Anesthesia for Congenital Heart Surgery

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CHAPTER 20 Anesthesia for Congenital Heart Surgery

This chapter describes the perioperative management of major forms of congenital heart disease (CHD) that require surgery with the use of cardiopulmonary bypass. Congenital cardiac lesions that are primarily addressed in the catheterization laboratory or without CPB are discussed in Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures.

Congenital anomalies of the heart and cardiovascular system occur in 7 to 10 per 1000 live births. Congenital heart disease is the most common congenital disease, accounting for approximately 30% of all congenital diseases. CHD has become the principal cause of pediatric heart disease as the incidence of rheumatic heart disease has declined. Ten percent to 15% of children with CHD have associated congenital anomalies of the skeletal, genitourinary, or gastrointestinal system. The U.S. population of adults with CHD, surgically corrected or uncorrected, is estimated to exceed 1 million and is increasing steadily. As a result, it is not uncommon for adult patients with CHD to present for noncardiac surgery (see Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures).

Transthoracic and transesophageal echocardiography has facilitated early, accurate diagnosis of congenital heart disease. Unlike in adults, who may have limited transthoracic echocardiographic windows, high-quality echocardiographic images in pediatric patients are easily obtained. Most neonates with CHD can have sufficient and thorough evaluation of their cardiac lesions by echocardiography and thus avoid catheterization studies for diagnosis and management. In some instances, catheterization and angiography are necessary to clearly delineate coronary or aortopulmonary collateral anatomy and other intracardiac defects, to assess pressure gradients, and to potentially intervene for palliative or reparative purposes. Fetal cardiac ultrasonography has permitted antenatal diagnosis of congenital heart defects, allowing subsequent perinatal management in specialized tertiary care centers. Imaging modalities such as cardiac magnetic resonance imaging (MRI) and three-dimensional echocardiography are being used with increasing frequency.

Advances in molecular biology have provided a new understanding of the genetic basis of CHD. Chromosomal abnormalities are associated with an estimated 10% of congenital cardiovascular lesions. Two thirds of these lesions occur in patients with trisomy 21; the other one third of lesions are found in patients with other chromosomal abnormalities, such as trisomy 13 and trisomy 18, and in patients with Turner’s syndrome. Conotruncal lesions (tetralogy of Fallot, interrupted aortic arch, truncus arteriosus, ventricular septal defects) are commonly associated with a 22q11.2 chromosomal deletion. This defect is associated with DiGeorge syndrome, velocardiofacial syndrome, and conotruncal anomaly face syndromes. These syndromes can be associated with hypocalcemia, immunodeficiency, facial dysmorphia, palate anomalies, velopharyngeal dysfunction, renal anomalies, and developmental, speech, and feeding disorders. The remaining 90% or so of congenital cardiovascular lesions are currently without defined genetic association and are postulated to be the results of interactions of one or more genes with external or environmental factors (e.g., rubella, ethanol, lithium, maternal diabetes mellitus, folate deficiency).

Signs and symptoms of congenital heart disease in infants and children often include dyspnea, poor feeding, poor growth, delayed physical development, and the presence of a cardiac murmur. The diagnosis of CHD is apparent during the first week of life in about 50% of patients, and before 5 years of age in virtually all remaining patients. Echocardiography is the initial diagnostic step if CHD is suspected.

Congenital heart disease can be associated with specific complications. For example, infective endocarditis is a risk associated with most congenital cardiac anomalies. Sudden death occasionally occurs in patients who undergo surgical correction of CHD, presumably reflecting the effects of chronic abnormal hemodynamic loads, myocardial scarring and fibrosis, damage to the cardiac conduction system, or underlying (and presently occult) abnormal molecular and ion channel defects. Cardiac dysrhythmias are not usually a prominent presenting feature of CHD but can be more common as patients age and pathophysiologic sequelae of abnormal cardiac structure, function, and surgery accrue (see later and Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures). Table 20-1 summarizes the pathophysiology and clinical picture associated with a wide variety of congenital heart defects. Table 20-2 summarizes the surgical repair options for each type of lesion.

