Intraoperative somatosensory evoked potentials(SEPs) are widely used for the early detections of cerebral ischemia during temporary occlusive procedures of the parent vessels in aneurysm surgery. Somatosensory evoked potentials in response to median nerve stimulation were monitored during 20 aneurysm procedures. Base line SEPs were obtained shortly after the induction of general anesthesia and were recorded continuously during the operation. Absolute latency and cortical SEP amplitude were subsequently determined. Statistical analysis confirmed that there were significant changes in latency and amplitude of cortical SEP after aneurysm clipping during the course of operation.

The false positive and false negative rate were 5% and 15%, respectively, where SEP latency increased by more than 10% or SEP amplitude decreased by more than 50% after the time of anesthetic induction. Monitoring of the SEPs during intracranial aneurysm surgery can help the surgeon in the management of proximal vessel control and reduce the morbidity of aneurysm operation.