Background and Objectives: This prospective, randomized, double-blind study was designed to determine whether reduction in volume from 20 to 10 mL of ropivacaine 0.5% for ultrasound-guided interscalene block might decrease the incidence of diaphragmatic paresis and preserve pulmonary function.

Method: Thirty patients scheduled for arthroscopic shoulder surgery were randomized to receive either 10 or 20 mL of ropivacaine 0.5% for interscalene block at the level of the cricoid cartilage. General anesthesia was administered for surgery, and the surgeon infiltrated lidocaine at the port sites. Hemidiaphragmatic excursion and pulmonary function tests were measured before block, 15 mins after block, and at the time of discharge from recovery room. Onset and duration of sensory dermatomal spread, motor block, pain scores, and analgesic consumption were recorded.

Results: Hemidiaphragmatic paresis occurred 15 mins after block performance in 14 of 15 patients in each group. At postanesthesia care unit discharge, 13 of 15 patients in each group continued to demonstrate hemidiaphragmatic paresis. Significant reduction of spirometric values (forced vital capacity, forced expiratory volume at 1 sec, and peak expiratory flow) occurred to a similar degree in both groups after block. Sensory dermatomal spread, motor block, pain scores, and analgesic consumption were not significantly different between groups.

Conclusions: Decreasing the volume for interscalene block from 20 to 10 mL did not reduce the incidence of hemidiaphragmatic paresis or impairment in pulmonary function, which persisted at discharge from recovery room. No significant differences in quality or duration of analgesia were observed.