Fig. 1. (continued on next page) The representative midlatency auditory evoked potential tracings (left ) and their power spectra (right ) of the patients who received xenon (Xe;A ), isoflurane (ISO;B ), sevoflurane (SEVO;C ), and nitrous oxide (N²O;D ). In each figure, the auditory evoked potential tracings represent (from top to bottom) preinduction awake, the awakening concentration, the 0.1-MAC-higher concentration, and (for figs. 1A–C) the 0.2-MAC-higher and 0.8 MAC concentrations. The short horizontal bars on the left side of the power spectra represent 0 power level. In each auditory evoked potential tracing, the wave of the first 10 ms consists of the brainstem response, where V is the most prominent peak, whereas the later component (10–100 ms) corresponds to the midlatency auditory evoked potential tracing. In the preinduction awake state, a typical periodic waveform with three distinct peaks—Na, Pa, and Nb—was observed.