Preoperative and Postoperative Care of the Infant with Critical Congenital Heart Disease
John M. Costello
Nguyenvu Nguyen
▪ INTRODUCTION
Congenital heart disease (CHD) is the most common birth defect, occurring in approximately 8 per 1,000 live births. Approximately one-third of all patients with congenital heart defects undergo surgical or transcatheter intervention as neonates or in early infancy. This strategy limits the sequelae of prolonged cyanosis and heart failure. However, a number of factors complicate the perioperative care of neonates and young infants. Immaturity of many organ systems is associated with limited physiologic reserve. Neonates have limited myocardial contractile reserve, likely related to developmental differences in myocyte filaments, contractile proteins, and calcium handling (1). Pulmonary functional residual capacity, fat and carbohydrate reserves, and ability to regulate temperature are all limited. Drug metabolism is altered by hepatic and renal immaturity, as well as total body water content.
This chapter provides an overview of the key issues, concepts, and strategies pertaining to the perioperative care of neonates and infants with critical CHD. We have allowed some overlap of information between this chapter and Chapter 30 in the interest of clarity. The expected presentation and clinical course of common congenital heart lesions are discussed, and the general principles that are widely applied to patient management are reviewed. The general perioperative pathophysiology and management strategies described in this chapter are intended to provide a frame of reference for evaluation and management of this patient population. Subtle variations in cardiac anatomy and physiology exist within each major category of heart defect, which must be fully appreciated when developing individualized medical management plans.
A continuum of care is essential for achieving optimal outcomes for neonates with complex cardiac disease, and thus this chapter contains a review of preoperative, intraoperative, and postoperative management. The first section covers general preoperative issues relevant to neonates with critical CHD. We then provide an overview of cardiopulmonary bypass (CPB) and its sequelae. Common postoperative pathophysiologic states and early postoperative complications are reviewed. For common types of CHD, we will discuss presentation, physiology, operative intervention, and postoperative complications. Heart transplantation is briefly discussed.
▪ PREOPERATIVE CARE
Prenatal Diagnosis
Critical CHD may be defined as a heart defect that typically requires surgical or transcatheter intervention during the first month of life to prevent death. Neonates with unrecognized critical CHD may develop severe cyanosis, respiratory distress, and shock, cumulating in end-organ injury. Such patients may be initially misdiagnosed with sepsis or respiratory conditions.
The prenatal diagnosis of critical CHDs is associated with several potential benefits. Genetic testing and family counseling may be performed. Selection of an appropriate hospital for delivery is facilitated, as fetuses that are likely to require surgical or transcatheter cardiac intervention in the neonatal period should ideally be born at a birthing center adjacent to a tertiary care pediatric cardiology center (2). Information from the fetal echocardiogram is useful to guide planning for initial stabilization after birth, such as the administration of a prostaglandin E1 (PGE1) infusion or the possible need for an emergent balloon atrial septostomy. Several studies have found that a prenatal diagnosis of CHD was associated with a reduction in preoperative morbidity and mortality (3,4). In contrast, the impact of in utero diagnosis of critical CHD on postoperative mortality is unclear. Some investigators have reported lower postoperative mortality in patients with a prenatal diagnosis of HLHS or d-TGA, whereas others found no such impact (4,5,6,7).
In most cases where a prenatal diagnosis is made, a cardiac defect is suspected during second-trimester obstetrical ultrasound screening, resulting in a referral to a pediatric cardiologist for a fetal echocardiogram. Less commonly, one or more maternal risk factors for CHD are present that warrant a fetal echocardiogram (Table 31.1) (8). Approximately one-half of fetuses with CHD are diagnosed prenatally (9,10,11). Detection rates vary from approximately 30% to 70% depending on the type of heart defect, intensity of screening, and geographic location (10,11,12). The majority of missed diagnoses may be attributable to a failure of detection during obstetrical ultrasound screening. Fetal echocardiography also has several known limitations. The quality of imaging is influenced by fetal position and maternal body habitus. Precise imaging of extracardiac vessels may be challenging. For example, false-positive and false-negative results may occur when evaluating a fetus for suspected coarctation of the aorta (10).
Fetuses with a prenatal diagnosis of critical CHD tend to be delivered at an earlier gestational age than do those with a postnatal diagnosis (5,9,13,14,15). This finding may be explained in part by the fact that mothers expecting a fetus with CHD often undergo frequent fetal monitoring in late gestation, with the potential that false positives of such testing occur more often than do true positives. Scheduled deliveries at 37 to 38 weeks’ gestational age also may be contributory. Recent observational data suggest that optimal outcomes are achieved when fetuses with critical CHD are delivered at 39 to 40 weeks’ gestational age (16,17,18). In the absence of fetal or maternal indications for earlier delivery, scheduling the elective delivery of fetuses with CHD prior to 39 weeks’ gestational age should generally be avoided.
Transitional Circulation
An appreciation of the fetal-placental circulation, as well as the normal transition from fetal to newborn circulation, is required to understand the timing and presentation of symptoms in neonates with CHD (see Chapters 11 and 16). Gas, nutrient, and waste exchange occur between the fetal and maternal circulations in the placenta. Oxygenated blood then returns to the fetus through the umbilical vein, partially bypassing the liver via the ductus venosus, and drains into the inferior vena cava. The oxygenated blood is preferentially shunted through the foramen ovale to the left atrium, from which it fills the left ventricle and is ejected out the aorta to supply the coronary circulation and the brain. Deoxygenated blood from the superior vena cava and distal inferior vena cava preferentially enters the right ventricle and is then pumped to the pulmonary artery. Due to the high pulmonary vascular resistance in utero, the majority of the deoxygenated pulmonary artery blood bypasses the lungs and flows through the ductus arteriosus into the descending aorta, supplying the lower body and placenta.
The transitional circulation begins when the umbilical cord is clamped immediately after birth. The ductus venosus functionally closes in the absence of flow from the placenta. As the
low-resistance placental circulation is no longer present, systemic vascular resistance rises. Pulmonary vascular resistance falls due to mechanical expansion of the lungs with respiration and higher oxygen tension. Blood ejected from the right ventricle now perfuses the lungs rather than entering the ductus arteriosus, and the increased blood returning to the left atrium leads to functional closure of the foramen ovale. The resultant increased oxygen tension contributes to functional closure of the ductus arteriosus. When the aforementioned events, in particular the fall in pulmonary vascular resistance and closure of the ductus arteriosus, occur in the setting of critical CHD, signs and symptoms will develop.
low-resistance placental circulation is no longer present, systemic vascular resistance rises. Pulmonary vascular resistance falls due to mechanical expansion of the lungs with respiration and higher oxygen tension. Blood ejected from the right ventricle now perfuses the lungs rather than entering the ductus arteriosus, and the increased blood returning to the left atrium leads to functional closure of the foramen ovale. The resultant increased oxygen tension contributes to functional closure of the ductus arteriosus. When the aforementioned events, in particular the fall in pulmonary vascular resistance and closure of the ductus arteriosus, occur in the setting of critical CHD, signs and symptoms will develop.
TABLE 31.1 Risk Factors for CHD That Warrant Consideration for Referral for Fetal Echocardiography | ||||||
|---|---|---|---|---|---|---|
| ||||||
Presentation of Critical Congenital Heart Disease
Many neonates with unrecognized critical CHD look well during the first few hours after birth. Prior to the onset of symptoms, CHD may be detected due to abnormal findings on physical examination (e.g., persistent cyanosis, respiratory distress, a pathologic heart murmur, or diminished femoral pulses). Chest radiograph (CXR) may increase the suspicion of CHD. Cardiac defects may also be detected during echocardiographic screening performed in neonates with known chromosomal abnormalities or noncardiac congenital malformations. As the ductus arteriosus constricts, signs and symptoms of cyanosis (inadequate pulmonary blood flow), shock (inadequate systemic blood flow), or some combination of these physiologic states may develop. Older neonates and infants with significant left-to-right shunting at the ventricular or great artery level may present with evidence of congestive heart failure. In these patients, as pulmonary vascular resistance drops, pulmonary blood flow increases and the systemic ventricle becomes volume overloaded.
Despite routine prenatal testing, postnatal physical examination, and observation for symptoms, approximately 20% of neonates with critical CHD are discharged from the normal newborn nursery prior to the recognition of the cardiac defect (19). Pulse oximetry screening for congenital heart defects in normal newborn nurseries has recently been shown to increase the detection of otherwise unsuspected critical congenital heart defects (20,21,22). A postductal oxygen saturation of less than 95% between 24 and 48 hours of life is often deemed an abnormal result. The routine use of pulse oximetry screening has been recommended by several authoritative bodies and is increasing in North America and Europe.
