V - Assessment of the Thoracic Surgical Patient
Editors: Shields, Thomas W.; LoCicero, Joseph; Ponn, Ronald B.; Rusch, Valerie W.
Title: General Thoracic Surgery, 6th Edition
Copyright 2005 Lippincott Williams & Wilkins
> Table of Contents > Volume I - The Lung, Pleura, Diaphragm, and Chest Wall > Section VI - Anesthetic Management of the General Thoracic Surgical Patient > Chapter 24 - Anesthesia for Pediatric General Thoracic Surgery
Chapter 24
Anesthesia for Pediatric General Thoracic Surgery
Babette J. Horn
Conditions requiring thoracic surgery may affect children of any age. Anesthetic considerations in the older child and adolescent are similar to those in the adult patient. It is in the newborn that the pediatric anesthesiologist encounters the greatest challenge. In addition to the technical problems created by the newborn's small size, unique anatomic, physiologic, and pharmacologic differences make neonatal anesthesia a field unto itself.
PHYSIOLOGIC CONSIDERATIONS IN THE NEONATE
Cardiovascular Adaptation
The cardiovascular system undergoes several changes during the transition to extrauterine life. Closure of the ductus venosus and foramen ovale converts the circulatory system from a parallel circuit to a series circuit (Figs. 24-1, 24-2 and 24-3). Hypoxia, hypercarbia, sepsis, and hypothermia can cause undesirable right-to-left shunting of blood through the foramen ovale and ductus arteriosus, the anatomic closure of which may not be complete until 2 weeks after birth. Pulmonary resistance, elevated during fetal life and immediately after birth, decreases rapidly at first and attains adult values by 2 months of age (Fig. 24-4). During this time, however, the pulmonary vascular resistance is labile, and considerable constriction and dilation can result from physiologic, pharmacologic, and environmental manipulations. The syndrome of persistent pulmonary hypertension of the newborn, characterized by refractory hypoxemia, hypercarbia, and acidosis, is common in patients with diaphragmatic hernias but can occur in virtually any stressed term infant.
Because it must work against increased resistance in utero, the right ventricle is hypertrophied and dominant in the newborn. Waugh and Johnson (1984) reported that both ventricles are noncompliant; their myocardial tissue has 30% fewer contractile elements than that of the adult.
Increases in preload cannot increase stroke volume because of the diminished contractility of the newborn myocardium (Fig. 24-5). Thornburg and Morton (1983) suggested that the infant is functioning on an unfavorable portion of Starling's curve; only a modest increase in filling pressure can precipitate congestive heart failure. The anesthesiologist must scrupulously avoid overzealous administration of intravenous fluids.
The cardiac output of a newborn (180 to 240 mL/kg/min) is two to three times the adult value relative to size. This difference reflects the greater oxygen consumption and metabolic rate in this age group. Increases in cardiac output are achieved primarily by increases in heart rate (normal, 120 to 160 beats/min) because the infant's myocardial contractility is relatively fixed. Sympathetic innervation of the heart is incomplete, as noted by Zaritsky and Chernow (1984), further impairing the ability to increase stroke volume. Systemic blood pressure is low in the newborn period (Table 24-1). Awareness of normal values is essential for the appropriate diagnosis and treatment of hypotension.
Respiratory Adaptation
Sarnaik and Preston (1982) reported the anatomic, mechanical, and functional peculiarities of the newborn respiratory system that increase the risk for arterial desaturation and hypoxemia. The trachea has an incompletely developed cartilaginous framework. Any extrathoracic obstruction, such as postextubation mucosal edema, causes tracheal collapse distally. Even a 1-mm ring of tracheal narrowing can cause severe respiratory distress because of the already small airway caliber (Fig. 24-6). The infant has a highly compliant chest wall because of a horizontally oriented rib
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cage. In diseases of poor lung compliance (e.g., pulmonary edema and atelectasis), excessive lung recoil results in greater retraction of the soft chest wall and more loss of functional residual capacity than would occur in older children with stiffer chest walls.
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Fig. 24-1. Course of circulation during transition from fetal-type circulatory pattern to adult-type circulatory pattern. Ao, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle. From Ryan JF, et al (eds): A Practice of Anesthesia for Infants and Children. Orlando, FL: Grune&Stratton, 1986, p. 176. With permission. |
When supine, the newborn's closing capacity impinges on tidal volume breathing. The resulting small airway collapse leads to atelectasis, ventilation-perfusion mismatch, and hypoxia. To prevent this situation from occurring intraoperatively, the anesthesiologist can use controlled ventilation and positive end-expiratory pressure.
Because of their high oxygen consumption and increased work of breathing, infants breathe at rapid rates of 30 to 50 breaths/min. Cook (1981) reported that the diaphragm of infants has a preponderance of fast twitch muscle fibers that are prone to early fatigue. Conditions causing increased work of breathing are therefore not tolerated for long periods of time, and hypercarbia and respiratory failure occur.
