A novel thrombelastograph tissue factor/kaolin assay of activated clotting times for monitoring heparin anticoagulation during cardiopulmonary bypass

We used a thrombelastograph (TEG) assay with tissue factor and kaolin (TEG TF/K) to measure activated clotting time (ACT) in 31 patients during cardiopulmonary bypass. For comparison, ACTs were also determined by a Hemochron Jr. Signature and a Hepcon HMS. The TEG TF/K correlated with both the Hepcon (r(2) = 0.789) and Hemochron (r(2) = 0.743) ACTs. The average ACT after heparin was 319 +/- 119 s (mean +/- sd) for the TEG TF/K compared with 624 +/- 118 s for the Hepcon instrument. To evaluate the effects of hemodilution on TEG TF/K and Hemochron assays, ACT assays were performed on blood diluted to 50% and titrated with heparin from 0 to 6 U/mL. Both instruments showed significant (P < 0.01) changes in the ACT-versus-heparin slope, but the 0 heparin intercept for the TEG TF/K ACTs was not significantly changed (P = 0.292), in contrast to that for the Hemochron device (P = 0.041). Both instruments also indicated the same 1.3:1 ratio of protamine to heparin for optimum heparin neutralization, with increasing ACTs at ratios >2.6:1. The TEG TF/K ACT assay rapidly monitors heparin anticoagulation, in addition to the capabilities of this instrument to monitor platelet function, clotting factors, and fibrinolysis.