Heparin therapy during extracorporeal circulation: deriving an optimal activated clotting time during cardiopulmonary bypass for isolated coronary artery bypass grafting.

Bull's seminal work on heparin therapy during cardiopulmonary bypass (CPB) was carried out over 30 years ago and has not been updated in the modern era. No correlation with postoperative blood loss was performed. The optimal activated clotting time (ACT) with regard to blood loss has not been established for patients undergoing CPB. A minimum ACT of 400 is based on the lack of visible formation of clots in the CPB circuit. The effect of heparin dose, sensitivity, metabolism, patient size, elective/urgent, protamine reversal regime, returned pump blood volume and heparin content, and average ACT during CPB with regard to postoperative blood loss and resternotomy was examined in a consecutive series of patients undergoing isolated coronary artery bypass surgery. One hundred forty-four patients undergoing isolated CABG were studied. Resternotomy was too infrequent an event to analyze. Univariate analysis revealed that an average ACT less than 500 or greater than 700 was associated with significantly increased postoperative blood loss (p = .001). Multivariate analyses revealed that body mass index (p < .0001) and total loading dose of heparin (p = .0031) were also significant factors affecting postoperative blood loss. We extended his work by analyzing postoperative blood loss. An average ACT between 500 and 700 in our series was associated with significantly lower blood loss than an ACT higher or lower. We hypothesize that an ACT below 500 is probably associated with a low-grade coagulopathy but not macroscopic clot formation in the CPB circuit, and above 700 heparin rebound may become important. Each unit should evaluate blood loss and determine the optimal ACT target for their program.