Chemical and neural control of breathing is different in the newborn. The response to hypoxia is paradoxic, characterized by a brief period of hyperpnea, followed by apnea. The central chemoreceptors have a diminished sensitivity to Pco2 compared with those of adults, that is, a higher Pco2 is needed to effect a similar increase in minute ventilation. Periodic breathing and apneic spells are common in the newborn, making close monitoring of respiratory function mandatory in the postoperative period.
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Fig. 24-2. Transitional circulation of the neonate when pulmonary vascular resistance is high. Desaturated blood is shunted from the right atrium (RA) across the foramen ovale to desaturate partially the left atrial (LA) blood. LV, left ventricle; RV, right ventricle. From Ryan JF, et al (eds): A Practice of Anesthesia for Infants and Children. Orlando, FL: Grune&Stratton, 1986, p. 176. With permission. |
Table 24-1. Relationship of Age to Blood Pressure | ||||||||||||||||||||||||||||||
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Fig. 24-3. Transitional circulation of the neonate when the pulmonary vascular resistance has fallen. Foramen ovale is closed, and no intracardiac shunting can occur at that point. Left-to-right shunting of fully saturated blood from the aorta across the patent ductus arteriosus into the pulmonary artery arterializes blood flowing to the lungs. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. From Ryan JF, et al (eds): A Practice of Anesthesia for Infants and Children. Orlando, FL: Grune&Stratton, 1986, p. 176. With permission. |
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Oxygen unloading at the tissue level is made more difficult by the high percentage of fetal hemoglobin in newborn erythrocytes. Because of its lower p50, hemoglobin F holds on to oxygen more tenaciously than does adult hemoglobin. The generally high hemoglobin concentration at birth (15 to 18 g/dL) is beneficial in increasing oxygen delivery to the cells (Fig. 24-7).
Metabolic Adaptation
Maintenance of normothermia is essential in the newborn. Adverse effects of hypothermia include apnea, hypoglycemia, metabolic acidosis, and increased oxygen consumption. Because of decreased subcutaneous tissue, a low surface area-to-volume ratio, and small body mass, the neonate has increased environmental heat losses. Nonshivering thermogenesis, mediated by catecholamine effects on brown fat deposits, is the primary heat-generating process in the newborn. This process increases oxygen consumption by as much as 200-fold. Methods of preventing heat loss intraoperatively include increasing ambient temperature and using radiant warmers, heating blankets, intravenous fluid warmers, and humidification of anesthetic gases. Baumgart and associates (1981) showed that covering
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the top of the head and extremities with plastic wrap effectively minimized evaporative heat losses during surgical procedures.
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Fig. 24-4. The changes in pulmonary vascular resistance during the 7 weeks preceding birth, at birth, and in the 7 weeks postnatally. Prenatal data derived from lambs. From Rudolph AM: Congenital Diseases of the Heart. Chicago: Year Book, 1974, p. 31. With permission. |
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Fig. 24-5. Right ventricular stroke volume and right atrial pressure relationships in a sheep fetus. From Ryan JF, et al (eds): A Practice of Anesthesia for Infants and Children. Orlando, FL: Grune&Stratton, 1986, p. 176. With permission. |
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Fig. 24-6. Diagram of relative cross-sectional area of infant and adult trachea. A. No tracheal edema. B. One millimeter of edema encircling tracheal lumen. |
The use of forced-air warming covers and passive heat- and moisture-exchanging filters has significantly diminished heat loss in pediatric surgical patients. Bissonnette and Sessler (1989), as well as Kurz and colleagues (1993), have corroborated the efficacy of these newer technologies for improved thermoregulation.
Hypoglycemia occurs frequently in this age group, especially in the premature or small-for-gestational-age infant or in the infant of a diabetic mother. Causative factors in the development of neonatal hypoglycemia include diminished hepatic glycogen stores, decreased gluconeogenetic capabilities, and decreased response to glucagon secretion. Blood glucose values should be monitored frequently, adjusting the intravenous dextrose concentration accordingly. Normal blood glucose values in the newborn are listed in Table 24-2.
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Fig. 24-7. Oxygen-hemoglobin dissociation curves with different oxygen affinities. In neonates with a lower p50 (20 mm Hg) and higher oxygen affinity, tissue oxygen unloading at the same tissue Po2 is reduced. From Motoyama EK, Cook DR: Respiratory physiology. In Smith RM (ed): Anesthesia for Infants and Children. St. Louis: CV Mosby, 1980, p. 67. With permission. |
Table 24-2. Normal Blood Glucose Values | ||||||||
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PHARMACOLOGIC CONSIDERATIONS IN THE NEONATE
Virtually all drugs used in the practice of adult anesthesia have been safely used in pediatric anesthesia. Because of the physiologic characteristics of the newborn, however, drug dosages are altered, and target organ responses are monitored carefully.
