The risk of stroke and death in the perioperative period following carotid endarterectomy ranges from 6 to 7 percent. While this risk may be reduced by aspirin therapy, the optimal aspirin dosage has not been established. Taylor and colleagues, of the ASA and Carotid Endarterectomy Trial, compared the effects of four different dosages of aspirin on the rate of perioperative complications among patients who underwent carotid endarterectomy.

A total of 2,849 patients were enrolled in the international study, which was conducted at 74 centers (48 in the United States, 19 in Canada, four in Australia and one each in Italy, Argentina and Finland). Patients were excluded from the study if they had undergone cardiac surgery in the previous 30 days, had a recent disabling stroke or were receiving an antiplatelet medication.

Four different dosages of aspirin were evaluated: 81, 325, 650 and 1,300 mg daily. No additional antiplatelet medication was permitted during the study. Each patient was assessed by a neurologist on entry into the study, at the time of hospital discharge, 30 days after carotid endarterectomy and, finally, three months after surgery. At the end of three months, 698 patients remained in the group receiving 81 mg of aspirin per day, 697 in the 325-mg group, 703 in the 650-mg group and 706 in the 1,300-mg group.

Patients in the four treatment groups were comparable with respect to age, sex, blood pressure, medical history, medication use and other pertinent variables. Compliance with aspirin therapy was over 90 percent during the first 30 days and over 86 percent during the three-month follow-up period.

Because no significant differences were noted between the two lower aspirin dosages (81 mg and 325 mg) and the two higher dosages (650 mg and 1,300 mg), the authors reported the results in these two groups. Efficacy analysis of 1,116 patients revealed that stroke occurred in 18 (3.2 percent) of those receiving low-dose aspirin and in 38 (6.9 percent) of those receiving high-dose aspirin. Myocardial infarction was also less frequent in the low-dose group (five patients, or 0.9 percent, versus 18 patients, or 3.3 percent). The mortality rate was 1.6 percent in the patients who received low-dose aspirin, compared with a mortality rate of 2.2 percent in those who received high-dose aspirin.

Hemorrhagic stroke was less common in patients taking lower dosages of aspirin, but the difference was not statistically significant. Ten patients in the 81-mg and 325-mg groups incurred a hemorrhagic stroke, compared with 17 patients in the 650-mg and 1,300-mg groups. The occurrence of other bleeding problems was not related to the aspirin dosage.

The authors conclude that the risk of death, myocardial infarction and stroke within three months of carotid endarterectomy is lower in patients who receive 81 mg or 325 mg of aspirin daily than in patients who receive 650 mg or 1,300 mg daily. The authors caution that the results of this study must not be over-generalized: the dosage required to prevent perioperative stroke in patients may differ from the dosage required for stroke prevention in the long-term management of patients at risk of stroke. The findings of this study are in contrast to those of the North American Symptomatic Carotid Endarterectomy Trial (NASCET), which showed that persons receiving higher dosages of aspirin had fewer strokes in the perioperative period.