present, and cyanosis may be difficult to detect. Palpation and auscultation remain the cornerstones of the cardiology examination. Particular attention should be paid to the presence of a brachial–femoral delay, indicating coarctation, and for left and right ventricular heaves. Detection of a new murmur frequently raises the question of whether it is benign or significant. Differentiating between a venous hum or ventricular outflow murmur and more serious murmurs requires specific examination (Table 20-9). When in doubt, consultation with a pediatric cardiologist is indicated. The child with a murmur who is asymptomatic, acyanotic, healthy, and gaining weight along appropriate percentiles and who has a normal S1 and S2 almost certainly will tolerate routine anesthesia without serious complications. Questions arise regarding the need for further cardiology follow-up, evaluation- and infective endocarditis (IE) prophylaxis (Table 20-10 and Box 20-6). When the history and physical examination indicate possible serious cardiac disease, a hematocrit, electrocardiogram (ECG), chest radiograph, and oxygen saturation (pulse oximetry) form the basis of the laboratory workup. In patients with known serious heart disease, the anesthesiologist should understand the anatomy and physiology of the defect. A hemodynamically inconsequential atrial septal defect, ventricular septal defect, mitral valve prolapse, or the presence of a bicuspid aortic valve may predispose the child to an untoward intraoperative event, and consultation with a pediatric cardiologist may be indicated. For most children with heart disease, it is prudent to obtain a recent consultation with the child's pediatric cardiologist.

Renal System

Asymptomatic renal disease, apart from bacteriuria, is rare in children. The likelihood of discovering a new renal lesion during routine physical examination done for the preanesthetic evaluation is almost nonexistent. The presence of hypertension (see Table 20-3) should indicate the need for urinalysis and electrolyte analysis.35 The unexpected presence of anemia also may indicate chronic renal disease. The anesthetic implications of renal disease in the presence of normal electrolytes, normal growth and development, and normotension are minimal. In infants, there may be the inability to concentrate urine or to handle a large fluid load, both of which dictate cautious fluid management perioperatively.

In the presence of serious preexisting renal disease, careful attention should be paid to the child's preoperative preparation. If the child requires dialysis (peritoneal dialysis or hemodialysis) to maintain optimal electrolyte levels and growth, consideration of dialysis on the day before surgery is indicated. Antihypertensive therapy, if required, should be optimized. Electrolytes should be monitored carefully. Particular attention is necessary concerning the serum potassium concentration. Serum potassium greater than 5.5 mEq/L is worrisome in children with renal disease. The propensity of succinylcholine to induce hyperkalemia in patients who may have a concurrent metabolic acidosis puts these patients at particular risk. Elective surgery should be canceled in the presence of a potassium level higher than the acceptable upper level of normal for the individual hospital's laboratory (5.5 mEq/L, generally). Regarding hematocrit in patients with chronic renal failure, there is some controversy. It is usual practice to accept a lower hematocrit (20%) in these children than would be normally tolerated. This is based on the assumption of chronic adaptation, which includes increased blood volume and increased cardiac output. These may be compromised during anesthesia. Although the child may be chronically adapted, it should be remembered that the reserve necessary to tolerate the stresses that may accompany anesthesia and surgery is markedly decreased. Preoperative erythropoietin therapy and transfusion before surgery may be administered if time allows.

Gastrointestinal System

The major anesthetic issues concerning the GI system center on a predisposition to aspiration pneumonitis. Children with increased gastric residual volumes and gastroesophageal reflux should be identified preoperatively. Those children who have a history of tracheoesophageal fistula, mental retardation, cerebral palsy, apnea, and recurrent aspiration pneumonia always should be suspected of having gastroesophageal reflux (Box 20-7).40,88 Careful scrutiny of medical records and questioning of the parents may indicate that gastroesophageal reflux has been evaluated in the past. If not, consultation with pediatricians might prove worthwhile. The history of recurrent aspiration pneumonia in a child with a predisposing condition raises the likelihood of aspiration during anesthesia, and a rapid sequence induction is indicated. The treatment of children with gastroesophageal reflux includes administration of antacids, histamine (H2) receptor antagonists, agents that encourage gastric emptying (metoclopramide), and the Sellick maneuver during induction and intubation.89 Consider awake intubation in young infants.

