The purpose of this study is to determine whether a small dose of Dexmedetomidine, when given either intravenously or as part of the interscalene nerve block solution, prolongs pain relief following shoulder surgery compared to local anesthetic solution alone.

Unilateral shoulder surgical procedures, including acromioplasty, rotator cuff repair and Bankart procedure generally allow the patient to go home the same day. However, post-surgical pain is often severe and it is common to encounter a delay in discharge from the hospital due to difficulty in pain control.

Single shot interscalene block is used in ambulatory shoulder surgery for its advantages that included a significant reduction in acute pain and analgesic requirements, prolonged time to first analgesic request, decreased incidence of nausea, as well as earlier hospital discharge. Previous studies have attempted to prolong the duration of the analgesia of interscalene block by administering additional drugs to the local anesthetics but these studies have had varying degrees of success. Dexmedetomidine has recently been considered as a potentially useful drug in prolonging nerve block analgesia. Various modes of administration of Dexmedetomidine have demonstrated a consistent effect on the duration of analgesia. So far, the systemic infusion of Dex has been shown to prolong both neuraxial and peripheral nerve blocks. When combined with local anesthetics in intravenous regional anesthesia 9IVRA), Dex enhanced the duration of analgesia. Furthermore, data from animal studies strongly support the use of Dex as a safe potent adjunct to local anesthetics capable of prolonging the duration of analgesia of peripheral nerve blocks.

The use of Dexmedetomidine as an adjunct in interscalene block has not been studied yet. This trial will study the effects of adding Dexmedetomidine as an adjunct to local anesthetics in interscalene brachial plexus block.

Inclusion Criteria:

• unilateral surgical shoulder procedures under general anesthetic
• English speaking patients
• ASA I-III patients
• BMI <38 kg/m2

Exclusion Criteria:

• proximal clavicular surgery
• preexisting neurological deficits or peripheral neuropathy
• known coronary heart disease, congestive heart failure, cardiomyopathies, or arrhythmias
• known cerebrovascular disease
• baseline heart rate <60 beats per minute or baseline systolic blood pressure <100 mm Hg
• medications that reduce heart rate (as beta-blockers, calcium blockers) known liver dysfunction or existing diseases known to cause hepatic or renal impairment
• severe bronchopulmonary disease
• local infection
• contra-indication to regional anesthesia (bleeding, coagulopathy)
• chronic pain disorders
• current use of over 30mg oxycodone or equivalent per day
• contraindication to a component of multimodal analgesia
• allergy to local anesthetics or dexmedetomidine
• history of significant psychiatric conditions that may affect patient assessment
• pregnancy
• inability to provide consent