Muscle relaxants such as succinylcholine and the nondepolarizing agents supplement almost all newborn anesthetics. Goudsouzian (1986) noted that infants require a larger dose of succinylcholine calculated on a per kilogram basis because of their increased extracellular fluid compartment. Goudsouzian and Standaert (1986), in an excellent review of the infant myoneural junction, discussed both the pharmacodynamic (immature neuromuscular junction) and pharmacokinetic (delayed excretion, increased diaphragm fatigue) reasons behind the abnormal response of newborns to nondepolarizing agents such as pancuronium. The intermediate-acting nondepolarizers atracurium, cisatracurium, vecuronium, and rocuronium have been used extensively in pediatric patients. Because of the shorter duration of action of all of these drugs and the rapid onset of paralysis in rocuronium, they are probably preferable to pancuronium for shorter procedures in very young patients.
Inhalation anesthetics such as nitrous oxide, halothane, and isoflurane are used frequently in pediatric thoracic surgical patients. Friesen and Henry (1986) and Brett (1987) and associates reported that all these agents cause dose-dependent depression of cardiac function. Wear (1982) and Duncan (1987) and their colleagues noted that their use impaired baroreceptor reflexes. Hypotension and bradycardia commonly occur when the potent inhalation agents are administered in high concentrations. The newer inhalation agent, sevoflurane, is being used with increasing frequency in pediatric anesthesia. Lerman and coauthors (1996) noted the rapid induction and emergence properties of sevoflurane in pediatric patients. This agent may depress
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myocardial function less than halothane, as described in a report by Holzman (1996) and colleagues. Because all potent inhaled anesthetics have a low therapeutic index in infants, they must be used sparingly, with close attention paid to blood pressure and heart rate. Waugh and Johnson (1984) and Eisele and associates (1986) reported that nitrous oxide can increase pulmonary vascular resistance, which in theory is undesirable in neonates with the potential for persistent pulmonary hypertension of the newborn. Clinical studies reported by Hickey and co-workers (1986), however, have shown that nitrous oxide can be used in infants without significant increase in right-to-left shunting.
Fentanyl, a synthetic short-acting potent narcotic, has been used extensively in neonatal anesthesia. Hickey and associates (1985) noted its beneficial effects in attenuating the pulmonary vasoconstrictive response to tracheal stimulation. Schieber and colleagues (1985), as well as Robinson and Gregory (1981), observed cardiovascular stability with fentanyl analgesia. Yaster (1987) achieved a satisfactory anesthetic state in newborns presenting for a variety of surgical emergencies with doses of fentanyl in the 10.0 to 12.5 g/kg range. Administration of greater than 5 g/kg of fentanyl, a modest dose, usually precludes tracheal extubation at the conclusion of surgery because this agent is a potent respiratory depressant. The newer, more potent narcotic sufentanil has been studied in pediatric patients undergoing cardiovascular surgical procedures. Extremely high doses in newborns were used by Anand and Hickey (1992) with positive results. The lower doses used by Moore and associates (1985) proved unsatisfactory when sufentanil was the sole anesthetic agent. For most pediatric thoracic surgical patients, sufentanil has no clear-cut benefit over the more familiar, less expensive fentanyl.
Barbiturates such as thiopental can be used as induction agents in newborns, but low doses should be used (2 to 3 mg/kg). Immaturity of the blood-brain barrier and a relatively high cerebral blood flow combine to deliver a large fraction of the injected drug to the brain, thus allowing a lower dose to be used with equal efficacy. In addition, the barbiturates are myocardial depressants, and unacceptable degrees of hypotension may result from use of large doses.
Ketamine is a potent amnesic and analgesic agent that can be given intravenously (1 to 2 mg/kg) or intramuscularly (5 mg/kg) for the induction of general anesthesia. White and co-workers (1982) noted that cardiovascular hemodynamics and spontaneous respirations are maintained because of sympathetic nervous system stimulation, accounting for the popularity of the drug in pediatric anesthesia. Ketamine causes copious salivation, so prior or concurrent administration of an antisialagogue (atropine, 20 g/kg intramuscularly or 10 g/kg intravenously) is necessary.
Propofol is a newer drug that has gained widespread use for induction and maintenance of anesthesia in adults. Its major advantages are short half-life, rapid recovery, and effective obtundation of airway reflexes. Age-dependent induction doses of 2 to 3 mg/kg were found effective based on work published by Westrin (1991). For maintenance of anesthesia, propofol is usually administered by infusion; Smith and co-workers (1994) reported on the higher infusion rate required by children as compared with adults. Dose-dependent decreases of heart rate and mean arterial blood pressure can be seen after propofol administration. An editorial written by Meakin (1995) cautions that the long-term use of propofol for sedation in the intensive care unit has been associated with metabolic acidosis, bradyarrhythmia, heart failure, and death.
