Wang C, et al. - Researchers evaluated the median effective dose (ED₅₀) of intravenous dexmedetomidine for sedation in elderly patients who were undergoing total knee arthroplasty (TKA) with peripheral nerve block (PNB). They administered a pre-calculated dose of dexmedetomidine for 10 min in young-old group (aged 65–74 years) and middle-old group (aged 75–85 years) who underwent PNB. Using the up-and-down method of Dixon and probit regression, ED₅₀ values of dexmedetomidine for adequate sedation were estimated. With no significant adverse hemodynamic or hypoxemic impacts, 0.57 μg/kg and 0.38 μg/kg were found to be the ED₅₀ of single-dose dexmedetomidine adjuvant to PNB in the young-old group and in the middle-old group, respectively. Overall, relative to the young-old group, the ED₅₀ of dexmedetomidine in the middle-old group decreased by 33%, with a mean age difference of 11 years between the two groups.