Concentrated or diluted heparin prophylaxis of postoperative deep venous thrombosis.

A concentrated and a diluted heparin solution (Vitrum AB) have been evaluated in a controlled blind study, using a standard dosage of 5 000 IU, given every 12 hours subcutaneously. 167 patients undergoing abdominal surgery were randomized into three groups: 63 received diluted heparin 5 000 IU/ml, 43 received concentrated heparin 25 000 IU/ml and 61 patients served as controls. 80 per cent of the patients suffered from malignant disease. Deep venous thrombosis (DVT), diagnosed with the 125I-fibrinogen method, was found in 16% of the patients receiving diluted heparin, in 23% of those receiving concentrated heparin and in 33% of the controls. To evaluate the amount injected, an in vitro experiment was performed in which the intended dose was 5 000 IU. The measured amount of the concentrated heparin solution was significantly less than 5 000 IU. It is concluded that the frequency of DVT after gastrointestinal operations can be reduced significantly (in the present study from 33 to 16%) by administering diluted calcium heparin every 12 hours for 6--8 days. The concentrated heparin solution did not significantly reduce postoperative DVT, possibly on account of variations in the dosage. Diluted heparin prophylaxis can be achieved without serious side effects.