Halothane hepatitis developing de novo in children appears to be exceedingly rare, occurring in perhaps less than 1 in 50|000 to 250|000 anesthetic inductions.90 The relationship between the occurrence of halothane toxicity in patients with previous liver damage and resulting hepatitis is unclear. Many premature infants have abnormal liver function tests and elevated bilirubins. Some children also may have hyperbilirubinemia and elevated transaminases. Although the advisability of using halothane under these circumstances is not clear, it probably is best avoided because suitable alternatives are available. Currently, sevoflurane has almost entirely replaced halothane in practice, and reports of hepatitis after sevoflurane are extremely rare.

Laboratory Investigations

It may seem surprising that the American Society of Anesthesiologists, the American College of Surgeons, and the American Academy of Pediatrics do not make any specific recommendations for preoperative testing in children.91 Specific laboratory testing that is indicated by information obtained from the chart review, history, and examination of the child is straightforward. Routine testing for healthy children remains controversial. In the past, guidelines that had been developed for adults were applied to children. These tests included a complete blood count, urinalysis, and chest radiograph. With the streamlining influence prevalent in health care systems today, critical appraisal of the need for these examinations has been undertaken. All aspects of the preoperative laboratory investigation have been questioned. The standard that required a routine chest radiograph in healthy children without symptoms or signs was abandoned.92 Recent experience with large numbers of outpatient anesthetics has raised serious questions about the need for routine performance of other laboratory tests. In general, preoperative laboratory testing should be dictated by the child's condition and status, rather than merely by the need for an anesthetic.66

Hematology

It generally is accepted that a preoperative hematocrit is unnecessary in most healthy children for operations in which significant blood loss is not expected. The value of a complete blood count and whether there is a role for determination of platelets and coagulation studies are also unclear. These decisions should be guided by patient considerations. There are developmental differences in the standard level of hematocrit (Table 20-11).93 For years, "normal" hematocrits were required for elective surgery. Later, the lower limit of normal (ie, hematocrit of 30% or a hemoglobin of >10 g/dL) became the requirement. Elective surgery probably should await attaining this level, short of transfusion. Iron and nutritional support are indicated. In the emergent situation, transfusion therapy may be indicated as directed by patient need, such as anticipated blood loss and cardiorespiratory status. Transfusion should not rely on arbitrary and unsupported boundary of "normal" hemoglobin.94

What are the essential considerations? In a healthy child with normal cardiorespiratory function, a fully saturated hemoglobin of 10 g/dL would require a cardiac index of 3.4 L/min/m2 to provide an oxygen delivery 3 times the average oxygen consumption. If the child's hemoglobin were 7 g/dL (hematocrit approximately 20%), a cardiac index of 4.8 L/min/m2 is required to maintain the same level of oxygen delivery. This is well within a healthy child's cardiac reserve and should represent no major difficulty. The assumptions underlying this are that the child remains 100% saturated, receives no cardiac-depressant drugs, and loses little blood. These circumstances frequently cannot be guaranteed during surgery and anesthesia, and this lack of guarantee is the key issue. The major concern is not for healthy children having minor surgery, but when surgery will result in blood loss and lower this margin of reserve further. A child whose hemoglobin drops to 5 g/dL from 10 g/dL should double cardiac output to around 6.6 L/min/m2 to maintain oxygen delivery. This remains well within the average child's cardiac reserve. If a child's hemoglobin drops to 2 g/dL from 7 g/dL intraoperatively, the child requires a cardiac index of nearly 17 L/min/m2 to maintain a marginal oxygen delivery, which is beyond the ability of even the healthy child's cardiovascular system to compensate for, especially when anesthetized.

