A strong primary outcome crosses the efficacy boundary at the interim analysis

This study will test the hypothesis that adding dexamethasone significantly prolongs the duration of ropivacaine and bupivacaine analgesia, and that the magnitude of the effect differs among the two local anaesthetics.. Participants will be patients undergoing shoulder surgery with an interscalene nerve block.

This is a double-blinded randomized study of four groups of patients undergoing shoulder surgery using interscalene nerve blocks. Participants will be randomized into one of four groups:

• Ropivacaine: 30 ml 0.5% ropivacaine plus 2 ml 0.9% saline (placebo) for interscalene block;
• Bupivacaine: 30 ml 0.5% bupivacaine plus 2 ml 0.9% saline (placebo);
• Ropivacaine and steroid: 30 ml 0.5% ropivacaine plus dexamethasone 8 mg (2 ml) mixed with the local anesthetic;
• Bupivacaine and steroid: 30 ml 0.5% bupivacaine plus dexamethasone 8 mg (2 ml) mixed with the local anesthetic.

The primary outcome is the duration of the interscalene nerve block which is time to first analgesic request after PACU discharge.

Kaplan-Meier survival density estimation and stratified Cox proportional hazard regression were used to compare groups.

Inclusion Criteria:

• Age between 18 and 75 years
• Patients undergoing shoulder procedures, such as rotator cuff repair, capsular shift, shoulder arthroplasty, subacromial decompression

Exclusion Criteria:

• Contraindications to interscalene block (Coagulopathy, infection at the needle insertion site, moderate to severe chronic obstructive pulmonary disease, contralateral pneumothorax or diaphragmatic paralysis)
• Pregnancy
• Pre-existing neuropathy involving the surgical limb
• Systemic glucocorticoid treatment (for 2 weeks or more) within six months of surgery
• Chronic opioid use (greater than 30 mg oral oxycodone equivalent per day)

14 days after surgery