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Background: Auxiliary drugs augment the effect of local anesthetic in intravenous regional anesthesia (IVRA). The aim of our study was to estimate the median effective dose (ED50) of Dexmedetomidine in elective upper limb Lidocaine 0.5% IVRA. Method: A prospective, double-blind, sequential study using modified Dixon's up and down method. Thirty patients scheduled for minor upper limb surgeries were recruited in the Study, however, we ended up analyzing data of 26 patients due to protocol violation. The first patient in this sequential trial was randomly selected and received a mixed solution of 0.5% lidocaine and 0.4 µg/kg of dexmedetomidine, with 0.1 µg/kg dose interval. If IVRA outcome was satisfactory, the dose went down for the next patient by 0.1 µg/kg. Vice versa, if the outcome was unsatisfactory, the dexmedetomidine dose was stepped up by 0.1 µg/kg. Sensory and motor block onset, recovery times, hemodynamic variables, surgical and tourniquet VAS scores and time to first analgesic request were recorded. Results: The series of patient responses to IVRA was satisfactory in 11 patients (42.3%) and unsatisfactory in 15 patients (57.6%) due to either surgical pain in 6 patients or tourniquet pain in the remaining 9 patients. In patients with satisfactory response to IVRA, intraoperative and postoperative mean arterial pressure and heart rate, compared with baseline (just prior to inflating the proximal cuff) measurement, showed no statistically significant differences (P = 0.754 and 0.324, respectively). Intergroup comparison of Patients with unsatisfactory response to IVRA time to first analgesic request showed no statistical difference (P > 0.05). Conclusion: the ED 50 of Dexmedetomidine (95% confidence interval, CI) as adjuvant for satisfactory 0.5% lidocaine IVRA was 0.7 µg/kg (0.6-0.8).

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