Atropine is used in pediatric anesthesia for its anticholinergic properties. In the aforementioned dose range, it counteracts undesirable bradycardia associated with halothane and succinylcholine administration, vagal stimulation during laryngoscopy, and intraoperative visceral traction. Slow heart rates can lead to a decrease in cardiac output because the newborn cannot compensate by increasing his or her stroke volume.
MONITORING
The purpose of monitoring any variable during an operation is to identify adverse trends before they become catastrophic events. Because of their diminished cardiopulmonary and metabolic reserves, infants require close intraoperative monitoring. Confounding the goal of vigilant invasive and noninvasive monitoring is the infant's small size, which can make even the simplest of procedures, such as applying electrocardiography leads, frustrating.
Standard Monitors
The following monitors are considered the standard of care in pediatric anesthesia.
Temperature Probe
Rectal or esophageal temperatures most closely approximate core temperature and are preferred over skin and axillary monitoring sites.
Electrocardiography
Cardiac rate and rhythm are the primary data obtained from this monitor. Ischemia detection is not as important in this age group because coronary artery disease is uncommon. Smaller electrodes are available for placement on the trunk, as well as limb leads designed for use around the wrists and ankles. Monitoring of T-wave changes may provide early detection of intravascular local anesthetic injection, as reported by Tanaka and Nishikawa (1999).
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Precordial or Esophageal Stethoscope
The thin chest wall of the infant permits auscultation of both heart and breath sounds with a precordial stethoscope. According to Smith (1980), this monitor is one of the most useful and important in pediatric anesthesia, especially during tracheoesophageal fistula (TEF) repair, when continuous use of an esophageal stethoscope is not possible.
Blood Pressure Cuff
Sizes to fit even the premature infant are now available. Usually the arm is not big enough to permit placement of a stethoscope, so only the systolic blood pressure is measured by looking for the to-and-fro movement of the sphygmomanometer needle.
Improved automated noninvasive blood pressure monitoring equipment for children has resulted in nearly universal use of this technology for accurate, reliable determination of systolic and diastolic pressures.
Oxygen Analyzer
The oxygen analyzer is inserted in the inspiratory limb of the anesthesia circuit. The American Academy of Pediatrics (1983), in its guidelines for perinatal care, and Lucey and Dangman (1984) emphasized that inspired oxygen concentrations must be measured carefully because prolonged hyperoxia can lead to retinopathy in the infant whose postconceptual age is less than 46 weeks, in whom the retina has not completely matured.
Pulse Oximeter
Pulse oximetry has become an integral part of anesthesia care in the United States. The American Society of Anesthesiologists has mandated its use in all anesthetics and in the postanesthetic care unit. Excellent detailed reviews of the theory and technology behind pulse oximetry have been published by Tremper and Barker (1989), Alexander and colleagues (1989), and Severinghaus and Kelleher (1992). In the operating room, pulse oximetry is used primarily for detection of hypoxemia, although the plethysmographic tracing of the pulse oximeter saturation also can be used to monitor the circulation. Whether the use of pulse oximetry has resulted in improved patient outcome as a result of better detection of hypoxic events is still the subject of intense investigation, both by outcome studies, such as that of Moller and associates (1993), and closed claims analysis. One study by Cot and colleagues (1991) of pulse oximetry in pediatric patients underscores the ability of this monitor to detect clinically unrecognized hypoxemia in both the operating room and the recovery room. For operations associated with a high risk for intraoperative hypoxemia, such as TEF repair, the use of pulse oximetry, as noted by Bautista and associates (1986), has made early detection of impaired oxygenation possible.
Capnography and Capnometry
Capnography and capnometry make possible the monitoring of end-tidal CO2 concentrations in exhaled gases of an anesthetized patient. Important intraoperative applications of this noninvasive technique, as summarized by Bhavani-Shankar and colleagues (1992), are (a) detection of esophageal intubation, circuit disconnect, and hypoventilation; (b) monitoring of CO2 production; and (c) detection of abnormal alveolar ventilation and respiratory patterns. Presumably, the universal use of capnography will result in improved clinical outcome by virtue of earlier detection of dangerous respiratory problems.
Effective capnographic monitoring of pediatric patients is complicated by their small tidal volumes. Contamination with fresh gas flow is a problem, especially when the CO2 sensor is placed too far from the endotracheal tube. Badgwell (1991) studied the accuracy of capnography as a function of sensor location in pediatric breathing circuits. The end-tidal CO2 approximated Paco2 most closely when the sensor was positioned within the endotracheal tube itself using a small aspirating catheter. For trending purposes, however, the sensor worked well when positioned conventionally, placed as close to the endotracheal tube as possible.
