Fig. 2. Effects of sevoflurane and nitrous oxide on ratings of pain intensity to cold. Each  bar is the mean across all subjects.  Brackets represent SEM. * Significant decrease from placebo (0% sevoflurane/0% nitrous oxide) ratings. + Significant increase from the 0% sevoflurane/30% nitrous oxide ratings. Reproduced from Janiszewski  et al. 33 ; used with permission.