Background and aims This prospective, randomized, double-blind study was designed to determine whether dilution in from 0.750% 10 ml (group T) to 0.375% 20 ml (group W) of total ropivacaine contents 75 mg for ultrasound-guided interscalene brachial plexus block (ISB) might increase the duration of postoperative analgesia and patient satisfaction score.

Methods 44 patients scheduled for arthroscopic shoulder surgery were randomized to receive either group W or T of ropivacaine 75 mg for ISB. General anesthesia was administered for surgery. Pulmonary function tests (forced vital capacity [FVC], forced expiratory volume at 1 sec [FEV1], and oxygen saturation) were measured before block and at the time of discharge from the recovery room. Performance, onset, and duration time of sensory, pain block, motor block, pain score, patient satisfaction score, analgesic consumption, and complications were recorded.

Results Both groups displayed the equivalent change in FVC, FEV1, and oxygen saturation from before block to discharge from the recovery room. Although sensory block onset time was faster in group T, complete block at 30 minutes no intergroup differences. Group T led to significantly increase requirement of intraoperative fentanyl and postoperative nausea and vomiting. After surgery, there were significant differences in block duration and patient satisfaction score. The pain score at postoperative 1, 2, 3, and 6 hours was not significantly different between groups. Each level of sensory and motor block scores was similar in both groups.

Conclusions Decreasing the concentration with dilution from ropivacaine 0.750 to 0.375%, increasing the volume 10 to 20 ml as the same contents 75 mg did increase block duration and patient satisfaction score.