Computerized Cortical Surface Electroencephalography after Temporary Middle Cerebral Artery Occlusion in Rabbits

Abstract

The sensitivity and regional specificity of intraoperative electroencephalographic (EEG) monitoring in cerebral ischemia was evaluated in a new experimental model of temporary focal cerebral ischemia in rabbits. EEG potentials were recorded directly from the cortical surface using a bipolar disc electrode grid and were analyzed by computer. Groups of 5 animals each underwent temporary occlusion of the left middle cerebral arterial trunk for 5, 10, 20, 30, 45, or 60 minutes. EEG data were recorded from the cortex proximal (temporal site) and distal (parasagittal site) to the middle cerebral arterial trunk during occlusion and 2 hours of reperfusion. EEG suppression was detected immediately after occlusion at the temporal site by analysis of power spectra in 29 of 30 rabbits (mean power, 32% of base line), by compressed spectral array (CSA) edge analysis in 23, and by analysis of the conventional EEG wave form in 24. Within 5 minutes after the start of occlusion, all 30 rabbits showed EEG power suppression and 26 showed decrease in the CSA edge frequency or in the routine EEG wave form. By the end of the occlusion period, EEG power at the temporal site had decreased to 20.5% of base line. At the parasagittal site, a lesser degree of EEG suppression was detected; 20 rabbits had an initial loss of EEG power (mean, 85.7% of base line), 13 had decrease in the CSA edge, and 7 had suppression of the EEG wave form. By the end of the occlusion period, spectral power at the parasagittal site had decreased in 25 of 30 rabbits to a mean of 86.9% of base line. After 2 hours of reperfusion, the degree of EEG recovery at the temporal site correlated inversely with the duration of the occlusion (P < 0.05). Recovery at the parasagittal site was generally earlier and more complete, indicating a lesser degree of ischemia. Two sham-operated control rabbits showed no significant changes in the conventional or the computer-analyzed EEG data during a 2-hour recording period. Twenty-four hours postoperatively, there were significant correlations between the duration of middle cerebral artery occlusion and neurological deficit (P < 0.001) and histological grade of injury (P < 0.01). At the temporal site, there was a significant correlation between neurological outcome and the recovery of spectral power at 30 (P < 0.05) and 120 (P < 0.05) minutes of reperfusion. Computerized EEG recording from the cortical surface is a rapid and sensitive method for regional mapping of cortical dysfunction during focal cerebral ischemia and is predictive of ultimate neurological outcome. This technique may be useful for experimental studies and intraoperative evaluation of cortical ischemia in humans.