Critical CHD may be broadly categorized into four major groups: ductal-dependent systemic blood flow, ductal-dependent pulmonary blood flow, transposition physiology, and total anomalous pulmonary venous return (TAPVR). Each of these categories is discussed below.
Ductal-Dependent Systemic Blood Flow
Neonates with ductal-dependent systemic blood flow will develop progressive shock upon constriction of the ductus arteriosus. Examples include critical coarctation of the aorta, critical aortic valve stenosis, hypoplastic left heart syndrome (HLHS), and interrupted aortic arch (IAA). If unrecognized at birth, such patients typically present within the 1st week or 2 of life with feeding difficulties, tachypnea, poor perfusion, and metabolic acidosis, a constellation of findings that may be mistaken for sepsis. Due to myocardial dysfunction and low cardiac output, pathologic heart murmurs may not be present, and accurate four-extremity blood pressure measurements may be difficult to obtain. Diminished or absent pulses in the lower extremities compared to the right axillary pulse and an increased right ventricular impulse are usually evident on physical examination. A high index of suspicion is required to make a timely diagnosis.
Ductal-Dependent Pulmonary Blood Flow
Neonates with ductal-dependent pulmonary blood flow will develop progressive cyanosis upon constriction of the ductus arteriosus. Critical pulmonary valve stenosis, severe tetralogy of Fallot, and pulmonary atresia are examples of lesions with important right ventricular outflow tract obstruction. Inadequate pulmonary blood flow leads to progressive hypoxemia, which if severe will lead to myocardial dysfunction and compromise of other organ systems. Lesions with complete intracardiac mixing of the systemic venous and pulmonary venous circulations, such as tricuspid atresia, or complex single ventricles, usually have variable degrees of obstruction to either the systemic or pulmonary circulations. Less commonly, no obstruction to either systemic or pulmonary blood flow is present, and in these cases, mild hypoxemia is present and congestive heart failure may develop in the first few weeks to months of life.
Transposition Physiology
Inadequate mixing between the systemic and pulmonary circulation is a unique physiologic state encountered in patients with d-transposition of the great arteries (d-TGA). In this common cyanotic heart defect, the systemic and pulmonary circulations are in parallel (Fig. 31.1). Neonates with d-TGA, an intact ventricular septum, and no significant outflow tract obstruction usually present with cyanosis soon after birth, which may worsen with constriction of the ductus arteriosus. Those with a significant ventricular septal defect (VSD) have less desaturation and can present later with congestive heart failure.
Total Anomalous Pulmonary Venous Return
Neonates with TAPVR present with cyanosis after birth. The severity of cyanosis may be mild in patients without pulmonary venous obstruction, and limited symptoms may be present. Those with obstructed pulmonary venous return present with respiratory distress, pulmonary edema, moderate-to-severe cyanosis, and acidosis.
Initial Evaluation and Stabilization of the Neonate with Suspected Congenital Heart Disease
Initial Evaluation
Any neonate with suspected CHD should undergo a focused evaluation. The course of labor should be reviewed, and factors that suggest acute infection, respiratory distress syndrome, or meconium aspiration should be noted, as they may indicate a primary respiratory cause for hypoxemia. A review of the maternal history may identify a known risk factor for CHD (Table 31.1). The physical examination focuses on the detection of dysmorphic features, cyanosis, or abnormal pulses. Respiratory distress may be present. Those with heart disease often have a shallow, rapid respiratory pattern (quiet tachypnea), as opposed to the more labored breathing pattern of neonates with primary pulmonary process. The precordium should be inspected and palpated for abnormal impulses and the heart auscultated for clicks, gallops, and/or a pathologic murmur. Four-extremity blood pressure measurements should be obtained. An arm-leg blood pressure gradient of greater than 10 mm Hg is suggestive of aortic arch obstruction. However, in the setting of a patent ductus arteriosus (PDA), the pressures may be equal despite the presence of a critical aortic coarctation or IAA.
 FIGURE 31.1 The circulation in transposition of the great arteries (TGA). A: The systemic and pulmonary circulations are in series in the normal circulation, whereas they are in parallel in TGA. Solid arrows, relatively unoxygenated blood; stippled arrows, oxygenated blood; dashed arrows, intercirculatory shunts. B: Circulation schema demonstrating flows and shunts in infants with TGA/intact ventricular septum. Note that the anatomic left-to-right shunt constitutes the effective SBF, and the anatomic right-to-left shunt constitutes the effective PBF. Ao, aorta; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; L → R, left-to-right; RA, right atrium; RV, right ventricle; R → L, right to left; PA, pulmonary artery; PBF, pulmonary blood flow; PV, pulmonary veins; SBF, systemic blood flow; SVC, superior vena cava. Reprinted from Paul MH, Wernovsky G. Transposition of the great arteries. In: Emmanouilides GC, Riemenschneider TA, Allen HD, et al., eds. Moss and Adams’ heart disease in infants, children and adolescents, including the fetus and young adult. Baltimore, MD: Williams & Wilkins, 1995:1154-1225, with permission. |
Pre- and postductal pulse oximetry measurements should initially be obtained in a neonate with suspected critical CHD. Differential cyanosis refers to a condition in which the lower body is more desaturated than is the upper body due to righttoleft shunting at the ductus arteriosus. Differential cyanosis may be present in a patient with severe pulmonary hypertension (in the absence of CHD) or aortic arch obstruction. Reverse differential cyanosis is observed when the upper body is more desaturated than is the lower body. Reverse differential cyanosis is only seen in neonates with d-TGA who also have aortic arch obstruction or severe pulmonary hypertension. In such patients, oxygenated blood is ejected from the left ventricle to the pulmonary artery and then through the PDA to the descending aorta, whereas deoxygenated blood from the right heart is ejected into the ascending aorta.
In a newborn with suspected CHD, interpretation of a CXR and 12-lead electrocardiogram (ECG) may provide further insights into the underlying cardiac diagnosis (see Chapter 30).
If an echocardiogram cannot be readily obtained for a cyanotic newborn, a “hyperoxia test” may help differentiate cyanotic heart disease from pulmonary disease. The hyperoxia test involves obtaining a right radial arterial blood gas analysis on room air and 100% inspired oxygen. The pCO2 is typically mildly decreased in newborns with cardiac disease and mildly elevated in those with pulmonary disease. The PaO2 is often between 25 and 40 mm Hg on room air in both patient groups. In 100% FiO2, the PaO2 will usually rise to 100 mm Hg or more in patients with pulmonary disease, provided that significant pulmonary artery hypertension is not present. In most neonates with cyanotic heart disease, however, the PaO2 will remain unchanged or only increase slightly. There are important limitations to the hyperoxia test. For example, some patients with ductal-dependent systemic blood flow (e.g., HLHS, critical coarctation of the aorta, critical aortic valve stenosis, IAA) may have a high PaO2 (>60mm Hg) in any arterial blood sample or a very high PaO2 (>150mm Hg) in a blood gas obtained from the right radial artery.
If the aforementioned evaluation is consistent with the presence of critical CHD, the neonate should be stabilized. A PGE1 infusion should be empirically initiated in neonates with suspected CHD who present with shock and those with cyanosis. Transport to a pediatric cardiology center should be promptly arranged. If transport time will be prolonged, an echocardiogram may be performed at the presenting institution to confirm the diagnosis and guide initial stabilization. The echocardiographer and the sonographer should ideally have experience with congenital heart lesions; otherwise, false-negative and false-positive evaluations may occur (23).
Initial Stabilization: Prostaglandin E1
The introduction of prostaglandin infusions to maintain ductal patency in the late 1970s represented a major advance for neonates with critical CHD (24). While receiving PGE1, neonates can be safely transported over long distances to congenital heart centers (25,26). Cardiac diagnostic testing may be obtained to allow optimal planning for intervention, and any noncardiac anomalies can be evaluated. Patients who present in shock can be medically managed on a PGE1 infusion for several days, allowing time for recovery of end-organ function prior to surgery.
PGE1 may be safely administered through a peripheral or central intravenous line. Dosing varies depending on the clinical scenario. A PGE1 infusion of 0.01 µg/kg/min will maintain ductal patency in neonates with presumed ductal-dependent systemic or pulmonary circulation (27). A higher dose of 0.05 to 0.1 µg/kg/min is used when the ductus arteriosus is constricted or functionally closed and a state of shock or severe cyanosis exists.
