Steady-state, measured plasma propofol (µg · ml⁻¹) and end-tidal sevoflurane concentration (vol %) versus observed response (defined as 0) or no response (defined as 1) to calling the person by name (NRCN), tolerance to shake and shout (TOSS), and tolerance to tetanic stimulation (TOTS). Box plots are used to show measured concentrations in the different remifentanil groups. Individual observations are shown with circles and are scattered and offset against the y axis to increase visibility. Red, green, and blue are used for the 0, 2, and 4 ng · ml⁻¹ remifentanil groups, respectively.