Fig. 2. Individual responses to bladder distension according to the up-and-down sequence in spinal cord–injured patients receiving sevoflurane–nitrous oxide anesthesia. When a patient showed an increase in systolic arterial blood pressure of 15% or more from the preprocedural value, the end-tidal concentration of sevoflurane given to the next patient was increased by 0.3% (positive response [ open symbols ]); whereas in the absence of an increase in systolic arterial blood pressure of 15% or more from the preprocedural value, the end-tidal concentration given to the next patient was decreased by 0.3% (negative response [ filled symbols ]). The horizontal dashed line represents EC50(effective concentration to block systolic blood pressure response to bladder distension in 50% of patients) calculated by the up-and-down method.