Deep vein thrombosis following hip surgery. Relation to activated factor X inhibitor activity: effect of heparin and dextran.

Activated factor X inhibitor (FXaI) activity was measured with a newly developed method during operation and during the postoperative period in 60 patients undergoing total hip replacement. The patients were randomly allotted to three groups. In two groups the effect of prophylactic treatment with dextran and low dose heparin were evaluated, while the third group served as a control. Postoperative deep vein thrombosis was diagnosed with plethysmography and venography and related to observed changes in inhibitor activity. The frequency of deep vein thrombosis was found to be 25, 47 and 33 per cent in the three groups respectively. With the test system for measurements of FXaI-activity which made it possible to determine both the overall ability of the plasma to neutralize FXa and the activity independent of any accelerator or antagonist of XaI-activity, it was possible to demonstrate inhibitor consumption in all groups including the heparin treated group where the overall inhibitor activity was increased. A marked decrease in inhibitor activity was usually observed in the patients developing postoperative thrombosis in the control group, while in the other groups the relationship was less clear.