TABLE 20-1 Pathophysiology and Clinical Picture of Congenital Heart Defects

Lesion Type Pathophysiology Clinical Signs and Symptoms
Shunt Lesion without Outflow Tract Obstruction
Shunt Lesions with Right Ventricular Outflow Tract Obstruction
Transposition Physiology (Intercirculatory mixing)
Single Ventricle Physiology
One-Ventricle Lesions
Two-Ventricle Lesions
Left Ventricular Obstructive Lesions
Mitral Stenosis
Aortic Stenosis
Coarctation
Mixing of Systemic and Pulmonary Venous Blood with Series Circulation
CHF

PAPVR

TAPVR

CHF, Congestive heart failure; PAPVR, partial anomalous pulmonary venous return; TAPVR, total anomalous pulmonary venous return.

TABLE 20-2 Classification of Congenital Heart Lesions and Associated Repairs

Lesion Type Repair
Shunt Lesions
Left-to-Right
Complete repair
Complete repair
Complete repair
Complete repair
Complete repair
Right-to-Left
Complete repair
Complete repair
Complete repair
No repair
Transposition Physiology
Complete repair
Single-Ventricle Physiology
One-Ventricle Lesions
Staging to Fontan
Staging to Fontan
Staging to Fontan
Two-Ventricle Lesions
Complete repair
Complete repair
Complete repair
Left Ventricular Obstructive Lesions
Mitral Stenosis
Complete repair
Aortic Stenosis
Complete repair
Coarctation
Repair with likely residual lesions
Mixing of Systemic and Pulmonary Venous Blood with Series Circulation
Complete repair

Pathophysiology of congenital heart disease

Although some congenital heart defects involve purely obstructive or regurgitant valvular lesions, shunts (both physiologic and anatomic) are a hallmark of CHD. The concepts of shunting (both physiologic and anatomic), single-ventricle physiology, and intercirculatory mixing require discussion.

Shunting

Shunting is the process whereby venous return into one circulatory system is recirculated through the arterial outflow of the same circulatory system. Flow of blood from the systemic venous atrium or right atrium (RA) to the aorta produces recirculation of systemic venous blood. Flow of blood from the pulmonary venous atrium or left atrium (LA) to the pulmonary artery (PA) produces recirculation of pulmonary venous blood. Recirculation of blood produces a physiologic shunt. Recirculation of pulmonary venous blood produces a physiologic left-to-right (L-R), whereas recirculation of systemic venous blood produces a physiologic right-to-left (R-L) shunt.

Effective blood flow is the quantity of venous blood from one circulatory system reaching the arterial system of the other circulatory system. Effective pulmonary blood flow is the volume of systemic venous blood reaching the pulmonary circulation, whereas effective systemic blood flow is the volume of pulmonary venous blood reaching the systemic circulation. Effective pulmonary blood flow and effective systemic blood flows are the flows necessary to maintain life. Effective pulmonary blood flow and effective systemic blood flow are always equal, no matter how complex the lesions. Effective blood flow is usually the result of a normal pathway through the heart, but it may occur as the result of an anatomic R-L or L-R shunt, as in transposition physiology.

Total pulmonary blood flow (image) is the sum of effective pulmonary blood flow and recirculated pulmonary blood flow. Total systemic blood flow (image) is the sum of effective systemic blood flow and recirculated systemic blood flow. Total pulmonary blood flow and total systemic blood flow do not have to be equal. Therefore, it is best to think of recirculated flow (physiologic shunt flow) as the extra, noneffective flow superimposed on the nutritive effective blood flow. These concepts are illustrated in Figures 20-1 to 20-3.

