Carotid endarterectomy: Lessons from intraoperative monitoring - A decade of experience

Objective: The authors analyzed a single institution's 10-year experience with intraoperative monitoring during 709 primary carotid endarterectomies and investigated the impact of contralateral internal carotid artery stenosis on carotid artery stump pressure (SP). Summary Background Data: Stump pressure reflects the combination of contralateral carotid artery anatomy, collateral intracranial vasculature, and systemic blood pressure. By controlling for blood pressure with a stump index (SI) (SI = [SP/mean arterial pressure] x 100), a correlation between pressure and contralateral carotid artery anatomy can be demonstrated. Although the use of SP has long been advocated as an indicator of adequate cerebral perfusion, its correlation with perioperative complications while using an intraluminal shunt has not been evaluated completely. Methods: From a series of 886 primary carotid endarterectomy cases, SP and mean arterial pressure were measured prospectively in 709 procedures. Temporary intraluminal shunts were used in cases with demonstrated contralateral carotid occlusion, prior cerebrovascular accident (CVA), or SPs less than 35 mmHg. Ipsilateral and contralateral angiographic degree of carotid stenosis was recorded at the time of the operation. Neurologic status was recorded prospectively for all 709 procedures. Operative electroencephalogram (EEG) changes and SP then were compared with the neurologic status of the patient in the perioperative period. Results: The mean SP for the group (n = 709) was 467 ± 15.3 mmHg (mean ± standard deviation [SD]) with a mean SI of 54.9 ± 22.6. The distribution for the SI is a more gaussian curve than that for SP. There were 19 ipsilateral CVAs (2 7%). The mean SP in the nonstroke group was 47.1 ± 15.2 mmHg (mean SI = 54.7 ± 16.5) compared with 31.9 ± 13.2 mmHg (mean SI = 38.8 ± 18.2) in the stroke group (p < 0.0001). Stroke rate for SP ≤ 35 mmHg was 7% (13/185) versus 1.1% (6/524) for SP > 35 (p < 0.0001). Stump index and SP are related to contralateral carotid artery stenosis. The pattern of SI or SP versus contralateral stenosis is biphasic, with an increase at 75%. If SI is ≤ 40, the mean contralateral stenosis is 55.1%; if SI is > 40, the mean contralateral stenosis is 35.1% (p < 0.05). Continuous EEG monitoring was completed for the 549 most recent operations. Patients who had a penoperative stroke had EEG changes observed during the procedure in only 6 of 12 cases (50% sensitivity), with 76% specificity. Using SP ≤ 35 mmHg, sensitivity was 68% and specificity was 75%. Conclusion: Low SPs are associated with perioperative stroke despite the use of shunts. This trend accelerates when SP ≤ 35 mmHg. There is an inverse correlation between contralateral carotid stenosis and SI or SP. A slight increase in pressure with contralateral stenosis greater than 50% may reflect increased collateral development secondary to chronic hypoperfusion. Stump pressure sensitivity is a better indicator of perioperative stroke than EEG monitoring, with a similar specificity.