Effect of intravenous dexmedetomidine on median effective concentration of ropivacaine for caudal block

Abstract:

Objective Caudal block，characterized by simple operation，small injury，rapid onset and definite anesthetic effect，is a common anesthesia method for children and adults undergoing lower extremity，urinary system or anorectal surgery. Intravenous dexmedetomidine（IV-DEX） is a commonly used sedative method during regional anesthesia，but it also shows synergistic effect on local anesthetics. This study aims to examine whether IV-DEX reduces the median effective concentration（EC₅₀） of local anesthetics for caudal block.Methods Sixty patients scheduled for elective hemorrhoidectomy were enrolled in the study and divided into intravenous-normal saline（IV-NS） group and IV-DEX group. In IV-NS group and IV-DEX group，20 mL saline and 1 μg/kg dexmedetomidine （diluted to 20 mL） were intravenously infused 15 min before caudal block， respectively. The EC₅₀ of ropivacaine for caudal block was determined by Dixon-Massey “up and down” sequential assignment method. Vital signs，hypotension， bradycardia，and other intraoperative adverse events requiring medical treatment were recorded.Results The EC₅₀ of ropivacaine for caudal block in IV-NS group was 0.280%，and that in IV-DEX group was 0.233%（P<0.05）. Compared with the IV-NS group，the EC₅₀ of ropivacaine in the IV-DEX group was decreased by 16.8%（P=0.000），and the difference was statistically significant. The incidence of hypotension，bradycardia，and other adverse events requiring medical treatment had no difference between the two groups.Conclusion IV-DEX can reduce the EC₅₀ of ropivacaine for caudal block，but it may lead to an increase in the incidence of hypotension and bradycardia. Therefore，the optimal synergistic dose of IV-DEX with local anesthetics still needs to be further explored.