In the United States, 40,000 children are born each year with congenital heart disease (CHD),¹ representing an incidence of 6 to 8 cases per 1000 live births.² Children with chromosomal abnormalities such as trisomy 21 (i.e., Down syndrome) have a greater incidence of CHD. Having a sibling with CHD increases the risk of CHD, as does the presence of other congenital abnormalities.³ With improving diagnostic techniques, many children with CHD are diagnosed in the antenatal or early postnatal period. Associated with this improvement in diagnostic ability is a trend in most centers to undertake definitive repair earlier, with many patients undergoing corrective surgery in the neonatal period. Overall, about one half of all children with CHD undergo cardiac surgery in the first year of life, and about 25% undergo surgery in the first month of life.^4,⁵

The perioperative management of children with complex cardiac defects requires a dedicated team of surgeons, cardiologists, anesthesiologists, intensivists, perfusionists, and nurses. Anesthesiologists caring for these children are challenged by some of the greatest physiologic aberrations encountered in clinical medicine. The anesthesiologists responsible for the care of these children require a comprehensive understanding of cardiac physiology and pathophysiology. The anesthesiologist must be able to adapt to each nuance of rapidly changing pathophysiology as it is encountered.

In addition to treating children with CHD, the pediatric cardiac anesthesiologist may also be responsible for the care of adults with CHD. This patient population with “grown-up CHD” is expanding as more children with CHD survive to adulthood. Along with CHD, they have some of the comorbidities of older age. The ideal approach for this group of patients is to be cared for in specialist units, but few are available. In the meantime, the care of these patients may fall to the most qualified physicians and the pediatric cardiac anesthesiologist. Some children have acquired rheumatic heart disease, some have cardiomyopathy, and others have undergone heart transplantation and require care from specialists.

For managing children with complex cardiac defects, there is increasing reliance on echocardiography and magnetic resonance imaging (MRI) to acquire diagnostic data. Although fewer children are being subjected to diagnostic angiography, more interventional cardiac catheterization procedures are being performed. Many conditions that would previously have been treated surgically are now treated in the angiography suite by interventional cardiologists, such as atrial septal defects (ASDs), patent ductus arteriosus (PDA), and ventricular septal defects (VSDs). Other interventions include dilating arteries with balloon catheters with and without stents and coiling of aberrant or excessive collateral vessels. The pulmonary artery is commonly balloon dilated and stented, and coarctation of the aorta is treated similarly by balloon dilation. Stenotic valves are also commonly dilated. These procedures have led to the risk being transferred from the angiography suite to the operating room.⁶ For the individual child, there has been a dramatic decrease in morbidity as increasing numbers of conditions are treated in the angiography suite, but the risks of complications that occur in the angiography suite have increased as more complex procedures are performed (see Chapter 20).

The Preoperative Visit and Evaluation

The preoperative visit is an important part of the overall management of anesthesia for children with CHD.⁷ The preoperative visit has several aims:

Medical assessment

Prescribing premedication

Providing information

Creating a relationship with the child and family

Formulating an anesthetic plan

Medical Assessment

The anesthesiologist must have a clear and detailed understanding of the cardiac pathophysiology, the surgery to be undertaken, and associated congenital abnormalities or medical conditions. The medical assessment includes collation of information from the history, physical examination, and review of imaging and laboratory data. Most diagnostic information is obtained from the medical record. Particular attention should be paid to the echocardiographic, MRI, angiographic, and other imaging data; the chest radiograph; and the electrocardiogram. Many centers have joint cardiac conferences where decisions about treatment are discussed in a multidisciplinary forum. Reports from these meetings are valuable in the preoperative assessment.

In addition to gathering this specific diagnostic information, a directed history and physical examination should be performed to assess the overall condition of the child. Attention should be directed toward assessing the degree of cardiac failure, cyanosis, or risks of pulmonary hypertension and the prior surgical procedures and how this information may alter access to the central circulation and placement of invasive monitors. The general nutritional state of the child should be assessed; poor growth and development may be a sign of severe CHD. Other information should be sought that may have a bearing on the anesthetic plan. For example, is this repeat surgery, and does it require a repeat sternotomy? This has a bearing on line placement because a femoral bypass may be required, and it should be avoided for line placement. The previous use of aprotinin is important because the risk of anaphylaxis is increased in a second exposure and particularly if it has been given in the previous 6 months.⁸

The type of surgery to be performed is important. For example, if a Blalock-Taussig shunt is placed on the left, the arterial line should not be placed in the left arm because the trace will be lost or distorted during subclavian cross-clamping. If a Glenn shunt is planned, a short internal jugular line can be useful to monitor pulmonary artery pressure, but it should be removed early in the postoperative period so as not to risk the formation of thrombosis in the superior vena cava (SVC).

Good veins should be sought and marked for the application of local anesthetic cream. This is useful in sick children even if an inhalational induction is planned because it allows placement of a venous cannula during a very light plane of anesthesia and avoids myocardial depression from high concentrations of inhalation anesthetics.

Prescribing Premedication

The use of sedative premedication can be useful in cardiac anesthesia, but this practice varies widely. Numerous medications may be used, and numerous recommendations exist. Premedication for infants younger than 6 months of age is usually unnecessary. Premedication for older, healthy children who show little anxiety and with whom good preoperative rapport can be established is often unnecessary. However, older children, particularly those who have undergone previous surgery, have fears about anesthesia and surgery. It is important to address the fears of these children. Sedative premedication may play a pivotal role in achieving adequate anxiolysis for separation from the parents and induction of anesthesia. I prefer to avoid premedication in children with severe congestive heart failure. Cyanotic children such as those with tetralogy of Fallot (TOF) often benefit from sedative premedication because crying and struggling during induction of anesthesia may worsen their cyanosis. However, it is important that these cyanotic children are well supervised after premedication because they have a blunted response to hypoxia.⁹ In the United States, supplemental premedication is sometimes administered under the direct supervision of the anesthesiologist in the preoperative facility, providing for a calm child and gentle separation from the parents. In the United Kingdom, where induction of anesthesia takes place in a dedicated anesthesia room, parents are present until after the induction, often making additional premedication unnecessary.

The most common premedication is oral midazolam (0.5 to 1.0 mg/kg).¹⁰ However, the effect of midazolam may be unpredictable and may cause dysphoria. Numerous other medications have been recommended for this purpose, including ketamine, clonidine, temazepam, and chloral hydrate. The use of these drugs is often dictated by local preferences and is not always evidence based.

Upper Respiratory Tract Infection and Cardiac Surgery

Otherwise healthy children undergoing elective noncardiac surgery in the presence of an upper respiratory infection (URI) are more likely to suffer respiratory complications (Table 15-1). These complications typically are minor, are easily managed, and usually result in minimal morbidity.¹¹^–¹³ The decision about whether to proceed with noncardiac surgery in a child with a URI is made on an individual basis.¹⁴

TABLE 15-1 Diagnosis of Upper Respiratory Tract Infection

At least two of the following signs plus confirmation by a parent:

Rhinorrhea

Sore or scratchy throat

Fever >100.4° F (38° C)

Data from Schreiner MS, O’Hara I, Markakis DA, Politis GD. Do children who experience laryngospasm have an increased risk of upper respiratory tract infection? Anesthesiology 1996;85:475-80.

The decision to proceed with cardiac surgery in children is difficult. Although children with cardiac failure are prone to multiple URIs, they may also have signs that can mimic URIs. Surgery may be relatively urgent, and postponing surgery exposes the child to an increased risk. Cardiac surgery in children with URIs results in a prolonged stay in the ICU and prolonged ventilation times, although overall hospital stay is not prolonged. There is an increased incidence of pulmonary atelectasis and an increase in postoperative bacterial infections. There appears not to be any statistically significant increase in mortality rates (4.2% with URIs versus 1.6% without URIs) or long-term sequelae in children with URIs who undergo cardiac surgery. The URI group was significantly younger and smaller, which may account in part for the greater but statistically insignificant increased mortality rate.¹⁵ Although this increase in mortality was not statistically significant, it does raise concerns about the risks posed by URIs before cardiac surgery. Children who are scheduled for a Glenn shunt or completion of the Fontan circulation may be at particular risk because an increase in pulmonary vascular resistance (PVR) can adversely affect outcome. It is prudent to postpone surgery in a child with a URI who is scheduled for elective cardiac surgery. If the surgery is urgent, discussion with the surgical team is required to correctly assess the risks and benefits to the child.

Perioperative Challenges in Pediatric Cardiac Anesthesia

Cyanosis

Children with cyanotic cardiac defects compensate for chronic hypoxia with increased erythropoiesis, increased circulating blood volume, vasodilation, and metabolic adjustments of factors, such as circulating 2,3-diphosphoglycerate (2,3-DPG). These changes allow greater tissue delivery of oxygen. The increase in blood viscosity with polycythemia leads to increased vascular resistance and sludging, which may result in renal, pulmonary, and cerebral thromboses, especially in dehydrated children.¹⁶ Long periods without oral intake preoperatively and postoperatively should be avoided in children with polycythemia, unless adequate intravenous hydration is provided.

PVR increases more than systemic vascular resistance (SVR) with an increasing hematocrit, further decreasing pulmonary blood flow in children who already have a compromised pulmonary circulation. Coagulopathies are common in children with cyanotic CHD and may adversely influence surgical hemostasis.^17,¹⁸ When the hematocrit exceeds 65%, excessive viscosity impairs microvascular perfusion and outweighs the advantages of increased oxygen-carrying capacity. Reduction of red blood cell volume can correct the coagulopathy and improve hemodynamics when increases in hematocrit are extreme.¹⁹

Intracardiac Shunting

In CHD, much of the pathophysiology involves communications between chambers or vessels that are normally separate, resulting in shunting of blood between ventricles, atria, the great arteries, or a combination of these, depending on the nature of the lesion. Management of shunting is a major consideration during anesthesia and requires an understanding of the factors that control shunting.

Restrictive and Unrestrictive Shunts

When communications are small, the size of the defect limits shunting and considerations of relative PVR and SVR become correspondingly less important in determining the amount of shunting. When there is a large pressure differential at the same level of the circulation on either side of a communication, the communication is restrictive. Flow is limited across the defect, and other factors determining shunt flow become less important. This is usually the situation in children with mild heart disease that is asymptomatic or minimally symptomatic, such as small ASDs and VSDs or a small PDA.

Dependent Shunting during Anesthesia

In children with dependent shunts, the direction and degree of intracardiac shunting are determined by the circulatory dynamics. Control of circulatory dynamics to minimize the shunt is a major goal of anesthesia management. Because shunting depends on the relationship between SVR and PVR, anesthesia management often revolves around control of relative vascular resistances.

In children with dependent right-to-left shunts, the shunt increases when SVR decreases or PVR increases. In children with dependent left-to-right shunts, the shunt increases when SVR increases and PVR decreases. In children with bidirectional or balanced shunting, changes in vascular resistance increase the net shunt away from the side with increased vascular resistance.

For practical purposes, acute increases in left-to-right shunts during anesthesia are of clinical importance in several situations. A substantial steal of systemic blood flow by the pulmonary circulation can occur in conditions such as atrioventricular (AV) canal, truncus arteriosus, and hypoplastic left heart syndrome. Left-to-right shunting is well tolerated, except when pulmonary steal leads to systemic hypotension, increasing acidosis or insufficient coronary perfusion. Shunting from right-to-left, because it is accompanied by at least some degree of arterial oxygen desaturation, is more frequently a problem during anesthesia.

Impaired Hemostasis

Hemostasis is impaired after bypass in infants and children. This results from a combination of immature coagulation factor synthesis, hemodilution after bypass, and a complex interaction involving consumption of clotting factors and platelets. At birth, the levels of vitamin K–dependent coagulation factors in healthy, full-term neonates are only 40% to 66% of adult values. During the first month of life, these levels increase to 53% to 90% of adult values.²⁰ However, in children with CHD, especially those with cyanosis or systemic hypoperfusion, coagulation factors often continue to be depressed due to impaired hepatic protein synthesis. Although antithrombin III levels are also low, true heparin resistance is rare in infants because of parallel decreases in coagulation factors.

At the onset of cardiopulmonary bypass (CPB), the introduction of the prime volume, which is two to three times greater than the child’s blood volume, dilutes the factor concentrations, particularly fibrinogen, to 50% of values before bypass and the platelet count to 30% of values before bypass. This degree of dilution occurs even when the pump circuit is primed with whole blood. Greater dilution may occur when packed red cells are used in the priming volume. At the conclusion of neonatal bypass, the activity of clotting factors is often extremely low, the fibrinogen concentration is frequently less than 100 mg/dL, and the platelet count has been reduced to 50,000 to 80,000/mm³.^21,²² In addition to these quantitative changes, functional changes in the platelets occur during bypass. Extracorporeal circulation causes a loss of platelet adhesion receptors, activation of platelets, and formation of leukocyte-platelet conjugates. Platelet adhesion receptors are more depressed in children with cyanotic compared with acyanotic cardiac defects. Heparin also impairs platelet function independent of CPB.²³

Cardiac surgery is associated with significant activation of the fibrinolytic system.²⁴ Inadequate heparin levels during CPB may also contribute to postoperative bleeding because inadequate anticoagulation may allow activation of the hemostatic pathways. Activation causes the consumption of platelets and clotting factors. The standard measurement of anticoagulation, the activated clotting time (ACT), shows a poor correlation with heparin levels in children undergoing CPB.²⁵ In one study, the use of heparin monitoring and heparin titration was associated with larger doses of heparin but smaller doses of protamine for antagonism.²⁶ Activation of clotting cascades is also reduced, decreasing bleeding in the postoperative period.²⁶ As a result of this multifactorial coagulopathy, blood loss is a greater problem in children than in adults and is a particular problem in neonates and small infants (see Chapter 17).²⁷

Strategies to Reduce Bleeding after Bypass

In an effort to normalize factors and platelets to effective concentrations, some medical centers use fresh whole blood in the cardiopulmonary circuit prime. In adult patients and an in vitro aggregation study, transfusion of fresh whole blood provided equal or greater hemostatic and functional benefit when compared with transfusion of platelet concentrates. In children, transfusion of fresh whole blood less than 48 hours from harvest is associated with less blood loss compared with transfusion of reconstituted whole blood (e.g., packed erythrocytes, fresh frozen plasma [FFP], and platelets).²⁸ However, fresh whole blood is often difficult to obtain. The units must be refrigerated for 24 to 48 hours while donor screening is performed, and storage causes significant platelet injury. Insistence on fresh whole blood places tremendous pressures on the transfusion service and donor center to coordinate the matching of donor types with recipient needs.

