 METHODS This single-centre, factorial design, double-blinded, randomized controlled superiority trial has four parallel groups and 1:1:1:1 randomization. Consenting and eligible adult ambulatory patients undergoing arthroscopic shoulder surgery will receive preoperative, ultrasound guided ISB with 30 millilitres mL of 0.5 bupivacaine and 4mg or 8mg of preservative free dexamethasone either intravenous or perineural. The remainder of the intraoperative and postoperative care is at the discretion of the attending anesthesiologist and surgeon. Based on previous work, with 70 patients per group, the study is at least 90 powered to detect a 3 hour difference in analgesia for dose or route, and a 4 hour synergistic interaction, even with a 5 attrition rate. Outcomes will be assessed by chart review and telephone follow up on postoperative day one, postoperative day 2 if necessary, and postoperative day 14. 