T143. Effect of anesthesia on electrocorticography for localization of epileptic focus: Literature review and future directions

Abstract

Introduction To investigate the effect of the anesthesia on the quality and reliability of electrocorticography (ECOG) for localization of the epileptic focus based on literature review. Although there is plethora of literature reporting on the utility of intraoperative ECOG for localization of the epileptic focus. Less is known about the effect of the anesthetic regimen and depth of anesthesia on quality of ECOG recording. Methods Literature review primarily through PubMed and book chapters. We also implemented snow-ball strategy. We included articles in which the anesthetic regimen during ECOG for localization of epileptic focus was reported. We excluded articles where the ECOG was solely used for mapping function or in tumoral cases. Results 54 studies were identified. 80% of the studies had a prospective design. There is no consensus in regards to the ideal regimen. Dexmedetomidine and synthetic opiates appear to be the most reliable in that they have little or no effect on the spiking focus and frequency. Studies on propofol provided conflicting evidence owing to methodological differences. There are no universal definition of the gold standard of localization and outcome measures. Majority of the studies reported positive yields (83%), and (6%) reported detrimental effects in regards to reliable epileptic focus localization raising concern over publication bias. Of the 43% of studies reporting on ‘spike activation’, 5 provided specifics on site of resection and correlation with surgical outcomes. Only two studies systematically evaluated the depth of anesthesia quantitatively. Excluding awake craniotomies, there are no reports of intraoperative awareness, however this side effect was not systematically evaluated with post-operative interviews. Conclusion Available studies provide useful information about the effect of anesthesia on ECOG. Prospective studies incorporating widely-accepted standards of localization and surgical outcomes are needed. Future studies may investigate systematically the effect of depth of anesthesia and the incidence of intraoperative awareness.