In practice, individual component therapy is used. In neonates and small infants with dilutional coagulopathy, platelets should be given in combination with cryoprecipitate to correct the defect in clotting. An initial dose of 10 mL of platelets/kg of body weight may need to be repeated. Platelets may be administered if bleeding persists and the platelet count is less than 100,000/mm³.²⁹ Cryoprecipitate contains high concentrations of fibrinogen, factor VIII, von Willebrand factor, and factor XIII. Fibrinogen and von Willebrand factor are required for platelet adhesion and aggregation to occur. Platelet adhesion and aggregation are the fundamental first steps in primary hemostasis (see Chapter 10). The subsequent step of platelet degranulation switches on the entire coagulation cascade and cannot take place without adhesion and aggregation.³⁰ Administration of FFP, for which there is no evidence of effectiveness in treating this type of coagulopathy, to the infant may excessively dilute the red cell mass and platelets.³¹

Transfusion guidelines have been described for adults and have been shown to reduce postoperative bleeding and transfusion requirements.^32,³³ However, similar guidelines have not been forthcoming for children in whom the practice appears to be more empirical. This is a less than ideal situation, and more work is urgently needed to produce well-validated guidelines. The thromboelastogram and the platelet count may be used to identify which children are likely to bleed after cardiac surgery.

Antifibrinolytics

The antifibrinolytics used in pediatric cardiac surgery include ε-aminocaproic acid (EACA) and tranexamic acid (TA). In many countries, aprotinin is no longer available, and in other countries, it has only very limited availability after its marketing license was withdrawn due to safety concerns. EACA and TA are lycine analogues that reduce bleeding after cardiac surgery in adults and children.^34,³⁵ They do not exert any antiinflammatory activity. Doses for pediatric cardiac surgery have not been clearly established.

Aprotinin is a serine protease inhibitor that has been studied thoroughly in adults. Early evidence demonstrated that it reduces bleeding, reduces the time taken to extubation, shortens ICU stay, and reduces overall mortality rates.³⁶ However, subsequent studies have contradicted these earlier findings.³⁷ The same volume of evidence has not been published for children, although several studies suggest that it is effective in reducing bleeding and that it reduces the time spent on the ventilator and in the ICU.³⁸^–⁴¹ An increased risk of renal failure or stroke in adults undergoing revascularization surgery has been reported.⁴² The same investigators reported an increase in the 5-year mortality rate for adults after the use of aprotinin in revascularization surgery.⁴³ Aprotinin has increased the 30-day mortality rate by as much as one third compared with TA or EACA.³⁷ Comparable data for children have not been forthcoming (see Chapter 18). Aprotinin is available for use in New Zealand, Australia, and Canada. It appears that the early data regarding increased death rates have not been supported by subsequent studies and that the benefits may outweigh risks in specific populations.⁴⁴

Topical Agents

The use of topical agents to promote clot formation and reduce bleeding in children after cardiac surgery is common. The most commonly used topical agents are fibrin sealants. Fibrin sealants mimic the stages of the blood coagulation process. Unlike the synthetic adhesives, they are biocompatible.⁴⁵ Fibrin sealants are usually sourced from plasma components, and most contain virally inactivated human fibrinogen and thrombin with different quantities of factor XIII, antifibrinolytic agents, and calcium.⁴⁵ When the fibrinogen and thrombin are mixed during the application process, the fibrinogen is converted to fibrin monomers. This results in the formation of a semirigid fibrin clot. By mimicking the later stages of the coagulation process, these sealants stop bleeding and assist in wound healing.⁴⁵ They have significantly reduced bleeding in children.⁴⁶

Ultrafiltration

Ultrafiltration is a process that removes ultrafiltrate from a child during and after CPB. It provides many benefits, including increasing the hematocrit, concentrating the clotting factors and platelets, increasing blood pressure, reducing PVR, and removing inflammatory mediators in the ultrafiltrate. It has significantly reduced bleeding after cardiac surgery in children.^47,⁴⁸

Desmopressin

Desmopressin acts by increasing plasma concentrations of factor VIII and von Willebrand factor. It has been effective in reducing bleeding after CPB in adult cardiac surgery.⁴⁹ Unfortunately, studies in children failed to demonstrate a similar effectiveness in reducing bleeding or transfusion requirements.⁵⁰

Anesthesia Management for Surgery Requiring Cardiopulmonary Bypass

Monitoring

Noninvasive monitoring during pediatric cardiac surgery includes pulse oximetry, five-lead electrocardiography, an automated blood pressure cuff, a precordial or esophageal stethoscope, continuous airway manometry, inspired and expired capnography, anesthetic gas and oxygen analysis, multiple-site temperature measurement, and volumetric urine collection. The pulse oximeter is especially important when managing children with congenital cardiac disease. At least two probes should be placed on different limbs in the event that one fails during the procedure. In children with cyanotic heart disease, conventional pulse oximetry overestimates arterial oxygen saturation as saturation decreases ⁵¹; this error tends to be exacerbated in the presence of severe hypoxemia.⁵² When monitoring children with a shunt across the ductus arteriosus, a probe should be placed on a right hand digit to measure preductal oxygenation, and a second probe should be placed on a toe to measure postductal oxygenation (children with a right-sided aortic arch may require the probe to be placed on a left-hand digit). Children undergoing repair of coarctation of the aorta should be monitored with a pulse oximeter on the right upper limb, because it may be the only reliable monitor during the repair, and blood pressure cuffs should be placed before and after the coarctation. These two cuffs may be cycled and the differential documented before and after surgical correction.

Monitoring end-tidal carbon dioxide tension (Petco₂) is of value in most children. However, in children with cyanotic-shunting cardiac lesions, the Petco₂ measurement may be less reflective of Paco₂ because of ventilation-perfusion mismatching.⁵³ Arterial blood gases are the most accurate measure of the adequacy of ventilation and oxygenation. To provide rapid decision making, it is helpful to have the blood gas analysis machine located in or near the cardiac operating room.⁵⁴

Monitoring ionized calcium concentrations is essential during surgical procedures in which significant quantities of citrated blood are infused rapidly or when entire blood volumes are replaced. Neonates are particularly prone to disturbances in their ionized calcium concentration when citrated whole blood, FFP, or platelets are infused. Those with limited cardiac reserve tolerate ionized hypocalcemia poorly because of their greater sensitivity to the myocardial effects of citrate infusion (see Chapter 10).⁵⁵ In isolation, the total serum calcium concentration is misleading.

Temperature monitoring during CPB is a critical guide to adequate brain cooling and to appropriate rewarming before separation from bypass. Because it is not practical to measure brain temperature directly, surrogate measuring sites are used. The tympanic membrane, nasopharyngeal, and rectum have been used; the nasopharyngeal site most closely matches true brain temperature and is the site at which temperature is most often monitored. The tympanic and rectal sites tend to overestimate the brain temperature.^56,⁵⁷ Measurement of skin temperature gives an indication about peripheral perfusion and provides information about adequate peripheral rewarming.

After induction of anesthesia, an arterial catheter should be placed in children who will undergo CPB. The radial artery may be percutaneously cannulated with relative ease, even in infants. In small infants, the femoral arteries are frequently used for arterial access, and the axillary arteries are commonly used. The brachial artery is avoided because it is an end artery. Catheters placed in the dorsalis pedis or posterior tibial artery often provide inaccurate hemodynamic data, especially after separation from bypass, and it may become difficult to sample blood for laboratory testing. In the rare circumstance that peripheral arterial cannulation cannot be accomplished, the surgeon may place a catheter in the internal mammary artery after sternotomy, and a sterile monitoring line may be passed over the drapes. Ultrasound guidance often is used for insertion of arterial catheters.

Central venous lines can be very useful. For cardiac surgical procedures, there are two commonly used methods of obtaining central access. The decision of which to use may be determined in part by institutional bias. In the first method, the cardiac surgeons expose the heart quickly and have it available for inspection and estimation of filling pressures. Central lines can be readily established from the field and handed off to the anesthesia team. These transthoracic central lines are useful but carry a small amount of risk.²⁸ In the second method, percutaneous insertion of central venous lines is particularly indicated for long, complex procedures, especially when access to the infant is limited or the heart is not exposed. Percutaneous cannulation of the central circulation through the internal jugular approach or the subclavian approach has been demonstrated to be safe.²⁹ However, it is important to appreciate that insertion of central venous lines through the internal jugular or subclavian route may fail or may be associated with pneumothorax, hemorrhage, and hematoma formation after puncture of major arteries.²⁹^–³¹ Cannulation of the external jugular vein may avoid some of these serious complications when the catheter can be successfully threaded into the central circulation.³² Increasingly, ultrasound-guided techniques are being employed to establish central venous access (see Chapter 48). In the United Kingdom, the use of ultrasound for the placement of these lines is recommended by the National Institute of Clinical Excellence (NICE), and ultrasound is used routinely for the placement of central lines.

In children with unrestrictive VSDs or ASDs, including hearts with a single ventricle or single atrium, central venous pressure is equivalent to left ventricular filling pressure. Cannulation of vessels that drain into the SVC should be approached with caution in children with univentricular anatomy who may undergo the Fontan procedure, because thrombosis of the SVC can be a devastating complication. In such circumstances, the femoral veins may be the preferred sites for venous pressure monitoring.

Pulmonary arterial catheters in children with intracardiac defects usually provide little more information than a simple central line, are difficult to insert without fluoroscopy, and may not provide meaningful measurements of cardiac output. As a result, they are rarely used in pediatric cardiac patients.

Transesophageal Echocardiography

Use of perioperative echocardiography has become the standard of care in the United States.^58,⁵⁹ In adult practice, anesthesiologists usually perform the TEE, but in children, the TEE is more commonly performed by a pediatric cardiologist. This may reflect the increased complexity of congenital lesions and the difficulty in accurately assessing these lesions and their repairs. TEE has been cost-effective when used routinely during pediatric cardiac surgery.⁶⁰ The use of TEE can have a significant impact on surgical and medical management. In one large study, a second bypass run was undertaken in 7.3% of cases based on the findings of the TEE. There was a surgical alteration in the management of 12.7% and medical alteration in 18.5% of cases. Pediatric cardiac anesthesiologists usually can perform TEE before and after bypass if they have received adequate training.⁶¹

The introduction of small probes with multiplane capability has greatly increased the use of TEE, even in infants and neonates.^62,⁶³ In 1999, a survey of centers in the United States indicated that 93% used intraoperative echocardiography and that all but one used TEE.⁶⁴ The American Society of Echocardiography and the Society of Cardiovascular anesthesiologists have published guidelines for performing a comprehensive intraoperative TEE in adults⁶⁵ and children.⁶⁶

Although the use of TEE in children usually is safe, complications do occur and may be more common in small infants.⁶⁷ Complications include damage to the mouth, oropharynx, esophagus, and stomach. Other complications include hemodynamic disturbance as a result of compression of the left atrium or other structures. Interference with the airway also occurs in a small number of cases. This includes inadvertent extubation, right main-stem intubation, and compression of the tracheal tube. However, the overall incidence is small, approximately 2%.⁶⁸ Information gathered from the TEE examination takes place before and after bypass and may be divided broadly into two categories: hemodynamic assessment with monitoring and structural diagnostic information. Hemodynamic information includes information about ventricular function and filling.⁶⁹ Diagnostic information relates to confirmation or otherwise of preoperative findings and assessment of the adequacy of the surgical repair.

Near-Infrared Spectroscopy

Cerebral near-infrared spectroscopy (NIRS) is becoming widely used during cardiopulmonary bypass in children. This noninvasive monitor is used to determine the degree of brain tissue oxygenation.^70,⁷¹ It is likely to lead to improved neurological outcomes after cardiac surgery although there is no clear evidence in humans (see Chapter 51).

Induction of Anesthesia

In the United Kingdom, induction of anesthesia takes place in an anesthesia room, which is immediately adjacent to the operating room, and the parents are almost always present for induction. Anesthesia is commonly induced while the child is sitting with or being held by a parent. It is possible to involve some parents to the extent that they can hold the mask for the child as he or she is anesthetized. After the child is asleep, he or she is transferred to the anesthetic trolley, where venous and arterial access is secured and the trachea is intubated. This practice differs from most centers in North America, where induction of anesthesia occurs in the operating room.

