The effects of inhaled nitrous oxide on some measures of attention

This study compared the sensitivity of various measures of attention to the effects of CNS depression, using a randomised single-blind two-period cross-over study. Nineteen healthy volunteers, 10 males and nine females, aged 20-49 took part in a single session in which they inhaled 15% nitrous oxide in oxygen or 100% oxygen (placebo) through a face-mask for 45 min, followed by a 10-min interval after which they received the other treatment in counterbalanced order. They performed a battery of five attention tasks and completed visual analogue scales starting 10 min after the beginning of each inhalation period. The most sensitive measures of the effects of this dose of nitrous oxide were letter cancellation, which had three target letters to cancel, and an auditory attention task with different stimuli to the two ears. Measures of concentrated attention without distractors (continuous attention task and continuous performance task) were less sensitive, though clear effects were seen at these doses. Tests of differing complexities may involve distinct functions which could be differentially affected by different classes of drug. Thus both simple and more complex tasks should be represented in studies assessing attentional function in detail.