Monitoring of somatosensory evoked potentials in carotid surgery: results, usefulness and limitations of the method.

We have monitored cortical somatosensory evoked potentials (SEP) during 177 carotid operations (167 carotid endarterectomies). An intraluminal shunt was always used for endarterectomy of the internal carotid artery (CEA). SEP was not readable in 21 operations. During 126 carotid operations, no alteration of SEP occurred. However, three patients had an immediate postoperative neurologic deficit while the SEP remained normal. Abnormal SEP occurred in 30 patients. In two cases irreversible loss of SEP was seen. Both patients awoke with a new neurologic deficit after the operation. We found reversible abnormal SEP in 28 cases. In 63 cases with contralateral stenosis, abnormal SEP caused by carotid clamping was observed in 15 (24%). The diagnostic sensitivity of intraoperative SEP monitoring in predicting neurologic outcome following carotid operation was 100% with a specificity of 40%. Monitoring of SEP during carotid surgery is a reliable and useful method to detect incipient cerebral ischemia and to determine the need for shunting. The prognostic value of SEP monitoring to predict postoperative neurologic deficits is limited by the low specificity of the method.