Electrophysiological (EEG-SSEP) monitoring during middle cerebral aneurysm surgery

SSEPs were monitored during 38 procedures for aneurysms of the middle cerebral artery. In 13 selected patients intraoperative barbiturate protection with sodium thiopental was performed during temporary M1 occlusion. Combined EEG monitoring, showing burst suppression typical pattern of electrical cortical activity, allows a minimal dosage (3-6.5 mg/kg) of thiopental to achieve brain protection. Any patient with TYPE I SSEP changes had a new postoperative neurological deficit. Five patients during temporary middle cerebral artery clipping showed TYPE II SSEP changes and only one, not achieving burst suppression EEG pattern, had transient postoperative neurological deficit. In two other patients, a progressive worsening of TYPE II SSEP was observed; this was due to excessive brain retraction without brain protection and had a prolonged postoperative neurological deficit. Four patients showed TYPE IV SSEP changes during temporary M1 occlusion, one of whom was a 52-year-old woman, who, in spite of brain protection with thiopental, had serious postoperative neurological sequelae. In this patient N20 amplitude and central conduction time did not have full recovery to the preocclusive values. This study suggests that combined electrophysiological monitoring may reduce complications due to excessive retraction of cerebral tissue, make temporary clipping safer and improve the results of middle cerebral artery aneurysm surgery.