A sequential allocation study to determine the ED(50) of Dexmedetomidine as an adjuvant to lidocaine intravenous regional anesthesia

BACKGROUND: Intravenous regional anesthesia is an easy and reliable anesthetic technique, but its use is limited by tourniquet pain. Clonidine is effective in overcoming this shortcoming when used with intravenous regional anesthesia at a dose of 1 μg/kg. Dexmedetomidine has also been used successfully at a dose of 0.5 μg/kg. OBJECTIVE: Based on the potency ratios of clonidine and dexmedetomidine (8 to 1) we hypothesize that a lower dexmedetomidine dose would provide patients with 50 min of pain free tourniquet time. METHODS: After informed consent, patients received intravenous regional anesthesia with lidocaine and dexmedetomidine following a sequential allocation scheme. The first patient received a dose of 0.5 μg/kg of dexmedetomidine. The dose was then adjusted in 0.1 μg/kg gradients for the following patients depending on the success of the previous block. If a patient experienced tourniquet pain prior to 50 min, the next patient received a higher dose. If not, the dose was decreased. Recruitment continued until 6 independent crossovers were observed with a minimum of 20 patients. The median effective dose ED(50) of dexmedetomidine was calculated using the modified up-and-down method. MAIN OUTCOME MEASURES: The median effective dose of dexmedetomidine (ED(50)) that provides 50 min of tolerance to the tourniquet during a lidocaine intravenous regional anesthesia by a sequential Dixon up-and-down allocation study. RESULTS: The ED(50) of dexmedetomidine that provided 50 min of tolerance to the tourniquet was 0.30 ± 0.06 μg/kg. CONCLUSION: We determined that the dexmedetomidine dose necessary to provide 50 min of pain free tourniquet time during intravenous regional anesthesia was higher than expected based on the relative alpha-2 adrenergic receptor selectivity of dexmedetomidine compared to clonidine. TRIAL REGISTRATION: Clinicaltrials.gov: Retrospectively registered (NCT05342870; registration date: 25/04/2022).