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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 4 h 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.

We investigated whether the dosage of heparin injected subcutaneously for the postoperative prophylaxis of thromboembolism influences efficacy. We considered prospective, controlled or comparative, randomized studies in which heparin was administered in a dosage of 5,000 U b.i.d. or t.i.d. subcutaneously. In major surgical procedures in general surgery, gynecology, urology and chest surgery, 2 × 5,000 and 3 × 5,000 U of heparin/day lower the frequency of postoperative deep venous thrombosis from about 30% to about one-fourth and one-third that amount, respectively. With regard to orthopedic/ traumatic surgery, in a study of only 40 patients, 2 × 5,000 U/day reduced the incidence of thrombosis by one-half. The use of the higher dosage resulted in a decrease in DVT in 5 of 7 reports, but the other two authors measured no prophylactic effect at all. Proof that subcutaneous heparin prophylaxis is also able to reduce the number of fatal postoperative pulmonary emboli has been produced only in the case of the higher dosage. In our own group of patients there is no correlation between body weight and frequency of hemorrhagic complications. In our patients there is no relation between malignant tumor as the primary disease and the occurrence of hemorrhagic complications. There is no evidence that the lower dosage causes fewer hemorrhagic complications than the higher dosage.

The laboratory control of low-dose heparin therapy is generally regarded as unnecessary. A laboratory study of the effects of low-dose heparin was performed using different methods: an amidolytic method and a method involving the inhibition of factor Xa in a coagulation test. Variations in partial thromboplastin time, recalcification clotting time, thrombin time and the plasma antithrombin HI levels were also studied. These tests were repeated (days 0, 1, 3, 8) in 27 women between the ages of 27 and 62 years who were undergoiing gynecological surgery. They received 5,000 IU of heparin either twice or thrice daily. There was no correlation between heparin levels in the blood and global clotting tests simultaneously performed. The plasma heparin levels varied between 0 and 0.15 IU/ml with both methods. A detectable heparin concentration on days 1, 3 and 8 was present in only half of the cases receiving the twice daily regimen. The plasma antithrombin III activity and concentration were not modified during treatment.

The study was carried out on 75 patients undergoing hip joint surgery. The efficacy of a prophylaxis of deep vein thrombosis (DVT) by acetylsalicylic lysine (ASL) and by a low dose heparin (LDH) combined with the ASL treatment was investigated using the 125I-fibrinogen test. DVT was not significantly decreased by the ASL application (53%) compared to the controls (60%). DVT occurred significantly less under the combined administration (27 %) than in the other two groups.