Patient State Index (PSI)-2 versus no observed response to calling the person by name (NRCN), tolerance to shake and shout (TOSS), and tolerance to tetanic stimulation (TOTS) during propofol and sevoflurane administration. Box plots are used to show the distribution of the PSI-2 index 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.