A third issue that frequently is raised is adaptation. The classic teaching is that children with renal disease tolerate lower hematocrits because they have had time to adapt. There is little evidence to demonstrate this is so; 2,3-diphosphoglyceric acid may not be increased in children with renal disease, and there is no reason to suggest that they have a shift in the oxyhemoglobin dissociation curve. The concept that they can adapt to lower levels of oxygen delivery or consumption is unsupported. If serious blood loss is expected perioperatively, the margin of safety is considerably less in patients who begin with low hematocrit.

As mentioned previously, there are no absolute guidelines for preoperative hematocrit, and at present, each anesthesiologist should decide on a standard for each child. Motoyama95 found that a hemoglobin of 7.5 to 8.5 g/dL will deliver oxygen to the tissues of children equivalent to what a hemoglobin of 10 g/dL will in adults. In neonates, 12 to 13 g/dL is necessary. This is largely related to shifts in the P50 (partial pressure of oxygen at which hemoglobin is 50% saturated).95 It seems reasonable that a hemoglobin of 8 g/dL in an ASA PS P1 child may be acceptable if no major perioperative blood loss is expected. A child who has chronic restrictive lung disease and is about to undergo scoliosis repair probably should have a hemoglobin higher than 10 g/dL (at least initially).

Many abnormalities can be discovered during preoperative laboratory screening.96 These abnormalities fall into 2 categories: those that are relevant to the anesthetic management of the child and those that are relevant to the child's general health. The degree to which a preanesthesia screening clinic wishes to be responsible for the general health care of children needs to be determined by each facility. There is a responsibility to ensure follow-up evaluation for abnormal laboratory tests that may be discovered coincidentally with preoperative assessment. O'Connor and Drasner97 reported that 17% of children who had a complete blood count (CBC) were anemic or had a microcytosis. Only 2 of these children had surgery canceled because of anemia (hemoglobins <10 g/dL).97 A mechanism to arrange follow-up evaluation with the pediatric clinic should be available, and communication should be assured.

Sickle Cell Disease

The American Academy of Pediatrics recommends that a sickle preparation or other screening test be performed in all children of African descent.98 Is it reasonable for the anesthesiologist to insist on receiving the results of a sickle cell preparation in all children of African descent requiring anesthesia and surgery?99 Is anesthetic management different for those who have sickle trait than for those who do not? Is it necessary to have a sickle cell preparation in nonanemic at-risk children? Anesthetizing a child with sickle cell disease who is anemic and with 95% sickle hemoglobin poses a major threat to that child and should never be undertaken without good reason. The likelihood of a child older than age 2 years with a normal hemoglobin having sickle cell disease is extremely low. If all children with hemoglobins less than 10 g/dL require further investigation, among the factors to be investigated, in addition to iron deficiency, is sickle hemoglobin status in at-risk children. This might not apply to neonates or infants who may have hemoglobin concentration greater than 10 g/dL and have sickle cell disease and high levels of sickle hemoglobin. Unless a sickle hemoglobin preparation is performed, cases might be missed in this population which is at risk for hypoxia and low cardiac output during anesthesia. Common practice is to perform a sickle cell preparation on all children of African descent unless their status is known and to screen for anemia in all other children. In those with positive sickle screen, hemoglobin electrophoresis is required.100,101 It should be noted that infants younger than age 4 months have maternal antibodies that interfere with performing a quick sickle index preparation. These children require hemoglobin electrophoresis to determine their sickle cell disease status.

