Interscalene Block and Dysfunction Diaphragmatic

It's a prospective monocentric randomized controlled clinical trial in 2 parallel groups in double blind. the study concerns patients undergoing arthroscopic shoulder surgery with ISB. The study seeks to show that interscalene injection of a small volume (\<8ml) of ropivacaine at a low concentration (0.1%) reduces the frequency of hemi-diaphragmatic paresis compared to low volume injection at the standard concentration (0.5%) in patients undergoing arthroscopic shoulder surgery with ISB. Randomization in one of the two arms: * Experimental group: \<8ml ropivacaine 0.1%. * Control group: \<8mL of ropivacaine 0.5%. Evaluation of diaphragmatic stroke by ultrasound and ventilatory function by spirometry and snip test before performing the ISB, then after installation of the ISB. Performing the surgical procedure under general anesthesia assessment of postoperative analgesia and patient satisfaction during the following 48 hours.