Side effects of PGE1 are listed in Table 31.2 (27,28). The most troublesome side effect of PGE1 infusion is apnea, which was reported in a prior era to occur in up to one-third of neonates (27,28). However, in the absence of prematurity or sedation, apnea is very uncommon when lower doses of PGE1 are used (e.g., 0.005 to 0.01 µg/kg/min), and thus most patients may be managed without intubation (27,29). Intubation has been traditionally recommended when neonates on PGE1 infusions required interhospital transport. However, recent data indicate that when compared to neonates on PGE1 who are spontaneously breathing, those who are electively intubated for interhospital transport experience more complications (25,30). Thus, in the absence of shock, severe cyanosis, or other confounding circumstances, it is reasonable to undertake the interhospital transport of neonates receiving a PGE1 infusion with a natural airway, provided that members of the transport team are experienced and prepared to intubate the patient’s trachea should the need arise. In a randomized trial, aminophylline was shown to minimize the occurrence of apnea in neonates receiving a PGE1 infusion (31). PGE1 is a potent vasodilator, and hypotension may occur following the initiation of the drug, particularly at higher doses or if narcotics are concurrently administered to facilitate procedures. Hypotension usually resolves with a dose reduction of PGE1 and volume administration.
TABLE 31.2 Side Effects of PGE1 Infusion | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||
Several nuances regarding the use of PGE1 in neonates warrant comment. In those with critical CHD who present with severe cyanosis in the delivery room, the etiology is most likely severe obstruction to pulmonary venous return or left atrial egress (e.g., HLHS with an intact atrial septum or severely obstructed TAPVR). Patients with d-TGA and a nearly intact atrial septum may also present with severe cyanosis soon after birth. In these patients, inadequate mixing between the systemic and pulmonary circulations is present (see Fig. 31.1), and higher doses of PGE1 will not alleviate cyanosis. Emergent transfer to a cardiac center is needed so that an atrial septostomy or operation may be performed. In neonates with obstruction to pulmonary venous return (i.e., obstructed TAPVR) or left atrial egress (i.e., TGA with intact ventricular septum and a restrictive atrial communication), clinical deterioration may occur following the initiation of a PGE1 infusion. These infants also will not improve with higher doses of PGE1 and require emergent surgical or transcatheter intervention. In the occasional neonate with congenital absence of the ductus arteriosus (e.g., tetralogy of Fallot with absent pulmonary valve syndrome; selected neonates with pulmonary atresia, VSD, and major aortopulmonary collateral arteries [MAPCAs]), a PGE1 infusion may worsen cyanosis by lowering systemic vascular resistance and thereby decreasing pulmonary blood flow.
Initial Stabilization: Airway, Access, and Oxygen Delivery
When endotracheal intubation is performed in a neonate with critical CHD, the use of induction agents should be considered to blunt the stress and vagal responses to laryngoscopy, decrease oxygen consumption, and provide pharmacologic paralysis to facilitate the procedure. The choice and dosing of specific medications depend on the clinical scenario and the airway skills of the clinician.
Stable intravenous access is required for all infants with critical CHD. A peripheral intravenous catheter may be initially adequate for some patients. The need for arterial and central venous access should be individualized, based on the heart defect, clinical presentation, and anticipated preoperative course. The use of umbilical vessels for initial vascular access should be considered, as the patency of other blood vessels may be important for future cardiac catheterizations and surgical procedures.
During the initial stabilization period, an assessment of systemic oxygen delivery should be made. Most neonates with critical CHD have adequate cardiac output and systemic perfusion following initial stabilization and infusion of PGE1. Those with depressed myocardial function and evidence of shock may benefit from inotropic infusions. Oxygenation and ventilation strategies should be used with a goal of minimizing pulmonary overcirculation. Arrhythmias and any potential noncardiac etiologies for shock (e.g., pneumothorax, sepsis, adrenal insufficiency) should be excluded. Anemia may be poorly tolerated in this patient population, and hemoglobin should be assessed. pH, blood glucose, and calcium levels should be monitored and corrected as needed.
Bacterial pneumonia and sepsis are often considered when a neonate presents with cyanosis and shock, and empiric antibiotics may be prescribed before the diagnosis of critical CHD is confirmed. If no source of bacterial infection is identified within 48 hours, the antibiotics may usually be discontinued. Although it has been suggested that the use of PGE1 increases the risk of bacterial infection, there are no published data to support this concept.
Interhospital Transport
The vast majority of neonates with critical CHD are born at outside birthing centers. These babies require interhospital transport to a congenital heart center for further evaluation and intervention. Experienced pediatric transport teams should be used when available (25,26). Decision making for this patient population is an iterative process as the clinical status evolves, and the need for close communication between the physicians at the birthing hospital, the transport team, and the clinicians at the receiving heart center cannot be overemphasized. During transport, care must be taken to maintain a normal patient temperature. Hypothermia may increase systemic vascular resistance, and fever may increase oxygen consumption and promote systemic vasodilation; both may be poorly tolerated in patients with limited cardiac reserve. Blood pressure and systemic oxygen saturation targets should be established and discussed with the transport team members based on the neonate’s cardiac physiology and gestational age. All clinicians involved in the transport process must appreciate the potentially deleterious impact of hyperventilation or excessive supplemental oxygen in some neonates with ductal-dependent systemic or pulmonary blood flow.
Evaluation at the Congenital Heart Center
Upon arrival to the tertiary care cardiac center, the receiving clinicians should obtain a report from the transport team. In addition to current supportive therapies, details that are useful to direct the diagnostic evaluation and initial management include the results of any fetal echocardiograms, complications of the pregnancy, family history, weight and gestational age at birth, presence and severity of cyanosis or shock prior to initial resuscitation, presence of any risk factors for infection, and suspected noncardiac congenital anomalies.
Cardiac Evaluation
A detailed physical examination includes a review of recent and current vital signs. Four-extremity blood measurements should be obtained to evaluate for signs of aortic arch obstruction. Pre- and postductal pulse oximetry levels should be interpreted in the context of the patient’s physiology. The cardiac examination begins with inspection and palpation of the precordium. An increased right ventricular impulse is often present with significant left ventricular outflow tract obstruction and/or pulmonary hypertension. Auscultation is performed with attention to splitting and quality of the second heart sound, systolic ejection clicks, and the presence of pathologic systolic or diastolic murmurs. The span of the liver is determined, and the quality of the peripheral pulses and perfusion is noted.
The ECG and a chest/abdominal radiograph (babygram) are reviewed with attention to features that may suggest an underlying specific cardiac diagnosis (see Chapter 30). The babygram should be evaluated for signs of abnormal visceral situs or heterotaxy and to ensure that any tubes or lines placed prior to transport remain in appropriate positions.
An echocardiogram is obtained to clarify anatomic and physiologic details. Complete diagnostic information may be obtained
in the vast majority of neonates with CHD using transthoracic echocardiogram (32). Cardiac magnetic resonance imaging (MRI) or computed tomography (CT) may be helpful to quantify ventricular volumes or clarify the anatomy of extracardiac vessels in selected cases. In the current era, limited indications exist for diagnostic cardiac catheterization. Coronary anatomy can usually be clarified by echocardiography, but occasionally angiography is required (e.g., in neonates with pulmonary atresia with intact ventricular septum). Neonates with pulmonary atresia, VSD, and MAPCAs typically require cardiac catheterization to define all sources of pulmonary arterial blood flow. Hemodynamic data (e.g., ratio of pulmonary to systemic blood flow, pulmonary vascular resistance) are occasionally obtained by cardiac catheterization in selected older infants and children, but these data are rarely necessary in neonates.
in the vast majority of neonates with CHD using transthoracic echocardiogram (32). Cardiac magnetic resonance imaging (MRI) or computed tomography (CT) may be helpful to quantify ventricular volumes or clarify the anatomy of extracardiac vessels in selected cases. In the current era, limited indications exist for diagnostic cardiac catheterization. Coronary anatomy can usually be clarified by echocardiography, but occasionally angiography is required (e.g., in neonates with pulmonary atresia with intact ventricular septum). Neonates with pulmonary atresia, VSD, and MAPCAs typically require cardiac catheterization to define all sources of pulmonary arterial blood flow. Hemodynamic data (e.g., ratio of pulmonary to systemic blood flow, pulmonary vascular resistance) are occasionally obtained by cardiac catheterization in selected older infants and children, but these data are rarely necessary in neonates.