Induction can be achieved using an intravenous or inhalational technique. Ketamine may be given intramuscularly or orally when intravenous access is difficult and mask induction is refused. The type of induction should be tailored to the child and the cardiac defect. If intravenous access has already been established, an intravenous induction is preferred. If intravenous access has not been achieved, a decision is made about the optimal induction technique. In severely ill children, it is advisable to obtain intravenous access before induction of anesthesia. The use of local anesthetic cream such as EMLA or Ametop Gel helps to reduce the pain of injection. Use of local anesthetic cream is also helpful if an inhalational induction is to be used because it allows insertion of an intravenous cannula during a much lighter plane of anesthesia. This requires that the appropriate veins are selected during the preoperative visit and that clear instructions are given to nursing staff about where the cream should be applied.

The most common inhalational induction agent is sevoflurane. Sevoflurane is very rapid acting and should be used with care in the child with CHD because high concentrations can produce bradycardia, hypotension, and apnea if not titrated carefully. Concentrations should be rapidly reduced after an adequate level of anesthesia is achieved. In children who are cyanotic with a right-to-left shunt and reduced pulmonary blood flow, inhalational inductions are slow. The addition of nitrous oxide can aid an inhalational induction in two ways. First, because it is odorless, it can be started before the introduction of the sevoflurane, allowing the child to be somewhat sedated before the stronger smelling agent is started. Second, it allows a smoother and more rapid induction compared with sevoflurane alone. Concentrations of up to 70% nitrous oxide can be used to smooth induction of anesthesia even in cyanotic children, but the nitrous oxide should be replaced with air and oxygen or 100% oxygen as soon as intravenous access is obtained and a muscle relaxant is given. It is not always necessary to use a mask for an inhalational induction because cupped hands are often more acceptable to the child, particularly one who is frightened of the mask. It is important to tell the child about each event before it happens and to demonstrate the action on yourself, a parent, or toy animal. You should also offer the child the opportunity to hold the mask, or if the child is accompanied by a parent, offer the child the choice of the parent holding the mask. Good premedication often aids this process (see Chapter 4).

For sick children in whom it may be preferable to use an intravenous induction, various options are available. For example, in neonates with coarctation of the aorta or with hypoplastic left heart syndrome who are not ventilated before coming to the operating room, one approach is to administer fentanyl in a dose of 2 to 3 µg/kg, followed by pancuronium and then by a very low dose (i.e., sedative dose) of sevoflurane or isoflurane. Fentanyl obtunds the hypertensive response to intubation, and the pancuronium maintains cardiac output by maintaining the heart rate. The very-low-dose volatile agent provides the sedation or anesthesia. In older children, etomidate is a very good induction agent, providing stable hemodynamics, although it does cause pain on injection. Ketamine is also widely used for intravenous induction in neonates and older children. Ketamine maintains or increases blood pressure, heart rate, and cardiac output. The exact mechanism of these effects of ketamine is unknown; ketamine may stimulate the release of endogenous stores of catecholamines, although it is a negative inotrope in the denervated heart.⁷² This negative inotropic effect may make ketamine a poor choice in children in whom catecholamine stimulation may already be maximal, such as in severe cardiomyopathy. It may also be a poor choice if tachycardia is undesirable, such as in the case of aortic stenosis.

Monitoring should ideally be applied before induction begins, but applying monitoring can upset the child, which can be detrimental (e.g., the child with TOF who begins to cry and precipitates a “tet spell”). A pulse oximeter probe may be the only monitor that is applied before induction of anesthesia. Sevoflurane or isoflurane may provide another advantage by offering a degree of ischemic preconditioning to the heart and to other organs, particularly the brain and kidney. In a double-blind study of adult patients undergoing coronary bypass grafting, exposure to 4% sevoflurane for 10 minutes before cross-clamping reduced the degree of myocardial dysfunction and renal damage postoperatively.⁷³ It is thought that the same effect is observed in children.⁷⁴

Maintenance of Anesthesia

Maintenance of anesthesia in children with CHD depends on the preoperative status and the response to induction of anesthesia. Whether inhalational agents, additional opioids, or other intravenous agents are used for maintenance depends on the tolerance of the child and postoperative plans for ventilation. If a primary opioid-based anesthetic is chosen, additional opioid should be administered on initiation of CPB to offset dilution from the pump prime and to maintain adequate opioid plasma concentrations. Awareness during adult cardiac surgery has been reported when amnestic agents are not used. Although small children may be unable to describe such events, the potential for awareness during pediatric cardiac surgery should not be underestimated. To prevent awareness, isoflurane may be administered through the membrane oxygenator with an anesthetic vaporizer or intravenous midazolam (0.2 mg/kg) may be administered. Alternatively propofol may be given by infusion during the bypass period to reduce the possibility of awareness.

Institution and Separation from Bypass

Before initiation of CPB, the surgeon requests heparin to be given. After administration of heparin (preferably flushed through a central venous catheter) but before the initiation of bypass, the ACT should be determined. The ACT measurement should be at least three times greater than the baseline value. When bypass is started, any additional anesthetic drugs should be administered, and ventilation should cease. Both hypertension and hypotension may complicate bypass. Blood pressure may be controlled within the normal range using α-adrenergic blockers or agonists such as phenylephrine and phentolamine. The child is usually cooled at this stage, using the nasopharyngeal temperature as a guide. If the heart is to be stopped, cardioplegia is given by the perfusionist after the aorta is cross-clamped to provide myocardial protection during the period of ischemia. Cardioplegia is usually repeated every 20 to 30 minutes, although it is not required if the surgery is performed while the heart is beating. Myocardial damage is related to the duration of the aortic cross-clamping and the effectiveness of the myocardial protection.

At an appropriate time during the surgery, the cross-clamp is removed, and perfusion to the heart is restored. The heart usually starts to beat in normal sinus rhythm, although this is not always the case. In the early phase of reperfusion, it is possible for various degrees of heart block to occur. However, these effects are usually short-lived, and as the effects of cardioplegia wear off, normal sinus rhythm is usually restored. In addition, heart block may result from damage to the conducting system during surgery.

After release of the cross-clamp, any inotropes or vasodilators that are required are usually started. Rewarming may have begun before release of the cross-clamp, but more commonly, the child is rewarmed after release of the clamp.

When the child has adequately rewarmed, as reflected by a normal core and minimal core-peripheral temperature difference, good heart function has returned, the child’s lungs are adequately ventilated, and any inotropes required have been started, the child is ready to be separated from bypass. If a TEE probe is in place, the heart should be scanned for the presence of air. If air is present, further de-airing should occur before attempting to come off bypass. In the initial stages after separating from bypass, additional volume can be administered by the perfusionist through the aortic cannula, usually under the direction of the surgeon or anesthesiologist. Many centers institute modified ultrafiltration at this point. This involves taking arterial blood from the aortic cannula and passing it through the ultra-fine filter. This blood, which is oxygenated and warm, is then reinfused into the right atrium. When this process is complete, a thorough TEE examination can be undertaken.

When the team is satisfied with the TEE result, the surgeon asks for protamine to be administered. Before this is done, the perfusionist and the surgical team should be informed that protamine is about to be administered. The surgeons should remove any pump suckers from the field, and the perfusionist should stop all pump suction. This is done to ensure that no protamine enters the bypass circuit in case it is necessary to go back on bypass for any reason. The ACT can be checked along with the blood gas analysis. The ACT should return to levels before bypass. Any blood products required are usually given after the administration of protamine, usually while the surgeons are achieving hemostasis. As soon as the chest is closed, the child can then be transferred to the ICU.

Control of Systemic and Pulmonary Vascular Resistance during Anesthesia

In some children with hypoplastic left heart syndrome (HLHS) who present for a Norwood procedure, excessive blood flow to the lungs resulting from a relatively low PVR and a relatively high SVR steals blood from the systemic circulation, leading to hypotension, myocardial ischemia, and progressive acidosis. However, when the reverse occurs and the PVR is greater than the SVR, the child develops progressive desaturation. Similar pathophysiology exists with other duct-dependent circulations and to some extent with other shunting lesions. It may prove difficult to manipulate the SVR and PVR predictably because control of PVR is poorly understood, vasoactive drugs usually are distributed on both sides of the circulation, and pharmacologic attempts to modify shunting have produced unpredictable results.⁷⁵ Despite these problems, several techniques have proved useful in manipulating the relative PVR and SVR. Potent inhalational anesthetics appear to reduce SVR more than PVR. PVR is decreased in children by increasing inspired oxygen to 100% and by hyperventilation to a pH of 7.6 or greater. Positive end-expiratory pressure, acidosis, hypothermia, and the use of 30% or less inspired oxygen can increase PVR. Because vasoconstrictors such as phenylephrine increase SVR more than PVR, they are effective acutely in reducing right-to-left shunting and increasing left-to-right shunting in the operating room.

During cardiac surgical procedures, a direct method of selectively increasing PVR or SVR is to have the surgeon place partially obstructing tourniquets around pulmonary arteries or the aorta to increase resistance so that flow to the opposite side of the circulation increases. Although these are only temporary measures, they may reestablish a better relative balance of resistances and a more normal physiology in a deteriorating clinical situation.

Anesthetic Drugs Used in Pediatric Cardiac Anesthesia

Inhalational Agents

Sevoflurane

Sevoflurane is the induction agent of choice in pediatric anesthesia.^76,⁷⁷ It is associated with little myocardial depression or dysrhythmias.⁷⁸^–⁸⁰ It has specific advantages over halothane when used in children with CHD, particularly in children younger than 1 year of age and in cyanotic children.⁸¹ In contrast to halothane, sevoflurane causes no reduction in heart rate at 1.0 and 1.5 minimal alveolar concentrations (MACs) in healthy children compared with awake values.⁸² However, at greater concentrations, it can slow the heart rate and cause respiratory depression. Both features are important in children with CHD because a slow heart rate reduces cardiac output and hypoventilation leads to hypercarbia and hypoxia, which can increase PVR. In the absence of nitrous oxide, sevoflurane causes less depression of myocardial contractility than halothane during induction of anesthesia. Sevoflurane does cause a mild decrease in SVR, but in common with halothane and isoflurane, it does not perturb the shunt between the right and left sides of the heart through an ASD or VSD when it is given in anesthetic concentrations of about 1 MAC in 100% oxygen.⁸³ Sevoflurane has caused conduction abnormalities in susceptible patients.⁸⁴ It should also be used with great caution in children with severe ventricular outflow tract obstruction (see Chapter 6).⁸⁵

Isoflurane

At equipotent concentrations, isoflurane causes similar hemodynamic depression in neonates and infants compared with halothane. Isoflurane typically is not used for induction of anesthesia because of the high frequency of laryngospasm (greater than 20%).⁸⁶ Inadequate ventilation because of laryngospasm or other causes quickly leads to large increases in PVR due to hypoxemia and hypercarbia. This increase in PVR and the resulting pulmonary hypertension is poorly tolerated in small children with heart disease, especially in the presence of right-to-left shunting (see Chapter 6).

Halothane

In the United States and the United Kingdom, the use of halothane has all but ceased, but it is still widely used in other parts of the world. It is included here for completeness. Uptake of halothane in infants younger than 3 months of age is more rapid than it is in adults. This also is the case for the uptake of halothane by the myocardium.⁸⁷ Although the effects of halothane on the human neonatal myocardium are unknown, young rodents have a reduced cardiovascular tolerance for halothane but require greater amounts for anesthesia.⁸⁸ Studies have shown a significant incidence of hypotension with bradycardia in infants with normal cardiovascular systems during induction with halothane.⁸⁹ During induction of anesthesia in normal infants, halothane decreases the cardiac index to 73% of awake values at 1.0 MAC and to 59% at 1.5 MAC.⁹⁰ The MAC for halothane in infants 1 to 6 months of age is the greatest of any age group.⁹¹ This increased anesthetic requirement in infants, combined with the immaturity of their cardiovascular system, explains in part the relative cardiovascular intolerance of halothane by infants. Atropine has been used intramuscularly before induction to partially compensate for the myocardial depression of halothane by reducing bradycardia and hypotension. Although halothane may produce some degree of hypotension, an increase in arterial saturation in children with cyanotic CHD may occur.⁹²

A careful induction with sevoflurane is usually well tolerated in children with mild to moderate heart disease. However, large concentrations of potent inhalational agents may be an unwise choice for induction in young infants with severe cardiac disease. In children of any age with marginal cardiovascular reserve and in those with severe desaturation of systemic arterial blood due to right-to-left shunting, inhalational anesthetic-induced myocardial depression and systemic hypotension are poorly tolerated. A more appropriate use of these anesthetic agents in children with severe heart disease is the addition of low concentrations of the inhalational agent to control hypertensive responses after an intravenous induction (see Chapter 6).