Single-Ventricle Physiology

Single-ventricle physiology describes the situation in which there is complete mixing of pulmonary venous and systemic venous blood at the atrial or ventricular level, and the ventricle (or the ventricles) then distribute output to both the systemic and pulmonary beds. As a result of this physiology (1) ventricular output is the sum of pulmonary blood flow (image) and systemic blood flow (image), (2) distribution of systemic and pulmonary blood flow is dependent on the relative resistances to flow (both intracardiac and extracardiac) into the two parallel circuits, and (3) oxygen saturations are the same in the aorta and the pulmonary artery. This physiology can exist in patients with one well-developed ventricle and one hypoplastic ventricle, as well as in patients with two well-formed ventricles.

In the case of a single anatomic ventricle, there is always obstruction to either pulmonary or systemic blood flow as the result of complete or near-complete obstruction to inflow or outflow (or both) from the hypoplastic ventricle. In this circumstance, there must be a source of both systemic and pulmonary blood flow to assure postnatal survival. In some instances of a single anatomic ventricle, a direct connection between the aorta and the pulmonary artery via a patent ductus arteriosus (PDA) is the sole source of systemic blood flow (e.g., hypoplastic left heart syndrome [HLHS]) or of pulmonary blood flow (e.g., pulmonary atresia with intact ventricular septum). This is known as ductal dependent circulation. In other instances of a single anatomic ventricle, intracardiac pathways provide both systemic and pulmonary blood flow without a PDA. This is the case when tricuspid atresia occurs along with normally related great vessels, a nonrestrictive ventricular septal defect (VSD), and minimal or absent pulmonary stenosis.

In certain circumstances, single-ventricle physiology can exist in the presence of two well-formed anatomic ventricles: (1) tetralogy of Fallot (TOF) with pulmonary atresia (in which pulmonary blood flow is supplied via a PDA or multiple aortopulmonary collateral arteries), (2) truncus arteriosus, and (3) severe neonatal aortic stenosis and interrupted aortic arch (in which a substantial portion of systemic blood flow is supplied via a PDA).

Table 20-3 lists a number of single-ventricle physiology lesions. All patients with single-ventricle physiology who have severe hypoplasia of one ventricle will ultimately undergo the staged surgeries that comprise the single-ventricle pathway and result in Fontan physiology (described later). Patients with single-ventricle physiology and two well-formed ventricles are usually able to undergo a two-ventricle repair. In some cases, the two-ventricle repair will be complete. In others, significant residual lesions (VSD, aortopulmonary collaterals) will remain. In patients with single-ventricle physiology, the arterial oxygen saturation (Sao2) is determined by the relative volumes and saturations of pulmonary venous and systemic venous blood flows that have mixed and reach the aorta (see Fig. 20-1).

TABLE 20-3 Anatomic Subtypes of Single-Ventricle Physiology

  Aortic Blood Flow from: Pulmonary Artery Blood Flow from:
HLHS PDA RV
Severe neonatal aortic stenosis PDA RV
IAA LV (proximal)PDA (distal) RV
PA with IVS LV PDA
Tetralogy of Fallot with pulmonary atresia LV PDA, MAPCAs
Tricuspid atresia, NRGA, with pulmonary atresia (type 1A) LV PDA, MAPCAs
Tricuspid atresia, NRGA, with restrictive VSD and pulmonary stenosis (type 1B) LV LV thru VSD to RV
Tricuspid atresia, NRGA, with non-restrictive VSD and no pulmonary stenosis (type 1C) LV LV thru VSD to RV
Truncus arteriosus LV and RV Aorta
DILV, NRGA LV LV thru BVF

BVF, Bulboventricular foramen; DILV, double-inlet left ventricle; HLHS, hypoplastic left heart syndrome; IAA, interrupted aortic arch; LV, left ventricle; MAPCAs, multiple aortopulmonary collateral arteries; NRGA, normally related great arteries; PA with IVS, pulmonary atresia with intact ventricular septum; PDA, patent ductus arteriosus; RV, right ventricle; VSD, ventricular septal defect.