Noncardiac Evaluation
Noncardiac organ systems should be selectively evaluated in neonates presenting with critical CHD. Basic laboratory studies are obtained to evaluate acid-base status, oxygenation and ventilation, and the renal and hematologic systems. The yield of routine head ultrasounds in asymptomatic term and near-term neonates with critical CHD is extremely low (33). A head ultrasound should be considered in neonates who are born at less than 35 weeks’ gestation or who present with severe cyanosis, shock, or signs of central nervous system injury or malformation. The need for specific evaluation of the gastrointestinal and renal systems is determined based on symptoms or suspected anomalies.
Noncardiac Structural Anomalies
Major noncardiac birth defects may be seen in up to 25% of neonates with significant CHD. For example, patients with conotruncal heart defects (e.g., tetralogy of Fallot, pulmonary atresia with VSD, IAA, truncus arteriosus) have an increased risk compared with the general population of having an associated oral cleft, omphalocele, tracheoesophageal fistula, or imperforate anus (34). There is an increased incidence of renal anomalies in infants with CHD who have other major congenital anomalies, and a screening renal ultrasound may be indicated in this subset of patients (35).
Visceral heterotaxy (i.e., heterotaxy syndrome) refers to a constellation of anomalies characterized by abnormal position and symmetry of certain viscera and veins that are usually associated with complex CHD. Asplenia or polysplenia are almost always present, as are abnormal systemic and pulmonary venous connections. Both lungs are typically trilobed (asplenia) or bilobed (polysplenia). Abnormal symmetry of the liver and stomach are common, as are abnormal mesenteric attachments and malrotation of the intestines. In such patients, an abdominal ultrasound may indicate the sidedness of the liver and spleen. An upper gastrointestinal series may be obtained to evaluate for the presence of intestinal malrotation.
Genetic Anomalies and Syndromes
A chromosomal abnormality or genetic syndrome may be identified in approximately 20% of neonates with CHD. Table 31.3 lists selected common chromosomal abnormalities and genetic syndromes, and the congenital heart lesions with which they are associated (36).
Prematurity and Low Birth Weight
Neonates with CHD have an approximately twofold greater risk of being born prematurely when compared to babies without birth defects (37,38). With the exception of those with d-TGA, neonates with CHD on average have a lower birth weight and have at least a twofold greater risk of being born at low birth weight (<2.5 kg) compared to healthy controls (Fig. 31.2) (37,39). This patient population also carries twofold greater risk of being born small for gestational age (SGA) (40,41). All of the issues inherent to prematurity, low birth weight, and SGA (see Chapters 22 and 23) may complicate the perioperative course for neonates with CHD.
TABLE 31.3 Selected Common Chromosomal Abnormalities and Genetic Syndromes Associated with CHD (See Also Table 30.5 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 FIGURE 31.2 Frequency distribution of birth weight expressed as standard deviation relative to control mean for gestational age in the New England regional infant cardiac program compared to normal. The difference between the normal babies and those with CHD is significant (p < 0.001), regardless of the coexistence of extracardiac anomalies (ECA). From Levy RJ, Rosenthal A, Fyler DC, et al. Birthweight of infants with congenital heart disease. Am J Dis Child 1978;132:249-254, with permission. |
Not surprisingly, outcomes are worse for premature and low-birthweight neonates and young infants who undergo cardiac surgery. Multicenter data indicate that prematurity carries a twofold adjusted odds of mortality in neonates and infants undergoing cardiac surgery (38,42). Consistent with data in babies without birth defects, those with critical CHD who are born at early term (37 to 38 weeks’ gestation) also have worse outcomes (16,17,18). Earlier gestational age at birth may also adversely affect neurodevelopmental outcomes in infants undergoing cardiac surgery (43). Hospital mortality is roughly twice as high for patients with a weight less than 2.5 kg when compared to patients undergoing similar operations with a weight between 2.5 and 4.0 kg (44). Limited data are available regarding outcomes of SGA neonates with CHD. In a single-center study, mortality was significantly higher for SGA neonates with HLHS when compared to similar patients whose weight at birth was appropriate for gestational age (45).
Given these outcomes, decision making regarding the timing of surgery for patients born at earlier gestational ages or at low birth weight is complex. Advantages of early intervention include establishment of a more favorable cardiac physiology, including (in some patients) the mitigation of cyanosis and ventricular pressure and volume loading conditions. The postoperative state may be more conducive to weight gain. Alternatively, a delayed surgical strategy may allow time for maturation of organ systems and weight gain, which may facilitate the technical conduct of the operation. Advances in CPB techniques and miniaturization of surgical equipment allow for the reasonably safe conduct of open-heart surgery in premature and low-birth-weight patients, with intraventricular hemorrhage rarely occurring. Some studies have concluded that a management strategy of prolonged medical therapy to achieve weight gain prior to surgery is fraught with complications related to infection, heart failure, and feeding intolerance (46,47). Other reports describe better outcomes with a period of medical management followed by delayed surgical intervention (48). Given conflicting data regarding the timing of surgery in this patient population, decision making must be individualized and tailored to institutional experience.
Preoperative Supportive Care: General Principles
Cardiopulmonary Management
A “balanced” circulation will provide optimal systemic and pulmonary blood flow in neonates with ductal-dependent CHD. Those with ductal-dependent systemic blood flow (e.g., HLHS, IAA) are at risk for developing poor systemic perfusion, myocardial dysfunction from volume overload, as well as coronary ischemia, renal insufficiency, and necrotizing enterocolitis (NEC). In these patients, hyperventilation and provision of supplemental oxygen may be detrimental by decreasing pulmonary vascular resistance, thereby increasing the pulmonary-to-systemic blood flow ratio (i.e., increased Qp/Qs), and creating additional “steal” from the systemic and coronary circulations.
Neonates with ductal-dependent systemic blood flow who are reasonably stable at presentation may be allowed to spontaneously breathe while awaiting surgical intervention. These neonates will typically have relatively high systemic oxygen saturations (90% or higher) and develop “quiet tachypnea” as pulmonary vascular resistance falls in the first few days of life but will usually maintain adequate systemic perfusion. Diuretics and low-dose inotropic support are occasionally used to alleviate pulmonary edema and support the volume-loaded ventricular myocardium. The management of patients with ductal-dependent systemic blood flow who develop significant overcirculation and shock is discussed in detail in the section on preoperative management of HLHS.
In neonates with ductal-dependent pulmonary blood flow, the ductus arteriosus often takes a tortuous course from the aorta to the pulmonary artery. This ductal anatomy is associated with increased resistance relative to that seen with ductal-dependent systemic blood flow. Excessive pulmonary overcirculation is less of a clinical concern in these patients.
Nutrition
The provision of preoperative nutrition to neonates with critical CHD is a poorly studied and controversial topic. The potential advantages of enteral nutrition must be weighed against the risk of inadequate mesenteric perfusion and predisposition for NEC. In some patients, the potential combination of myocardial dysfunction, cyanosis, and diastolic runoff through the ductus arteriosus may result in inadequate mesenteric oxygen delivery. In one large, retrospective study, approximately 3% of neonates admitted to a busy cardiac intensive care unit (ICU) developed NEC (49). Independent risk factors for developing NEC were prematurity, a history of resuscitation from severe cyanosis or shock, HLHS, or the presence of diastolic runoff through the ductus arteriosus or other aortopulmonary connections. The risk-benefit ratio for providing enteral nutrition must be individually determined for each patient and reassessed over time. Several reports suggest that cautious enteral feeding of at-risk patients is appropriate, but practice varies widely within and between centers (50).
▪ INTRAOPERATIVE CARE
Surgical Strategy
The initial reports of complete repair for selected congenital heart defects in neonates and young infants emerged in the late 1960s and early 1970s (51,52,53). Aided by advances in surgical technique and equipment, myocardial protection, cardiac anesthesia, and perioperative care, the strategy of early primary repair is now applied to most complex congenital heart lesions (54). Neonates with certain lesions that were considered before the 1980s to be inoperable, such as HLHS, currently undergo staged surgical palliation with relatively good outcomes (55,56).
The rationale for early intervention is based largely on the desire to minimize the sequelae of uncorrected complex CHD. In unoperated patients, cyanosis and heart failure may lead to failure to thrive, impairment of cognitive function due to chronic hypoxemia, paradoxical thromboembolism, and the development of pulmonary vascular obstructive disease. Thus, for most patients, early cardiac surgical intervention is desirable in order to limit the duration of preoperative cyanosis and heart failure and the many complications associated with these states (57,58,59). Postoperative complications including pulmonary hypertensive crises are also reduced using a strategy of early surgical intervention (60).
