 In this factorial design study, 280 participants having outpatient, arthroscopic shoulder surgery will be randomized into 4 equal sized groups. All participants will receive a standardized interscalene brachial plexus block and 4mg or 8mg of dexamethasone given by the intravenous or perineural by the nerve with the nerve block route just prior to their surgery. The purpose of this study is to determine which dose and route of dexamethasone provides the longest duration of pain control and the fewest side effects after surgery. The investigators hypothesize that giving dexamethasone by the perineural route, and by higher doses, will result in the longer durations of pain control, without increased side effects. 