Assessment of recovery from nitrous oxide-oxygen sedation using neuropsychometry.

This study measured changes in adult performance following prolonged exposure (90 minutes) to nitrous oxide at psychosedative levels. Using a repeated-measures randomized blind design, experimenters exposed 12 subjects to four treatment combinations. These included: room air for 90 minutes (baseline); 100% oxygen for 90 minutes; nitrous oxide-oxygen sedation for 90 minutes followed by 100% oxygen for 2 minutes; and 90 minutes of nitrous oxide-oxygen sedation followed by 10 minutes of 100% oxygen. Following each treatment, participants were asked to perform six standard neuropsychological tests together with a rating scale measurement where subjects self-evaluated their respective levels of alertness. The tests were: digit span; digit symbol; paced auditory serial addition; controlled word association; letter cancellation; and grooved pegboard. Two-way analysis of variance revealed significant differences between mean scores for treatments on only two tests, grooved pegboard (P less than 0.05) and controlled word association (P less than 0.05). There was also a significant difference in mean scores obtained for the rating scale (P less than 0.001). These findings indicate that psychomotor performance and verbal fluency were affected by prolonged exposure to nitrous oxide even after recovery periods. No impairment of vigilance, immediate memory, or mental tracking could be detected as measured by the other tests. Subjective reports by the subjects accurately reflected their underlying impaired status.