Shoulder surgery is associated with moderate to severe postoperative pain. Interscalene brachial plexus block is considered by many as the gold standard for treating postoperative pain and consists of injecting local anaesthetics close to the nerves of the brachial plexus in the neck. Duration of analgesia is between eight to twelve hours depending on the type of administered drugs. Dexamethasone 4 mg is a steroid routinely injected intravenously in anaesthesia for the prophylaxis of postoperative nausea and vomiting. Recently, different trials have demonstrated that combining 4 to 8 mg of dexamethasone with local anaesthetics for a perineural injection may prolong the duration of analgesia up to 24 hours. In a meta-analysis including 29 trials and 1695 patients, investigators have recently demonstrated through a meta-regression that a dose of 4 mg is sufficient and represents a ceiling dose, without neurological complications. The objective of this multicenter randomised controlled double-blinded trial is to determine the optimal dose of perineural dexamethasone. For that purpose, investigators will include a total of 150 patients divided in 5 groups: local anaesthetics with placebo, or with dexamethasone 1, 2, 3 and 4 mg.

Inclusion Criteria:

• patients scheduled for elective shoulder arthroscopy
• duration of surgery less than 4 hours

Exclusion Criteria:

• allergy to local anaesthetics
• history of neck surgery
• history of neck radiotherapy
• severe respiratory disease
• diabetic patient
• chronic pain condition
• pregnancy
• patient suffering from cancer
• patient with addicted disease