Mini-dose heparin has been shown to be useful in the prophylaxis of postoperative venous thrombosis. Mechanism(s) by which low-dose heparin is/are thought to protect against venous thrombosis include:

a. Enhancement of antithrombin III activity

b. A decrease in thrombin availability

c. Inhibition of platelet aggregation and subsequent platelet release action

Low-dose heparin is thought to protect against venous thrombosis through three different mechanisms. First, antithrombin III activity with its inhibition of activated Factor X is enhanced by only trace amounts of heparin; second, there is a decrease in thrombin availability that prevents its activation and thus its fibrin-stabilizing effect; and third, small doses of heparin may inhibit the second wave of platelet aggregation and subsequent platelet release reaction. The standard doses of heparin administered (5000 units bid) does not affect aPTT.