Nitrous Oxide

Nitrous oxide should be avoided for maintenance of anesthesia in children with CHD because of the risk of enlarging intravascular air emboli and the potential to increase the PVR. Nitrous oxide may expand microbubbles and macrobubbles, increasing obstruction to blood flow in arteries and capillaries. In all children with right-to-left shunts, there is a potential for these bubbles to be shunted directly into the systemic circulation and coronaries. Care must be taken to ensure that no air bubbles are accidentally injected into the veins. Adverse outcomes after coronary air embolism are exacerbated by nitrous oxide.⁹³ The hemodynamic effects of venous air embolism are increased by nitrous oxide, even without paradoxical embolization.⁹⁴ In children with preexisting right-to-left shunts, paradoxical air embolism is clearly a potential problem; but even those with large left-to-right shunts can transiently reverse their shunts. This is particularly true during coughing or a Valsalva maneuver, when the normal transatrial pressure gradient is reversed. Several studies have demonstrated right-to-left shunting of microbubbles of air after injection of saline into the right atrium during these maneuvers.⁹⁵^–⁹⁷ Because coughing and Valsalva maneuvers may occur during anesthesia induction, even the most rigorous attention to avoiding air bubbles in intravenous lines may not prevent small amounts of air from reaching the systemic circulation. Microbubbles have also been observed after CPB.⁹⁸

Nitrous oxide can increase PVR in adults.^99,¹⁰⁰ However, in a 50% inspired concentration, it does not appear to affect PVR or pulmonary artery pressure in infants.¹⁰¹ Nitrous oxide mildly decreases cardiac output at this concentration.¹⁰² Avoidance of the use of nitrous oxide has been suggested in children with limited pulmonary blood flow, pulmonary hypertension, or depressed myocardial function. In the well-compensated child who does not require 100% inspired oxygen, nitrous oxide (usually at concentrations of 50%) may be used during induction of anesthesia but discontinued before tracheal intubation. If a reduced inspired oxygen concentration is indicated to maintain an appropriate balance between PVR and SVR after tracheal intubation, air may be added to the inspired gas mixture (see Chapter 6).

Intravenous Induction Agents

Ketamine

Ketamine is a dissociative anesthetic agent that is a good analgesic. It increases blood pressure, heart rate, and cardiac output. Although the mechanism of the stimulation of blood pressure and heart rate has not been established, it is thought to stimulate the release of endogenous stores of catecholamines. Ketamine exerts a negative inotropic effect on the denervated heart.¹⁰³ I think that this combination of effects makes it a poor choice for children in whom sympathetic stimulation may already be maximal, such as in those with severe cardiomyopathy. It is also a poor choice if tachycardia is undesirable, such as in a child with aortic stenosis. Ketamine is thought to have minimal effect on PVR in children with CHD as long as the airway and ventilation are well preserved,^104,¹⁰⁵ although it has occasionally increased PVR in children undergoing cardiac catheterization. Ketamine is quite a versatile anesthetic that may be administered intramuscularly and orally when intravenous access is difficult or an inhalational induction is contraindicated. The usual intravenous dose of 2 mg/kg produces a very predictable response, and an intramuscular dose of 8 to 10 mg/kg (combined with 0.1 mg/kg of intramuscular midazolam) is less predictable. The oral dose of ketamine is 5 to 6 mg/kg. The use of ketamine varies greatly from one institution to another, with some units using it extensively and others using it rarely (see Chapter 6).

Etomidate

Etomidate is a very safe drug, with an LD₅₀ to ED₅₀ ratio of 26 in animals models.¹⁰⁶ This ratio indicates that the lethal dose (LD) is 26 times greater than the effective dose (ED). It is a short-acting anesthetic with little effect on systemic blood pressure, heart rate, and cardiac output after a single dose in healthy children.¹⁰⁷ Etomidate has a favorable hemodynamic profile even when used in shocked children and appears to have a low risk of clinically important myoclonus or status epilepticus, pain on intravenous injection, and nausea and vomiting.^108,¹⁰⁹ The major concern about etomidate is the increased mortality rates reported when it is administered as a continuous infusion. This grave side effect has been attributed to adrenal suppression.¹¹⁰^–¹¹² The inhibition of steroid synthesis occurs after a prolonged infusion and after a single dose of etomidate, and it has created a controversy about its use as an anesthetic agent, particularly in the ICUs in some jurisdictions.¹¹³ However, newer analogues of etomidate have addressed these deficiencies and may lead to a surge in its use in the future (see Chapter 6).

Propofol

Propofol is a rapidly acting intravenous hypnotic agent that may be administered as a single dose or by continuous infusion. It has no analgesic properties. Propofol has mild antiemetic properties.¹¹⁴ Its short duration of action is the result of rapid redistribution and metabolism, which also allows the drug to be given by continuous infusion without accumulation. Induction doses decrease SVR, blood pressure, and cardiac output; the effect on heart rate varies. The ED₅₀ for propofol in infants and small children is greater than it is in adults.¹¹⁰^–¹¹⁷ If propofol is given very slowly, smaller doses are required to achieve the anesthetic state, although the induction time increases. A slower infusion also results in more stable hemodynamics.¹¹⁸ Pain on injection and involuntary movement after intravenous propofol have been concerns that have been overcome (see Chapter 6). Although propofol can be used safely in children with CHD, it is typically avoided as an induction agent in those with severe CHD because of its effects on SVR and blood pressure. It should be avoided in those with a fixed cardiac output such as severe aortic or mitral stenosis because it may cause severe hypotension. It can be used by infusion during CPB to reduce awareness and may be particularly useful if an early extubation is planned (see Chapter 6).

Opioids

Fentanyl

As in adults with severe cardiac disease, intravenous fentanyl combined with pancuronium and 100% oxygen or air and oxygen provides an excellent induction technique in very sick children with CHD, although it is not an amnestic. Inclusion of intravenous midazolam or another amnestic agent is strongly urged to avoid awareness. In neonates and infants, the use of high-dose opioid anesthesia provides excellent hemodynamic stability, with suppression of the hormonal and metabolic stress response.^119,¹²⁰ When fentanyl or other opioids are combined with nitrous oxide, the negative inotropic effects of nitrous oxide may be evident, particularly in sicker children.¹²¹ The high-dose fentanyl technique is effective in preterm neonates undergoing ligation of a PDA.¹²² In high-risk, full-term neonates and in older infants with severe CHD, the high-dose fentanyl technique in doses of up to 75 µg/kg, combined with pancuronium maintains stable hemodynamics during induction, tracheal intubation, and surgical incision.¹²³ Oxygen saturation is well maintained and often improves during induction, even in cyanotic children.¹²⁴ The cardiac index, SVR, and PVR in infants given 25 µg/kg of fentanyl do not change significantly.¹²⁵ Combining pancuronium with fentanyl is desirable because the vagolytic effects of pancuronium offset the potential vagotonic effects of fentanyl. The hemodynamic stability reported in infants with the combination of high-dose fentanyl and pancuronium may not be replicated when other muscle relaxants are used (see Chapter 6).¹²⁶

Sufentanil

Sufentanil (5 to 20 µg/kg), an alternative to fentanyl, is 5 to 10 times more potent than fentanyl but has a large margin of safety.¹²⁷ It is highly lipophilic and is rapidly distributed to all tissues. It is infrequently used in infants and children with CHD.

Remifentanil

Remifentanil is an ultra-short-acting opioid that is rapidly metabolized in the plasma and tissue by nonspecific esterases to an inactive metabolite. It has a very brief elimination half-life, with a context-sensitive half-life of only 3 minutes, independent of the duration of infusion. In pediatric cardiac surgery, it is an attractive alternative to fentanyl that provides intense analgesia during the most stimulating parts of surgery but facilitates rapid awakening and weaning from mechanical ventilation without residual opioid effect. Its pharmacodynamics are unaffected by CPB.¹²⁸ It provides stable hemodynamic conditions in children, although there is a tendency toward bradycardia and systemic hypotension.¹²⁹^–¹³¹ It has no negative inotropic effect, even in the failing heart.¹³²

A significant concern is the development of acute tolerance with increasing analgesic requirements after discontinuing remifentanil.¹³³^–¹³⁵ Some studies have suggested that this is not clinically important.¹³⁶ Strategies to prevent tolerance to remifentanil have included intravenous magnesium infusions as well as nitrous oxide.^137,¹³⁸ Remifentanil is also used for prolonged sedation of children in the ICU. Many units have moved toward early extubation and discharge from the ICU after cardiac surgery (i.e., fast tracking), and remifentanil is a useful drug in this setting (see Chapter 6). Consideration must be given to transitioning to a longer-acting opioid before discontinuation of remifentanil.

Neuromuscular Blocking Drugs

Pancuronium has been studied in depth in children with CHD. When administered over a 60- to 90-second interval, pancuronium maintains heart rate and blood pressure.¹⁴⁰ An intubating bolus dose of pancuronium may produce tachycardia and increase cardiac output. This bolus dose effect is sometimes desirable to support cardiac output in infants in congestive heart failure because their stroke volume is fixed. Pancuronium may be the muscle relaxant of choice when high-dose opioid techniques are used to offset the vagotonic effects of opioids such as fentanyl. Other muscle relaxants are also widely used, particularly if they are to be extubated in the operating room or early in the ICU.

Long-Term Neurocognitive-Developmental Outcomes Associated with Anesthesia

Concerns have been raised about the possibility that many of the anesthetic agents such as inhalational anesthetics, propofol, ketamine, and midazolam may cause long-term neurocognitive-developmental problems in neonates and young infants.¹³⁹ This effect is thought to result from the neuronal apoptosis caused by these agents. The opioids have not been implicated in these changes, but this may change in time. There is no evidence to directly link anesthetic exposure in infancy to long-term neurocognitive defects. There is much ongoing research in this area (see Chapter 23).

Regional Anesthesia

The use of regional anesthesia to provide pain relief during and after cardiac surgery in adults also reduces the stress response to surgery and may reduce morbidity and mortality. In adults undergoing cardiac surgery, the benefits of regional anesthesia include earlier extubation, fewer respiratory complications, a reduction in renal failure, fewer strokes, and less myocardial damage after CPB.¹⁴¹^–¹⁴³ In animals, thoracic epidural anesthesia reduces myocardial damage after coronary occlusion.¹⁴⁴ The same benefits may be achieved by using intrathecal (spinal) analgesia. High spinal anesthesia using bupivacaine reduces the stress response to CPB and β-adrenergic dysfunction and improves cardiac performance after cardiac surgery in adults.¹⁴⁵

Good research into regional anesthesia and analgesia in pediatric cardiac surgery is limited. Caudal morphine has been used to provide postoperative analgesia and has produced good analgesia for about 6 hours while reducing analgesic requirements for up to 24 hours.¹⁴⁶ Two retrospective studies in children^147,¹⁴⁸ included a variety of regional anesthetic techniques. Most children were extubated in the operating room, although ∼4% of them required reintubation within 24 hours. Adverse effects included emesis (39%), pruritus (10%), urinary retention (7%), postoperative transient paresthesia (3%), and respiratory depression (1.8%). The rate of adverse effects was less with a thoracic catheter epidural approach compared with various caudal, lumbar epidural, and spinal approaches. Hospital duration of stay was unaffected by the presence of regional anesthesia complications. Although this study appears to indicate that regional analgesia is safe, the numbers in the study are too small to conclude that regional analgesia is safe for pediatric cardiac surgery.

The use of regional anesthesia in cardiac surgery for children remains controversial.^149,¹⁵⁰ The main concern is the risk of bleeding and the potential for disastrous neurologic complications. The risks may be greater in children than in adults because of the presence of collateral vessels, increased venous pressure, coagulopathy related to cyanosis, and the use of aspirin. There remain many unanswered questions regarding neuraxial block in children, such as the true incidence of epidural hematoma, the time delay required between placement of the epidural catheter and full anticoagulation, and the correct management of a bloody tap. The estimated risk of epidural hematoma during cardiac surgery in adults is 1 case per 1000 patients and 1 case per 2400 patients for spinal and epidural block, respectively.¹⁵¹ Whether the risks are similar or greater in children cannot be determined because, the numbers of children involved in studies are too small. A large, randomized, prospective study to evaluate a true risk-benefit ratio without bias is needed; until such data are available, various commentators have advised great caution with the use of regional analgesia for cardiac surgery, and some have suggested that it may not be possible to perform the study required because of ethical considerations.¹⁵²

Fast Tracking

Fast tracking refers to abbreviating the perioperative period of children undergoing cardiac surgery. It should include every phase of the child’s journey from referral and preoperative evaluation to less invasive surgery, early weaning from respiratory support, extubation, and discharge from the ICU and hospital.

Early extubation of pediatric patients after cardiac surgery offers advantages in terms of cost and reduced morbidity associated with longer ICU stays.¹⁵³^–¹⁵⁷ The success of this approach depends on the close teamwork of a multidisciplinary team, with every member of the team working toward the same goal. Successful fast tracking usually requires the development of care pathways to ensure that the quality of patient care is not compromised.¹⁵⁸ Early extubation and discharge from the ICU requires preplanning and the adoption of a technique that facilitates this goal. The use of very large doses of fentanyl is not appropriate; alternative techniques have been used, including smaller doses of fentanyl in combination with inhalational agents^159,¹⁶⁰ or the use of remifentanil in combination with inhalational agents or with propofol. Others have advocated regional anesthesia as a means of speeding extubation, but this approach remains controversial. It is important to choose a neuromuscular blocking drug with a shorter duration of action than pancuronium to ensure that it is easy to reverse the neuromuscular block at the end of surgery. Other important considerations to ensure that early extubation is a success include adequate pain relief in the form of intravenous paracetamol (where available), patient-controlled or nurse-controlled analgesia, and antiemetics because nausea appears to be more of a problem in children who are extubated early.

