Effects of nitrous oxide on psychological performance.

Thirty healthy volunteers took part in this double-blind crossover study comparing 15 percent nitrous oxide in oxygen with 100 percent oxygen. They received each treatment for 45 minutes, in counter-balanced order, with no break between treatments. Central nervous system (CNS) effects of nitrous oxide were assessed by a battery of performance tests and by the Visual Analog Scales. The Digit-symbol Substitution Test showed significant slowing with nitrous oxide as did Symbol-digit Substitution and Sentence Verification. Subjects rated themselves as more drowsy, dizzy, abnormal, drunk, and muzzy on nitrous oxide than on oxygen. Significant carryover effects were seen only for the Alert-Drowsy scale at 2.5 minutes after the start of treatment, and not at any later time point. These results show that the onset and offset of the CNS effects of 15 percent nitrous oxide are sufficiently rapid to permit the study of two treatment periods within a single experimental session.