Intercirculatory Mixing

Intercirculatory mixing is the unique situation that exists in transposition of the great arteries (TGA) (see Fig. 20-2). In TGA, there are two parallel circulations because of the existence of atrioventricular concordance (right atrium to right ventricle [RA-RV], and left atrium to left ventricle [LA-LV]) and ventriculoarterial discordance (right atrium to aorta [RV-Ao], and left ventricle to pulmonary artery [LV-PA]). This produces a parallel rather than a normal series circulation. In this arrangement, parallel recirculation of pulmonary venous blood in the pulmonary circuit and systemic venous blood in the systemic circuit occurs. Therefore, the physiologic shunt or the percentage of venous blood from one system that recirculates in the arterial outflow of the same system is 100% for both circuits.

Thus, this lesion is incompatible with life unless there are one or more communications (atrial septal defect [ASD], patent foramen ovale [PFO], VSD, PDA) between the parallel circuits to allow intercirculatory mixing. In the presence of mixing, arterial saturation (Sao2) is determined by the relative volumes and saturations of the recirculated systemic and effective systemic venous blood flows reaching the aorta (see Fig. 20-3).

General Approach to Anesthetic Management

Preparation for Anesthesia

Preparation for anesthesia begins with a thorough assessment of the patient’s medical and surgical conditions (as with any preoperative assessment). Also necessary is a complete understanding of the patient’s “original” cardiac anatomy and physiology, any previous surgical or catheterization procedures and complications, the present status of the patient’s anatomy and pathophysiology, current medications, and involvement of other organ systems (e.g., renal insufficiency). Also necessary is detailed knowledge of the anatomic and functional information contained in the most recent diagnostic studies (echocardiography or Doppler on most patients, and often catheterization and cardiac MRI data as well), as well as of the planned procedure and its acute physiologic consequences and potential complications.

Basic operating room preparation begins with the considerations common to all pediatric anesthesia, including the presence of appropriately sized airway; ventilator; monitoring; cardioversion, defibrillation, and external pacing (including external pads or paddles and internal paddles of appropriate sizes); temperature control (capability for warming and cooling); blood and fluid administration; and vascular access equipment and supplies. In addition, an extra blood pressure cuff and pulse oximeter should be on hand in case the need arises for some specific lesions. Size-appropriate equipment and supplies (including vascular ultrasound devices and pressure monitoring transducers) to perform peripheral and femoral arterial and central venous cannulation and pressure monitoring are necessary. In addition to standard drugs, one should have predrawn and hence immediately available syringes containing weight-appropriate concentrations of emergency drugs including epinephrine, calcium (gluconate or chloride salt), phenylephrine, and atropine. Other agents, such as sodium bicarbonate, glucose, potassium chloride, antiarrhythmics (e.g., adenosine, procainamide), β-blockers, heparin, and inotropes and other vasoactive drugs for infusion (e.g., dopamine, dobutamine, epinephrine, phenylephrine, milrinone, vasopressin, nitroglycerin, nitroprusside, esmolol) should be immediately available. Many find it helpful to complete a patient-specific emergency card for each patient that contains weight-based concentrations, dosages, and bolus volumes or infusion rates for the most frequently used agents before starting the case.

No one anesthetic induction technique is suitable for all patients with congenital heart disease. The patient’s age, cardiopulmonary function, degree of cyanosis, and emotional state all play roles in the selection of an anesthetic technique. Intravenous administration of induction agents clearly affords the greatest flexibility in terms of drug selection and drug titration and allows prompt control of the airway. We believe that intravenous induction is the preferred technique in the majority of patients, including those with significantly impaired ventricular systolic function, significant obstruction to blood flow (e.g., severe aortic stenosis), and systemic or suprasystemic pulmonary artery pressures. In all patients, ensuring adequacy of the airway and gas exchange is a preeminent consideration.