Additional Monitors
Additional monitoring devices are frequently used in pediatric thoracic surgery.
Indwelling Arterial Pressure Line
An indwelling arterial pressure line is an invaluable intraoperative aid. Beat-to-beat display of the blood pressure facilitates early detection of hypotension, which can result from hypovolemia or decreased venous return related to great vessel compression. Samples for blood gas, hemoglobin, and glucose analyses are obtained easily from an indwelling arterial catheter. Several sites for cannulation exist, each with its own advantages and drawbacks. The right radial artery provides access to preductal blood, but insertion of even a 22-gauge catheter may be technically difficult in a newborn. Umbilical artery catheterization is relatively easy in the first 24 hours of life, but it carries the risks for lower extremity vasospasm and embolization of particulate matter to other major arterial vessels.
Doppler Ultrasonic Flow Detector
The Doppler device provides auscultatory confirmation of systolic pressures when placed over the radial or brachial
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artery and used in conjunction with a blood pressure cuff. Whyte and associates (1975) reported excellent agreement between Doppler readings and transduced blood pressure values.
Central Venous Pressure Monitor
Information regarding intravascular volume status and mixed venous oxygen content can best be obtained from central venous pressure monitoring. Short (5 to 8 cm), small-bore (4 to 5F) catheters are available that can be percutaneously placed in the central circulation from a variety of insertion sites, including subclavian, internal, and external jugular and femoral veins. Insertion time is longer and success rate lower with patients less than 6 months of age.
SPECIFIC PROBLEMS REQUIRING THORACOTOMY IN NEWBORNS
Congenital Diaphragmatic Hernia
Although repair of a congenital diaphragmatic hernia is not accomplished by thoracotomy (see Chapter 51), it traditionally has been included in discussions of neonatal thoracic surgical emergencies. Based on innovative investigation, the term emergency may no longer be correct. Work done by Nakayama (1991) and Sakai (1987) and their associates demonstrates deterioration in pulmonary mechanics after emergent surgery in infants with congenital diaphragmatic hernia. Both groups of authors recommend a period of stabilization before operative treatment. During this stabilization period, the infant may receive pharmacologic treatment for pulmonary hypertension (tolazoline, dobutamine) as described by Ein (1980) and Drummond (1981) and their colleagues. Unconventional modes of ventilatory support (e.g., extracorporeal membrane oxygenation, high-frequency ventilation) have been used successfully by Bohn (1991) and O'Rourke and associates (1991). Because of the growing realization that the degree of pulmonary hypoplasia is an important determinant of ultimate survival, Bohn and colleagues (1987) made an attempt to quantitate disease severity so that treatment could be stratified based on predictors of outcome.
Proper airway management is essential to ensure the best possible outcome. Endotracheal intubation should be preceded by oxygenation with a bag and mask. Positive-pressure ventilation is contraindicated to avoid distending intrathoracic bowel and thereby increasing the infant's respiratory distress. Once an artificial airway is established, vigorous hyperventilation (Paco2 25 to 30 mm Hg) can be instituted.
Tracheoesophageal Fistula
Anesthetic management of infants with TEF may be complicated in the presence of prematurity, coexisting malformations, and aspiration pneumonia. Premature infants can have hyaline membrane disease, which may make intraoperative oxygenation and ventilation difficult. Additional malformations are commonly seen in neonates with TEF. VACTERL is one common grouping of malformations including vertebral, anal, cardiac, tracheoesophageal, renal, and limb anomalies in varying combinations. Aspiration pneumonitis, if it has occurred preoperatively, may complicate intraoperative ventilatory management and cause postoperative morbidity.
Preoperative evaluation of infants with TEF should include a complete blood count and chest radiography. The lung fields are inspected for infiltrates suggestive of aspiration pneumonia or for air bronchograms and reticular granular densities consistent with hyaline membrane disease. Cardiomegaly, increased pulmonary vascularity, or a right-sided aortic arch may indicate the presence of significant congenital heart disease. Our patients are evaluated by a neonatologist preoperatively, and a cardiologist is consulted if evidence of congenital heart disease exists.
Over a period of years, the surgical management of TEF has been modified. Gastrostomy under local anesthesia followed by right thoracotomy for TEF repair is not being performed as frequently. Rather, a single anesthetic is administered for TEF repair. Gastrostomy is done only for those cases in which the anatomy or medical condition warrant it.
