What should be included in the preoperative assessment?
A thorough history and physical examination are essen-tial to assess the significance of the heart disease and how well it is managed. Most congenital cardiac anomalies are associated with a pathologic murmur.
The two major sequelae of significant congenital heart disease are congestive heart failure and cyanosis. Congestive heart failure should be controlled with digitalis, diuretics, and/or an afterload-reducing agent prior to any elective intervention. Drug therapy should be maintained perioper-atively. Adequate serum potassium levels and avoidance of hypocarbia are important to avoid digitalis toxicity in the patient taking digitalis. Control of congestive heart failure will improve pulmonary function and reduce the possibil-ity of perioperative hypoxemia or respiratory failure.
Cyanosis is a feature of cardiac lesions with right-to-left shunting, limited pulmonary blood flow, and/or venous admixture to the systemic circulation. Severe hypoxemia results in polycythemia with a concomitant increase in blood volume and viscosity, neovascularization, alveolar hyperventilation to maintain arterial normocarbia, and a poorly defined coagulopathy. Clubbing or osteoarthropa-thy of the distal phalanges of the fingers and toes is indica-tive of longstanding cyanotic heart disease. Increased blood viscosity increases cardiac work by increasing peripheral vascular resistance. Cerebral and/or renal thrombosis may occur with high hematocrits, particularly in the presence of dehydration. At hematocrits greater than 60–65%, oxygen transport is not improved and the fre-quency of serious thrombotic complications and coagu-lopathy increases. To improve organ perfusion and reduce cardiac workload, the hematocrit should be kept below these levels, if necessary by hemodilution. In most cases, increasing hematocrits are an indication for cardiac sur-gery to either improve pulmonary blood flow or correct the lesion. Because of the danger of hemoconcentration with prolonged fasting, preoperative fasting (NPO) times should be held to a minimum in cyanotic children or the patient should be hydrated intravenously.