Comparison between two different concentrations of a fixed dose of ropivacaine in interscalene brachial plexus block for pain management after arthroscopic shoulder surgery: a randomized clinical trial.

Background To compare the effects of two different concentrations of a fixed dose of ropivacaine used in ultrasound-guided interscalene brachial plexus block for postoperative analgesia after arthroscopic shoulder surgery. Methods This prospective, randomized, double-blind study included 62 patients who underwent arthroscopic surgery under general anesthesia. The patients were randomly assigned to receive ultrasound-guided interscalene block with 75 mg of ropivacaine at one of two concentrations: 0.75% (10 ml; group C) or 0.375% (20 ml; group V). Time to onset of sensory and motor blockade, degree of motor and sensory blockade, pulmonary function changes, analgesic duration of the interscalene block, postoperative opioid requirement within 24 hours, postoperative pain scores, satisfaction score related to pain control, and incidence of complications related to the block were recorded. Results Although the time to onset of sensory blockade was shorter for group C (P = 0.015), successful blockade was achieved at 30 min after the interscalene block in both groups. The analgesic duration of the interscalene block was not significantly different between the groups. The amount of opioid used within 24 hours after surgery was significantly reduced for group V compared with group C (P = 0.016). Conclusion Compared with 10 ml of 0.75% ropivacaine, 20 ml of 0.375% ropivacaine did not prolong the analgesic duration of interscalene block. Nevertheless, it could be effective for the reduction of postoperative opioid requirement within 24 hours after surgery.