A randomized double-blinded study assessing the effect of different doses of transnasal dexmedetomidine on the median effective concentration of ropivacaine for a caudal block.

Background: Perineural administration of dexmedetomidine (PN-DEX) can enhance the efficacy of local anesthetics used in regional nerve blocks while decreasing the median effective concentration (EC50) of these anesthetics. Intranasal administration of dexmedetomidine (IN-DEX) is more accessible for sedation during regional anesthesia because of its non-invasive systemic administration and demonstrates synergism with local anesthetic. However, it remains unclear whether IN-DEX affects the EC50 of local anesthetics used in caudal blocks.

Methods: This study was a prospective, single-center, double-blind, randomized controlled trial. Patients scheduled to undergo elective hemorrhoidectomy were included and divided into three groups. Furthermore, 0.01 mL/kg of normal saline and 1 μg/kg and 2 μg/kg of dexmedetomidine were dripped into both nostrils of the patients in groups IN-NS, IN-DEX1, and IN-DEX2, respectively. These were administered 15 min before the caudal block. The initial concentration of ropivacaine was set at 0.4%, which was then varied by 0.025% using the up-and-down sequential allocation method. Vital signs, instances of hypotension and bradycardia with treatment, and other adverse reactions were recorded and compared.

Results: The EC50 values of ropivacaine were 0.275% (95% confidence interval (CI), 0.254-0.296%) in group IN-NS, 0.257% (95% CI, 0.238-0.276%) in group IN-DEX1, and 0.216% (95% CI, 0.195-0.236%) in group IN-DEX2. The EC95 values of ropivacaine were 0.315% (95% CI, 0.295-0.370%) in group IN-NS, 0.297% (95% CI, 0.278-0.351%) in group IN-DEX1, and 0.256% (95% CI, 0.236-0.310%) in group IN-DEX2. Compared to group IN-NS, the EC50 value of ropivacaine in IN-DEX2 was significantly decreased by 21.4% ( = 0.001), while there was no significant difference between group IN-NS and IN-DEX1 ( = 0.125). There were no differences in hypotension and bradycardia with treatment among the different groups.

Conclusion: IN-DEX decreased the EC50 of ropivacaine for the caudal block, and there was a specific dose-dependent effect for IN-DEX. The side effects were similar across all groups.