Induction techniques and airway management are important controversial issues in the anesthetic care of infants having TEF repair. The relative merits and drawbacks of available induction techniques are debated by pediatric anesthesiologists. Awake endotracheal intubation has the advantage of maintaining spontaneous breathing. Should intubation prove problematic, the patient will still be able to ventilate spontaneously and, it is hoped, will not become hypoxic. In vigorous term infants, however, awake intubation can be difficult to perform and may be associated with intraventricular hemorrhage. Critics also contend that the procedure is inhumane and that some anesthesia should be provided before manipulating the airway. Many advocate an intravenous rapid-sequence induction using muscle relaxants. This technique results in ideal intubating conditions because the patient is paralyzed; however, use of paralysis necessitates the use of positive-pressure ventilation. Care must be taken to avoid gastric distention by using rapid respiratory rates and low tidal volumes, and hypoxia can occur if the endotracheal tube cannot be expediently positioned appropriately. Buchino and associates (1986) reported severe respiratory compromise and death from persistent wedging of the endotracheal tube in the fistula. To avoid this catastrophe, Andropoulos and colleagues (1998) advocate prethoracotomy bronchoscopy for all patients to evaluate the size and location of the fistula. High-risk lesions (low-lying, large fistulae) that might predispose the patient to intraoperative ventilatory problems can be identified and managed appropriately. Reeves and associates (1995)
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reported their experience with preoperative bronchoscopy in two infants with TEF. A Fogarty embolectomy catheter was inserted into the fistula, thereby occluding it and preventing loss of ventilation through it.
The ideal endotracheal tube tip position is just above the carina but below the fistula. Because the distance between the carina and the TEF may be only several millimeters, proper positioning of the endotracheal tube requires meticulous care. One way to achieve proper position of the endotracheal tube is by deliberate endobronchial intubation, verified by loss of breath sounds over the left hemithorax, with subsequent withdrawal of the tube until bilateral breath sounds are detected. If a gastrostomy tube is present, the end is placed under water, and the absence of bubbling is verified. If bubbling occurs, then the endotracheal tube lies above the fistula and has been withdrawn too far.
Anesthesia can be maintained by the combination of inhalational agents and judicious use of narcotics. Intraoperative problems include hypotension from great vessel compression, hypoxia, and hypercarbia from lung retraction and endotracheal tube obstruction from secretions and clotted blood. In the otherwise healthy newborn without preoperative cardiopulmonary problems, extubation is usually possible at the conclusion of the operation. Premature infants, infants with serious associated anomalies, and those whose intraoperative courses have been complicated are usually brought back to the high-risk nursery with their endotracheal tubes in place. Some centers have been using caudal epidural catheters to deliver postoperative analgesia to these patients.
Congenital Lobar Emphysema
Although infants with congenital lobar emphysema may develop respiratory distress immediately after birth, most children are diagnosed after 1 month of age. Tachypnea, cyanosis, and diminished breath sounds over the affected side are the usual presenting symptoms and signs. The degree of respiratory distress is occasionally so severe that endotracheal intubation is performed before arrival in the operating room. Regardless of where the intubation is done, it is important to begin any airway manipulation with several minutes of preoxygenation with bag and mask. Positive-pressure ventilation further distends the hyperinflated lobe and should be avoided if at all possible. Gupta and colleagues (1998) have successfully managed two infants with congenital lobar emphysema requiring thoracotomy with selective bronchial intubation. However, the benefit of avoiding hyperinflation of the emphysematous lobe must be balanced against the risk for hypoxemia should a right-sided endotracheal tube bypass the right upper lobe bronchus.
Thoracotomy for removal of the emphysematous lobe is the usual surgical management of this problem. If the cardiopulmonary status allows, anesthesia is induced by having the infant breathe a mixture of halothane in 100% oxygen. Nitrous oxide and positive-pressure ventilation are avoided to prevent further increases in the size of the affected lobe. Clinically unstable or rapidly deteriorating infants are best managed by emergent awake intubation. If possible, anesthesia is maintained with halothane, oxygen, and spontaneous ventilation. Arterial blood gas analysis, however, often shows progressive hypoventilation and respiratory acidosis after the patient is placed in the lateral position. In this case, it may be necessary to provide gentle manual positive pressure until the chest is opened and compression of the good lung is relieved. At this point, pulmonary status improves substantially. After lobectomy, most infants show complete return to normal of the arterial blood gas values. Tracheal extubation at the conclusion of the surgical procedure is routine. Goto and associates (1987) mentioned the possible role of high-frequency jet ventilation in the intraoperative management of patients with congenital lobar emphysema.
THE OLDER CHILD
In general, anesthetic considerations for thoracic surgery in the older child are no different from those in the adult. One exception is the child with cystic fibrosis (CF). Because of its early onset and chronic course, CF is managed primarily by pediatric subspecialists. Failure of medical therapy to control pulmonary problems such as bronchiectasis and recurrent pneumothoraces may necessitate surgery. The excellent discussion of CF by Maclusky and Levison (1990) provides background knowledge to ensure a safe perioperative course.
