Source-level Cortical Power Changes for Xenon and Nitrous Oxide–induced Reductions in Consciousness in Healthy Male Volunteers

Abstract

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. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

An Electroencephalogram Metric of Temporal Complexity Tracks Psychometric Impairment Caused by Low-dose Nitrous Oxide

“…This is similar to previous studies. [10][11][12][13][14] In general, the serial sevens test results worsened (fig. 4A) and the complexity metric decreased (fig.…”

“…Nitrous oxide has been reported to cause inconsistent changes in the EEG power spectrum, but often there is an increase in power (amplitude) in high-frequency bands (>14 Hz, beta and gamma), with a relative decrease in power in the alpha and delta frequency bands (7 to 14 and 1 to 4 Hz). 10 The power reduction in alpha and delta bands 11 is localized in the frontal region 12,13 and most pronounced at higher inspired concentrations (40 to 60%). 12,14,15 Nitrous oxide also reduces spatial connectivity in parietal (at 60% N 2 O) and frontal (16 to 30% N 2 O) regions.…”

“…12,14,15 Nitrous oxide also reduces spatial connectivity in parietal (at 60% N 2 O) and frontal (16 to 30% N 2 O) regions. 13,16 Changes in spatial connectivity are often accompanied by changes in complexity in the time domain.…”

Space-time resolved inference-based whole-brain neurophysiological mechanism imaging: application to resting-state alpha rhythm

“…Here we summarise the key details of the data. For further information see previous papers 22, 50 . Twenty-two volunteers were recruited.…”

“…This method is referred to here as the semi-analytic Kalman filter (AKF) and creates a more accurate and computationally efficient method which allows, in the examples presented here, the modelling of the whole brain with 4714 NMMs, and provides high spatial and temporal resolution imaging (6mm source spacing, 400 Hz sampling rate). To demonstrate the utility of the framework, we applied it to beamformed MEG recordings of healthy human male subjects 22 to investigate the brain-wide neurophysiological mechanisms of eyes-closed resting-state alpha oscillations. Each MEG source time-series derived from beamforming is treated as proportional to the local extracellular dipole current formed by the combination of population averaged excitatory and inhibitory synaptic currents associated with cortical pyramidal cells 2, 23 .…”