Low dose heparin in major surgery: clinical relevance of plasma heparin concentrations

56 patients undergoing elective major surgery received low dose heparin prophylaxis, 5,000 IU 2 h before surgery and every 8 h for 7 days. The patients were tested by the 125I-fibrinogen uptake test, which, if positive, was controlled by venography. The heparin concentrations were measured by the method of DENSON and BONNAR and by the chromogenic method of TEIEN et al. in blood samples drained immediately before and after surgery and on the 1st and 5th postoperative day 2 and 4h after the injection of heparin. The values were found higher when estimated by the method of DENSON and BONNAR than by the chromogenic method. Deep vein thrombosis (DVT) developed in 11 patients, and in 10 of them within the first 48 after the operative procedure, in 1 after 4 days. The preoperative values were not lower in the patients who developed DVT, and the heparin concentrations found on the 1st and 5th postoperative day were at the same level as in those who did not develop DVT.