Intraoperative Management and Cardiopulmonary Bypass
An understanding of intraoperative events including the conduct of CPB is required to provide care for patients recovering from cardiac surgery. Once the patient has been anesthetized in the operating room, additional arterial and central venous access is obtained if necessary. A Foley catheter is typically placed. In the absence of contraindications, a preoperative transesophageal echocardiogram probe may be placed for pre- and postbypass imaging.
The majority of cardiac operations performed in neonates and infants require the use of CPB. The primary function of CPB is to temporarily replace the major functions of the heart and lungs while surgical interventions are performed on these organs. A typical CPB circuit used to perform these functions includes venous cannula(s) that drain systemic venous blood from the vena cavae or systemic venous atrium, a reservoir, a heat exchanger, a membrane oxygenator, a roller pump, a filter, and an arterial cannula to return blood to the aorta. Before initiation of CPB, the circuit is “primed” with standardized quantities of crystalloid solution, albumin, mannitol, sodium bicarbonate, heparin, calcium, and packed red blood cells. The patient is anticoagulated with heparin for the duration of CPB and cooled to a variable extent to minimize metabolic needs and oxygen consumption. Because hypothermia causes increased viscosity and red cell rigidity, hemodilution is used during hypothermic CPB.
To obtain a motionless heart for intracardiac repairs, the aorta is cross-clamped, and a potassium-rich cardioplegia solution is injected into the proximal ascending aorta. Asystole develops once the cardioplegia perfuses the coronary circulation. Myocardial protection is achieved through a combination of cardioplegia administration and hypothermia. Following placement of the aortic cross-clamp, blood from aortopulmonary collateral vessels will continue to return to the left atrium. To eliminate the left atrial blood return and facilitate certain complex left heart operations, deep hypothermic circulatory arrest (DHCA) may be used. “Deep hypothermia” refers to cooling of the core temperature to 18°C to 20°C. During circulatory arrest, the CPB pump is shut off and the perfusion cannula may be removed from the surgical field, creating optimal conditions for an accurate repair. Circulatory arrest times longer than 45 to 50 minutes may be associated with increased postoperative neurologic complications (61). Regional perfusion techniques have recently been designed to minimize or avoid the use of circulatory arrest, although evidence that such techniques improve neurodevelopmental outcomes is lacking (62,63). Following rewarming and weaning from CPB, the adequacy of the repair is assessed by some combination of vascular pressure measurements, CO-oximetry, and transesophageal echocardiogram (for small neonates and those with a contraindication to placement of a transesophageal echocardiogram probe, an epicardial echocardiogram may be obtained). Once the surgeon is satisfied with the repair, protamine is administered to reverse the effect of heparin. Additional blood components and antifibrinolytic agents may be administered to control bleeding.
Exposure to CPB triggers a cascade of complex neurohumoral and inflammatory responses that may impair myocardial, pulmonary, renal, and hematologic function. During CPB, formed elements of the blood are exposed to artificial surfaces and sheer stress. Ischemia-reperfusion injury occurs, as does microembolization of gas bubbles and particulate matter. The release of endogenous catecholamines, vasopressin, and endothelin and activation of the renin-angiotensin-aldosterone axis occur, all of which contribute to elevation of systemic and pulmonary vascular resistances and fluid retention. A generalized inflammatory response occurs, and the complement, coagulation, and fibrinolytic systems are activated. Capillary leak also occurs, related to fluid retention, the inflammatory response, and dilution of plasma proteins. White blood cells and platelets are also activated, leading to additional release of inflammatory mediators and proteolytic enzymes. Pulmonary leukosequestration occurs, as does oxygen free radical generation, and abnormal gas exchange and decreased pulmonary compliance may be evident. Platelet counts fall following CPB, and clotting factors are diluted, predisposing patients to bleeding. Myocardial systolic dysfunction may occur, manifesting as a low cardiac output state. Patients who are exposed to prolonged CPB times are at risk for postoperative morbidity and mortality. Several pharmacologic agents and management strategies may be employed in the operating room to minimize these adverse effects of CPB. Mannitol is administered to the priming solution to induce osmotic diuresis and act as an antioxidant. Multiple small trials have shown that corticosteroid administration blunts the inflammatory response to CPB; however, data regarding impact on important clinical outcomes are conflicting (64,65,66,67).
To aid in the removal of edema and hemoconcentrate the infant’s blood, ultrafiltration is typically used during rewarming on CPB. An additional technique known as modified ultrafiltration (MUF) may be used immediately following CPB. By removing fluid and inflammatory mediators, MUF may have favorable effects on hemodynamic indices, blood product requirements, and total body water balance.
Postoperative Care
Stabilization in the Intensive Care Unit following Surgery
Following the operation, the ICU service should obtain a standardized handoff from the anesthesiologist and the surgeon (68). Included in this handoff are details about the anesthetic regimen, the operative findings and surgical procedure performed, as well as duration of CPB, aortic cross-clamp, and circulatory arrest (if applicable). If performed, the results of the transesophageal echocardiogram and any pressure or CO-oximetry measurements should be communicated. Information regarding vascular access, pacing wires, chest drains, and intraoperative arrhythmias or other complications should be discussed.
Invasive hemodynamic monitoring is used in nearly all neonates and infants following cardiac surgery. One or more central venous lines are typically placed in the operating room. Sites for line placement are chosen depending upon the patient’s anatomy, anticipated postoperative course, and clinician preference. Some clinicians prefer to avoid placement of central venous lines in the subclavian and jugular veins in patients with single-ventricle physiology due to concerns for thrombosis of the upper extremity systemic veins. Intracardiac lines may be inserted by the surgeon prior to chest closure through the right atrial appendage to the right atrium (RA line) or through the right upper pulmonary vein or left atrial appendage to the left atrium (LA line).
A pulmonary artery catheter may be placed through an internal jugular or subclavian vein, the right atrium, or right ventricular outflow tract. These catheters are infrequently used in the current era but may be informative in selected patients at high risk for postoperative pulmonary hypertension, residual VSDs, or residual right ventricular outflow tract obstruction. Continuous monitoring of pulmonary artery pressure provides precise knowledge of the severity of pulmonary hypertension and immediate feedback as to the effectiveness of interventions to lower pulmonary artery pressure. Significant lability in pulmonary artery pressures during suctioning of the endotracheal tube or awakening from sedation may be a sign that a patient is not ready to be weaned. Measurement of a step-up in oxygen saturation from a superior vena cava or right atrial catheter to a pulmonary artery catheter may be helpful for the detection of significant residual left-to-right shunting (69). A pullback pressure tracing from the pulmonary artery to the right ventricle may be obtained at the time of removal of the pulmonary artery catheter, which quantifies any residual gradient across the right ventricular outflow tract. Some pulmonary artery catheters also have a thermistor tip, thus allowing cardiac output to be calculated by the thermodilution technique.
Proper interpretation of intracardiac and vascular pressure measurements (markers of ventricular loading conditions) is beneficial for the detection of residual lesions, the titration of volume administration, and the implementation of interventions that modify vascular tone. Interpretation of the atrial waveforms may provide insight into the presence of significant atrioventricular valve regurgitation or rhythm disturbances.
An arterial line facilitates continuous blood pressure monitoring and frequent arterial blood gas sampling. Care should be taken to ensure that blood pressure measurements are accurate. Dampened waveforms or pressures measured distal to stenotic arteries may give the false impression of hypotension. For example, arm blood pressure measurements in a patient who has, or had in the past, an ipsilateral Blalock-Taussig shunt may be diminished due to subclavian arterial stenosis or occlusion. The waveform and pulse pressure may be informative as the cardiac pathophysiology. For example, significant diastolic runoff may produce a wide pulse pressure in the presence of a systemic-to-pulmonary shunt, aortopulmonary collateral arteries, or severe aortic regurgitation. A narrow pulse pressure, along with tachycardia and hypotension, may signify cardiac tamponade. Patients who underwent repair of coarctation or aortic arch reconstruction should have four-extremity blood pressure measurements taken to document any residual aortic arch gradient.
A variety of factors may contribute to erroneous data obtained from invasive monitoring, including inappropriate transducer
height, and bubbles or clots in the catheters. Information obtained from invasive monitoring cannot be used in isolation but, when placed in the context of the overall clinical picture, can be very useful to guide management in the early postoperative period.
height, and bubbles or clots in the catheters. Information obtained from invasive monitoring cannot be used in isolation but, when placed in the context of the overall clinical picture, can be very useful to guide management in the early postoperative period.
