Bispectral index changes in carotid surgery

Intraoperative monitoring of cerebral ischemia with shunting during carotid endarterectomy (CEA) remains controversial. Our objective was to evaluate the sensitivity and specificity of BIS changes during carotid clamping in relation to shunted patients in awake CEA.

Eighty CEAs under cervical block were included. There were two patient groups: with clinical signs of cerebral ischemia (shunted patients) and without signs of cerebral ischemia (nonshunted patients). Data were based on bispectral index (BIS) values and neurological monitoring at different surgery time points, with special attention paid during carotid clamping. BIS values were compared between shunted and nonshunted patients. Sensitivity and specificity, along with positive and negative predictive values of a percentage BIS value decrease during carotid clamping from baseline BIS values, were calculated in both patient groups.

Shunting was performed in 11 patients with cerebral ischemia at carotid clamping. Mean BIS values were 82.82+/-11.98 in shunted patients and 92.31+/-5.42 in nonshunted patients at carotid clamping (p<0.001). Relative decreased BIS values in relation to basal BIS values were 13.57% in shunted patients and 3.68% in nonshunted patients (p<0.05). The percentage decrease in BIS was 14%, sensitivity was 81.8% (95% CI 49.9-96.8), and specificity was 89.7% (95% CI 79.3-95.4).

BIS monitoring during carotid clamping is an easy, noninvasive method which correlates with cerebral ischemia in patients undergoing CEA. A decrease>or=14% from the basal BIS value presents a high negative predictive value, and ischemia is unlikely without a decrease. Nonetheless, a decrease may not always indicate cerebral ischemia with a low positive predictive value.