[Perioperative plasma antithrombin activity with "low-dose" heparin prophylaxis. Perioperatively acquired antithrombin III deficiency as a cause for the failure of heparin prophylaxis?].

Antithrombin III activity was estimated using a chromogenic substrate perioperatively in the plasma of 200 patients undergoing major elective abdominal surgery during low-dose heparin prophylaxis. With an initial value of 10.9 +/- 2 IU/ml there was a mean postoperative lowering of plasma antithrombin activity in all patients with a minimum on the second postoperative day. In patients with empirically established increased risk of thromboembolism the postoperative depression of antithrombin was significantly more pronounced (P less than 0.01) than in the control groups. An increased risk prevailed particularly in patients with malignant diseases and in major surgery, i.e. of prolonged duration. In such cases with increased risk of thromboembolism routine assessment of antithrombin III is recommended.