Heparin Resistance in the Pre-Cardiotomy Patient

Patients who undergo heart surgery utilizing cardiopulmonary bypass are systematically anticoagulated with heparin. Heparin is also used for anticoagulation in patients with myocardial infarctions. A discrepancy has been observed in reactivity to heparin in the operating room between patients who are on intravenous heparin and those who are not. A comparison study utilizing 40 patients was performed. Group A consisted of 20 patients who had no heparin therapy history preoperatively. Group B consisted of 20 patients who had been on intravenous heparin therapy for up to four hours prior to their surgery. All patients were coronary artery bypass grafting candidates and were heparinized for cardiopulmonary bypass, utilizing a 3000u/kg protocol with a target activated clotting time (ACT) of 480 seconds. Heparin lot numbers were evenly distributed between the two groups. Group A demonstrated a mean post heparin bolus ACT or 541 seconds, while group B showed a mean ACT or 358 seconds. The nonheparin therapy patients required a mean additional perioperative heparin dose of 3,800 units to maintain the ACT above 480 seconds. The heparin therapy patients had a mean additional dose or 16,500 units. Patients who receive IV heparin therapy prior to cardiopulmonary bypass may require additional heparin to adequately anticoagulate them for extracorporeal circulation.