Fig. 1. Measured pre- and postincision fentanyl concentrations for all patients (n = 25). Solid lines represent the patients (n = 20) in whom the pre- and postincision plasma fentanyl concentrations were within 35% of each other. Actual differences in concentrations of fentanyl between preincision and postincision samples used for data analysis ranged from −25.0 to +25.0%. Dashed lines represent the patients in whom differences between the pre- and postincision plasma fentanyl concentrations exceeded 35% and were not included in the calculation of the Cp50and Cp50-BAR.