Heparin kinetics in vascular surgery

Currently there is little information available about the efficacy of heparin during vascular surgery or of the effects of surgical trauma on heparin kinetics. This study was undertaken to evaluate the kinetics of heparin therapy during vascular surgery. Nine patients undergoing major vascular surgery (one carotid, one common iliac and seven aortic operations) were studied both preoperatively and intra-operatively, each patient acting as his own control. Following determination of control activated partial thromboplastin time (APTT) and plasma heparin levels, heparin (100 u/kg body weight) was administered intravenously. Heparin dosage ranged form 4500 units to 8600 units with a mean dose of 6500 units. Plasma heparin and APTT levels were then measured at 10 minute intervals for 1 hour and 20 minute intervals for a second hour. The mean pre-operative and intra-operative APTT levels at ten minutes attained maximal values of 6.6±3.7 and 8.8±1.7 times the control respectively. At the end of 2 hours the mean APTT remained greater than 2.5 times the control in both groups. Mean plasma heparin level was 0.83±0.04 units at 10 minutes and was almost identical in both groups. Heparin level was not a reliable indicator of anticoagulant effect as most patients achieved the same levels but had markedly differing APTT results. The result of this study suggest that excessive doses of heparin may be used in vascular surgery and that surgical trauma does not significantly alter sensitivity to heparin. Based on these results and results from further studies using a lower heparin dose (50 u/kg), suggestions are made for a protocol for the use of heparin in peripheral vascular surgery.