CF is the most common lethal inherited disorder of whites. This autosomal recessive disease occurs in 1 in 2,000 live births. Generalized exocrine gland dysfunction is the hallmark of this disease. Involvement of the pulmonary, cardiovascular, and gastrointestinal systems is of greatest concern for the anesthesiologist.
The pulmonary exocrine glands of CF patients secrete abnormally tenacious mucus. Impaired mucociliary clearance of this mucus, combined with a predisposition to chronic endobronchial bacterial colonization, causes progressive pulmonary damage. Bronchiectasis develops as a result of peribronchial inflammation and leads to airway collapse and air trapping. Shunting of blood through large bronchopulmonary collateral vessels may occur, with the potential for massive hemoptysis should these vessels rupture. Repeated cycles of infection, especially with Pseudomonas species, and pulmonary damage lead to chronic hypoxemia and ultimately cor pulmonale. However, as noted by FitzSimmons (1993), even though improved medical management in the past 20 years has resulted in doubling of the mean survival age to 28 years, most CF patients die of chronic pulmonary disease and secondary cardiac failure.
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Gastrointestinal involvement in CF occurs as a result of exocrine pancreatic insufficiency. Malnutrition and malabsorption are present to a variable extent in most patients. Inadequate levels of fat-soluble vitamins, especially vitamin K, can be problematic. Hypovitaminosis K can contribute to severe bleeding problems perioperatively.
Medical management of the patient with CF consists of the following: chest physiotherapy to aid in mobilization of secretions, antibiotic therapy for prevention and treatment of infection, bronchodilator therapy for airway hyperreactivity, and aggressive nutritional support. Situations that may require surgical intervention include severe bronchiectasis, recurrent pneumothoraces, and life-threatening hemoptysis.
Marmon and associates (1983) emphasized that preoperative optimization of the patient's medical condition is essential. This effort requires cooperation among the surgeon, pediatrician, and anesthesiologist. CF patients ideally are hospitalized several days before elective thoracic surgery to institute aggressive chest physiotherapy and antibiotic coverage. Nutritional status should be made optimal as well, including hyperalimentation if necessary. Preoperative laboratory studies establish the patient's baseline pulmonary status. These include hemoglobin, chest radiography, coagulation profile, pulmonary function tests, and arterial blood gas analysis. Pulse oximetry and transcutaneous CO2 are acceptable substitutes. If the patient has cor pulmonale or is receiving diuretics, additional information from echocardiography or serum electrolytes may be indicated.
Regional anesthesia is preferable to general anesthesia in patients with CF, but this technique is usually not suitable for thoracic surgical procedures. Use of a general anesthetic with volatile agents such as halothane or isoflurane has been successful in these cases. Avoidance of nitrous oxide permits use of high inspired oxygen tension and prevents expansion of air-containing pulmonary bullae by the more diffusible N2O. The use of intravenous agents such as narcotics and benzodiazepines is discouraged to minimize postoperative respiratory depression. Although a review article by Lamberty and Rubin (1985) cited a high perioperative complication rate of 10%, the current complication rate may be lower, in part because of better patient selection, preoperative preparation, and intraoperative monitoring.
It is essential to avoid soiling the contralateral lung during pulmonary resection for bronchiectasis. Use of a double-lumen endotracheal tube is helpful if the patient's size permits. Experience with bronchial blockers has been limited in smaller patients.
Patients with CF may require intensive care after a long, difficult procedure, especially if their preoperative medical condition was poor or if unexpected intraoperative problems arose. Most patients, however, can be extubated in the operating room after thorough tracheal suctioning. They should receive oxygen therapy with pulse oximetry monitoring throughout their stay in the postanesthesia care unit and for 24 hours postoperatively.
Postoperative pain relief is an important aspect of the patient's care. Administration of narcotics is usually not recommended because of the risk for hypoventilation with subsequent hypercarbia and hypoxia. Alternative methods of postoperative analgesia include intercostal nerve block performed by the surgeon in the operating room, epidurally administered local anesthetic, or intravenous nonnarcotic medications such as ketorolac. Ideally, pain control is managed by or with the assistance of a hospital-based pain service.
VIDEO-ASSISTED THORACIC SURGERY
Video-assisted thoracic surgery (VATS) is being used with increased frequency in a variety of pediatric surgical cases including lung biopsy, excision of mediastinal masses, and management of pleural fluid and air collections. This approach is also gaining popularity in the surgical management of scoliosis. Video-assisted exposure of the anterior thoracic spine for scoliosis correction has the theoretical advantages of decreased blood loss, postoperative pain, and shoulder dysfunction.