Complications associated with central lines are uncommon but include air embolus, thrombus, infection, bleeding, and arrhythmias (70). When using LA lines in patients with two-ventricular repairs, and with any central line in those with single-ventricle physiology, care must be taken not to inject air into the systemic circulation. Complications at the time of intracardiac catheter removal include retention and bleeding; the latter has been shown to occur more commonly with pulmonary artery catheters (71,72). Consideration should be given to coagulation status and surgical availability when removing intracardiac lines and pulmonary artery catheters.
Assessment of the heart rhythm is an important part of the initial evaluation following surgery. The heart rate and rhythm should be continuously monitored at the bedside, and these data should be reviewable on a telemetry system. An ECG is usually obtained in the immediate postoperative period to serve as a new baseline should the patient subsequently develop a tachyarrhythmia or myocardial ischemia. Atrioventricular synchrony is important for optimizing cardiac output. Temporary pacing wires may be placed before chest closure in the operating room. These pacing wires may be interrogated when attempting to clarify arrhythmia mechanism. They also may be used to pace-terminate certain tachyarrhythmias and are effective for pacing in the setting of junctional ectopic tachycardia (JET), heart block, or other bradyarrhythmias. Sensing and capture thresholds should be assessed regularly. These wires are quite safe and may be removed at the bedside when no longer clinically indicated.
Temperature should be monitored and regulated closely. High temperature increases metabolic demands and may adversely affect hemodynamics and neurodevelopmental outcomes, whereas hypothermia may increase systemic vascular resistance and cause bradycardia.
A directed physical examination should be performed to assess the cardiopulmonary status and adequacy of the surgical repair. Any murmurs or gallops should be noted, although dressings and chest tubes may limit the auscultatory findings. It is common to hear a friction rub in the first few days following cardiac surgery, usually due to accumulation of a small amount of fluid in the pericardial space. The liver span should be noted. Adequate chest rise and breath sounds should be noted bilaterally. The quality and symmetry of peripheral pulses and perfusion of the extremities are useful means of assessing the adequacy of the systemic circulation. Caution must be used when attempting to estimate the adequacy of cardiac output by assessing capillary refill or peripheral-core temperature gradients, as both have a poor correlation with cardiac index, systemic vascular resistance index, and lactate levels (73).
Chest tubes should be assessed for location and proper function. In infants, the tubes may generally be removed when drainage falls to less than 20 to 30 mL/d and when there is no evidence for chylothorax or air leak. A CXR should be obtained upon admission to the ICU and for the first few days after surgery, as critically ill infants have a high percentage of films with an abnormality requiring intervention (74). Particular attention should be given to the location of all tubes and lines, as well as the heart size and lung fields.
The surgeon will occasionally leave the chest “open” after a Norwood procedure and other complex neonatal operations, with the skin closed using a Silastic patch, until hemodynamic stability can be achieved, bleeding controlled, and myocardial edema can decrease (75,76). The risk for mediastinitis may be increased when the chest is left open, and prophylactic antibiotics are typically continued during this time period (75). Delayed sternal closure may be performed in a few days in the operating room or in the ICU. Of note, much higher doses of narcotics are required during sternal closure when compared to most other procedures performed in the ICU. When the sternum is closed, respiratory compliance may decrease, necessitating additional ventilatory support.
Cardiopulmonary interactions play an important role in the physiology of neonates and infants following cardiac surgery (77). Arterial oxygen saturation is monitored continuously by pulse oximetry. Arterial blood gas analyses are obtained frequently, and attention should be given to ensure adequate oxygenation and ventilation for the individual patient’s physiology. Manipulations of PaCO2, PaO2, pH, and mean airway pressure may be used in the context of the patient’s physiology to modulate hemodynamics. Mechanical ventilation and sedation are also useful to minimize oxygen consumption in patients with limited cardiopulmonary reserve. Respiratory acidosis may increase pulmonary vascular resistance, and efforts should be made in most cases to avoid it (78). Low functional residual capacity may predispose patients to atelectasis and increased pulmonary vascular resistance, whereas pulmonary overdistension may increase pulmonary vascular resistance and decrease cardiac output. More generous tidal volumes are often needed after CPB when compared to those typically used in patients receiving mechanical ventilation for parenchymal lung disease.
Although early extubation policies have been reported for older infants and children, most neonates and young infants receive at least 12 to 24 hours of mechanical ventilation following congenital heart surgery. Criteria for extubation following cardiac surgery in neonates and infants are similar to those used in other patient populations. These include the presence of adequate cardiac output, appropriate neurologic status to maintain the airway, muscular strength to support respiratory pump function, acceptable gas exchange, and the absence of significant arrhythmias, bleeding, or fever.
Standard laboratory values need to be assessed in the early postoperative period. Electrolytes, including magnesium and ionized calcium levels, are monitored and corrected as needed. A complete blood count is initially obtained daily, and hemoglobin levels are monitored more frequently. In general, a hemoglobin level of 10 to 12 g/dL is appropriate for infants following a two-ventricular repair, and a hemoglobin level of 13 to 15 g/dL is reasonable for infants following a palliative operation with ongoing cyanosis. Relative anemia may place unnecessary workload on the myocardium, and transfusion of erythrocytes will improve oxygen delivery following pediatric cardiac surgery. An assessment of coagulation status (prothrombin and partial thromboplastin times [PTTs] and platelet count) is often obtained soon after CPB and repeated as clinically indicated.
In addition to the physical examination, several clinical parameters may be used to assess the adequacy of cardiac output and oxygen delivery in the immediate postoperative period. The presence of a metabolic acidosis, as quantified by a base deficit or lactate level, suggests inadequate systemic cardiac output and requires investigation. Lactic acidosis develops when inadequate tissue oxygen delivery leads to anaerobic metabolism. Following congenital heart surgery, elevated lactate levels in infants and children upon admission to the ICU are associated with increased morbidity and mortality (79). Venous oxygen saturation may be measured to estimate cardiac output. Urine output and markers of renal function (blood urea nitrogen and creatinine) provide a good estimate of the systemic cardiac output. Oliguria may be seen for 12 to 24 hours after complex cases, but improvement should occur thereafter in most patients. Infants often require inotropic support following CPB, and low-dose dopamine or milrinone is the initial drug of choice at many centers. Inotropic support is discussed in more detail in the “Low Cardiac Output” section below.
Infants may develop significant fluid retention following CPB, which may impair myocardial, respiratory, and gastrointestinal function. Strategies used to minimize this problem in the operating room, including the use of steroids and ultrafiltration, were discussed earlier. Despite the presence of total body fluid overload,
intravascular volume depletion is common in the first few hours following surgery due in part to capillary leak, and one or more fluid boluses may be required. Diuretics are typically initiated 12 to 24 hours after surgery, either as bolus doses or as continuous infusion. Electrolyte disturbances, particularly hypokalemia, hyponatremia, and a hypochloremic metabolic alkalosis, are commonly encountered as diuresis occurs in the first few days following CPB.
intravascular volume depletion is common in the first few hours following surgery due in part to capillary leak, and one or more fluid boluses may be required. Diuretics are typically initiated 12 to 24 hours after surgery, either as bolus doses or as continuous infusion. Electrolyte disturbances, particularly hypokalemia, hyponatremia, and a hypochloremic metabolic alkalosis, are commonly encountered as diuresis occurs in the first few days following CPB.
Analgesia is provided for all patients following cardiac surgery. High-dose fentanyl is well tolerated and blunts the stress response in neonates following CPB (80). Morphine or other narcotics are commonly used in the early postoperative period. Benzodiazepines or dexmedetomidine may be administered for amnesia and sedation. Neuromuscular-blocking agents may be used in selected patients to eliminate ventilator dyssynchrony and minimize oxygen consumption in patients with labile hemodynamics.
Gastrointestinal tract motility is decreased following cardiac surgery. Contributory factors include the inflammatory effects of CPB, anesthesia, fluid retention, narcotics, and (in some cases) high central venous pressures or low cardiac output. If these considerations are anticipated to preclude the initiation of enteral nutrition for several days, then parenteral nutrition may be administered. Histamine-2 receptor antagonists may be administered to minimize the risk of upper gastrointestinal bleeding.
