Congenital Heart Disease

Congenital Heart Disease

Preoperative Considerations

Congenital heart disease encompasses a seemingly endless list of abnormalities that may be detected in infancy, early childhood, or, less commonly, adult-hood. The incidence of congenital heart disease in all live births approaches 1%. The natural history of some defects is such that patients often survive to adulthood ( Table 21–17). Moreover, the number of surviving adults with congenital heart disease is steadily increasing, possibly as a result of advances in surgical and medical treatment. An increasing number of patients with congenital heart disease may therefore be encountered during noncardiac surgery and obstetric deliveries. Knowledge of the

anatomy of the original heart structure defect and of any corrective repairs is essential prior to anesthetiz-ing the patient with congental heart disease (CHD).

The complex nature and varying pathophysiol-ogy of congenital heart defects make classification difficult. A commonly used scheme is presented in Table 21–18. Most patients present with cyano-sis, congestive heart failure, or an asymptomatic abnormality. Cyanosis is typically the result of an abnormal intracardiac communication that allows unoxygenated blood to reach the systemic arterial circulation (right-to-left shunting). Congestive heart failure is most prominent with defects that either obstruct left ventricular outflow or mark-edly increase pulmonary blood flow. The latter is usually due to an abnormal intracardiac commu-nication that returns oxygenated blood to the right heart (left-to-right shunting). Whereas right-to-left shunts generally decrease pulmonary blood flow, some complex lesions increase pulmonary blood flow—even in the presence of right-to-left shunt-ing. In many cases, more than one lesion is present.

In fact, survival (prior to surgical correction) with some anomalies (eg, transposition, total anoma-lous venous return, pulmonary atresia) depends on the simultaneous presence of another shunting lesion (eg, patent ductus arteriosus, patent foramen ovale, ventricular septal defect). Chronic hypox-emia in patients with cyanotic heart disease typi-cally results in erythrocytosis. This increase in red cell mass, which is due to enhanced erythropoietin secretion from the kidneys, serves to restore tissue oxygen concentration to normal. Unfortunately, blood viscosity can also rise to the point at which it may interfere with oxygen delivery. When tissue oxygenation is restored to normal, the hematocrit is stable (usually <65%), and symptoms of the hyper-viscosity syndrome are absent, the patient is said to have compensated erythrocytosis. Patients with uncompensated erythrocytosis do not establish this equilibrium; they have symptoms of hypervis-cosity and may be at risk of thrombotic complica-tions, particularly stroke. The last is aggravated by dehydration. Children younger than age 4 years seem to be at greatest risk of stroke. Phlebotomy is generally not recommended if symptoms of hyper-viscosity are absent and the hematocrit is <65%.

Coagulation abnormalities are common in patients with cyanotic heart disease. Platelet counts tend to be low-normal, and many patients have subtle or overt defects in the coagulation cascade. Phlebotomy may improve hemostasis in some patients. Hyperuricemia often occurs because of increased urate reabsorption secondary to renal hypoperfusion. Gouty arthritis is uncommon, but the hyperuricemia can result in progressive renal impairment.

Preoperative Doppler echocardiography is invaluable in helping to define the anatomy of the defect(s) and to confirm or exclude the existence of other lesions or complications, their physiologi-cal significance, and the effects of any therapeutic interventions.

Anesthetic Management

Th is population of patients includes four groups: those who have undergone corrective cardiac sur-gery and require no further operations, those who have had only palliative surgery, those who have not yet undergone any cardiac surgery, and those whose conditions are inoperable and may be awaiting car-diac transplantation. Although the management of the first group of patients may be the same as that of normal patients (except for consideration of prophy-lactic antibiotic therapy), the care of others requires familiarity with the complex pathophysiology of these defects. Even patients who have had corrective surgery may be prone to the development of periop-erative problems (Tables 21–19 and 21–20). Some surgical procedures eliminate the risk of endocar-ditis, whereas others increase the risk through the use of prosthetic valves or conduits or the creation of new shunts.

For the purpose of anesthetic management, con-genital heart defects may be divided into obstructive lesions, predominantly left-to-right shunts, or pre-dominantly right-to-left shunts. In reality, shunts can also be bidirectional and may reverse under cer-tain conditions.