Fig. 1
Dixon up-and-down plots for each group. The plasma target concentration of sufentanil in groups S0, S1, S2, S3 and S4 was 0.0, 0.1, 0.3, 0.5 and 0.7 ng ml− 1, respectively. The empty (solid) circle represents the negative (positive) reaction to hemodynamics parameters, and the triangle indicates the intersection of negative and positive reactions. The ninth patient was given the same concentration of sevoflurane both in group S2 and group S3. To get six crossovers, 14, 14, 18, 20 and 15 patients were needed in groups S0-S4, respectively