Abstract PR509

Abstract

Background & Objectives: Dexmedetomidine is a selective α-2-adrenoceptor agonist which might be used as a local anesthetic (LA) adjuvant for peripheral nerve block. Previous study had showed that dexmedetomidine could suppress the peak amplitude of Na+ current in neuronal cells. We designed this study to determine the minimum effective volume (MEV) of ropivacaine with or without dexmedetomidine for ultrasound-guided supraclavicular brachial plexus block (SBPB), to quantify the sparing effect of dexmedetomidine on the MEV of ropivacaine. Materials & Methods: Thirty-four adult patients scheduled for forearm and hand surgeries under SBPB were randomized into two groups: Group R (0.75% ropivacaine) and Group RD (0.75% ropivacaine plus dexmedetomidine 30 µg). A successful block was defined as complete loss of cold sensation at the sensory dermatomes of four main nerves within 45 min after completed LA injection. The MEV of ropivacaine with or without dexmedetomidine was determined by using up-and-down method introduced by Dixon and Massey. Results: The MEV for 0.75% ropivacaine was 15.5 ml [confidence interval (CI) 95%: 13.9-17.2 ml] in Group R vs. 14.0 ml (CI 95%: 12.5-15.6 ml) in Group RD. Dexmedetomidine decreased the MEV of ropivacaine by about 10%. Systolic arterial blood pressure and heart rate levels were lower in group RD than in group R, and sedation level was higher in group RD than in group R. There were no differences in the incidence of paraesthesia, nerve stimulation, vascular puncture, systemic toxicity to LA, and bradycardia. Conclusion: Perineuraxial dexmedetomidine 30 µg produced a 10% reduction of MEV of ropivacaine for ultrasound-guided SBPB.