A PROSPECTIVE RANDOMISED CONTROLLED STUDY OF MINI-DOSE WARFARIN PROPHYLAXIS OF DEEP VEIN THROMBOSIS IN MAJOR SURGERY

A prospective randomised study has been undertaken to assess the clinical effectiveness of oral anticoagulation using minidose warfarin (1 mg daily for 2-4 weeks before major gynaecological surgery) compared with conventional oral anticoagulant prophylaxis and an untreated randomised control group. The conventional oral anticoagulant prophylaxis was based on a therapeutic range of 1.5 - 2.0 INR at the time of operation and 2.0 - 3.0 INR post-operatively. Overall the mini-dose warfarin group showed no pre-operative prolongation of the prothrombin time with the Manchester Reagent although a minority of patients showed a 1-2 second prolongation of the prothrombin time before operation. Post operatively the mini-dose warfarin group showed an exaggerated prolongation of the prothrombin time which normally occurs after operation and was observed in the untreated controls. Factor VII assays paralleled these findings. Minidose warfarin, while not prolonging the prothrombin time before operation, resulted in delayed platelet aggregation with the Chandler's tube technique in almost all patients.

The incidence of deep vein thrombosis has been reduced in both mini-dose and conventional dose oral anticoagulant series compared with the untreated- group. It appears that the minimal changes in the prothrombin time, factor VII and platelet aggregation tests, observed in the mini-dose warfarin group, may offer sufficient protection against post-operative thrombosis in a moderate risk group undergoing abdominal or pelvic surgery.