GENERAL PRINCIPLES OF CARDIAC SURGERY



Surgical results are excellent in simple abnor­malities such as uncomplicated atrial septal de­fects, but the mortality and morbidity are higher for repair of more complex lesions such as te-trology of Fallot. Results also depend oh whether the surgery is corrective or palliative; i.e., lesions that are incompletely corrected at the time of sur­gery inherently have less favorable outcome. Overall ventricular function is one of the most im­portant determinations of cardiac surgical risk.

The prognosis for postoperative recovery of left ventricular function differs depending on the un­derlying disease. For example, left ventricular function may not improve postoperatively in a pa­tient with a large myocardial scar from previous infarction, whereas the patient with left ventric­ular dysfunction secondary to aortic stenosis is likely to show improvement in left ventricular function upon correction of the aortic stenosis.

The general medical status of the patient may affect cardiac surgical results. For example, ab­normal pulmonary function is a common cause of complications after cardiac surgery. In addition to pre-existing primary lung diseases such as chronic obstructive pulmonary disease, pulmo­nary hypertension secondary to heart disease may increase the risk of surgery. Severe irreversible pulmonary hypertension from left-to-right shunts (for example, ventricular septal defect) is a con­traindication to surgery, but pulmonary hyperten­sion and increased pulmonary vascular resistance secondary to mitral stenosis usually resolves after surgical correction. The pre-existence of chronic renal failure increases the risk of acute renal fail­ure in the postoperative period. Even mild hepatic disease may be exacerbated after cardiac surgery, increasing the risk of acute hepatic failure. Pre­existing neurological defects may be exacerbated by cardiopulmonary bypass but usually eventu­ally return to baseline. In patients with serious carotid artery obstruction, care must be taken to maintain flow during cardiopulmonary bypass to minimize the risk of neurological injury.
All noncardiac medical conditions should be investigated and treated before cardiac surgery. Most medications required for optimal medical management should be administered up until the evening before or day of surgery, including beta blockers and antihypertensive medication. Con­tinuous monitoring of the electrocardiogram, ar­terial pressure, central venous pressure, and pul­monary arterial and wedge pressures is usually initiated prior to induction of anesthesia to obtain baseline values. An intra-aortic balloon counter­pulsation device may be inserted preoperatively in selected high-risk patients.

Complications of cardiopulmonary bypass in­volve those related to the cannulation and the technical institution of bypass and those related to the secondary effects of extracorporeal circu­lation on various organ systems. An example of the first category is a dissection of the aorta while introducing the aortic cannula. Pulmonary, renal, or neurological dysfunction is common following cardiopulmonary bypass, especially if disease is pre-existent.

Convalescence after cardiac surgery depends on the extent of pre-existing cardiac and noncardiac disease, the direct trauma of the operation, and the response to cardiopulmonary bypass. The thermodirution cardiac output should be period­ically monitored in the early postoperative hours. The adequacy of arterial pressure, peripheral pulses, skin temperature, urinary output, arterial blood gases, and mixed venous oxygenation is pe­riodically assessed. Arterial pressure may be apoor indicator of adequate output after surgery be­cause peripheral arterial resistance may be mark­edly elevated. If cardiac output is insufficient, the patient may require fluids, afterload reduction, in­otropic drugs and/or improvement in oxygena­tion. Measurement of left ventricular filling pres­sure is important to assess adequacy of fluid volume. If bradycardia is present, pacing via sur­gically implanted temporary wires (preferably atrial or AV sequential pacing) may optimize car­diac output. If pharmacological manipulation does not improve cardiac output, intra-aortic bal­loon counterpulsation may be required and may be of more value than inotropic agents if ischemia or arrhythmias are a particular problem. Tachy­arrhythmias must be treated vigorously. Exacer­bating factors such as hypoxia, anemia, or elec­trolyte abnormalities should be corrected. The pacing wires can be used to terminate atrial tachy­arrhythmias such as atrial flutter! Complex ven­tricular arrhythmias are treated with lidocaine as the drug of first choice. Atrial tachyarrhythmias may require treatment with digoxin, beta block­ers, or in some cases membrane-active agents such as procainamide.

Ventilation with positive end-expiratory pres­sure should be employed but used cautiously in patients with chronic obstructive pulmonary dis­ease. Patients are usually extubated within four to eight hours after surgery but sometimes not until the next morning.

If bleeding occurs postoperatively, examination of hematological parameters such as fibrinogen, platelets, and coagulation times should be ob­tained. Blood and blood products should be ad­ministered as indicated. Drainage from pleural and pericardial tubes should be monitored, and if excessive the patient may need to be returned to surgery for exploration. Cardiac tamponade is an occasional complication requiring early reopera­tion.