<prompt> The most common complication of interscalene block:-Phrenic blockPneumothoraxHypotensionHorner syndrome  <response>: A properly performed interscalene block universally blocks the ipsilateral phrenic nerve. Interscalene Block: Side Effects Diaphragmatic hemiparesis from ipsilateral phrenic nerve block 100 incidence, 25 reduction in pulmonary function Pneumothorax Permanent neurologic injury Blockade of vagus, recurrent laryngeal, and cervical sympathetic nerves Horners syndrome Epidural or subarachnoid injection Veebral aery injection Severe hypotension and bradycardia Bezold-Jarisch reflex The interscalene block is indicated for procedures on the shoulder and proximal humerus as well as the lateral two thirds of the clavicle. The interscalene block can also be utilized for surgery of the arm or forearm; however, the higher incidence of incomplete blockade of the inferior trunk with this technique may provide inadequate analgesia in the ulnar distribution. The patients positioning and comfo, the surgeons preferences, and the duration of surgery may necessitate coadministration of a general anesthetic. An interscalene catheter may be inseed for prolonged postoperative analgesia 