Changes in blood coagulation are believed to be involved in the aetiology of postoperative thromboembolism. Antithrombin III (AT III) is the most important natural inhibitor of thrombin activation and hence thrombogenesis. This study investigated the nature of a hypercoagulable state in total hip replacement by measurement of AT III in the perioperative period, giving a quantitative assessment of coagulation. Antithrombin III levels fell in all patients after surgery. However, the degree of the fall and the timing of the fall were variable. Eight percent of patients had abnormally low AT III prior to operation, indicating that this proportion of our patients are in a procoagulant state even before surgery. One third of patients had a clinically significant reduction (below 70% of normal) in AT III level after surgery. In this group the fall in AT III was maximal at 2 hours after division of the femoral neck. Careful correction for haemodilution provided new evidence for active consumption of antithrombin III in the perioperative period. By 24 hours after surgery the level of AT III was not significantly different from preoperative levels (p>0.7), even in the group with a clinically important reduction. These findings support only a transient period of hypercoagulability after total hip replacement. The “at-risk” period of venous thrombosis has been shown to be at least several weeks after surgery and the transient nature of the fall in AT III suggests that venous thrombosis is unlikely to be due to hypercoagulability alone.
Intermittent pneumatic compression to prevent proximal deep venous thrombosis during and after total hip replacement