Some clinicians advocate extubating the trachea in the operating room, whereas others advocate waiting until the child is in the ICU. Delaying the extubation until the child is in the ICU may save operating room time and may reduce the risks of cardiovascular instability, bleeding, and hypothermia.¹⁶¹ Despite these concerns, the tracheas of many children are extubated in the operating room with good outcomes.

Cardiopulmonary Bypass

Cardiopulmonary bypass is discussed in Chapter 17.

Stress Response to Cardiac Surgery

Cardiac surgery and CPB are altered physiologic conditions associated with exaggerated stress responses characterized by the release of numerous metabolic and hormonal substances, including catecholamines, cortisol, growth hormone, prostaglandins, complement, glucose, insulin, and β-endorphins.^162,¹⁶³ The cause of the elaboration of these substances is multifactorial: contact of blood with foreign surfaces, low perfusion pressure, anemia, hypothermia, myocardial ischemia, low levels of anesthesia, and nonpulsatile flow. Other factors that contribute to the increase in stress hormones are delayed renal and hepatic clearance and exclusion of the pulmonary circulation during extracorporeal circulation.¹⁶⁴

Neonates of all viable gestational ages, older infants, and children have nociceptive systems that are sufficiently developed and integrated with brainstem cardiovascular control centers to trigger humoral and circulatory responses to pain and stress.¹⁶⁵ Substantial humoral, metabolic, and cardiovascular responses to painful and stressful stimulation during surgery have been documented in neonates of all gestational ages and in older infants.^166,¹⁶⁷ Hormonal stress responses in neonates subjected to cardiac and noncardiac operations are threefold to fivefold greater than those in adults after similar surgeries. Circulatory responses to stressful stimuli in children include systemic and pulmonary hypertension.

Humoral stress responses are particularly extreme during and after cardiac surgery. These responses are characterized by increases in circulating catecholamines, glucagon, cortisol, β-endorphins, growth hormone, and insulin; circulating concentrations of catecholamines may increase by as much as 400% over baseline preoperative concentrations. This is evidence of a massive activation of sympathetic outflow in response to surgical stimulation. Some of these responses may continue for several days postoperatively.¹⁶⁸

It has been suggested that such extreme stress responses and neuroendocrine activation may be associated with greater morbidity and mortality. In adults, intraoperative adrenergic activation of 50% above baseline is associated with significant postoperative alterations in β-adrenergic receptor function, including increased β-receptor density and decreased receptor affinity. Mortality among adults with severe congestive failure is associated with increased levels of hormones regulating cardiovascular function, including aldosterone, epinephrine, and norepinephrine.¹⁶⁹ In neonates undergoing cardiac surgery, increased concentrations of stress hormones may be associated with increased mortality rates.¹⁶⁸

The metabolic response to stress in children includes increased oxygen consumption, glycogenolysis, gluconeogenesis, and lipolysis. These metabolic responses cause substantial intraoperative and postoperative catabolism. The metabolic responses are usually related to changes in plasma cortisol, catecholamines, and other counterregulatory hormones such as glucagon and growth hormone. The most prominent clinical effects that result from activation of these processes are perioperative hypoglycemia and hyperglycemia, lactic acidemia, and negative nitrogen balance extending well into the postoperative period. Neonates and infants tolerate such metabolic derangements poorly. Their impaired tolerance is the result of a relative lack of endogenous reserves of carbohydrates, proteins, and fats; the large metabolic cost of rapid growth; a high obligate requirement for glucose by the relatively large brain; the immature hormonal control of intermediary metabolism; and the limited functional capabilities of immature enzyme systems in the metabolic organs. Severe stress responses superimposed on the normal neonatal and infant physiology may be poorly tolerated. However, it remains unclear whether these metabolic alterations may provide some beneficial effects for mobilizing the bodily resources to provide a metabolic milieu for healing tissues or they are purely maladaptive, resulting in detrimental effects on postoperative outcome.

Another factor is the potential effect of stress-induced hyperglycemia on the neurologic outcome. Neonates and young infants are capable of substantial rates of glucose production, mainly from glycogenolysis and gluconeogenesis during surgical stress that can result in hyperglycemia. Such hyperglycemic responses may be associated with poorer neurologic outcomes, particularly after a period of cerebral ischemia.¹⁷⁰ The use of high doses of fentanyl (more than 50 µg/kg) has reduced the hormonal stress response and resultant hyperglycemia and may lessen the risk of neurologic injury.¹⁷¹

In sufficient doses, opioids can blunt the stress responses in neonates, infants, and adults.¹⁷²^–¹⁷⁴ This blunting results in a more normal, homeostatic humoral and metabolic milieu in the circulation by reducing neuroendocrine activation and levels of regulating hormones. In infants, the use of high-dose opioids for major surgical procedures and postoperative sedation substantially attenuates the neuroendocrine response to surgically induced pain and stress. Catecholamine release that results from intraoperative stress responses may predispose the vulnerable myocardium to dysrhythmias. In neonates with HLHS, sudden ventricular fibrillation occurred in 50% during surgical manipulation under halothane anesthesia. This incidence was dramatically reduced when high doses of fentanyl were introduced as the primary analgesic/sedative.¹⁷⁵ With the use of high-dose opioids, intraoperative ventricular fibrillation has virtually disappeared as a problem in this group of neonates.¹⁷⁶ In several studies, opioids have been shown to increase the ventricular fibrillation threshold in isolated cardiac Purkinje fibers and to alter action potential duration similar to that with class III antiarrhythmic agents.^177,¹⁷⁸ Even electrophysiologic events in the neonatal heart, in addition to humoral and hemodynamic responses, may be altered by using high-dose fentanyl anesthesia to attenuate the effects of pain and stress.

Reducing the Stress Response to Surgery and Bypass

Corticosteroids

Corticosteroids are used in many centers in an attempt to reduce the inflammatory response to surgery and bypass.¹⁷⁹ However, there is a huge variability in the formulation of the corticosteroids used, the doses, the timing of administration, and the indications for their use. The literature lacks adequate evidence for the use of corticosteroids, although several small studies in humans and animals suggest they confer a benefit.^180,¹⁸¹ Many investigators have called for a large multicenter study to determine the benefit of corticosteroids before bypass and the optimal dose and timing.¹⁸²

Aprotinin

Aprotinin, which was originally used to reduce bleeding after CPB, is now also appreciated to confer significant antiinflammatory effects.¹⁸³^–¹⁸⁷ In adults, it reduces mortality and length of ICU stay.¹⁸⁸ In children, it improves pulmonary function in the postoperative period and reduces the time to extubation and ICU stay. However, aprotinin is no longer available for routine use in the United States or continental Europe. In the United Kingdom, it is available for use on a named patient basis, but its use has been dramatically reduced as a result.

Allopurinol

Allopurinol is thought to provide protection against oxygen free radicals during reperfusion by inhibiting xanthine oxidase. It reduces oxygen free radical production and may reduce neurologic and cardiac damage after deep hypothermic cardiac arrest.¹⁸⁹ This strategy does not appear to have developed widespread use.

Ischemic Preconditioning

The heart is capable of short-term rapid adaptation to brief ischemia such that during a subsequent, more severe ischemic insult, myocardial necrosis is delayed. The infarct-delaying properties of ischemic preconditioning have been observed in all species studied. Five minutes of ischemia is sufficient to initiate preconditioning, and the protective period lasts for 1 to 2 hours. Laboratory experiments have demonstrated that the stimulation of adenosine receptors initiates preconditioning and the intracellular signal transduction mechanisms involve protein kinase C and adenosine triphosphate (ATP)-dependent potassium channels, although there may be some differences between species. An analysis of studies of myocardial infarction in humans has demonstrated that some adults who report having had angina in the days before infarction have a better outcome after their infarction in part due to the ischemic preconditioning. More direct evidence has come from an investigation of adults undergoing percutaneous transluminal angioplasty in whom the ST-segment changes induced by balloon inflation were more marked during the first inflation than the second. In adults undergoing coronary artery bypass grafting, the decline in ATP content during the first 10 minutes of ischemia was reduced in those subjected to a brief preconditioning protocol.¹⁹⁰^–¹⁹⁴

It may be possible to protect organs other than the heart by ischemic preconditioning. It may even be possible to protect organs remotely by producing a period of ischemia in one area such as a limb, which then confers protection to remote organs.¹⁹⁵ Cheung and coworkers have demonstrated that the use of a blood pressure cuff to produce short periods of limb ischemia can produce beneficial effects on the heart, lungs, and generalized inflammatory response.¹⁹⁶

Glucose-Insulin and Potassium

The use of glucose-insulin and potassium has been advocated for more than 40 years in adult cardiac surgery. It is thought to protect the myocardium from the effects of ischemia caused by aortic cross-clamping.¹⁹⁷^–²⁰⁰ Its effects have not been studied in children undergoing cardiac surgery.

Anesthesia Considerations for Specific Cardiac Defects

Discussion of anesthesia considerations for repair of every form of CHD is beyond the scope of this chapter. However, a brief discussion of the problems that may be encountered during repair of the more common congenital heart lesions is presented. It is useful to group lesions together because the management principles can be applied more generally within groups (Table 15-2).

TABLE 15-2 Classification of Congenital Heart Disease

Simple Left-to-Right Shunt: Increased Pulmonary Blood Flow

Atrial septal defect (ASD)

Ventricular septal defect (VSD)

Patent ductus arteriosus (PDA)

Endocardial cushion defect (e.g., atrioventricular septal defect [AVSD])

Aortopulmonary window (AP window)

Simple Right-to-Left Shunt: Decreased Pulmonary Blood Flow with Cyanosis

Tetralogy of Fallot (TOF)

Pulmonary atresia

Tricuspid atresia

Ebstein anomaly

Complex Shunts: Mixing of Pulmonary and Systemic Blood Flow with Cyanosis

Transposition of the great arteries (TGA)

Truncus arteriosus

Total anomalous pulmonary venous connection (TAPVC)

Double-outlet right ventricle (DORV)

Hypoplastic left heart syndrome (HLHS)

Obstructive Lesions

Interrupted aortic arch

Simple Left-to-Right Shunts

Simple left-to-right shunts increase pulmonary blood flow. If the shunt is large, blood flow to the lungs can be as much as threefold to fourfold greater than normal, resulting in volume loading of the right heart. This can lead to right atrial enlargement and right ventricular enlargement that is perhaps associated with tricuspid and pulmonary regurgitation. This combination results in cardiac failure (Table 15-3).

TABLE 15-3 Clinical Features of Cardiac Failure in Children

Failure to thrive

Difficult feeding

Breathlessness

Recurrent chest infection

Medical management of these children is primarily achieved with diuretics. If pulmonary blood flow is large and left untreated, pulmonary vascular disease begins to develop, resulting in pulmonary hypertension. In the early stages, the changes are reversible, but in time, the changes may become irreversible.²⁰¹^–²⁰⁶ Eisenmenger syndrome refers to severe pulmonary hypertension that leads to suprasystemic pulmonary artery pressures that cause the shunt to reverse, leading to cyanosis. The previous left-to-right shunt reverses to become a right-to-left shunt. At this point, the child’s condition becomes inoperable.

Increasingly, definitive surgery is being performed at a younger age to reduce the risk of developing pulmonary vascular disease. If early definitive surgery is not possible, a pulmonary artery band is applied to reduce pulmonary blood flow. This is performed through a sternotomy incision but without the need for CPB. This provides the infant the opportunity to grow, postponing the need for definitive surgery without increasing the risk of developing pulmonary hypertension. In the presence of significantly increased pulmonary blood flow, pulmonary vascular disease is often severe and irreversible by 1 year of age. Definitive surgery should be performed between 3 and 6 months of age to avoid this complication.

Atrial Septal Defect

ASD is a common heart defect in children, occurring in 1 of 1500 live births and accounting for approximately 10% of all CHD.²⁰⁷ Several types of ASDs exist.

Patent foramen ovale (PFO) is a normal fetal communication between the two atria that usually closes soon after birth. The PFO remains patent in up to 30% of people. PFO is usually left untreated in children.

Primum ASD (Fig. 15-1, A) is located in the inferior part of the atrial septum close to the AV valve and may be associated with a cleft mitral valve. This is a variant of AV septal defect (AVSD).

Secundum ASD (see Fig. 15-1, B) is found in the region of the fossa ovalis and results from a deficiency in the septum secundum.

Sinus venosus ASD (see Fig. 15-1, C) occurs high in the atrial septum, often close to the opening of the SVC. It may be associated with partial anomalous pulmonary venous drainage.

Coronary sinus ASD (i.e., unroofed coronary sinus) is a defect in the atrial wall allows blood to flow from the left atrium to right atrium through the coronary sinus.

Common atrium has a complete absence of the atrial septum. The AV valves may be abnormal or unaffected.

FIGURE 15-1 A, Diagram of a primum atrial septal defect (ASD) with the great vessels removed to show the left-to-right shunt through the defect and a cleft of the mitral valve (MV), also called a partial atrioventricular septal defect (AVSD). B, Diagram of a secundum ASD with the great vessels removed to show the left-to-right shunt through the defect. C, Diagram of a sinus venosus ASD shows the left-to-right shunt through the defect close to the superior vena cava (SVC) and an anomalous pulmonary vein (PV) draining to the right atrium (RA). IVC, Inferior vena cava; LA, left atrium; LV, left ventricle; RV, right ventricle.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Many ASDs can be closed using a percutaneous, transcatheter device. PFO and secundum ASDs are most commonly closed using this technique.

