BISPECTRAL EEG INDEX DURING NITROUS-OXIDE ADMINISTRATION

Background Nitrous oxide (N2O) is a commonly used sedative for painful diagnostic procedures and dental work. The authors sought to characte rize the effects of N2O on quantitative electroencephalographic (EEG) variables including the bispectral index (BIS), a quantitative paramet er developed to correlate with the level of sedation induced by a vari ety of agents. Methods Healthy young adult volunteers (n = 13) were gi ven a randomized sequence of N2O/O-2 combinations via face mask Five c oncentrations of N2O (10, 20, 30, 40, and 50% atm) mere administered f or 15 min (20 min for the first step). EEG was recorded from bilateral frontal poles continuously. At the end of each exposure, level of sed ation was assessed using primarily the Observer Assessment of Alertnes s/Sedation (OAA/S) scale. Results: One subject withdrew from the study because of emesis at 50% N2O. N2O (50%) increased theta, beta, 40-50 Hz, and 70-110 Hz band powers. BIS and spectral edge frequency during 50% N2O/O-2 did not differ significantly from baseline values. Abrupt decreases from higher to lower concentrations frequently evoked a prof ound, transient slowing of activity. No significant change in OAA/S wa s detected during the study. Conclusions: Although the spectral conten t of the EEG changed during N2O administration, reflecting some pharma cologic effect, the subjects remained cooperative and responsive throu ghout, and therefore N2O can only be considered a weak sedative at the tested concentrations. Despite changes in the lower and higher freque ncy ranges of EEG activity, the BIS did not change, which is consisten t with its design objective as a specific measure of hypnosis.