BackgroundThe median effective dose (ED 50) of sedative dexmedetomidine adjuvant to peripheral nerve block (PNB) has not yet been verified in elderly patients. This study assessed the ED 50 of intravenous dexmedetomidine for sedation in elderly patients who were undergoing total knee arthroplasty (TKA) with PNB.MethodsForty‐two patients aged 65–85 years were included and stratified into two groups according to age: young‐old group (aged 65–74 years) and middle‐old group (aged 75–85 years). After the PNB was performed, a pre‐calculated dose of dexmedetomidine was administered for 10 min. The Observer's Assessment of Alertness/Sedation scale, bispectral index score, blood pressure and heart rate were recorded. ED 50 values of dexmedetomidine for adequate sedation were estimated by the up‐and‐down method of Dixon and probit regression.ResultsThe ED 50 of single‐dose dexmedetomidine adjuvant to PNB was 0.57 μg/kg (95% confidence interval [CI], 0.47–0.65) in the young‐old group and 0.38 μg/kg (95% CI, 0.28–0.46) in the middle‐old group. The ED 50 of dexmedetomidine differed significantly between the two groups (P < 0.001). In addition, no significant adverse hemodynamic or hypoxemic effects were noted.ConclusionWe determined the ED 50 for sedation using intravenous dexmedetomidine adjuvant to PNB in elderly patients. The ED 50 of dexmedetomidine in the middle‐old group decreased by 33% compared with that in the young‐old group with a mean age difference of 11 years between the two groups.

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