Unexpectedly high rate of phlebographic deep venous thrombosis following elective general abdominal surgery among patients given prophylaxis with low-molecular-weight heparin.

• One hundred ninety-four patients undergoing elective general abdominal surgery were randomized in a single-blind study to receive one daily subcutaneous injection of a low-molecular-weight heparin, dalteparin sodium (2500 IU, n=97) or nadroparin calcium (3075 IU, n=97), two regimens that are approved in Europe to prevent deep venous thrombosis. On the eighth postoperative day, bilateral ascending leg phlebography (n=185) showed the presence of deep venous thrombosis in 45 cases (24.3%; 95% confidence interval, 18% to 31%), with a significantly higher rate (on intention-to-treat) among the patients who received the lower dosage (30 vs 15 deep venous thromboses). We conclude that the two regimens of low-molecular-weight heparin that were used in this study failed to prevent postoperative phlebographically proved deep venous thrombosis in one of four patients. ( Arch Surg. 1993;128:326-328)