Identification of heparin resistance during cardiac and vascular surgery.

An investigation of the response of the activated clotting time to systemic heparinization during cardiopulmonary bypass and peripheral vascular surgery was prompted by the death from clotting of a patient with endocarditis while undergoing valve replacement. The activated clotting time during cardiopulmonary bypass was thereafter maintained at 300 to 400 seconds. Consumption of heparin sodium, derived from an individual dose-response curve, was 0.01 to 3.86 units/kg/min. There was no correlation between initial heparin resistance and the subsequent rate of consumption. Some patients undergoing peripheral vascular surgery required additional heparin after an initial standard dose of 8,000 units so as to maintain their activated clotting time at twice the control values. These data are discussed in relation to previous articles, and recommendations are made for adequate intraoperative heparinization.