For the pediatric anesthesiologist caring for a patient having a minimally invasive thoracoscopic procedure, the greatest challenge lies in obtaining safe, effective one-lung anesthesia. The smallest size of a mass-produced double-lumen endotracheal tube routinely used for one-lung anesthesia in adults is 26F (5.5-mm internal diameter). In general, patients weighing less than 40 kg do not have tracheal lumens large enough to allow passage of this size of endotracheal tube. Univent tubes (Fuji Systems Corporation, Tokyo, Japan), which are single-lumen endotracheal tubes with a self-contained movable bronchial blocker, are available in sizes suitable for small infants and children. Hammer and associates (2002) recently reported their experience with a new balloon-tipped, open-ended bronchial blocker (Cook Critical Care, Bloomington, IN, U.S.A.) inserted through an indwelling tracheal tube using a multiport adapter. The open-ended bronchial blockers used with the Univent and Cook products permit oxygen insufflation and collapsed lung drainage during the procedure. Alternative techniques to isolate the lungs include selective bronchial intubation and use of a closed-ended embolectomy catheter inserted alongside the endotracheal tube as a bronchial blocker. Because endobronchial intubation with a single-lumen tube often blocks the right upper lobe, modification of the endotracheal tube (notching of the distal end after removal of the Murphy eye) has been advocated by Tan and co-workers (1999) in an effort to decrease this risk. Successful isolation of the lungs can be a time-consuming process
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in the smaller patient. An otolaryngologist's presence is often necessary for proper placement of a bronchial blocker, which, according to Borchardt and associates (1998), is associated with a risk for bronchial tear. The actual operating time may be increased for VATS compared with open thoracotomy in the pediatric population because of technical difficulties in achieving satisfactory one-lung anesthesia.
POSTOPERATIVE ANALGESIA
Schechter and associates (1986) noted that interest in postoperative pediatric pain control has dramatically increased in recent decades. Research in the areas of neonatal pain perception and narcotic administration in children, as reported by McGrath and Johnson (1988), has heightened physician awareness that these patients experience postoperative pain and that adequate relief of pain may improve overall outcome, especially in children undergoing thoracotomy.
Coe and colleagues (1991) and Craig (1981) summarized the well-described decrease in pulmonary function testing results after these operations, believed to result in part from poor respiratory effort caused by pain. Adequate analgesia was found by Shulman and co-workers (1984) and Conacher (1990) to ameliorate this problem. A more extensive metaanalysis of the effects of postoperative analgesic therapies on pulmonary outcome was published by Ballantyne and associates (1998). Their analysis showed that adequate relief of pain with epidural opioids, local anesthetics, or both significantly decreased morbidity from pulmonary infections, hypoxia, and atelectasis after thoracotomy in adults; however, successful analgesia did not prevent decreases in pulmonary function tests, specifically forced expiratory volume in 1 second, vital capacity, and peak expiratory flow.
Postoperative pain relief in pediatric patients following thoracotomy may be provided by a variety of methods: systemic analgesics, epidurally administered local anesthetics with or without narcotics, and other regional techniques. Narcotics are the cornerstone of postoperative parenteral analgesia. Patient-controlled analgesia (PCA), as described by Berde and colleagues (1991), has become commonplace in the postoperative pediatric population. This technique provides greater patient satisfaction with a lower incidence of side effects when compared with intramuscular injections. Nonnarcotic parenteral agents such as ketorolac and indomethacin have been used successfully in the management of postthoracotomy pain both in adults and children, as reported by Pavy (1990) and Watcha (1992) and their associates.
Successful regional anesthesia probably affords the most complete relief of postthoracotomy pain but is not without risk. Epidural delivery of a dilute local anesthetic and narcotic is the most commonly selected regional technique. In the older child as in the adult, a thoracic epidural catheter inserted before anesthetic induction can be used. In smaller children, the catheter can be threaded into the thoracic epidural space from a caudal insertion site, as described by Tsui and associates (1999) and Gunter and Eng (1992). Because of the child's inability to cooperate, the epidural catheter is frequently inserted under general anesthesia. The risk-to-benefit ratio of this practice, especially with insertion in the thoracic region, has been hotly debated by pediatric anesthesiologists, as summarized in editorials by Krane and colleagues (1998), Ross and Koh (2000), and Desparmet (1999).
An alternative regional technique is intrapleural analgesia, in which local anesthetic is delivered into the intrapleural space by a catheter inserted intraoperatively. McIlvaine (1988) has reported good results with this technique, but it has not gained widespread popularity.
Use of these less traditional, more invasive methods of analgesia requires close patient monitoring and supervision of both the family and nursing staff. Many hospitals offer an anesthesiology-based multidisciplinary pain service to implement appropriate postoperative analgesia and to ensure its safety and efficacy. Ready (1988) and Shapiro (1991) and their colleagues have reported the successes of their respective pain services.
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