RESUMO
The reasons for the highly variable response of patients to heparin remain incompletely understood. Empirical maintenance of the activated clotting time (ACT) at levels of 400 to 480 seconds appears to be safe for cardiopulmonary bypass (CPB). For patients with ACT responses lower than predicted for initial heparin doses, titration with additional heparin has been customary. In 44 patients undergoing cardiopulmonary bypass, 20 patients were identified as having initial ACTs of 300 seconds or less after receiving 300 units per kilogram of heparin. In 11 of them, ACTs were titrated to 400 to 480 seconds with additional heparin. Nine were given 2 units of fresh frozen plasma shortly after institution of CPB. In this group, there was significant augmentation of the ACT immediately after infusion of plasma. No differences in total heparin dosages given during CPB were found between 24 control patients with initially acceptable ACTs and the group receiving fresh frozen plasma. In contrast, more heparin was necessary in the patients with a low ACT titrated with heparin alone. Data also indicated that protamine sulfate requirements were substantially lower after administration of plasma than were those in either the control or the heparin-titrated, low ACT group. Fresh frozen plasma appears to "normalize" the heparin-ACT dose-response curve in heparin-resistant patients and to lessen total heparin requirements during CPB.
