Newly Published
Perioperative Medicine  |   February 2020
Source-level Cortical Power Changes for Xenon and Nitrous Oxide–induced Reductions in Consciousness in Healthy Male Volunteers
Author Notes
  • From the Centre for Human Psychopharmacology (A.P., L.K., D.L.) and the Centre for Mental Health (W.W.), Swinburne University of Technology, Melbourne, Australia; the Faculty of Information Technology, Monash University, Melbourne, Australia (L.K.); the Department of Anaesthesia and Pain Management, St. Vincent’s Hospital Melbourne, Melbourne, Australia (J.C., S.M.); the School of Pharmacy, The University of Auckland, New Zealand (S.M.); and the Department of Medicine, The University of Melbourne, Parkville, Melbourne, Australia (D.L.).
  • Part of this work was presented at The Science of Consciousness in Tucson, Arizona, April 4, 2018.
    Part of this work was presented at The Science of Consciousness in Tucson, Arizona, April 4, 2018.×
  • Submitted for publication March 8, 2019. Accepted for publication January 2, 2020.
    Submitted for publication March 8, 2019. Accepted for publication January 2, 2020.×
  • Correspondence: Address correspondence to Dr. Liley: Department of Medicine, The University of Melbourne, Parkville, VIC 3010, Australia. dliley@unimelb.edu.au. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Perioperative Medicine / Central and Peripheral Nervous Systems
Perioperative Medicine   |   February 2020
Source-level Cortical Power Changes for Xenon and Nitrous Oxide–induced Reductions in Consciousness in Healthy Male Volunteers
Anesthesiology Newly Published on February 5, 2020. doi:https://doi.org/10.1097/ALN.0000000000003169
Anesthesiology Newly Published on February 5, 2020. doi:https://doi.org/10.1097/ALN.0000000000003169
Abstract

Editor’s Perspective:

What We Already Know about This Topic:

  • Xenon and nitrous oxide are high-affinity N-methyl-d-aspartate receptor antagonists

  • Stepwise comparison between the dose-dependent effects of xenon and nitrous oxide on cortical spectral power has not been previously reported

  • Electroencephalography and magnetoencephalography imaging are complementary, and their combination leads to high resolution recording of neural activity

What This Article Tells Us That Is New:

  • Magnetoencephalography and electroencephalography recordings at increasing equivalent dose of xenon and nitrous oxide show distinct effects of these two drugs on neural activity

  • While xenon increased low-frequency delta and theta activity, nitrous oxide induced alpha power depression

  • These observations suggest that, despite their high affinity to the N-methyl-d-aspartate receptor, xenon and nitrous oxide are acting via distinct mechanisms to modulate neural activity

Background: Investigations of the electrophysiology of gaseous anesthetics xenon and nitrous oxide are limited revealing inconsistent frequency-dependent alterations in spectral power and functional connectivity. Here, the authors describe the effects of sedative, equivalent, stepwise levels of xenon and nitrous oxide administration on oscillatory source power using a crossover design to investigate shared and disparate mechanisms of gaseous xenon and nitrous oxide anesthesia.

Methods: Twenty-one healthy males underwent simultaneous magnetoencephalography and electroencephalography recordings. In separate sessions, sedative, equivalent subanesthetic doses of gaseous anesthetic agents nitrous oxide and xenon (0.25, 0.50, and 0.75 equivalent minimum alveolar concentration–awake [MACawake]) and 1.30 MACawake xenon (for loss of responsiveness) were administered. Source power in various frequency bands were computed and statistically assessed relative to a conscious/pre-gas baseline.

Results: Observed changes in spectral-band power (P < 0.005) were found to depend not only on the gas delivered, but also on the recording modality. While xenon was found to increase low-frequency band power only at loss of responsiveness in both source-reconstructed magnetoencephalographic (delta, 208.3%, 95% CI [135.7, 281.0%]; theta, 107.4%, 95% CI [63.5, 151.4%]) and electroencephalographic recordings (delta, 260.3%, 95% CI [225.7, 294.9%]; theta, 116.3%, 95% CI [72.6, 160.0%]), nitrous oxide only produced significant magnetoencephalographic high-frequency band increases (low gamma, 46.3%, 95% CI [34.6, 57.9%]; high gamma, 45.7%, 95% CI [34.5, 56.8%]). Nitrous oxide—not xenon—produced consistent topologic (frontal) magnetoencephalographic reductions in alpha power at 0.75 MACawake doses (44.4%; 95% CI [−50.1, −38.6%]), whereas electroencephalographically nitrous oxide produced maximal reductions in alpha power at submaximal levels (0.50 MACawake, −44.0%; 95% CI [−48.1,−40.0%]).

Conclusions: Electromagnetic source-level imaging revealed widespread power changes in xenon and nitrous oxide anesthesia, but failed to reveal clear universal features of action for these two gaseous anesthetics. Magnetoencephalographic and electroencephalographic power changes showed notable differences which will need to be taken into account to ensure the accurate monitoring of brain state during anaesthesia.