Somatosensory Evoked Potentials Before and During Surgery in Patient with Cerebral Aneurysm

ABSTRACT

It has been known that the electrical activity of the brain is related to regional cerebral blood flow, and cerebral ischemia developed during the management of aneurysmal subarachnoid hemorrhage(SAH) is one of the major causes of morbidity and mortality. Somatosensory evoked potentials(SEPs) in response to median nerve stimulation at wrist have been recorded before and during surgery in 31 patients with aneurysmal SAH and 30 normal control subjects. The central conduction time(CCT), the time between the N4 peak recorded from the second cervical spine and the N20 peak recorded from the sensory cortex, were observed as an indicator of cortical activity. The results were as follows, 1) In patients with aneurysmal SAH, CCT recorded before surgery were not different from that of controls. 2) In patients with aneurysmal SAH, CCT recorded during surgery were found to be significantly increased by administration of anesthetics. 3) During surgery in aneurysmal SAH, CCT tended to be increased by brain retraction. 4) During surgery in aneurysmal SAH, CCT changes relative to the temporary occlusion of the parent artery were quite variable, ranging from rapid disappearance of N20 by only 2 minutes of temporary occlusion to no significant change after 20 minutes of occlusion. The rapid disappearance of N20 within 2 minutes after temporary occlusion was highly likely to be associated with appreciable neurologic deficit after surgery. These results suggest that somatosensory evoked potentials during the management of patients with aneurysmal SAH is considered to be a valuble indicator of cortical function, especially when temporary occlusion was performed to prevent premature rupture of cerebral aneurysm during surgery.