Taha AM, et al. - In this randomized controlled blind study including 72 patients scheduled for shoulder arthroscopy, researchers compared the frequency of the phrenic nerve block between low volume interscalene vs infraclavicular-subomohyoid blocks. Before induction of general anesthesia, low volume interscalene block was administered to patients by using 5 mL of ropivacaine 0.5% (LVS group) or infraclavicular-subomohyoid block using 25 mL of ropivacaine 0.5% (ISO group). Before the block and after surgery, they measured diaphragmatic excursion using ultrasound. A phrenic nerve block was concluded if the ratio of postoperative to pre-block excursions was <25%. The duration of analgesia, the 24-hour morphine requirement, and patient satisfaction were also assessed. A significantly less frequent phrenic nerve block was observed with the infraclavicular subomohyoid block vs the low volume interscalene block, with no difference found in postoperative analgesia. In terms of the duration of analgesia, the morphine consumption, and the patient satisfaction, the two groups did not differ significantly. Considering infraclavicular subomohyoid block for patients who cannot tolerate a phrenic nerve block may be relevant.