Sevoflurane, halothane, isoflurane, and fentanyl plus midazolam do not change the ratio of pulmonary-to-systemic blood flow (image) in children with atrial and ventricular septal defects when cautiously administered with 100% oxygen (Laird et al., 2002). Sevoflurane (1 minimum alveolar concentration [MAC]) and fentanyl plus midazolam have no significant effect on myocardial function in patients with a single ventricle (Ikemba et al., 2004). Halothane (1 and 1.5 MAC) depresses cardiac index and contractility more than comparable levels of sevoflurane, isoflurane, and fentanyl plus midazolam anesthesia (Rivenes et al., 2001). In addition, halothane anesthesia may result in more severe hypotension and emergent drug use than sevoflurane anesthesia in children with CHD (Russell et al., 2001).

Intravenous Induction

Many of these patients come to the operating room with functioning intravenous (IV) access. For those without it, effective premedication may facilitate IV placement and allow the attendant risks of mask induction in this population to be avoided. In some patients, oral midazolam (0.5 to 1.0 mg/kg) may suffice. Others have used oral combinations of meperidine (3 mg/kg) and pentobarbital (4 mg/kg) successfully in this group of patients (Nicolson et al., 1989). Ketamine (∼3 to 6 mg/kg) and midazolam (1 mg/kg) given orally in combination can be quite effective in terms of producing deep sedation and conditions favorable for IV placement and subsequent intravenous induction (Auden et al., 2000).

High-dosage synthetic narcotics in combination with pancuronium (0.1 mg/kg) are commonly used for intravenous induction in neonates and infants. The vagolytic and sympathomimetic effects of pancuronium counteract the vagotonic effect of synthetic opioids. In patients with a low aortic diastolic blood pressure and a high baseline heart rate, vecuronium (0.1 mg/kg) or cisatracurium (0.2 mg/kg) may be used without affecting heart rate. In older children with mild to moderately depressed systolic function, lower dosages of a synthetic opioid can be used in conjunction with etomidate (0.1 to 0.3 mg/kg) (Sarkar et al., 2005).

Ketamine (1 to 2 mg/kg) is a useful induction agent. For patients with both normal and elevated baseline pulmonary vascular resistance (PVR), ketamine causes minimal increases in pulmonary artery pressure as long as the airway and ventilation are supported (Morray et al., 1984). The tachycardia and increase in systemic vascular resistance (SVR) induced by ketamine may make it unfavorable for use in patients with systemic outflow tract obstructive lesions (Williams et al., 2007).

The myocardial depressive and vasodilatory effects of propofol and thiopental make them largely unsuitable as induction agents except in patients with simple shunt lesions in whom cardiovascular function is preserved (Williams et al., 1999b).

An alternative to IV induction in patients with difficult peripheral IV access is intramuscular induction with ketamine (3 to 5 mg/kg), succinylcholine (2 to 5 mg/kg), and glycopyrrolate (8 to 10 mcg/kg). Glycopyrrolate is used to reduce airway secretions associated with ketamine administration and to prevent the bradycardia that may accompany succinylcholine administration. The required dosage of succinylcholine per kilogram body weight is highest in infants. This technique provides prompt induction and immediate control of the airway with tracheal intubation. It is useful when it is anticipated that initial IV access will have to be obtained via the internal or external jugular vein or the femoral vein. One potential problem is that the short duration of action of succinylcholine limits the period of patient immobility. An alternative technique combines intramuscular ketamine (4 to 5 mg/kg), glycopyrrolate (8 to 10 mcg/kg), and rocuronium (1.0 mg/kg). This technique is limited by the longer time interval until attainment of adequate intubating conditions and the longer duration of action of rocuronium as compared with succinylcholine.

Specific lesions

Atrial Septal Defect

Atrial septal defect accounts for about one third of the congenital heart disease detected in adults, with the frequency in women two to three times that in men. See related video online at www.expertconsult.com.

imageStrictly speaking, an ASD is a communication between the left and right atrium resulting from a defect in the intraatrial septum, which consists of a central membranous portion and a thicker inferior and superior fatty limbus. The central membranous portion is formed by tissue of the septum primum, ultimately forming the fossa ovalis. This membrane lies posterior to the superior aspect of the fatty limbus.