Anesthesia Considerations

These children can frequently be extubated on the operating table or early in the ICU, and smaller doses of opioids can be used. Alternatively, short-acting drugs (e.g., remifentanil) administered by infusion and possibly in combination with propofol are useful if early extubation is planned.

The problems of postoperative pulmonary hypertension are seldom encountered.

Ventricular Septal Defect

VSD is the most common congenital defect in children, occurring in 1.5 to 3.5 of 1000 live births and accounting for 20% of CHD (Fig. 15-2, A).²⁰⁸ Four types are described: subarterial (5%), perimembranous (80%), inlet (5%), and muscular (10%). If the flow through the VSD is small, it is referred to as restrictive, but if the flow is large, it is called unrestrictive. It is possible to close a small percent of VSDs using a percutaneous, transcatheter device.

FIGURE 15-2 A, Diagram of a ventricular septal defect (VSD) shows a left-to-right shunt. B, Diagram of a complete atrioventricular septal defect (AVSD) with the great vessels removed to show the left-to-right shunt through both atrial and ventricular components of the defect and a single common atrioventricular (A-V) valve. Ao, Aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Anesthesia Considerations

Inotropic support may be required postoperatively.

Postoperative pulmonary hypertension may be a problem if the left-to-right shunt has been significant preoperatively or if the surgery is undertaken late.

Atrioventricular Septal Defect

AVSDs are also known as AV canal defects or endocardial cushion defects, and they result from a defect in the AV septum. The incidence is about 0.2 cases per 1000 live births, and they account for about 3% of CHD. They are commonly associated with trisomy 21, TOF, and DiGeorge syndrome (Table 15-4). Two common types of AVSD exist:

Partial AVSD usually consists of a primum ASD with a cleft in the anterior mitral valve leaflet (see Fig. 15-1, A).

Complete AVSD consists of a large septal defect with atrial and ventricular components and a common AV valve (see Fig. 15-2, B).

TABLE 15-4 Clinical Features and Concerns of DiGeorge Syndrome

Absent or small thymus

T-cell abnormality with associated immunodeficiency

Hypoparathyroidism with associated hypocalcemia

Dysmorphic features, particularly a small mouth

Increased surgical morbidity and mortality

Irradiated blood products needed to prevent graft-versus-host disease

Other descriptions of AVSD refer to balanced or unbalanced conditions, depending on whether the AV valve is stenotic or atretic or some of the valve chordae are straddling (i.e., crossing to the other side of the ventricular septum. The hemodynamic effects associated with AVSD include shunting at the atrial or ventricular level and AV valve regurgitation.

Anesthesia Considerations

If the child has trisomy 21, the anesthesia implications need to be managed.

Inotropes are frequently required.

Postoperative pulmonary hypertension may occur.

TEE is particularly helpful in assessing the repair of the left AV valve.

Heart block may occur postoperatively.

Aortopulmonary Window

Aortopulmonary window is a rare CHD defect in which there is a communication between the main pulmonary artery and the ascending aorta, and it accounts for 0.1% of CHD (Fig. 15-3). Four types are classified according to the size and exact position of the defect.²⁰⁹ A left-to-right shunt is usually present. These children present with heart failure and are at risk for pulmonary vascular disease if not treated early. It is frequently associated with other cardiac and noncardiac anomalies:

VACTERL: vertebral anomalies, anal atresia, cardiac defect, tracheoesophageal atresia, renal anomalies, and limb abnormalities

CHARGE: coloboma of the eye and central nervous system anomalies, heart defects, atresia of the choanae, retardation of growth and development, genital or urinary defects, and ear anomalies

CATCH-22 association (i.e., mnemonic for DiGeorge syndrome): cardiac defect, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia (velocardiofacial syndrome), with 22q11 chromosome microdeletion (see Table 15-4)

FIGURE 15-3 Diagram of an aortopulmonary window shows a left-to-right shunt through the defect. Ao, Aorta; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Anesthesia Considerations

Postoperative pulmonary hypertension may be problematic.

Inotropes may be required.

Patent Ductus Arteriosus

The ductus arteriosus, a remnant from the fetal circulation, extends from the descending aorta to the main pulmonary artery and usually closes soon after birth. However, it remains patent in approximately 1 of 2500 live births and accounts for about 10% of all CHD (Fig. 15-4). In the fetus, blood from the right ventricle is directed into the pulmonary artery, but because of the high PVR, it flows into the descending aorta. After birth, the PVR decreases, and blood flows from the aorta to the lungs. PDA is common in preterm infants, and its presence may explain an ongoing requirement for mechanical ventilation. In these infants, a left thoracotomy is required to ligate or divide the PDA. It may also occur in older children; but at this age, percutaneous closure by an interventional cardiologist is the preferred approach. The anesthesia implications are similar to those of other lesions described with left-to-right shunts preoperatively.

FIGURE 15-4 The diagram of a patent ductus arteriosus shows a left-to-right shunt. Ao, Aorta, IVC, inferior vena cava; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

In many centers, PDA closure in preterm infants who weigh less than 1000 g and who are already mechanically ventilated is undertaken in the neonatal intensive care unit (NICU). This avoids the need to transfer these very small infants to the operating room and the associated problems, particularly hypothermia.

Preoperative requirements include the following:

Crossmatched blood

Antibiotics (risk of endocarditis)

Vitamin K

Particular perioperative risks include the following:

Difficulty ventilating or hemoglobin desaturation because of lung retraction

Tearing the PDA with massive hemorrhage

Inadvertent ligation of the aorta or pulmonary artery

Endocarditis

Paradoxical air embolism

Monitoring

Monitoring includes the use of all standard monitors, including end-tidal carbon dioxide assessment, and two additional pulse oximeters should be placed, one on the right hand and one on a lower limb. If the pulse is lost from the lower limb during a test clamping of the duct, it may indicate that the aorta has been clamped inadvertently. At my institution, all the requirements are stipulated in a protocol and monitoring and other requirements are in place before the arrival of the operating room team.

Invasive blood pressure monitoring is helpful if already established but is not usually placed if not already in place. Monitors used in non–operating room sites may not be compatible with the electrocautery equipment, resulting in loss of monitoring whenever the cautery is used.

Anesthesia Considerations

A dedicated intravenous line for fluids and drugs with a long (100 to 150 cm), low-caliber extension to allow access from a distance (space around the cots in NICU is limited)

High-dose opioids

Muscle relaxation

The tracheal tube should have only a small air leak. A large leak may prevent adequate ventilation during lung retraction (recheck security and correct position of the tip of the tube after repositioning in the decubitus position, before starting surgery).

Intercostal nerve block by surgeon at the completion of surgery

Glucose-containing fluids maintained at basal rates

Simple Right-to-Left Shunts

Tetralogy of Fallot

TOF is the most common cyanotic CHD defect and accounts for 6% to 11% of CHD. It has four features (Fig. 15-5):

VSD

Overriding aorta

Right ventricular outflow tract obstruction (RVOTO)

Right ventricular hypertrophy

FIGURE 15-5 The diagram shows the features of the tetralogy of Fallot: ventricular septal defect, overriding aorta, right ventricular hypertrophy, and pulmonary stenosis. Pulmonary and subpulmonary obstructions are shown. The result is right-to-left shunting leading to cyanosis. Ao, Aorta; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

The RVOTO ranges from mild to severe, and the level of the obstruction also varies. Commonly, a dynamic subpulmonary infundibular obstruction is present. Dynamic narrowing of the infundibulum is frequently the cause of hypercyanotic episodes, also known as tet spells, in which there is an increase in the shunting of blood from right to left. However, the RVOTO may also be at the level of the pulmonary valve or main or branch pulmonary arteries. Pulmonary atresia may exist as a variant of TOF. Children with pulmonary atresia who have well-developed pulmonary arteries derive their pulmonary blood supply from a PDA, but those with hypoplastic pulmonary arteries derive their pulmonary blood supply from major aortopulmonary collateral arteries.

The right-to-left shunt and cyanosis observed in children with TOF results from a combination of the RVOTO and VSD. The degree of hypoxemia depends on the relationship between the RVOTO and the SVR that determines the degree of right-to-left shunting. TOF may be associated with a large number of other cardiac and extracardiac anomalies. Extracardiac anomalies include DiGeorge syndrome (see Table 15-4) and trisomy 21.

Hypercyanotic Episodes

Hypercyanotic spells are episodes of cyanosis that occur in 20% to 70% of untreated children. They may be initiated by crying or feeding, and they may occur during anesthesia. The cause of these spells is unclear, but metabolic acidosis, increased Paco₂, circulating catecholamines, and surgical stimulation have all been implicated.

Management of a tet spell requires urgent intervention. Early and aggressive use of a vasoconstrictor is essential. Phenylephrine should be premixed and in a syringe for immediate use in a concentration of 100 µg/mL. The initial dose is 0.5 to 1 µg/kg, which is repeated and doubled in 1-minute intervals until a satisfactory response is observed. Preterm infants may require as much as 30 µg/kg. Management may require any of the following:

Surgical Management

The optimal surgical management of children with TOF remains controversial. The choice is between initial palliation with a systemic-to-pulmonary shunt followed by a complete repair when the infant is older and complete repair during the neonatal or early infant period. The current trend is toward early complete repair.^210,²¹¹ Complete repair involves closure of the VSD and relief of the RVOTO. Relief of the RVOTO most commonly requires a transannular patch that involves a right ventriculotomy. Right ventricular dysfunction is a particular problem after repair, and a degree of pulmonary regurgitation is usually present if a transannular patch has been done. Junctional ectopic tachycardia (JET) is a particular risk after complete correction.

Anesthesia Considerations

Systemic-to-Pulmonary Shunt.

The systemic-to-pulmonary shunt typically is a modified Blalock-Taussig shunt. This is a shunt from the subclavian artery to a branch pulmonary artery.

The patient is usually a neonate or small infant.

Sedative premedication is useful to prevent crying during induction, which may provoke a hypercyanotic spell.

There is a risk of a hypercyanotic spell during induction and surgery.

Inhalational or intravenous induction is appropriate.

Surgery is usually performed through a thoracotomy (left or right) but may be through a sternotomy.

CPB is not usually required.

Arterial and central venous access is required.

Tracheal tube should be snug, with no or minimal air leak because lung retraction during surgery makes ventilation very difficult.

The arterial line should not be in the arm on the side that the shunt will be placed because the subclavian artery will be clamped, and the arterial pressure will be lost.

Hemodynamic and respiratory disturbance can be problematic during surgery.

The surgeon may request a small dose of heparin.

Bleeding may occur after clamps are released; be prepared for a blood transfusion.

Postoperatively, the pulmonary blood supply predominantly depends on the size of the shunt. If the shunt is too small, the infant may have a low saturation level; if the shunt is too large, the infant may develop heart failure or pulmonary edema and hypotension.

Pulmonary blood flow also depends on systemic blood pressure; the greater the blood pressure, the more blood flows to the lungs and the higher the saturation.

Milrinone is often combined with norepinephrine because the norepinephrine increases the low diastolic pressure created by the shunt but does not produce the unwanted tachycardia seen with epinephrine.

A period of postoperative ventilation may be required.

Complete Repair.

If the child is scheduled for early complete correction with no systemic pulmonary shunt, the child is likely to be a neonate or small infant. These children remain at risk for hypercyanotic spells. However, if the child has had a shunt placed previously, he or she is likely to be older and much less likely to have a hypercyanotic episode. Some children with less severe disease may not require a shunt and may be operated on when they are a bit older because they remain asymptomatic. Good sedative premedication is important in those at risk for hypercyanotic episodes.

Both intravenous and inhalational induction agents are appropriate.

CPB is required.

Right ventricular dysfunction and pulmonary regurgitation may be postoperative problems.

Too much of an inotrope may worsen RVOTO postoperatively by dynamic narrowing of the RVOT.

Milrinone may be particularly useful because it promotes diastolic relaxation of the stiff right ventricle.

Pyrexia and excessive β-adrenergic stimulation may help precipitate junctional ectopic tachycardia postoperatively.

Surgeons frequently measure right ventricular pressure to assess the quality of the repair.

Perioperative echocardiography is useful in assessing repair and right ventricular function.

Complex Shunts.

In complex shunts (i.e., mixing shunts), there is mixing of pulmonary and systemic blood flow, with resulting cyanosis.

Transposition of the Great Arteries

Transposition of the great arteries (TGA) is common and accounts for about 6% of all CHD. It frequently occurs as an isolated lesion and is rarely associated with extracardiac anomalies. The operation most commonly performed in these infants is the arterial switch operation (ASO), the short- and long-term results of which have improved to such an extent that children with a good repair can expect a normal life.

TGA refers to the situation in which the aorta arises from the morphologic right ventricle and the pulmonary artery arises from the morphologic left ventricle (Fig. 15-6). In this ventriculoarterial (VA) discordance, the atria are related to the ventricles in the normal way (i.e., AV concordance). This results in two circulations that run in parallel rather than in series, which is the normal anatomic arrangement. Without some mixing of the two circulations, the systemic circulation would remain completely deoxygenated. However, some mixing does occur through the PDA or through a VSD that is present in approximately 25% of cases. If there is no VSD and mixing is inadequate, ductal patency is maintained after birth with an intravenous prostaglandin E₁ infusion, and a balloon atrial septostomy is performed urgently in the neonatal period.

