Nitrous oxide analgesia: a psychophysical evaluation using verbal descriptor scaling.

The effect of 33% nitrous oxide/67% oxygen was compared with 100% oxygen and air on verbal reports of either sensory intensity or unpleasantness of sensations associated with painful electrical tooth pulp stimulation. Forty-eight subjects used words describing the sensory intensity (i.e., weak, mild, strong) or degree of unpleasantness (i.e., annoying, unpleasant, distressing) to assess the sensations produced by a broad range of tooth pulp stimuli. Within the experimental session, a given subject assessed the painful sensations under all three treatments delivered through a nasal inhaler in a double-blind manner. The incorporation of within-subject placebo (nasal inhaler + air) and active placebo (nasal inhaler + oxygen) controls allowed for rigorous assessment of the components of nitrous oxide analgesia. The results of this study suggest that 33% nitrous oxide analgesia reduces the intensity but not the unpleasantness of painful tooth pulp sensations. Further, 100% oxygen provides no analgesic effect.