In Vivo and In Vitro Evaluation of the Heparin Management Test versus the Activated Coagulation Time for Monitoring Anticoagulation Level in Aprotinin-Treated Patients during Cardiac Surgery

Introduction: Monitoring whole blood anticoagulation therapy with the activated coagulation time (kaolin ACT) and the heparin management test (HMT) were correlated in vivo with the plasma anti-activated factor X (anti-Xa) heparin concentration in patients who received variable doses of aprotinin and in vitro in the presence of increasing concentrations of aprotinin.

Methods: In 38 elective cardiac surgical patients who received an average heparin dose of 400 IU/kg and an average total aprotinin dose of 3.6 10(6) kallikrein-inhibiting units (KIU), ACT and HMT were measured in duplicate 6 times intraoperatively at predetermined intervals. Blood samples at each interval were also assayed for the anti-Xa plasma heparin concentration with the IL Test heparin chromogenic assay. The influence of increasing concentrations of aprotinin on HMT and ACT was also measured in vitro by using blood samples containing 6 IU/mL heparin from 6 additional patients after adding specific aliquots of aprotinin to achieve concentrations of 50, 100, 200, and 300 KIU/mL aprotinin. Linear regression analysis was used to compare HMT and ACT against anti-Xa. A P level <.05 was required for statistical significance.

Results: Duplicate measurements were taken at all intervals, and HMT and ACT values were significantly correlated, both with each other (r = 0.86; P < .01) and with anti-Xa activity (HMT, r = 0.81 [P < .01]; ACT, r = 0.71 [P < .01]). Aprotinin prolonged both the kaolin ACT and the HMT time in a dose-dependent manner (P < .05), and its influence was significantly less in vivo on the HMT time than on the kaolin ACT (P < .001).

Conclusions: The abilities of the HMT and the kaolin ACT to measure anticoagulation effects were not significantly different. Aprotinin prolonged both the kaolin ACT and the HMT time in a dose-dependent manner, but the HMT was significantly less affected by aprotinin in vivo. The HMT is a reliable alternative to measuring the ACT in cardiac operations and may offer greater accuracy in aprotinin-treated patients.