Dexamethasone has been tested as an effective adjuvant to prolong the effect of local anesthetics for peripheral nerve blocks, both perineurally and intravenously. The purpose of this study is to investigate the effect of the addition of dexamethasone (5mg) at different time to a standard ropivacaine solution (0.5%) on analgesic duration of interscalene block.

Interscalene brachial plexus block (ISB) is regarded as the standard of care for anesthesia and analgesia for shoulder surgery by providing the superior analgesia and reducing opioid consumption. After several hours when the effects of single injection ISB wear off, the patients often suffer moderate to severe pain of the surgical insult and required strong opioid analgesia. Efforts to prolong ISB duration by adding adjuvants to local anesthetic (eg. clonidine, dexmedetomidine) have been studied with promising results. Dexamethasone, has been added to local anesthetic solutions for ISB and has demonstrated promise in preliminary studies. Perineural dexamethasone (8-10mg) in conjunction with local anesthetic prolongs the duration of ISB with an effect sizes ranging from 40% to 75% (absolute effect ~ 6 to 10 hours). Dexamethasone, however, is only approved for intramuscular or intravenous administration and therefore perineural use is currently off-label. Intravenous administration of dexamethasone was reported to have similar effects as perineural route indicating the possible mechanism for prolonging analgesic duration might be due to the systemic effects of dexamethasone. We hypothesized: should that is the reason, systemic administration of dexamethasone at different time may provide similar effects on the duration of peripheral nerve block. Dexamethasone is a slow effect cortisone with long half-time, it is widely used at the beginning of surgery to prevent postoperative nausea and vomiting. A trial that demonstrates enhanced block quality and duration associated with intravenous dexamethasone at different time may allow us to achieve prolonged duration of effect if dexamethasone is used in perioperative period for different purpose. This would further identify the possible mechanism of dexamethasone to prolong the analgesia effect of local anesthetics.

Inclusion Criteria:

• Patients undergoing arthroscopic shoulder surgery at Shanghai Sixth People's Hospital.
• ASA functional status class I to II
• Age 18 to 70 years
• BMI ≤ 35 kg/m2

Exclusion Criteria:

1. Lack of patient consent
2. Allergy to dexamethasone or ropivacaine
3. BMI > 35 kg/m2
4. Contraindications to low dose dexamethasone including peptic ulcer disease, systemic infection, glaucoma, active varicella/herpetic infections, diabetes mellitus
5. Contraindications to ISB including severe Chronic Obstructive Pulmonary Disease (Forced expiratory volume < 40% predicted), coagulopathy, pre-existing neurologic deficit in ipsilateral upper extremity, localized infection
6. Pregnant or nursing females
7. Chronic opioid use defined as > 30mg oral morphine or equivalent per day