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Intraoperative monitoring of the somatosensory evoked potentials and cerebral blood flow during aneurysm surgery--safety evaluation for temporary vascular occlusion.

Somatosensory evoked potentials (SEPs) and cerebral blood flow (CBF) were monitored during temporary vascular occlusion in 67 aneurysm operations to evaluate the usefulness of SEP as an indicator for cerebral ischemia. The SEP N20 component completely disappeared during temporary vascular occlusion in 24 cases, 23 of which demonstrated complete recovery following recirculation and had no postoperative neurological sequelae. The only one with postoperative sequelae demonstrated rapid, within 1 minute, loss of N20 followed by no recovery. Another eight cases showed prolongation of central conduction time during vascular occlusion and had no postoperative sequelae. The SEP N20 attenuation reflected the CBF reduction in the middle cerebral artery (MCA) territory during MCA occlusion. However, CBF changes in the internal carotid artery (ICA) territory during ICA occlusion greatly varied. No detectable changes in SEP were found during anterior cerebral artery occlusion for anterior communicating artery aneurysms. This study indicates that intraoperative SEP monitoring is useful to detect ischemia in the MCA territory and that rapid disappearance of the N20 component is a danger signal.