CELITE AND KAOLIN PRODUCE DIFFERING ACTIVATED CLOTTING TIMES DURING CARDIOPULMONARY BYPASS UNDER APROTININ THERAPY

Since the introduction of the proteinase inhibitor aprotinin in cardia c surgery, a strong increase of the activated clotting time (ACT) duri ng the extracorporeal circulation phase (ECC) was reported in many cli nical studies, but with a lack of correlation between ACT and heparin concentration. In searching for a cause of this inconsistency we inves tigated different surface activators of the ACT in a clinical study. D uring ECC ACT was measured in parallel, using a Hemochron(R) device an d corresponding tubes (nominally 12 mg celite activator) for celite AC T, and a HemoTec(R) device with corresponding double tubes (nominally 0.1 ml kaolin activator) for kaolin ACT. Under the conditions of ECC, the kaolin ACT values (482 +/- 145 sec) were significantly lower than the celite ACT values (985 +/- 267 sec). These results were confirmed in ex-vivo experiments using an activated partial thromboplastin time (aPTT) model. With heparin alone, aPTT activated with celite and kaoli n were similar. Including aprotinin in this model, the celite aPTT sho wed no correlation to the heparin concentration, whereas the kaolin aP TT remained well correlated to the heparin concentration and similar t o the values without aprotinin. With aprotinin alone there were no cha nges of the aPTT times, whereas the celite ACT times were without any correlation. Our results indicate that using kaolin instead of celite the ACT measurements under aprotinin therapy stay in the same ranges a s without application of aprotinin: aprotinin has no detectable influe nce on kaolin-activated ACT. In our opinion, kaolin should be used as the surface activator for ACT measurements under the conditions of ECC , heparinization, and aprotinin therapy. Simply changing the heparin d osage or elevating the time limit of celite-activated ACT as has been recommended by several authors is illegitimate, because of the lack of correlation between celite-activated ACT and heparin concentration.