Point-of-care ultrasound of the diaphragm after proximal brachial plexus block for shoulder surgery: a prospective observational study

Introduction This observational study evaluates diaphragmatic excursion and thickening fraction before and after proximal analgesic brachial plexus block in 99 patients undergoing shoulder surgery. Methods This study has a prospective, observational, blinded design and evaluates three methods of sonographic assessment: (1) the excursion of the dome of the diaphragm, (2) the thickening fraction of the zone of apposition, and (3) the excursion of the zone of apposition. All three methods of assessment were used prior to and within 30 min of a proximal brachial plexus block for shoulder surgery. The blocks were all ultrasound-guided and were either an interscalene block or a superior trunk block with 15–20 mL of ropivacaine 0.5% or bupivacaine 0.25% with 1:400 000 epinephrine. The type of block was not randomized and was left to the discretion of the anesthesiologist performing the nerve block. Results Assessment of the excursion of the zone of apposition and the thickening fraction was possible bilaterally in all patients. Assessment of the excursion of the dome of the diaphragm was consistently possible on the right side but only possible in about half of the patients (48.8% preblock and 46.3% postblock) on the left hemithorax. The median decrease in diaphragmatic function was between 42% and 82% dependent upon the type of nerve block, patient sex, and method of evaluation. One patient developed complete plegia, and three-quarters of all patients developed >50% weakness. Female sex and interscalene block were associated with greater weakness. Conclusion The data suggest that the assessment of the excursion of the zone of apposition on the lateral aspect of the chest using a linear probe is consistently successful in measuring both baseline and postblock values of diaphragmatic excursion, and thus it may be a helpful tool in the perioperative period. Future studies are needed to establish use in other clinical settings as well as assessment of learning curves and reliability of this emerging technique.