Does sickle trait pose a threat to older children who may not be anemic but who have some amount of sickle hemoglobin? Although there are some anecdotal stories of sickling and rare vasoocclusive phenomena in children with sickle cell trait during anesthesia with resulting hypothermia, ischemia, and hypoxia, sickle cell trait generally is associated with less than 40% of hemoglobin S in the circulating blood.101 This is the target level that is obtained with transfusion protocols for sickle cell disease. Prudent avoidance of tourniquets that cause blood stasis and hypoxia in the affected limb probably is wise in patients with sickle cell trait. Anesthetic management will not vary because the routine goals of anesthesia (avoidance of hypoxia, hypothermia, hypovolemia, and hypotension) are as important in routine anesthetic management as they are for patients with sickle cell trait.101,102

In patients with sickle cell disease, preoperative treatment is directed at reducing sickle hemoglobin to less than 40%. Chronic transfusion, exchange transfusion, and acute blood transfusion are reported to be useful in achieving this goal.98,103

Leukocyte Counts

In one study, leukocyte counts were abnormal only in patients who were ill or otherwise suspected of having an infection.66,93 No occult leukocytosis was discovered in 463 preoperative screening evaluations.97 When indicated by suspicion of sepsis, infection, fever, or respiratory tract infection, a CBC might be useful in arriving at the diagnosis; however, routine leukocyte determination does not appear to be warranted.

Urinalysis

Routine urinalysis is part of preoperative recommendations in children. Apart from providing a possible contribution to routine health screening, the relevance to anesthetic management is unclear.66,104 In children who are febrile, have congenital anomalies of the urinary tract, or have suspected renal function anomalies, urinalysis might be beneficial. In otherwise healthy children in whom urinalysis can be difficult to obtain and unreliable, abnormal results appear to occur in 15% of children and usually are asymptomatic bacteriuria.97 The majority of these are either false-positive results, clinically insignificant, or previously known. In only 2 of 453 cases was surgery canceled, and both of these were canceled because of suspected colonization or asymptomatic bacteriuria, which was of no anesthetic relevance. In afebrile, ASA PS P1 children with no history of renal disease, most centers have abandoned routine urinalysis.

Screening for pregnancy varies widely from center to center. The evidence that anesthesia, per se, is deleterious to the continued pregnancy or the fetus is extremely sparse. On the other hand, the logistic, behavioral, privacy, and social implications of testing all female children of child-bearing age for pregnancy, with or without consent, are quite complex. Each institution must resolve these issues for itself.

Drug Levels

In children who are receiving therapeutic drugs, it frequently is worthwhile to know whether the therapeutic level has been achieved. The 2 major areas in which this is of concern are in children with epilepsy and asthma. Obtaining routine blood levels of theophylline (although now only rarely used) and anticonvulsants to ensure compliance with therapy and adequate levels for the perioperative management appears to be a wise precaution. It is not so clear what should be done when an abnormal result is found. Does an asymptomatic healthy child with a nontherapeutic drug level require therapy? Should therapeutic levels of indicated drugs be achieved before elective surgery? These decisions may require input from the child's primary care physician and perhaps a pediatric neurologist in children with epilepsy. Frequently, it is worthwhile to inform the primary caregiver that the level is subtherapeutic so that the drug can be discontinued before surgery. There is a caveat. Discontinuing anticonvulsants may lead to withdrawal seizures, which is not a pleasant prospect perioperatively. Asymptomatic children with low theophylline levels may not be wheezing on the day of examination but may develop wheezing on the day of surgery and may have serious underlying bronchial hyperreactivity, which may pose difficulties intraoperatively. Our current practice is if a child requires theophylline to suppress wheezing episodes, the child requires therapeutic theophylline levels perioperatively. If this is not possible, knowing the level will allow the anesthesiologist to specifically direct therapy intraoperatively if required. Further testing is guided by the patient's underlying medical condition.

Preoperative assessment for elective surgery should be done early enough to allow all special investigations to be performed before surgery. Consultation with other services and the performance of other investigative procedures, such as computed tomography (CT) scans, ECGs, and echocardiograms, should be timed so that the results will be available to the anesthesiologist before induction of anesthesia. Deciding that such information is important preoperatively but acting before it is obtained or reported sets the stage for medical or legal misadventures.

