[Relationship between minimum alveolar concentration and electroencephalographic bispectral index as well as spectral edge frequency 95 during isoflurane/epidural or sevoflurane/epidural anesthesia].

: To investigate the relationship between minimum alveolar concentration (MAC) and electroencephalographic variables, we measured the bispectral index (BIS) and the spectral edge frequency 95 (SEF 95) in 17 patients undergoing elective surgery during isoflurane/epidural (n = 8) or sevoflurane/epidural (n = 9) anesthesia. Patients received 2.0 MAC end-tidal concentrations of isoflurane or sevoflurane, and the BIS and the SEF 95 were recorded after 15 min of an unchanged end-tidal concentration. The concentration of the inhalational agent was decreased to 1.2 MAC, and measurements were repeated again. During isoflurane anesthesia, the BIS increased significantly (3.6 +/- 3.9 at 2.0 MAC, 43.5 +/- 9.2 at 1.2 MAC [mean +/- SD]). In contrast, the BIS did not change significantly during sevoflurane anesthesia (35.3 +/- 8.4 at 2.0 MAC, 42.8 +/- 6.1 at 1.2 MAC). There were significant differences in the BIS and the SEF 95 at 2.0 MAC between isoflurane and sevoflurane groups. In contrast, the BIS and the SEF 95 showed no difference at 1.2 MAC between the groups. These findings suggest that different inhalational anesthetics may have different effects on the BIS and the SEF 95.