Monitoring of heparin in vascular surgery

In patients heparinized for surgery on the infrarenal aorta, the degree of anticoagulation by heparin of stasis blood (taken from below the aortic clamp) was compared with that obtained in circulating blood taken from a forearm artery. A measurement of activated partial thromboplastin time (APTT) was made on a venous blood sample taken from each patient before 5000 units of heparin was administered intravenously. Further measurements of APTT from static blood and from circulating arterial blood were made at 3, 15, 30, and 60 minutes after heparinization. Samples taken below the aortic clamp showed measurements of APTT lower than those from circulating arterial blood at 15, 30, and 60 minutes (p < 0.05 paired Wilcoxon rank sum test). Current methods for administering and monitoring heparin may not provide an adequate degree of anticoagulation in static blood during vascular surgery. The consequences, if any, of inadequate anticoagulation in vascular surgery need further study.