NPO Status and Preoperative Fasting

Of all the shibboleths of pediatric anesthesia, perhaps the one most time honored and most frequently under attack is the duration of preoperative fasting. The days of NPO after midnight for all children who require surgery is over. For years, we have realized that small infants, with their unique glucose and fluid requirements, do not benefit by being NPO for 12 hours before surgery. Serious hypovolemia with intraoperative hypotension and hypoglycemia is the result.66,105 Concerns have been raised about hypoglycemia occurring in older children after a prolonged fast.105–107 There also are concerns about comfort and the need for the imposition of starvation on children preoperatively. The goal is to reduce gastric volume and minimize the risk of aspiration pneumonia perioperatively. There are many studies looking at factors predisposing to gastric acid aspiration and lung injury and their relationship to gastric residual volumes. The fact remains that perioperative aspiration pneumonia is remarkably rare (a fact that may attest to the success of severe NPO restrictions).

There is little evidence that in a healthy child prolonged fasts are required to ensure minimal gastric volumes. NPO for solid foods and large meals for 8 hours before surgery should be maintained because gastric volumes may be increased for up to 6 hours. The question becomes less clear with fluids. Several studies demonstrate that ad lib clear liquids up until 2 hours before surgery are associated with lower gastric volumes and higher pHs than those found in fasting patients.108,109 If this is the case, the recommendation ought to be to encourage oral clear fluids preoperatively rather than to limit them. Studies demonstrate that not only is there no major burden of hypoglycemia placed on the healthy child by fasting, but that feeding the child clear liquids is not associated with increased gastric volumes.110

The final factor that needs to be considered is whether one should change an age-old guideline for a more liberal approach that may be confusing and lead to unintended changes in other requirements. The guideline of NPO after midnight perhaps is draconian, but it is clear to all concerned. No solids after midnight and clear liquids up to 1 hour before surgery ad lib, if the patient is healthy, without gastroesophageal reflux, or other significant GI disease, certainly is less clear. These liberal rules are bound to be applied in inappropriate situations, potentially leading to catastrophe. Some major institutions allow clear liquids until 1 to 2 hours before surgery in their outpatients, and a large series reported from the Children's Hospital of Philadelphia reports no incidence of gastric aspiration after years of this approach.109 ASA guidelines indicate fasting for clear liquids from 2 hours preinduction. Communication, education, monitoring current protocols, and flexibility in approach, based on known facts, should form the guidelines for anesthesia practice. This is no less true regarding preoperative fasting rules. The trend is toward more liberal fasting requirements for clear liquids (Table 20-12).111,112

One final question: What are clear liquids? Water, glucose water, and commercially available pediatric electrolyte solutions are clear. Some institutions consider breast milk a clear liquid and cow's milk a solid food. Breast milk is not emptied as rapidly as clear liquids from the stomach, and the ASA guidelines state breast milk should not be given within 4 hours of induction. Some institutions encourage gelatin (no additives) and fruit juices, including pulp-free orange juice, as perfectly allowable. It is unlikely that there will be hard scientific data to aid the anesthesiologist in these decisions. The application of common sense and the provision of clear instructions for families are essential. Simplicity is best. Adhering to local protocols is important to avoid confusion and ignoring stated regulations is detrimental to the organized anesthetic care of children.

Intraoperative treatment of critically ill children can present the anesthesiologist with great challenges. The use of cardiovascularly active anesthetic agents in critically ill children can demand the most meticulous anesthesia care. Thorough preoperative evaluation and preparation is essential to ensure optimal intraoperative management. A rigorous, compulsive systematic evaluation of critically ill children is essential, and although it follows the basic outline of systems review, the underlying assumption is that the severity of illness in each system is much worse than in the patient for elective surgery.

