Heparin in the Treatment of Critically Ill Patients on the ICU

Abstract

Not all physicians will realize that, when they inject 1 ml of heparin in a patient, they in fact inject a cocktail of more than 100 different molecules. Heparin consists of a large number of glycosaminoglycans of various molecular size (4–20 kDa) (Fig. 1) that are isolated from the intestines or lungs of pig or cow [1]. Heparin is able to bind to antithrombin III, thereby more than 1000-fold potentiating the inhibitory effect of antithrombin III on coagulation factors IIa (thrombin) and Xa. Besides this anticoagulant effect, heparin (and in particular its high molecular weight constituents) may also inhibit platelet function [2]. Although the subject of some controversy in the past, heparin does not appear to exert thrombolytic activity. The weight of evidence suggests that heparin has no direct effect on clot lysis, but strongly inhibits the recurrent formation of thrombotic deposits during the process of endogenous fibrinolysis [3].