In vivo heparin response and consumption in patients before and during arterial reconstructive surgery

This study investigated the effects of heparin in patients with peripheral arterial disease, before and during operation. The relation between heparin dosage and heparin response and consumption were calculated from changes in the activated clotting time (ACT). Before operation, 38 patients were each given 10,000 units of heparin by intravenous injection and ACT was measured after 5, 10, 20, 30 and 60 minutes. Assuming a linear relation between heparin dosage and ACT, a dose of heparin was calculated which should double the normal ACT. This was given during operation in 21 patients while a standard dose of 7,500 units of heparin was given to another 10 patients. ACT was measured during operation at the same time intervals as before operation. ACT was always at its highest level at the 5 minute test and was always still raised at 60 minutes, both before and during operation. No significant correlation was found between ACT, heparin response or heparin consumption, and the patients' ages, sex, body weights and creatinine levels, either before or during operation. It was not possible to predict the intraoperative response from the preoperative test. It is concluded that the heparin effect should be monitored during operation in each patient if the best dose response is to be obtained.