Common Postoperative Complications
Low Cardiac Output
The product of heart rate and stroke volume determines cardiac output. Stroke volume is determined by preload, afterload, and contractility. Low cardiac output may thus be caused by abnormalities in one or more of these variables. An alteration in the heart rate or rhythm may impact cardiac output, and this is discussed further in the subsequent section on arrhythmias. Decreased preload may be related to intravascular volume depletion, which may occur from hemorrhage, diuresis, capillary leak, or cardiac tamponade. Increased afterload may result from pulmonary hypertension, peripheral vasoconstriction, or ventricular outflow obstruction. A decrease in myocardial contractility may result from a combination of factors including acidosis, electrolyte imbalance, hypothermia, or myocardial injury secondary to inflammation, a ventriculotomy, or ischemia-reperfusion injury. Low cardiac output, when defined as a cardiac index less than 2 L/min/m2, occurs following approximately 25% of complex two-ventricle neonatal repairs (Fig. 31.3) (81). Signs of low cardiac output include tachycardia, hypotension, poor peripheral perfusion, poor urine output, and metabolic acidosis. A detailed assessment must be undertaken to identify the cause in order to initiate proper and timely treatment to avoid endorgan failure.
 FIGURE 31.3 Scatter plots showing serial measurements of cardiac index as determined by thermodilution techniques in 122 patients after the arterial switch operation for TGA. Cardiac index fell during the first postoperative night, returning to baseline values by 24 hours after surgery. There was no significant difference between patients randomized to DHCA and those randomized to low-flow CPB (LF). Values are depicted as the mean and one side of each 95% CI. Reprinted from Wernovsky G, Wypij D, Jonas RA, et al. Postoperative course and hemodynamic profile after the arterial switch operation in neonates and infants. A comparison of low-flow cardiopulmonary bypass and circulatory arrest. Circulation 1995;92:2226-2235, with permission. |
A suboptimal surgical repair with significant residual intracardiac shunts, ventricular outflow or aortic obstruction, systemic or pulmonary venous stenosis, and/or valvular lesions may be the primary etiology for low cardiac output. The incidence of unplanned cardiac reinterventions following neonatal cardiac surgery may be as high as 5% to 10% (82). Early identification of significant residual lesions requires an appreciation of the anticipated “normal” postoperative course, close attention to the physical examination and data obtained by various monitoring modalities, open communication with the cardiovascular surgeon, and a high index of suspicion. In patients with a suspected residual lesion, cardiac imaging (usually starting with an echocardiogram) will be helpful to define the extent of the problem (83).
Treatment of low cardiac output in neonates differs in some respects from that in older children and adults due to differences in maturation-dependent cardiovascular physiology. Because neonates have a greater ratio of noncontractile to contractile myocardial mass, ventricular diastolic compliance is diminished. They also have a limited ability to increase stroke volume, which is relatively fixed at approximately 1.5 mL/kg. Thus, the cardiac output is heart rate dependent in this patient population. Heart rate may be optimized by pacing or by using intravenous infusions of chronotropic agents including dopamine or epinephrine. For infants with advanced second-degree or complete heart block, atrioventricular sequential pacing will increase cardiac output. Other postoperative arrhythmias are discussed in detail below.
Optimization of cardiac loading conditions is a key component to the management of the infant with low cardiac output. As described by the Frank-Starling mechanism, augmentation of the end-diastolic volume increases the number of interactions between actin and myosin molecules, resulting in a larger stroke volume and thus higher cardiac output. Hypovolemia may result in decreased ventricular filling and lower cardiac output. Certain cardiac operations in infants, such as repair of tetralogy of Fallot or truncus arteriosus, may result in impaired right ventricular compliance, and additional preload may be needed early after surgery to maintain cardiac output. Volume replacement should be guided by close attention to filling pressures, arterial pressures, and physical examination signs including gallops, liver distention, and peripheral pulses. The type and amount of fluid replacement is based upon the hematocrit, albumin level, and percentage of volume loss. Boluses of fluid are typically given in aliquots of 5 to 10 mL/kg over several minutes. A left atrial pressure above 14 to 16 mm Hg rarely produces an additional increase in cardiac output, and a left atrial pressure above 20 mm Hg may cause pulmonary edema. Of note, due to the large venous capacitance, right atrial pressures may not necessarily reflect the volume administered and should not be used in isolation to estimate preload.
Afterload, defined as the sum of forces that oppose systolic performance, is best quantified by systolic wall stress and vascular impedance, both of which are difficult to measure at the bedside. Elevated vascular resistance can significantly reduce stroke volume and the extent and velocity of wall shortening, resulting in decreased cardiac output and ventricular function. Increased vascular resistance is commonly seen following CPB in neonates (81). Physiologic factors such as hypoxia, acidosis, hypothermia, and pain may further increase systemic and pulmonary vascular resistance. Increased afterload may be due to residual right or left ventricular outflow tract obstruction. In the setting of decreased cardiac contractility, increased afterload may be a compensatory response necessary to maintain systemic blood pressure.
Vascular resistance, and thus afterload, can be pharmacologically decreased by vasodilatation of the systemic and pulmonary vascular beds. Systemic afterload reduction may be beneficial for patients with significant aortic or mitral valve regurgitation, left ventricular dysfunction, hypertension, or Norwood physiology. Afterload reduction in the pulmonary circulation may be beneficial for infants with tricuspid valve regurgitation, right ventricular dysfunction, and pulmonary hypertension. In addition to its inotropic properties, milrinone is a direct vasodilator of the systemic and pulmonary vascular beds. Milrinone has been shown to reduce the incidence of low cardiac output syndrome in infants and children undergoing complex two-ventricular repairs in a multicenter trial (84). Other vasodilators such as sodium nitroprusside, nitroglycerine, and nicardipine may be administered as infusions to reduce afterload. With the use of any vasodilators, volume augmentation may be necessary to fill the expanded vascular space and maintain adequate preload. Inhaled nitric oxide is used as a selective vasodilator of the pulmonary vascular bed, thereby decreasing right ventricular afterload. Positive-pressure ventilation may be used to reduce wall stress and left ventricular afterload in two-ventricle hearts (85,86).
Cardiac contractility is the load-independent ability of the myocardium to generate force. Contractility may be intrinsically impaired preoperatively. Intraoperatively, contractility may be depressed by medications, anesthesia, myocardial ischemia-reperfusion injury, an extensive ventriculotomy, or myocardial resection. Postoperatively, hypoxia, acidosis, and certain pharmacologic agents may all compromise contractility. Myocardial contractility may be enhanced with pharmacologic agents. Several inotropic drugs are currently available, and each has its own characteristic effects that may be more suitable for use in various clinical situations.
Dopamine activates dopaminergic, alpha, and beta receptors, depending on the dosage used. When prescribed at 1 to 5 µg/kg/min, dopamine preferentially dilates mesenteric and renal vessels and increases renal blood flow. Dosing at 5 to 10 µg/kg/min tends to increase cardiac output with a mild increase in heart rate. Higher doses of dopamine (10 to 20 µg/kg/min) are usually avoided after cardiac surgery unless vasoconstriction is desired. Low-dose dopamine is the initial drug of choice to increase myocardial contractility at many centers.
Dobutamine, a synthetic catecholamine, acts primarily on myocardial beta receptors. Contractility increases with infusion of dobutamine, but there may be less effect on heart rate or vascular tone than with dopamine.
Milrinone is a phosphodiesterase inhibitor that exerts a positive inotropic effect by increasing intracellular levels of cyclic AMP, leading to improving cardiac contractility. It also has lusitropic properties and acts as a direct vasodilator of the systemic and pulmonary vascular beds. Milrinone has been shown to improve hemodynamics in neonates with existing low cardiac output and decrease the incidence of low cardiac output syndrome in patients less than 6 years of age undergoing a biventricular repair (84).
Patients who have marked myocardial dysfunction that does not improve with one or a combination of the first-line agents listed above may respond to intravenous epinephrine at 0.01 to 0.05 µg/kg/min. When administered in this dosage range, epinephrine primarily activates beta-1 cardiac receptors, causing increased inotrope, and beta-2 peripheral receptors, causing reduced afterload. High-dose epinephrine (>0.1 µg/kg/min) is not frequently used because of marked alphaadrenergic action and adverse effect on renal perfusion. Occasionally, an infant may have vasodilatory shock with inappropriately low systemic vascular resistance refractory to conventional inotropic or vasopressors. Adjunction therapy with vasopressin infusion may restore cardiac output and reduce inotropic requirement (87). Infants with refractory low cardiac output, myocardial dysfunction, and impending cardiovascular collapse may benefit from reopening of the sternotomy incision in the ICU. The combination of edema of the myocardium and other mediastinal structures and any fluid or blood collections around the heart may contribute to poor ventricular filling and compliance. Reopening the chest will expand the mediastinal space until edema improves, and any fluid collections or blood clots can be easily removed.
