Fragmin: dose-dependence and mechanisms of clottingTM: dose-dependence and mechanisms of clotting (LMWH) : dose-dependence and mechanisms of clottingvs: dose-dependence and mechanisms of clotting heparin for anticoagulation during : dose-dependence and mechanisms of clottingin vitro: dose-dependence and mechanisms of clotting recycling of human blood in cardiopulmonary bypass circuits: dose-dependence and mechanisms of clotting

Abstract

Low-molecular-weight heparin (LMWH) (FragminTM) vs heparin was studied in vitro in order to investigate its antithrombotic efficacy in the isolated thrombogenic link of cardiopulmonary bypass (CPB). Fresh human blood (400 ml) with various dosages of the anticoagulant was recycled in a CPB circuit for 120 min. The standard dosage of heparin (1500IU, n=6) was compared with a lower dosage (1000IU, n = 3) and several dosages of FragminTM (IU anti-FXa): 750 (n = 1), 1500 (n = 3), 2 100 (n = 4) and 2500 (n = 3). Clotting occurred in three FragminTM experiments at dosages of 750,1500 and 2100 IU. This was associated with short activated clotting time (ACT) and activated partial thromboplastin time (aPTT) but was independent of the levels of anti-FXa, FVIII, von Willebrand factor and prothrombin complex. It was concluded that at least twice the dose of FragminTM (anti-FXa), compared with heparin, was required, suggesting that thrombin inhibition is crucial for the antithrombotic efficacy of heparin in CPB circuits. Absence of fibrinoly tic markers suggests that the well known enhancement of fibrinolysis often seen during CPB, is not due to heparin interaction with normally circulating blood components, but rather to interaction with the vessel walls or to the surgical trauma itself.