Abstracts

Rationale: Although there is a 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. This study aims 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 and a pilot prospective study.   Methods: Literature review primarily through PubMed and book chapters. We also implemented snowball 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. For the prospective analysis with studied the effect of regimen consisted of Sevoflurane at 0.2-0.5 mac – Remifentanil 0.1-0.25 ug/kg/min and dexmedetomidine  0.2-0.5 mcg/kg/hr. We compared spiking count in the intraoperative settings to the spike count to different times during extraoperative epilepsy monitoring.  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 is 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 assessed with post-operative interviews. Conclusions: 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. Funding: RA wishes to acknowledge research support by the Swebilius Trust, American Epilepsy Society, CTSA Grant Number 1KL2TR001862-01 from the National Center for Advancing Translational Science (NCATS), a component of the National Institutes of Health (NIH). The contents are solely the responsibility of the authors and do not necessarily represent the official view of NIH.