Two hundred twelve patients undergoing elective arthroscopic shoulder surgery were randomized to receive either an interscalene block (ISB, n=106) or a costoclavicular block (CCB, n=106) as the sole anesthetic under monitored anesthesia. The primary outcomes were the proportion of patients achieving complete motor blockade of the suprascapular nerve (SSN) and the incidence of hemidiaphragmatic paralysis (HDP). Secondary outcomes included other nerve blockade characteristics, procedural complications, postoperative pain scores, and patient satisfaction. Outcomes were assessed up to 30 minutes post-block and up to 24 hours postoperatively. Overall, the results revealed that although non-inferiority was not demonstrated at 20 minutes for SSN motor blockade, the CCB reached similar blockade levels by 30 minutes and resulted in significantly fewer adverse respiratory effects, including HDP and dyspnea. These findings suggest that the CCB is a promising alternative to the ISB, particularly in patients with pulmonary risk factors.