BackgroundThe most common measure to compare potencies of volatile anesthetics is minimum alveolar concentration (MAC), although this value describes only a single point on a quantal concentration‐response curve and most likely reflects more the effects on the spinal cord rather than on the brain. To obtain more complete concentration‐response curves for the cerebral effects of isoflurane, sevoflurane, and desflurane, the authors used the spectral edge frequency at the 95th percentile of the power spectrum (SEF95) as a measure of cerebral effect.MethodsThirty‐nine patients were randomized to isoflurane, sevoflurane, or desflurane groups. After induction with propofol, intubation, and a waiting period, end‐tidal anesthetic concentrations were randomly varied between 0.6 and 1.3 MAC, and the EEG was recorded continuously. Population pharmacodynamic modeling was performed using the software package NONMEM.ResultsThe population mean EC50values of the final model for SEF (95) suppression were 0.66 +/‐ 0.08 (+/‐ SE of estimate) vol% for isoflurane, 1.18 +/‐ 0.10 vol% for sevoflurane, and 3.48 +/‐ 0.66 vol% for desflurane. The slopes of the concentration‐response curves were not significantly different; the common value was [Greek small letter lambda] = 0.86 +/‐ 0.06. The Ke0value was significantly higher for desflurane (0.61 +/‐ 0.11 min‐1), whereas separate values for isoflurane and sevoflurane yielded no better fit than the common value of 0.29 +/‐ 0.04 min (‐1). When concentration data were converted into fractions of the respective MAC values, no significant difference of the C50values for the three anesthetic agents was found.ConclusionsThis study demonstrated that (1) the concentration‐response curves for spectral edge frequency slowing have the same slope, and (2) the ratio C50(SEF95)/MAC is the same for all three anesthetic agents. The authors conclude that MAC and MAC multiples, for the three volatile anesthetics studied, are valid representations of the concentration‐response curve for anesthetic suppression of SEF95.