Long-latency somatosensory evoked potentials during carotid endarterectomy.

Scalp recorded somatosensory evoked cortical responses (SSEP) may be measured under general anesthesia to assess the electrical responsiveness of the brain. Such potentials were measured in 25 patients undergoing carotid endarterectomy without shunt. Electrical unresponsiveness occurred bilaterally in one patient and unilaterally in one patient. The patient with unilateral electrical silence developed a perioperative stroke, the only stroke in this series. Analysis of the SSEPs recorded from these patients suggests that profound ischemia produces electrical silence: that intermediate degrees of ischemia produce prolonged interpeak latencies and decreasing amplitudes in the SSEP. This modality seems to offer promise as an intraoperative monitor during cerebrovascular surgery.