Figure 31-13 Response of systolic blood pressure (BP, mm Hg) to skin incision as a function of end-tidal isoflurane concentration. Filled squares, systolic blood pressure before stimulation; open squares, systolic blood pressure after stimulation; lower oblique line, regression line to systolic blood pressure before stimulation (r = -.46); upper line, regression line to systolic blood pressure after skin incision (r = .0002); shaded area, 95% confidence interval for regression lines; vertical arrow, median effective isoflurane concentration for the motor response of the stimulation pattern. (Redrawn from Zbinden AM, Petersen-Felix S, Thomson DA: Anesthetic depth defined using multiple noxious stimuli during isoflurane/oxygen anesthesia. II. Hemodynamic responses. Anesthsiology 80:261, 1994.)