RESUMO
OBJECTIVE: To evaluate whether patients with positive or negative heparin antibodies who received heparin preoperatively by continuous infusion developed cardiovascular changes upon heparin administration prior to cardiopulmonary bypass. DESIGN: Clinical trial. SETTING: Single institution, academic hospital. PARTICIPANTS: Eighty (80) patients with good ventricular function on low-dose heparin infusion prior to surgery. INTERVENTIONS: Patients were divided into 2 equal groups: group A had negative heparin antibodies (% ratio < 0.26), group B had positive heparin antibodies (% ratio > 1.2). All patients received heparin, 400 units/kg, prior to institution of cardiopulmonary bypass. Cardiovascular changes, activated coagulation time (ACT), and histamine levels were measured before and 5 minutes after administration of heparin. Platelets also were counted before and 6 hours after surgery. MEASUREMENTS AND MAIN RESULTS: Significant hypotension and decreased cardiac index occurred in patients with positive heparin antibodies who received heparin prior to cardiac surgery. Histamine levels increased significantly 5 minutes after heparin administration. Significant thrombocytopenia occurred 6 hours after surgery in group B patients. There was a good correlation between heparin antibodies, histamine levels, thrombocytopenia and cardiovascular changes. Group B patients also had heparin resistance as manifested by a lower ACT after the loading doses of heparin. CONCLUSION: Patients with positive heparin antibodies pretreated with heparin prior to surgery developed a type of immune-mediated cardiovascular changes and postoperative thrombocytopenia.