In search of Universal Cortical Power Changes Linked to NMDA-Antagonist based Anesthetic Induced Reductions in Consciousness

Summary

Equivalent stepwise subanesthetic doses of the NMDA-antagonists nitrous oxide (N2O) and xenon (Xe) produce distinct, frequency-dependent changes in cortical oscillatory source power, measured with simultaneous magnetoencephalography (MEG) and electroencephalography (EEG). At the highest Xe concentration (42%, 1.30 MAC-awake), delta and theta band power significantly increased in both MEG and EEG. N2O administration reduced frontal alpha power more strongly than equivalent Xe doses. N2O alone increased MEG (but not EEG) high-frequency gamma power, with occipital low gamma and widespread high gamma rises. These results demonstrate divergent MEG and EEG signatures of dissociative anesthesia.

Study at a glance

Abstract

B. Abstract Background. Despite their intriguing nature, investigations of the neurophysiology of N-methyl-D-aspartate (NMDA)-antagonists Xenon (Xe) and nitrous oxide (N 2 O) are limited and have revealed inconsistent frequency-dependent alterations, in spectral power and functional connectivity. Discrepancies are likely due to using low resolution electroencephalography restricted to sensor level changes, concomitant anesthetic agent administration and dosage. Our intention was to describe the effects of equivalent stepwise levels of Xe and N 2 O administration on oscillatory source power using a crossover design, to explore universal mechanisms of NMDA-based anesthesia. Methods. 22 healthy males participated in a study of simultaneous magnetoencephalography and electroencephalography recordings. In separate sessions, equivalent subanesthetic doses of gaseous anesthetic agents N 2 O and Xe (0.25, 0.50, 0.75 equi MAC-awake) and 1.30 MAC-awake Xe (for Loss of Responsiveness) were administered. Source power in various frequency bands was computed and statistically assessed relative to a conscious baseline. Results. Delta (l-4Hz) and theta (4-8Hz) band power was significantly increased at the highest Xe concentration (42%, 1.30 MAC-awake) relative to baseline for both magnetoencephalography and electroencephalography source power (p<0.005). A reduction in frontal alpha (8-13 Hz) power was observed upon N 2 O administration, and shown to be stronger than equivalent Xe dosage reductions (p=0.005). Higher frequency activity increases were observed in magnetoencephalographic but not encephalographic signals for N 2 O alone with occipital low gamma (30-49Hz) and widespread high gamma (51-99Hz) rise in source power. Conclusions. Magnetoencephalography source imaging revealed unequivocal and widespread power changes in dissociative anesthesia, which were divergent to source electroencephalography. Loss of Responsiveness anesthesia at 42% Xe (1.30 MAC-awake) demonstrated, similar to inductive agents, low frequency power increases in frontal delta and global theta. N 2 O sedation yielded a rise in high frequency power in the gamma range which was primarily occipital for lower gamma bandwidth (3049 Hz) and substantially decreased alpha power, particularly in frontal regions. Clinical trial number and Registry URL Not applicable. Prior Presentations Pelentritou Andria, Kuhlmann Levin; Lee Heonsoo; Cormack John; Mcguigan Steven; Woods Will; Sleigh Jamie; Lee UnCheol; Muthukumaraswamy Suresh; Liley David. Searching For Universal Cortical Power Changes Linked To Anesthetic Induced Reductions In Consciousness. The Science of Consciousness April 4 th 2018. Tucson, Arizona, USA. Summary Statement Not applicable.