ObjectiveTo investigate the effect of local application of dexmedetomidine on median effective concentration (EC50) of ropivacaine for sciatic nerve block in diabetic foot patients.MethodsFifty\|seven diabetic foot patients who were undergoing elective unilateral lower limb foot and ankle surgery were divided into two groups: control group (Group C) and dexmedetomidine group (Group D).Both groups underwent ultrasound guided saphenous nerve block combined with popliteal sciatic nerve block.Saphenous nerve block was performed using 0.5% ropivacaine 10 mL, while sciatic nerve block was performed using ropivacaine with 20 mL of ropivacainein Group C, but mixture of ropivacaine and 1 μg/kg dexmedetomidine in Group D.The concentration of ropivacaine was determined by up and down sequential trial.The initial concentration was set at 0.5%, and the ratio between the two successive concentration was 1∶1.2, and the capacity was set at 20 mL.If the sensory blockade of the sciatic nerve was complete within 30 minutes after the injection, the dose for the next case reduced by a concentration gradient, otherwise the higher concentration would be applied in the next case.The EC50 and 95% confidence interval of ropivacaine were calculated.ResultsThe EC50 and 95% confidence interval of ropivacaine were 0.26% (0.23%, 0.29%) in Group C and 0.22% (0.18%, 0.25%) in Group D.The EC50 of ropivacaine was lower in Group D than in Group C (P<0.05).7 patients (23%) in group D had bradycardia, which was higher than that in group C (4%) (P<0.05).All patients returned to normal heart rate after intravenous injection of 0.5 mg atropine. No adverse reactions such as local anesthetic intoxication or hypotension or hypoxemia or excessive sedation were observed in both groups.ConclusionThe EC50 of ropivacaine for sciatic nerve block in diabetic foot patients could be decreased by local application of 1 μg/kg dexmedetomidine