ASDs are classified by their location (Fig. 20-6). There are four morphologic types: ostium secundum defects, ostium primum defects, inferior and superior sinus venosus defects, and coronary sinus (CS) defects. Although they are classified as ASDs, sinus venosus and CS defects are not truly defects in the intraatrial septum. Secundum ASDs account for 80% of all ASDs. Whereas a PFO results from incomplete fusion of an intact fossa ovalis membrane with the superior aspect of the fatty limbus, an ostium secundum ASD is the result of actual deficiencies in the membrane (septum primum) of the fossa ovalis. Isolated ostium primum ASDs, also known as partial atrioventricular canal defects, are discussed later (see Atrioventricular Canal Defects). The isolated ostium primum defect extends from the inferior intraatrial septum fatty limbus, to the crest of the intact ventricular septum.

Both types of sinus venous defects are associated with partially anomalous pulmonary venous return. In the case of the superior defect, anomalous drainage of the right upper pulmonary vein into the junction of the superior vena cava (SVC) and the RA is the most common finding. In the case of the inferior defect, scimitar syndrome (anomalous drainage of the right upper and lower pulmonary veins to the junction of the inferior vena cava [IVC] and RA, aortopulmonary collaterals to the right lower lobe, and hypoplasia of the right lung) can be seen.

Clinical Presentation

The physiologic consequences of ASDs are the same regardless of the anatomic location and reflect the shunting of blood from one atrium to the other; the direction and magnitude of the shunt are determined by the size of the defect and the relative compliance of the ventricles. A small defect (less than 0.5 cm in diameter) is associated with a small shunt and no hemodynamic sequelae. When the diameter of the ASD approaches 2 cm, it is likely that left atrial blood is being shunted to the right atrium (the right ventricle is more compliant than the left ventricle), resulting in increased pulmonary blood flow. A systolic ejection murmur audible in the second left intercostal space may be mistaken for an innocent flow murmur. The electrocardiogram (ECG) may reflect right axis deviation and incomplete right bundle branch block. Atrial fibrillation and supraventricular tachycardia may accompany an ASD that remains uncorrected into adulthood. The chest radiograph is likely to reveal prominent pulmonary arteries. Echocardiography is the mainstay of diagnostic imaging for these patients, with catheterization usually reserved for assessment of pulmonary artery pressures when indicated.

Because they initially produce no symptoms or striking findings on physical examination, ASDs may remain undetected for years. Symptoms resulting from large ASDs include dyspnea on exertion, supraventricular dysrhythmias, right heart failure, paradoxical embolism, and recurrent pulmonary infections. Prophylaxis against infective endocarditis is not recommended for patients with an ASD unless a concomitant valvular abnormality (mitral valve prolapse or mitral valve cleft) is present. Supraventricular dysrhythmias and pulmonary hypertension can increase in frequency, even for moderately sized defects, as patients enter the second and third decades of life.

Some small ostium secundum ASDs can be primarily closed, whereas larger defects are patched, usually with pericardium. An alternative is nonoperative device closure of secundum ASDs in the cardiac catheterization laboratory (see Chapter 21, Congenital Cardiac Anesthesia: Non-Bypass Procedures). Primum ASDs generally require patch closure and suture closure of the anterior leaflet mitral cleft. Sinus venous defects without partially anomalous pulmonary venous return can be closed primarily with a patch. An alternative procedure is performed when the pulmonary vein or veins anomalously enter the SVC. The SVC is transected above the origin of the anomalous vein or veins, and the SVC orifice is directed across the defect into the LA with a pericardial patch. The distal end of the SVC is then anastomosed in an end-to-end fashion to the roof of the RA appendage, recreating SVC-to-RA continuity.