Stump pressure, electroencephalographic changes, and the contralateral carotid artery: another look at selective shunting.

Background: Selective shunting during carotid endarterectomy is associated with the lowest operative stroke rate; therefore, patient selection for carotid shunting is critical. Electroencephalography (EEG) can detect ischemic brain cell dysfunction before irreversible injury. The carotid stump back pressure (CSP) has been inconsistent in determining the need for shunting, and contralateral carotid disease has had a variable impact. The purpose of this study was to evaluate CSP and operative EEG changes, and to determine the effect of contralateral carotid artery disease on determining the need for carotid shunting.

Methods: In 140 consecutive carotid procedures, operative EEG and CSP were monitored, and contralateral carotid disease was documented. The carotid stump pressure/mean arterial pressure index (CSP/MAP) was also calculated to determine if this was a better indicator of the need for shunting than the CSP alone.

Results: There was a 58% incidence of EEG changes when the CSP was < or = 25 mm Hg, 32% with a CSP of 26 to 50 mm Hg, and 4% with a CSP > 50 mm Hg. There was a 43% incidence of EEG changes and lower CSP among patients with a contralateral occlusion, both of which were significantly different from patients with a patent contralateral carotid artery. Three patients with CSP > 50 mm Hg had EEG changes, but none had a contralateral occlusion. Two patients had permanent neurologic deficits, and 2 had transient deficits. Excluding combined procedures, operative stroke rate was 0.8%.

Conclusions: A CSP of < 50 mm Hg achieved a sensitivity of 89% in patients who developed ischemic EEG changes during carotid clamping, and a pressure > 50 mm Hg had a negative predictive value of 96%. However, a CSP of < 50 mm Hg had a positive predictive value of only 36%. Neither the addition of the status of the contralateral carotid artery or the calculation of the CSP/MAP improved the sensitivity of the CSP in determining the need for shunting. Operative EEG monitoring remains the most sensitive guide to carotid shunting in patients undergoing carotid endarterectomy under general anesthesia.