Effect of Sevoflurane Anesthesia on Intraoperative Spikes, High-Frequency Oscillations, and Phase-Amplitude Coupling in MRI-Normal Hippocampus

Abstract

Introduction: The purpose of this study was to determine the effect of sevoflurane anesthesia on spikes, high-frequency oscillations (HFO), and phase-amplitude coupling using a modulation index (MI) in MRI-normal hippocampus, with the aim of evaluating the utility of intraoperative electrocorticography (ioECOG) in identifying the epileptogenic hippocampus during sevoflurane administration. Methods: Eleven patients with intractable temporal lobe epilepsy with a normal hippocampus on MRI underwent extra-operative electrocorticography (eoECoG) evaluation. Patients were assigned to the Ictal (+) or Ictal (−) group depending on whether the parahippocampal gyrus was included in the seizure onset zone. IoECoG was performed under 0.5 and 1.5 minimum alveolar concentration. The rates of spikes, ripples, fast ripples (FR), ripples on spikes (RonS), fast ripples on spikes (FRonS), and MI HFO (3-4 Hz) were evaluated. Results: During the ioECoG procedure, sevoflurane administration was found to significantly increase the rate of spikes RonS, FRonS and MI HFO (3-4 Hz) in the Ictal (+) group (P < 0.01). In contrast, the Ictal (−) group exhibited a paradoxical increase in the rate of ripples and FR (P < 0.05). Conclusions: Our findings indicate that the administration of sevoflurane during ioECOG in patients with MRI-normal hippocampus can lead to a dose-dependent enhancement of epileptic biomarkers (spikes, RonS, FRonS, and MI (HFO 3-4)) in the epileptogenic hippocampus, while paradoxically increasing the rate of ripples and FR in the non-epileptogenic hippocampus. These results have significant implications for the identification of the MRI-normal hippocampus that requires surgical intervention and preservation of the non-epileptogenic hippocampus.