 BACKGROUND RATIONALE Interscalene brachial plexus blockade ISB has emerged as the choice method of analgesia for arthroscopic shoulder surgery performed on an outpatient basis. The ISB is typically administered as a single injection of local anesthetic prior to surgery. Benefits include reduced pain, opioid consumption and postoperative nausea and vomiting on the first postoperative day. However, the limited duration of analgesia with a single injection of local anesthetic, typically 12 to15 hours, is inadequate for many patients. Recent interest in prolonging the analgesic duration of single injection ISB has been focused on the addition of various adjuncts to the local anesthetic, with varying degrees of success. 