Estimation of minimum effective volume 90% (MEV90) of 0.5% Ropivacaine® in ultrasound-guided interscalene nerve block for postoperative analgesia in arthroscopic shoulder surgery: A prospective observational dose finding study and assessment of diaprhagmatic function.

Background and objectives: Ultrasound-guided ISB is the most widely-used nerve block in upper limb surgery. The aim of this study was to determine the MEV90 of 0.5% ropivacaine in ISB for analgesia in arthroscopic shoulder surgery.

Methodology: Double-blind observational post-authorization study of a medicinal product for human use. Thirty-two ASA I-III patients aged between 18 and 75 years undergoing arthroscopic shoulder surgery were recruited. We used the Dixon up-down method, whereby the dose is increased or decreased by 1 ml depending on the failure or success of the block. The initial dose was 20 ml of 0.5% ropivacaine. The study was stopped after achieving the minimum 5 negative-positive deflections. Secondary variables were the duration of the block, total analgesia consumption over the first 24 h, and incidence of DP.

Results: The effective LA dose for postoperative analgesia in arthroscopic shoulder surgery was 6.8 ml in 50% of patients (MEV50) (90% CI 6.234-7.465) and 7.733 ml in 90% of patients (MEV90) (90% CI 7.393-9.109). Median sensory block duration was 772.5 min. The incidence of partial and total DP in QB was 34% and 41%, respectively.

Conclusion: A dose of 7.733 ml of 0.5% ropivacaine provides effective postoperative analgesia in arthroscopic shoulder surgery in 90% of patients. This lower dose reduces the likelihood of side effects.