Effect of local anesthetic concentration (0.2% vs 0.1% ropivacaine) on pulmonary function, and analgesia after ultrasound-guided interscalene brachial plexus block: A randomized controlled study

Objective. This study aims to assess diaphragmatic excursion and measure pulmonary functions as measures of the degree to which the phrenic nerve is blocked after ISB with two different concentrations of ropivacaine: 0.2% and 0.1%. Design. Randomized, double-blinded study. Setting and Patients. Ambulatory surgical facility. Subjects. Fifty patients undergoing shoulder arthroscopy for rotator cuff repair. Methods. Patients were randomized to receive ultrasound- guided ISB with 20mL of either 0.2% or 0.1% ropivacaine. Diaphragmatic excursion was measured using M-mode ultrasound. Pulmonary functions were assessed by portable spirometer. Additional outcome data included oxygen saturation in post-anesthesia care unit (PACU), pain scores, quality of recovery scores (QOR), and opioid consumption over 72 hour period after surgery. Results. Forced vital capacity (FVC) was significantly reduced 30 minutes after block placement and in PACU in the 0.2% group when compared with the 0.1% group (P=0.04, P= 0.03, respectively). Forced expiratory volume (FEV1) was also significantly decreased in the 0.2% group in PACU when compared with the 0.1% group (P=0.04). There were no significant differences in pain scores, length of stay, and total opioid consumption in PACU. Patients who received 0.2% ropivacaine had a longer block duration (18 vs 11.9 hours, P=0.04) and used less opioid in the 72 hours after surgery (55mg vs 102mg codeine equivalents, P50.02), when they were compared to their counterparts who received 0.1% for their block. Conclusion. 0.1% ropivacaine may impair pulmonary function less than 0.2% ropivacaine. The clinical significance of these differences needs to be further studied.