Examination of the optimal midazolam dose required for loss of puncture memory at the time of spinal anesthesia

BACKGROUND: We examined midazolam ED50 according to age that was necessary for loss of puncture memory at the time of spinal anesthesia and determined whether we could estimate the presence of puncture memory from the degree of sedation after midazolam administration. METHODS: We enrolled patients with ASA PS 1 or 2 and patients from 50 to 80 years of age who had been planned for surgery with spinal anesthesia. We divided the patients into groups according to their age--50s, 60s, and 70s as L, M, and H groups, respectively. We evaluated the degree of sedation with six phases of scores after intravenous administration of midazolam and spinal anesthesia was performed. The midazolam dose was based on the ups and downs method. RESULTS: The midazolam ED50s required for the loss of puncture memory in groups L, M, and H were 0.043, 0.035, and 0.026 mg x kg(-1), respectively. We estimated the association between the sedation degree score after midazolam administration and the puncture memory from ROC curve, but AUC was 0.56 for all cases. CONCLUSIONS: The midazolam ED50 required for the loss of puncture memory decreased with age but it was difficult to estimate puncture memory from the degree of sedation.