ABSTRACT
BACKGROUND: Both low volume interscalene and infraclavicular-subomohyoid blocks were suggested to provide shoulder analgesia with low risk of phrenic nerve block. The aim of this study was to compare the frequency of the phrenic nerve block between these two techniques. METHOD: Seventy-two patients scheduled for shoulder arthroscopy were included in this randomized controlled blind study. Before induction of general anesthesia, patients received low volume interscalene block using 5 mL of ropivacaine 0.5% (LVS group) or infraclavicular-subomohyoid block using 25 mL of ropivacaine 0.5% (ISO group). The diaphragmatic excursion was measured (using ultrasound) before the block and after surgery. If the ratio of postoperative to pre-block excursions was <25%, a phrenic nerve block was concluded. Secondary outcomes were: the duration of analgesia, the 24-hour morphine requirement, and patient satisfaction. RESULTS: The phrenic nerve was blocked in 88.9% of patients in LVS group vs 5.6% in ISO group (P < 0.001). There was no significant difference between the two groups with regard to the duration of analgesia, the morphine consumption, and the patient satisfaction. CONCLUSION: Compared with the low volume interscalene block, the infraclavicular subomohyoid block resulted in a significantly less frequent phrenic nerve block and with no difference in postoperative analgesia. Therefore, it may be relevant to consider for patients who cannot tolerate a phrenic nerve block.
