Evaluation of coagulation during cardiopulmonary bypass with a heparinase-modified thromboelastographic assay

Abstract

Thromboelastography (TEG) is a useful method of assessing perioperative coagulation function in patients undergoing cardiac surgery. The presence of significant amounts of heparin in blood samples, however, prevents determination of changes in coagulation function by TEG or introduces artifactual error if samples contain heparin that is not present in vivo. For these reasons, whole blood coagulation function monitoring with TEG has not been feasible during cardiopulmonary bypass (CPS) with heparin anticoagulation. In this study, data obtained from 42 volunteers are presented to describe the effects of heparinase on TEG variables in the presence and absence of heparin. These data indicate that heparinase does not affect TEG parameters of whole blood not containing heparin and reverses the TEG effects of low levels of heparin contamination. Subsequently, 51 patients undergoing coronary artery surgery were studied using a modified TEG assay that incorporates in vitro application of heparinase to allow measurement of TEG parameters before, during, and after CPS. Heparinase-modified TEG assays facilitated diagnosis of heparin contamination in preoperative blood samples and permitted baseline TEG evaluation in patients receiving preoperative heparin infusions. Heparinase modified TEG assays revealed declines in α and MA values during CPS, which persisted and significantly correlated with values after protamine infusion ( α: r = 0.77, P = 0.001; MA: r = 0.78, P = 0.001). After CPS, heparinase-modified TEG assays revealed no evidence of residual heparin in 50% of 12 samples with activated clotting times (ACT) _ ̆ 140 seconds and that 21 of 39 patients had evidence of residual heparin despite ACT values < 140 seconds, consistent with the relative insensitivity of ACT and the greater sensitivity of TEG to very low levels of heparin. The use of heparinasemodified TEG assays during CPS also permitted detection of significant fibrinolysis in one patient before protamine administration. The data gathered in this study indicate the utility of the heparinase-modified TEG assay to monitor whole blood coagulation during CPB, identify the presence of heparin in TEG samples before systemic heparin therapy or protamine reversal, and evaluate platelet-fibrinogen interaction in patients receiving systemic heparin.