The dose-related effects of halothane, enflurane, and isoflurane on the rat EEG were evaluated qusntitstively by spectral analysis of the EEG recorded from the rat skull. The anesthetics were inhaled by animal ventilator into 10L glass bottle, in which the preparated rats were placed, at various concentrations, and then bipolar EEG was recorded from the rat skull and its spectrum was calculated by power speetral analysis. The density of each spectral bands (delta 1-3.25, theta 3.5-7.75, alpha 8-12.25, and beta 13-31.75Hz), total density, delta ratio, spectral edge frequency, and medisn power frequency were derived from the spectra. With inspection of conventional EEG, 1.5 MAC of hslothane revealed spindles, but higher dose decreased the amplitude. 1.5 MAC of enflurane revealed a lot of spike waves but 2.0 MAC revealed several spike waves and decreased the amplitude, and 1.5 MAC isoflurane revealed isolated spike waves but 2.0 MAC revealed cerebro- electrical silence. In quantitative spectral analysis of EEG, significant EEG changes were identified during inhalation of all anestheties. In halothane dominent frequencies in EEG were delta waves at 1.5 MAC and 2.0 MAC. In enflurane dominent waves in EEG were theta waves at 1.5 MAC and 2.0 MAC and in isoflurane those were theta waves. Taken together, these findings suggest that analysis for EEG parameters derived from power spectral analysis could be applied to determine the depth of halothane, enflurane, and isoflurane anesthesia.
Anesthesia ; Anesthetics ; Animals ; Electroencephalography* ; Enflurane* ; Glass ; Halothane* ; Inhalation* ; Isoflurane* ; Rats* ; Skull ; Spectrum Analysis ; Ventilators, Mechanical