Median Effective Volume of 0.2% Ropivacaine for Ultrasound-Guided Axillary Brachial Plexus Block in Children Aged 6-10 Years: A Prospective Dose-Finding Study Using Up-and-Down Sequential Allocation.

The optimal dose for ultrasound-guided axillary brachial plexus block (ABPB) in children remains poorly defined. This study aimed to find the median effective volume (EV50) of ropivacaine (0.2%) for ABPB in children aged 6-10 years. A prospective, double-blind, dose-finding trial using the Dixon up-and-down method was conducted. Pediatric patients (aged 6-10 years, ASA I-II) undergoing unilateral elbow or below-elbow surgery were enrolled. Ultrasound-guided ABPB was performed using a dual-injection technique with supplemental musculocutaneous nerve blockade. The initial volume of ropivacaine (0.2%) was 0.5 mL/kg, adjusted by 0.05 mL/kg based on the previous patient's response. The study continued until seven inflection points were observed from failure to success. EV50 and EV95 (95% effective volume) were calculated using isotonic regression and bootstrapping, with 95% confidence intervals (CIs). Patient demographics, postoperative pain scores, and adverse events were monitored. Twenty-nine patients were enrolled. The EV50 was 0.350 mL/kg (95% CI: 0.197-0.362 mL/kg), and the EV95 was 0.395 mL/kg (95% CI: 0.385-0.396 mL/kg). No adverse events were observed during the perioperative period. This study provides evidence-based dosing parameters for 0.2% ropivacaine in pediatric ABPB, aiding clinicians in optimizing efficacy and safety. The findings support age-specific precision in pediatric regional anesthesia.