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.