Fig. 3. Determination of desflurane concentration–electroencephalographic effect relation for a patient during surgical stimulation. (A) End-tidal desflurane concentrations and Bispectral Index versus time. According to a randomized protocol, desflurane vaporizer settings were increased and decreased. (B ) End-tidal desflurane concentrations versus Bispectral Index. An hysteresis loop was observed. (C ) Desflurane effect-site concentrations, gained by simultaneous pharmacokinetic and pharmacodynamic analysis, versus Bispectral Index. Open circles = Bispectral Index; solid line = pharmacodynamic model.