FIGURE 15-6 Diagram of transposition of the great arteries (TGA) shows an intact ventricular septum. The aorta (Ao) arises from the right ventricle (RV ), and the pulmonary artery (PA) arises from the left ventricle (LV ). The coronary arteries arise from the aorta. These children are cyanotic. ASD, Atrial septal defect; IVC, inferior vena cava; LA, left atrium; PDA, patent ductus arteriosus; RA, right atrium; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

In TGA with an intact ventricular septum, the ASO should be performed early in the neonatal period, preferably in the first 2 to 3 weeks of life, because the left ventricle is exposed only to the pressure of the pulmonary circulation. The longer this situation is allowed to continue, the less the left ventricle is able to adapt to the work required to pump blood at systemic pressure after the ASO. However, if there is an unrestrictive VSD, the left and right ventricles are exposed to systemic blood pressure, and the left ventricle is better conditioned to perform the work of the systemic ventricle after the ASO.

If untreated, most infants with TGA die in the first year of life of hypoxia and heart failure. Pulmonary vascular disease develops early and contributes to this high mortality rate.^212,²¹³ The mechanism for the early development of pulmonary vascular disease is complex and not simply related to high pulmonary blood flow. However, the presence of a VSD further accelerates this process. These infants are at risk for pulmonary hypertensive crises in the postoperative period.²¹⁴

Surgical Options

Arterial Switch Operation.

An ASO is the operation of choice if the intracardiac anatomy is appropriate. The ASO involves transecting the two main arterial trunks distal to their respective valves and switching them to produce VA concordance (Fig. 15-7). It also involves disconnecting the coronary arteries from the “old” aorta and reconnecting them to the neoaorta. This restores anatomic and physiologic normality. The coronary anatomy varies widely in TGA but must be well assessed preoperatively because moving the coronary arteries to the neoaorta is difficult but crucial to a successful outcome. In some cases, the coronary arteries run in the wall of the aorta (intramural), and this poses particular difficulties for the surgeon. Ventricular function after surgery depends largely on unrestricted flow in the coronary arteries.

FIGURE 15-7 Diagram of an arterial switch operation. A, The original anatomy. The aorta (Ao), pulmonary arteries (PA), and coronary arteries are disconnected from their origins. B, The PA is moved anterior to the Ao. C, The Ao is connected to the left ventricle (LV), and the PA is connected to the right ventricle (RV). D, The coronary arteries are connected to the neoaortic root. E, Final configuration. IVC, Inferior vena cava; LA, left atrium; RA, right atrium; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Mustard and Senning Procedures.

The Mustard and Senning procedures are ASOs. They involve the use of intraatrial baffles to redirect deoxygenated blood from the venae cavae to the left atrium, left ventricle, and pulmonary artery and oxygenated pulmonary venous blood to the right atrium, right ventricle, and aorta. They create AV discordance, restore physiologic but not anatomic normality, and leave the physiologic right ventricle as the systemic ventricle. These procedures were performed as definitive procedures before the arterial switch became successful but are rarely used today as definitive repairs. They are still used as palliation in children with TGA, VSD, and pulmonary vascular disease.²¹⁵ In these cases, the VSD is left open.

Rastelli Procedure.

The Rastelli procedure is used in children with TGA, VSD, and left ventricular outflow tract obstruction (LVOTO). The procedure closes the VSD in a way that directs blood from the left ventricle to the aorta. The pulmonary artery is ligated just distal to the pulmonary valve, and a valved conduit is inserted from the right ventricle to the pulmonary artery. The result is continuity between the left ventricle and aorta and between the right ventricle and the pulmonary artery, and the LVOTO (i.e., subpulmonary area) is bypassed. In the past, the Rastelli procedure was performed at 2 to 3 years of age with a Blalock-Taussig shunt performed for palliation in the neonatal period. However, there is a trend toward neonatal Rastelli repair without the need for a shunt.

Anesthesia Considerations for the Arterial Switch Procedure

The patient is a neonate in the first few weeks of life.

Inhalational or intravenous induction is possible.

Invasive arterial and central venous lines are required. If VSD closure is required, bicaval cannulation may be required for CPB, and because an internal jugular central venous pressure line may interfere with this, a femoral central venous pressure line may be preferable. If the patient does not have a VSD, a single venous cannula in the atrium can be used for CPB, and the internal jugular vein can be used.

Myocardial ischemia occurring after the cross-clamp is removed may be related to coronary air emboli or poor coronary anastomoses. A generous perfusion pressure after removal of cross-clamp encourages flushing air from coronary arteries. If ischemia results from an anatomic problem with the coronary arteries, they may need to be redone with a second bypass run.

TEE or epicardial echo is useful in assessing adequate de-airing, myocardial function, and adequacy of coronary anastomoses.

Post-CPB myocardial dysfunction may result from one or more of the following:

An inherently poor left ventricle

Poor myocardial protection

Poor coronary transference

Coronary air

The anesthesiologist should anticipate pulmonary hypertension.

Inotropes are almost always required. Dopamine or epinephrine can be used, and milrinone is a particularly useful agent in these cases because it is an inodilator.

After the repair, the pulmonary artery is anterior to the aorta. Any dilation of the pulmonary artery as a result of pulmonary hypertension can lead to coronary compression and myocardial ischemia.

The left ventricle is frequently noncompliant, and volume should be increased with care and in small amounts. Left atrial pressure can rise quickly if fluid is given injudiciously.

Coagulopathy after bypass is common.

Antifibrinolytics are often used.

Truncus Arteriosus

Truncus arteriosus is a rare congenital heart defect that occurs in about 0.7 of 1000 live births and accounts for about 1% of all CHD. The basic lesion is that of a common arterial outlet for the aorta and pulmonary artery associated with a single valve and a VSD (Fig. 15-8). The three types depend on how the pulmonary arteries arise from the aorta and on the size of the aorta. Blood mixes at the arterial level with a resultant high pulmonary blood flow. This leads to heart failure and early development of pulmonary hypertension. Surgery must be performed early in life to prevent pulmonary hypertension from becoming irreversible. Truncus arteriosus is associated with DiGeorge syndrome (see Table 15-4). Irradiated blood products should be used and calcium concentrations carefully monitored.

FIGURE 15-8 The diagram of a truncus arteriosus shows the common truncal valve and mixing of red and blue blood. Ao, Aorta; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Surgical repair involves separating the systemic from the pulmonary circulation and closure of the VSD. The pulmonary artery or arteries are disconnected from the aorta, and the truncal valve is repaired. The pulmonary arteries are then connected to the right ventricle, usually with a valved conduit. Circulatory arrest may be required. The early postoperative mortality rate is 5% to 25%. Factors that particularly influence mortality are truncal valve stenosis, coronary abnormalities, and low birth weight.

Anomalous Pulmonary Venous Connection

Anomalous pulmonary venous connection (i.e., drainage) comprises about 2.5% of CHD and may be total (TAPVC) or partial (PAPVC). In TAPVC, all four pulmonary veins insert into an anomalous site, and in PAPVC, a subset of the veins insert into an anomalous site and the remaining veins insert into the left atrium. Survival is usually good but depends on the site of insertion (e.g., infracardiac survival is poorer than supracardiac and cardiac types) and the size of the venous confluence at the insertion into the left atrium. Three types of TAPVC exist:

In supracardiac TAPVC, the pulmonary veins connect to the SVC through an ascending vertical vein (Fig. 15-9, A).

In cardiac TAPVC, the pulmonary veins connect to the right atrium through the coronary sinus (see Fig. 15-9, B).

In infracardiac TAPVC, the pulmonary veins connect to the inferior vena cava (IVC) through a common vein, which traverses the diaphragm (see Fig. 15-9, C).

FIGURE 15-9 A, In the diagram of a supracardiac total anomalous pulmonary venous connection (TAPVC), the main arteries are removed. The pulmonary veins (PVs) drain through the innominate vein to the right atrium (RA), and there is an atrial septal defect (ASD). The result is a left-to-right shunt. These children are cyanotic. The veins may also be obstructed, leading to pulmonary hypertension. B, In the diagram of an intracardiac TAPVC, the pulmonary veins drain to the RA. There is a ventricular septal defect, and the effect is to create a left-to-right shunt. The veins may also be obstructed, which can lead to pulmonary hypertension. C, In the diagram of an infracardiac TAPVC, the PVs drain through the ductus venosus to the RA. An ASD exists, and the circulation results in a right-to-left shunt; the child is blue. The veins may also be obstructed. IVC, Inferior vena cava; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Infants with pulmonary venous obstruction, pulmonary hypertension, and reduced pulmonary blood supply usually present early with cyanosis and tachypnea. The degree of cyanosis depends on the size of the ASD and the associated right-to-left shunt and on the degree of mixing of systemic and pulmonary venous blood. Children without pulmonary venous obstruction and pulmonary hypertension usually have few symptoms.

Anesthesia Considerations

The patient may be a neonate.

Heart failure can occur.

Pulmonary edema may be present.

There is a risk of pulmonary hypertension preoperatively and postoperatively; nitric oxide may be required after surgery.

Circulatory arrest may be used, and profound hypothermia may be required.

Coagulopathy may occur after bypass.

Antifibrinolytics are often used.

Hypoplastic Left Heart Syndrome

The incidence of HLHS in the United States is about 2 cases per 10,000 live births. In Europe, this figure is probably reduced because many mothers with a prenatal diagnosis of HLHS opt for pregnancy termination.

The anatomic features of HLHS (Fig. 15-10) include the following:

Hypoplastic left ventricle

Mitral stenosis or atresia

Aortic stenosis or atresia

Hypoplastic aortic arch

Duct-dependent circulation

FIGURE 15-10 Diagram of hypoplastic left heart syndrome shows a very small left ventricle (LV), mitral valve, aortic valve, and aortic arch. Pulmonary venous blood drains to the left atrium (LA), then through an atrial septal defect (ASD) to the right atrium (RA), and from there through the right ventricle (RV) to the pulmonary artery (PA). A patent ductus arteriosus (PDA) provides blood to the systemic circulation. Ao, Aorta; IVC, inferior vena cava; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

The prognosis for infants who are born with HLHS has improved dramatically. Previously, virtually all of these infants died of this condition, but in some centers, most children now survive at least into childhood.²¹⁶ The longer-term outlook has not been fully determined, and many hurdles remain.

The diagnosis of HLHS is usually made in the prenatal period, although it can be difficult and is sometimes missed. At birth, neonates present with tachypnea, tachycardia, and cyanosis, and a systolic murmur can be heard.

Surgical Palliation

The aim of surgery is to convert the anatomy of the HLHS into a single-ventricle type circulation in which the right ventricle becomes the single systemic ventricle and the pulmonary blood flow is supplied passively from the SVC and IVC (i.e., Fontan circulation). This is done by a series of three operations known as Norwood stage I, Norwood stage II (hemi-Fontan), and Norwood stage III (Fontan).

Norwood Stage I.

The Norwood stage I operation is performed in the neonatal period. It involves reconstructing the aortic arch so that it arises from the pulmonary trunk. The pulmonary valve becomes the neoaortic valve. The branch pulmonary arteries are disconnected from the pulmonary trunk, and a new pulmonary blood supply is provided by a shunt from the subclavian artery (i.e., Blalock-Taussig shunt) or from the right ventricle (i.e., Sano modification) (Fig. 15-11).²¹⁷ If the ASD is restrictive, it is enlarged.

FIGURE 15-11 Diagram of the Norwood stage I operation. A, The main pulmonary artery (PA) is disconnected from the right ventricle (RV). B and C, The aortic arch is reconstructed with homograft and connected to the RV, which becomes a single ventricle. D, Pulmonary blood is then supplied by a Blalock-Taussig shunt from the subclavian artery to the pulmonary artery. The children remain cyanotic. Ao, Aorta; ASD, atrial septal defect; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; PDA, patent ductus arteriosus; RA, right atrium.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Norwood Stage II.

The Norwood stage II (hemi-Fontan) operation takes place at about 6 months of age. It involves taking down the shunt that was created at the first operation and creating a new connection from the SVC to the pulmonary arteries (i.e., a bidirectional or Glenn shunt). The result is a pulmonary blood supply that is provided by systemic venous blood from the SVC. Flow is passive and depends on pulmonary artery pressures remaining low. The infants remain cyanotic with arterial saturations in the mid-80s because desaturated blood from the IVC continues to flow into the heart and the systemic circulation (Fig. 15-12).

FIGURE 15-12 Diagram of Norwood stage II (hemi-Fontan) operation. The Blalock-Taussig shunt is disconnected, and a Glenn shunt is created by connecting the superior vena cava (SVC) to the pulmonary artery (PA). ASD, Atrial septal defect; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

Norwood Stage III.

The Norwood stage III (Fontan) operation converts the anatomy into a Fontan circulation. The surgery involves connecting the IVC through an extracardiac or intracardiac conduit to the pulmonary artery. This creates a single-ventricle or Fontan circulation (Fig. 15-13). The single right ventricle pumps blood to the systemic circulation, and the pulmonary blood supply is provided by passive flow by systemic venous blood from the SVC and IVC. The PVR must remain low because any increase will dramatically reduce pulmonary blood flow. It is common for a small hole (i.e., fenestration) to be created between the extracardiac conduit and the right atrium so that if the PVR rises, blood will be directed to the right atrium and allow cardiac output to be maintained. In this situation, the child becomes cyanotic, but cardiac output is maintained, a much safer situation than a state of low cardiac output. Postoperatively, increased systemic venous pressure may cause pleural effusions, an enlarged liver, or protein-losing enteropathy. Later, if PVR remains consistently low, the fenestration can be closed with a transvenous device.

