Fig. 2

Sequential diagrams and dose-effect diagrams of intranasal dexmedetomidine and oral midazolam in sedation for pediatric MRI examination in group D and group M. In the sequential diagrams (A and C), the patient sequence number (X-axis) is the order of child exposures using the modified Dixon’s up-and-down method. The assigned dose levels are presented on the Y-axis. A successful sedation dose is denoted by a solid circle, while a failed sedation dose is denoted by a hollow circle. Dose-effect curves of intranasal dexmedetomidine and oral midazolam (B and D) indicate the effective rate of sedation (X-axis) related to the drug dose (Y-axis) by using probit analysis. The ED50 (95% CI) and ED95 (95% CI) of intranasal dexmedetomidine were 0.39 µg kg^− 1 (95% CI 0.30 to 0.46 µg kg^− 1) and 0.55 µg kg^− 1 (95% CI 0.47 to 1.00 µg kg^− 1), respectively, in group D. The ED50 (95% CI) and ED95 (95% CI) of oral midazolam for sedation were 0.17 mg kg^− 1 (95% CI 0.01 to 0.29 mg kg^− 1) and 0.35 mg kg^− 1 (95% CI 0.26 to 2.56 mg kg^− 1), respectively, in group M. Group D was designed to determine the ED50 of intranasal dexmedetomidine. Group M was designed to determine the ED50 of oral midazolam. DEX, dexmedetomidine; CI, confidence interval; ED50, median effective dose; ED95, 95% effective dose; MRI, magnetic resonance imaging