Successful management of the circulation after cardiac surgery requires knowlege and understanding of the preoperative condition of the patient and of perioperative events. Preoperative factors include the nature and severity of the cardiac lesion (distribution of coronary artery disease and ventricular function or quantitation of the valve lesion) and associated changes such as pulmonary hypertension. Medication may include b-blockers, calcium-channel antagonists, angiotensin-converting enzyme inhibitors, nitrates, diuretics, and aspirin, and these drugs may exert effects postoperatively by, for example, promoting bleeding (aspirin) or promoting arrhythmias due to electrolyte imbalance (diuretics). Associated conditions include hypertension, peripheral vascular disease, diabetes, and renal dysfunction; patients may have unrelated but important conditions such as hypothyroidism.

The heart suffers inevitable injury during surgery because aortic cross-clamping causes a degree of myocardial ischemia. This may be aggravated by prolonged cross-clamping or suboptimal myocardial protection. Hypothermia, used to reduce oxygen demand on bypass, may have harmful effects, and reperfusion after cross-clamp removal causes a well-defined injury. Revascularization may be incomplete or inadequate, so that surgery may not increase myocardial oxygen delivery sufficiently. Cardiopulmonary bypass also has circulatory effects; the extracorporeal circuit induces a systemic inflammatory response which includes alterations in coagulation and platelet function predisposing to bleeding that may be worsened by inadeqate reversal of systemic heparinization. Rewarming is rarely complete, and the priming volume of the bypass circuit provides an obligatory crystalloid and/or colloid load.

The circulation of the patient after cardiac surgery will be influenced by pre- and postoperative medication, preoperative myocardial and circulatory function, surgical events, and the effects of cardiopulmonary bypass, hypothermia, and the myocardial protection regimen employed.

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