FIGURE 15-13 Diagram of Norwood stage III (Fontan) operation. The Fontan circulation is created by connecting the inferior vena cava (IVC) to the pulmonary artery (PA) with a conduit. A fenestration is shown between the conduit and the right atrium (RA). ASD, Atrial septal defect; LA, left atrium; LV, left ventricle; RV, right ventricle; SVC, superior vena cava.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

The long-term problem for these children is that the morphologic right ventricle that becomes the systemic ventricle fails over time. The only recourse is heart transplantation.^218,²¹⁹

Anesthesia Considerations

Norwood Stage I.

The anesthesiologist must understand the anatomy and physiology of HLHS.

Balance between systemic and pulmonary circulations is maintained by balancing PVR and SVR. If the PVR decreases, blood flow will be directed away from the systemic circulation and the lungs will be flooded. This results in hypotension and hypoperfusion with increasing acidosis. If PVR increases, cyanosis will increase. Before anesthesia, these infants are best managed spontaneously breathing in room air with a prostaglandin E₁ infusion to maintain ductal patency. However, if mechanical ventilation is required, it is important to maintain normal to high Paco₂ and very low Fio₂, usually with air.

Air should be available for transfer to the operating room, or a self-inflating bag should be used.

High-dose opioid technique is preferred.

Venous access is gained through the femoral or umbilical veins. The internal jugular vein is avoided because narrowing of the SVC would jeopardize the Glenn shunt.

Profound hypothermia may be required.

Postoperative myocardial dysfunction is common, and inotropes are required.

Balancing systemic and pulmonary blood flow remains an issue after bypass. Some centers use the long-acting α-adrenergic blocker phenoxybenzamine after bypass to reduce SVR variability, allowing greater concentrations of oxygen to be used and an overall increase in oxygen delivery.²²⁰ The alternative approach is to combine a vasodilator such as milrinone with dopamine or epinephrine to achieve a similar effect. I prefer to deliver a bolus dose of milrinone (25 µg/kg over 20 minutes during rewarming), followed by an infusion of 0.3 µg/kg/min in combination with epinephrine, 0.05 to 0.1 µg/kg/min.

Coagulopathy may occur after bypass.

Antifibrinolytics are often used

The sternum is frequently left open, and closure may be delayed for several days.

Norwood Stage II.

The procedure is carried out with CPB.

Cardioplegia is not used. The heart remains beating, and inotropes are seldom required.

Venous access is achieved through the femoral veins. However, only a single side should be used because femoral bypass is occasionally required. A short temporary cannula is useful in the internal jugular vein. It reflects the pulmonary artery pressure after anastomosis of the SVC to the pulmonary artery. It is removed early in the postoperative period to avoid any possibility of thrombosis in the SVC.

This is repeat surgery, and external defibrillator pads should be attached.

Antifibrinolytics may be used

The aim is early extubation. Positive intrathoracic pressure reduces flow in the Glenn shunt.

Infants should be nursed with the head up at 30 degrees after surgery.

Norwood Stage III.

Surgery is carried out with CPB but usually without cross-clamping the aorta.

PVR must remain low postoperatively, careful management of the lungs is important to minimize atelectasis, and nitric oxide is occasionally required.²²¹

If an inotrope is required, milrinone is a good choice because of its beneficial effects on PVR.

Early extubation is beneficial in terms of hemodynamics.

Large amounts of fluid may be required in the early postoperative period.

Aortic Stenosis

Obstruction to the LVOT can occur at the valvular, subvalvular, or supravalvular area or in various combinations, and it is common, accounting for up to 10% of CHD.^222,²²³ Congenital valvar aortic stenosis is frequently associated with a bicuspid valve. Severe critical aortic stenosis in neonates occurs in approximately 10% of cases and requires urgent treatment. Supravalvular aortic stenosis may be associated with Williams syndrome.²²⁴

Despite the many anatomic varieties of aortic stenosis, the resulting pathophysiology remains essentially the same. There is an increasing imbalance between oxygen supply and demand (i.e., impaired coronary blood flow due to low coronary perfusion pressure plus increased workload on the left ventricle leading to subendocardial ischemia), left ventricular hypertrophy, and a risk of left ventricular failure. There is always the risk of sudden death, especially with Williams syndrome. The age at which the child presents is a risk factor; younger children are most at risk. Two thirds of those presenting in the first 3 months of life will require inotropic or ventilatory support before treatment.²²⁵

Treatment Options

Treatment options depend on the patient’s age and the severity and type of lesion. In neonates with critical aortic stenosis, an urgent valvuloplasty is required. It can be performed surgically using CPB, but it typically is performed using transluminal balloon angioplasty in the cardiac catheterization laboratory.²²⁶ Complications in this age group include ventricular fibrillation, aortic incompetence, or residual aortic stenosis.

In the older child, several surgical approaches may be used, depending on the anatomy. Transluminal balloon valvuloplasty commonly is performed in older patients. The most common complications of valvuloplasty are aortic incompetence and residual aortic stenosis. Valve replacement with a mechanical valve or bioprosthetic valve is delayed as long as possible because of the long-term problems associated with the anticoagulation needed with a mechanical valve and because of the inevitable calcification of the bioprosthetic valve. An alternative surgical option is the Ross procedure, which involves moving the pulmonary valve into the aortic valve position and using a homograft in the pulmonary position. The need for reoperation with the Ross procedure is reduced because the systemic valve (i.e., neoaortic valve) grows with the child and calcification of the homograft in the pulmonary position is slow. There is no need for anticoagulation.²²⁷^–²²⁹

Anesthesia Considerations

A crucial aim of anesthesia is to maintain the balance of oxygen supply and demand. This involves maintaining a normal heart rate (no tachycardia or bradycardia), maintaining SVR to preserve coronary perfusion, avoiding hypertension, and avoiding myocardial depression.

Anesthesia for neonates having surgery with CPB is similar to other neonatal cardiac surgery.

For transluminal balloon valvuloplasty

The catheter crossing the aortic valve and inflation of the balloon can lead to dramatic cardiovascular changes. Cardiac output decreases, myocardial ischemia occurs, and bradycardia is common. In neonates, ventricular fibrillation may occur after passing the wire across the valve. The anesthesiologist must be prepared to resuscitate the neonate quickly, and drugs, particularly epinephrine, should be immediately available.

It is possible the child will remain ventilated after the procedure because ventricular function can remain poor for some time.

Arterial access is needed by the cardiologist for the procedure, but pressure is not always displayed. An independent arterial line is very useful.

Occasionally, adenosine is given to slow or stop the heart at the time of balloon inflation to prevent damage to the valve by the inflated balloon being expelled through it. However, this practice is not universal.

Coarctation of the Aorta

Coarctation of the aorta is discrete narrowing of the aorta, and it accounts for about 5% of CHD. The lesion is often isolated with no other associated abnormalities. This type of lesion, however, may occur in association with other cardiac abnormalities such as VSD, aortic arch, or aortic valve abnormalities. The coarctation may be preductal, juxtaductal, or postductal, depending on the relationship to the ductus arteriosus. The most common form presenting in the neonatal period is the preductal type. Preductal coarctation is associated with minimal collateral circulation below the coarctation and requires prostaglandin to maintain ductal patency. Juxtaductal and postductal coarctations are characterized by the development of collateral vessels that supply the area below the coarctation. This is important because the spinal cord is supplied by these collaterals, and these vessels supply the spinal cord during aortic cross-clamping.

In practical terms, children with coarctation of the aorta can be classified in two groups. One group presents in the neonatal period with preductal coarctation with few collaterals and very poor left ventricular function. The second group of children (usually older than 1 year of age) have well-developed collaterals and better left ventricular function. Neonates often present with poor left ventricular function and may be in heart failure. Femoral pulses are often weak, and patients usually have a progressive acidosis. Differences between the systolic systemic blood pressures in the right arm (before stenosis) and left leg (after stenosis) may indicate the presence of a coarctation of the aorta.

Anesthesia Considerations

Neonatal Repair.

These infants are sick, with poor left ventricular function. They should be treated very carefully, and the anesthesiologist should not be misled by an infant who looks reasonably well.

Some infants are already intubated and ventilated, and some may be receiving an inotrope such as dopamine.

Intravenous access often is established to give prostaglandin E₁; this intravenous line can also be used to administer induction agents. I prefer to give incremental doses of fentanyl (up to 5 µg/kg) and then a muscle relaxant and to supplement this with a very low dose of isoflurane (0.3% to 0.5%). This can be omitted if hypotension ensues.

Inotropes may be required before surgery, and they should be available.

Ideally, the arterial line should be placed in the right arm to allow blood pressure measurement during arterial cross-clamping. The left subclavian may be partially obstructed during the repair. Some have advocated an arterial line below the coarctation to measure perfusion pressure during cross-clamping, but this may be very difficult in practice because femoral pulses are usually absent.

A central venous line should be placed.

Surgery usually takes place through a left thoracotomy without the use of CPB. The lung is retracted, and ventilation may be problematic. The endotracheal tube must fit snugly and have a minimal leak because a tracheal tube with a large leak may make ventilation very difficult.

Paraplegia may occur in about 1% of cases and is thought to result from hypoperfusion during aortic cross-clamping.^230,²³¹ To reduce the chance of spinal cord damage, infants should be cooled to 34° C or 35° C before the cross-clamp is applied, although this approach is not evidence based. Normocarbia and upper limb blood pressure should be maintained. Low-dose anticoagulation may be applied. A short cross-clamp time is thought to be important.

Epidural anesthesia is occasionally used, but I have not adopted this approach.

Postoperative hypertension may be a problem, and a vasodilator such as sodium nitroprusside may be required.

Anesthesia for the Older Child.

These children usually are not as sick as the neonates.

Issues about vascular lines are similar to those in neonatal repair.

Careful intravenous induction with a combination of fentanyl and an induction agent of choice is standard. Etomidate is a good anesthetic because of its cardiovascular stability.

Although a collateral blood supply is present, the spinal cord remains at risk during the cross-clamping, and the same precautions taken with neonates should be taken with these children.

An oral cuffed tracheal tube is useful because early extubation is the norm.

Postoperative hypertension is a common problem, and good analgesia combined with sodium nitroprusside and β-blockers is usually required. Up to 30% of children eventually develop long-term hypertension that will require therapy.

Some of these children are managed with balloon angioplasty with or without stent placement. Rupture of the aorta is a risk in these patients, and the institution in which the procedure is undertaken should be in a position to deal with this possibility.

Interrupted Aortic Arch

Interrupted aortic arch is a rare anomaly, accounting for less than 1% of CHD. In this condition, disruption occurs between the ascending aorta and descending aorta (Fig. 15-14). The three types depend on where the disruption takes place. A PDA is present and is required to supply the descending aorta. A VSD is also common. Interrupted aortic arch is frequently associated with a 22q11 deletion and results in the DiGeorge syndrome (see Table 15-4).²³²

FIGURE 15-14 Diagram of an interrupted aortic arch. The patent ductus arteriosus (PDA) supplies the body below the interruption. Ao, Aorta; ASD, atrial septal defect; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

(Modified from May LE. Pediatric heart surgery: a ready reference for professionals. Milwaukee: Maxishare; 2005.)

These children are often small for gestational age and are started on a prostaglandin infusion to maintain ductal patency. They are often sick with progressive acidosis and poor cardiac output. There is increasing pulmonary blood flow as the duct closes. Surgical repair depends on the presence of associated lesions, particularly a VSD. In the single-stage repair, the arch is reconstructed, and the VSD is closed. The two-stage repair involves repair of the aortic arch and banding of the pulmonary artery to limit blood flow to the lungs. The VSD is closed in a later stage of the procedure. Either way, deep hypothermic circulatory arrest is likely to be employed. Some centers use selective regional perfusion to try and limit neurologic injury.²³³ The early and late mortality rates are high. Higher mortality rates correlate with small size, acidosis preoperatively, and associated cardiac lesions.²³⁴

Transport and Transfer to a Pediatric Intensive Care Unit

After surgery is completed, cardiac surgical patients need a period of intensive care. The first phase of this care is transport of the children from the operating room to the PICU. This is a potentially hazardous time and requires good organization, teamwork, and appropriate equipment. Guidelines exist for the safe transport of these children.²³⁵

Transport to the PICU can be defined as a preparatory phase, transport phase, and stabilization phase.²³⁶ During the preparatory phase, the estimated time of arrival in the PICU is communicated with the PICU. The bed space is prepared, ventilator and monitors are configured in an appropriate way, and any additional interventions that may be required are made ready. In my institution, a form is sent to the PICU that indicates the child’s age and weight, the ventilator settings that will be required, the number of transducers that will be required, and the infusions that are running. After arrival in the PICU, two basic tasks need to be undertaken: transfer of technology and transfer of information. It is better to allow the technology transfer to occur before the information handover. This includes ensuring that all the monitors are connected and working appropriately, that the ventilator is connected and delivering adequate ventilation, that all infusions are working, and that drains and urinary catheter are all in place with baseline readings documented. After this has been accomplished, a single handover of information should be done with all of the appropriate personnel present, and it should include information given by the anesthesiologist and surgeon. In my institution, a checklist is followed to ensure that no important information is omitted. It is important to avoid a large number of information handovers between individuals rather than a single, comprehensive handover with all the relevant personnel present.