Safety and efficacy of fixed-dose heparin in carotid endarterectomy

OBJECTIVE: Although fixed dosage of heparin is frequently used during vascu lar surgery, there are very few studies that document the appropriateness o f this type of dosing. We have undertaken a prospective study to determine the physiological response to a fixed dose of heparin, using a conventional measure of anticoagulation, and have correlated this measure with complica tions. METHODS: We studied 140 consecutive patients undergoing elective carotid en darterectomy. Serial activated clotting times (ACT values) were obtained in duplicate before administration of heparin, 15 minutes after application o f a carotid artery cross-clamp, and 1 hour after administration of 5000 U o f heparin by intravenous bolus. Postoperatively, patients were assessed for new neurological deficits (transient ischemic attack and stroke) and neck hematomas. A battery of neuropsychometric tests was performed in 49 patient s at baseline and on the day after carotid endarterectomy to identify subtl e new neurological deficits. RESULTS: ACT values were found to be highly reproducible, with less than a 1.5% difference between duplicate baseline samples. Although all patients r eceived 5000 U of heparin, the dose received per kilogram of body weight va ried considerably (44-116 U/kg), as did ACT values at both 15 minutes (178- 423 s) and 1 hour (173-390 s). Nevertheless, there was a significant correl ation between heparin dose per kilogram and ACT values at 15 minutes (r = 0 .45) and at 1 hour (r = 0.38) postinfusion, as well as ACT ratios (final AC T/initial ACT) at 15 minutes (r = 0.43) and at 1 hour (r = 0.34) after hepa rin bolus. Eight patients (5.7%) developed postoperative wound hematomas, o ne of which (0.7%) required reoperation. No patient had a stroke, but one p atient had a transient ischemic attack, and 19 (39%) of 49 patients demonst rated significant early postoperative neuropsychometric deficits. Although the incidence of neck hematoma was not influenced by the heparin dose (P = 0.23), the ACT value at 15 minutes (P = 0.71) or 1 hour (P = 0.61), or the ACT ratio (P = 0.68), the only severe hematoma requiring reoperation occurr ed when the maximal ACT value was more than 400 seconds. Although performan ce on neuropsychometric tests did not appear to be statistically influenced by heparin dosing, the ACT value, or the degree of ACT elevation, there wa s a trend for deficits to be associated with lower heparin doses. CONCLUSION: Fixed heparin dosing achieves safe and efficacious anticoagulat ion in the great majority of patients having carotid endarterectomy, with 5 000 U expected to result in 15-minute and 1-hour ACT values of 175 to 425 s econds and 170 to 390 seconds, respectively. Although weight-based heparin dosing may reduce the incidence of subtle complications (hematoma formation or decline on neuropsychometric tests) and may result in more predictable 15-minute and 1-hour ACT values (85 U/kg; 225-375 and 200-340 s, respective ly), no statistically compelling clinical advantage could be demonstrated. Therefore, either weight-based or fixed dosing is acceptable, with both obv iating the need for routine pre-clamp ACT confirmation, thereby saving oper ative time and expense.