In patients with excessive or prolonged inotropic or vasopressor needs following CPB, a state of relative adrenocortical insufficiency may exist. Myocardial beta receptor down-regulation may occur in infants and small children with CHD in the perioperative period. Corticosteroids, probably acting by improving vascular tone and up-regulating adrenergic receptors, may facilitate weaning of highdose catecholamine infusions (88).
Thyroid hormone plays an important role in the regulation of the cardiovascular system. Decreased levels of triiodothyronine (T3) and thyroxine levels occur in some infants following CPB (89). Clinical trials in such patients have found marginal benefits with thyroid hormone repletion following CPB (90,91).
Arrhythmias
Arrhythmias may compromise cardiac output following cardiac surgery. Prolonged CPB and aortic cross-clamp times and higher postoperative serum troponin levels are associated with the development of arrhythmias (92). When the atria contract against a closed atrioventricular valve during certain arrhythmias, cannon A waves (i.e., an increase in amplitude of the atrial pressure waveform) are typically seen. A specific arrhythmia diagnosis may often be obtained with a 12-lead ECG. If the mechanism remains unclear, an atrial electrogram may be obtained. One technique is to connect the two leg leads of the ECG to the temporary atrial pacing wires, and the two arm leads are placed on the patient’s arms in the usual fashion. A rhythm strip of leads I, II, and III is then recorded. With this configuration, lead I will be a surface electrogram, and a sharp atrial electrogram (indicating atrial depolarization) is produced in leads II and III, which may be compared to the surface QRS complex in lead I to determine the relationship of P waves to the QRS complexes.
Nearly any type of arrhythmia may occur following infant CPB. Premature atrial complexes (PACs) are occasionally seen and may be related to central lines, electrolyte disturbances, or surgical incisions; they are usually benign. Reentrant forms of supraventricular tachycardia (SVT), such as atrial flutter and atrioventricular reentrant tachycardia, occasionally occur following cardiac surgery in infants. Although rate-related aberrancy and antegrade conduction over accessory connections may occur, in most cases of SVT, the QRS complex in tachycardia is similar in morphology and axis to that seen on the baseline postoperative ECG. Note that the baseline QRS complex may be wide if a bundle branch block developed during surgery.
Atrial flutter is more likely to be seen following complex atrial baffling procedures. Atrial flutter is characterized by a rapid, regular atrial rate with variable atrioventricular conduction. Adenosine may be helpful diagnostically as the flutter waves will persist in the presence of atrioventricular block. Atrial flutter may be terminated using rapid atrial pacing or synchronized cardioversion. Atrioventricular reentrant tachycardia may be seen in infants with accessory connections (i.e., Ebstein anomaly, L-looped ventricular inversion). Preexcitation (Wolff-Parkinson-White syndrome) may be present on the ECG in sinus rhythm. Atrioventricular tachycardia is characterized by retrograde P waves following the QRS complex in a one-to-one relationship and is terminated with adenosine, rapid atrial pacing, or synchronized cardioversion. Atrioventricular nodal reentrant tachycardia is uncommon in infants. Retrograde P waves are typically hidden in the QRS complex. Termination may be achieved using adenosine, rapid atrial pacing, or synchronized cardioversion.
Ectopic atrial tachycardia is an uncommon form of SVT following congenital heart surgery. It is characterized by an automatic
atrial rhythm with “warm-up” and “cool-down” behavior at its onset and termination. Treatment strategies include normalization of electrolytes and temperature, minimizing inotropic infusions, and administration of a variety of antiarrhythmic agents including beta-blockers and amiodarone.
atrial rhythm with “warm-up” and “cool-down” behavior at its onset and termination. Treatment strategies include normalization of electrolytes and temperature, minimizing inotropic infusions, and administration of a variety of antiarrhythmic agents including beta-blockers and amiodarone.
JET is a common type of SVT seen in the postoperative period in neonates and infants, particularly following repair of the tetralogy of Fallot or VSDs (93). JET is an automatic rhythm originating from the bundle of His and, although thought to be caused by some form of trauma to the AV node during surgery, may occasionally be seen following cardiac surgical interventions distant from the AV node. Electrophysiologic characteristics of JET include a QRS morphology similar to that seen in sinus rhythm; atrioventricular dissociation with the ventricular rate faster than the atrial rate, or 1:1 retrograde conduction; “warm-up” behavior as seen with automatic arrhythmias; and failure to respond to adenosine, overdrive pacing, or cardioversion. Cannon A waves will have variable amplitude in patients with JET if ventricular-atrial (V-A) dissociation is present, but a constant increased amplitude will be present if the junctional rhythm is conducted to the atria in a 1:1 retrograde pattern. A 12-lead ECG or interrogation of temporary atrial pacing wires will confirm the diagnosis. Although JET usually resolves spontaneously in the first few days following surgery, hemodynamic compromise often occurs when the ventricular rate exceeds 170 to 180 beats/min. Treatment is individualized based on the patient’s heart rate and hemodynamic status. Strategies include fever control, provision of adequate analgesia to limit endogenous catecholamine release, minimizing the use of exogenous catecholamines, normalization of electrolytes and acid-base status, atrial pacing at a rate faster than the junctional rate, and mild hypothermia (94,95). If these measures are insufficient, medications to consider include amiodarone, esmolol, and procainamide. As these drugs have negative inotropic and chronotropic properties, close monitoring of hemodynamics and backup pacing capabilities are desirable.
Premature ventricular contractions (PVCs) may reflect myocardial irritability, electrolyte disturbances, or hypoxia. Lidocaine is often administered for frequent PVCs or nonsustained ventricular tachycardia (VT). VT is characterized by a fast, wide QRS complex that differs in morphology and axis compared to the postoperative baseline and has either 1:1 retrograde V-A conduction or V-A dissociation. The presence of complex ventricular ectopy or VT is suggestive of myocardial ischemia, and patients who had coronary manipulation as a component of their operation may warrant evaluation of myocardial function and coronary blood flow. Sustained VT with hemodynamic compromise may be terminated by synchronized cardioversion. Pharmacologic therapy, starting with either lidocaine or procainamide, may be considered for patients with hemodynamically stable VT. Ventricular fibrillation (VF) is characterized by a wide, complex, irregular rhythm that requires immediate defibrillation, starting at 2 J/kg. Chest compressions should be performed during pulseless VT or VF until a perfusing rhythm is reestablished.
Surgical complete heart block is typically apparent when the patient is rewarmed following CPB but less commonly may develop in the first few days following surgery. Temporary atrioventricular sequential pacing is used for initial treatment. The capture threshold of the temporary ventricular pacing wire should be determined frequently in patients who have developed or are at high risk for complete heart block. If atrioventricular conduction does not return for at least 7 days, a permanent pacemaker is indicated to prevent low cardiac output and sudden death (96).
Pulmonary Hypertension
The contemporary practice of cardiac surgical intervention in early infancy has been associated with a decreased incidence of pulmonary hypertensive crises for patients with many complex congenital heart defects. However, this complication continues to complicate the postoperative course of selected patients in the current era (97,98). Pulmonary hypertension following infant CPB may be caused by a combination of preoperative, intraoperative, and postoperative factors (Table 31.4). Infants with obstructed pulmonary venous return, mitral stenosis, long-standing pulmonary hypertension, or left ventricular outflow obstruction (critical aortic valve stenosis or coarctation of the aorta) may have increased pulmonary vascular resistance. Down syndrome is also a risk factor for severe postoperative pulmonary hypertension (99). CPB is associated with increased pulmonary vascular resistance in infants and children (81,100). The conduct of CPB is associated with partial ischemia of the pulmonary vasculature, leading to endothelial cell dysfunction and decreased endogenous production of nitric oxide. CPB leads to increased plasma levels of catecholamines, endothelin 1, and other pulmonary vasoconstrictors. In infants, prolonged CPB time has been associated with increased pulmonary vascular resistance in the postoperative period (97). The presence of significant pulmonary hypertension soon after weaning from CPB is predictive of subsequent pulmonary hypertension in the ICU and the need for prolonged ventilatory support. Postoperatively, large residual left-to-right shunts or obstruction to pulmonary venous or distal pulmonary arterial blood flow, or left ventricular outflow tract obstruction, all may cause pulmonary hypertension. Noxious stimuli, particularly suctioning of the endotracheal tube, may trigger a pulmonary hypertensive crisis.
TABLE 31.4 Factors Contributing to Perioperative Pulmonary Hypertension in Infants with Complex CHD |
|---|