Establishing rapport with a child in an intensive care unit can range from difficult to impossible. An unconscious, heavily sedated, paralyzed child requiring mechanical ventilation and neuroresuscitation will not be communicative. Discussing the anesthesia care with the child's family often may be awkward because survival is the parents' primary concern. Before contacting the family, it is essential that the anesthesiologist be completely familiar with the child's problems so that the parents can be confident that all physicians who are caring for their child are knowledgeable and concerned. Many parents have bonded with the intensive care unit staff and transferring their child's care to other physicians can provoke anxiety. The anesthesiologist needs to demonstrate concern and state that the intraoperative care and management will be as meticulous as that provided for the child in the intensive care unit. Although it is natural to focus entirely on the child's immediate surgical needs or indication for admission to the intensive care unit, other problems that may have anesthetic importance should be sought as they would be in a routine evaluation. A systems review, previous drug and allergy history, and family history should not be neglected.

Neurologic Status

The level of consciousness, presence of CNS injury, intracranial pressure, and neurologic deficits specifically should be determined. Psychotropic drugs, sedatives, and other obtunding agents that may supplement, augment, or interact with anesthetic agents should be identified. Some children in the intensive care unit will be essentially anesthetized at transfer to the operating room, whereas others may have received little medication. Complete review of current neurologic status and psychotropic drugs is mandatory.

Respiratory Status

Respiratory evaluation should be meticulous. The level of oxygen required, respiratory rate, ventilatory rate, tidal volume, airway pressures, and arterial blood gases form the basis of this information. If the child requires a ventilator, it is necessary to be familiar with the degree of ventilatory support the child requires, including the fraction of inspired oxygen (FiO2), mean airway pressure, peak end-expiratory pressure, and respiratory rate. A blood gas just before transfer to the operating room may provide critical information. Anesthesia machine ventilators, although more than adequate for patients with normal pulmonary function, may be inadequate in those with advanced stages of lung disease. The anesthesiologist should be able to organize sophisticated ventilatory support in the operating room when indicated. This should be done before transfer of the child to the operating room in conjunction with respiratory therapy.

Cardiovascular System

Complete familiarity with the child's hemodynamic function is essential. All patients in the critical care unit should be suspected of having compromised cardiovascular function and borderline oxygen delivery. Complete evaluation of perfusion status, temperature, and hemodynamic information as obtained from invasive monitor catheterization should be reviewed and optimized. Optimization of intravascular volume and the hematocrit and availability of blood products should be ensured. A review and optimization of cardiovascular drugs the child is receiving should be undertaken. It is necessary to ensure that constant, uninterrupted delivery of cardiovascular drugs and infusions be continued during transportation. Finally, an ECG and review of the child's rhythm history for the presence of cardiac dysrhythmias should be conducted.

Renal Status

Recent urine output, fluid requirements, creatinine, and blood urea nitrogen (BUN) should be reviewed. Renal function should be assessed and may have an important bearing on the use of neuromuscular relaxants, intraoperative fluid requirements, and electrolyte status. Electrolyte abnormalities are common in those with critical illness and may lead to cardiorespiratory failure and cardiac dysrhythmias intraoperatively. These, in general, should be corrected preoperatively.

Gastroenterology

All patients who are ill enough to require admission to an intensive care unit should be suspected of having full stomachs. Acute, critical, and chronic illnesses delay gastric emptying. Even though the child may have been NPO for a prolonged period, hypersecretion and high gastric acid content may predispose the child to aspiration on induction. Patients who have suffered trauma and for whom no NPO history is available should, as a precaution, be treated as having full stomachs.

Laboratory Tests

Laboratory investigation should be reviewed thoroughly. At a minimum, baseline CBCs, electrolyte profiles, calcium, and blood gases are essential. Therapeutic levels of drugs, such as theophylline and anticonvulsants, are indicated, if the child is receiving them. A final check to ensure cross-matched blood is available, when indicated, is prudent.

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