[Quantified EEG and CNV changes during inhalation of nitrous oxide].

Inhaling nitrous oxide produces a mix of depressive and activating effects on the central nervous system. In 9 volunteers, 25% and 50% nitrous oxide caused muscle relaxation, psychomotor slowing, and a shift in EEG toward slower waves with less alpha and more theta and delta activity, along with reduced amplitude of auditory evoked potential components. At the same time, it heightened sensory perceptions, caused perceptual illusions, and maintained high and prolonged contingent negative variation amplitude, suggesting CNS activation. This dual effect indicates a dissociative action at different levels of the central nervous system.

Study at a glance

Abstract

The present study constitutes an approach to the action mechanisms of nitrous oxide (N2O) by assessing both the subjective effects induced by the inhalation of this anaesthetic gas, and their electrophysiological correlates, i.e., spontaneous EEG, analyzed by a Fourier algorithm, AEP and CNV. The experiment was conducted single blind in 9 volunteers under 3 recording conditions: inhalation of air, of a mixture of 25% N2O--75% O2, and of a mixture of 50% N2O--50% O2. A latin-square design was used. Polymorphic effects of N2O were evidenced on behaviour and on CNS: some of the behavioural manifestations could evoke a depression of SNC: muscle relaxation with difficulty of motor initiation, psychomotor slowing, slower EEG with diminution of the percent alpha component and increase in the percent theta and delta, loss of amplitude of both exogenous (N1) and endogenous (P300) components of the AEP. Conversely, other manifestations were observed that are compatible with an activation of the CNS: increase of sensory perceptions, appearance of perceptual illusions, maintenance of a high CNV amplitude and lengthening of its duration. This dual effect of N2O suggests a dissociative action at the different levels of the CNS.