The Effects of Dexamethasone on Low Dose Interscalene Brachial Plexus Block

Interscalene brachial plexus block (ISB) is regarded as the standard of care for analgesia after shoulder surgery providing superior analgesia and reducing opioid consumption. Shoulder surgery, previously requiring inpatient admission for pain control, is now commonly performed on an ambulatory basis facilitated by ISB analgesia. The effects of single injection ISB dissipate after several hours unmasking the moderate to severe pain of the surgical insult and require strong opioid analgesia. Efforts to prolong ISB duration by increasing local anaesthetic (LA) dose are limited by their pharmacodynamics and narrow therapeutic window. To address some of these issues faced with prolonging ISB analgesia the addition of perineural adjuvants to local anesthetic (eg. clonidine, dexmedetomidine), have been investigated in an attempt to prolong peripheral nerve block duration with limited success. However, the corticosteroid 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. There are several reasons that warrant a new randomized trial. Chiefly, all of the previous trials do not reflect modern regional anesthetic practice. These trials utilized peripheral nerve stimulation (PNS) and local anesthetic volumes of 30 to 40 ml. Modern ultrasound guided ISB (US-ISB) allows for more accurate, targeted deposition of local anesthetic with volumes ranging from 5 to 10 ml with no difference in block efficacy or duration compared to larger volumes (≥20ml). An ideal solution would be a local anesthetic with adjuvant mixture that allowed administration of lower volumes but with prolonged analgesic duration. The use of low dose local anesthetic with dexamethasone could be one such solution. A trial that demonstrates enhanced block quality and duration associated with perineural dexamethasone added to low dose local anesthetic may allow us to achieve both prolonged duration of effect and reduced side effects due to unwanted local anesthetic spread. This would create further significant benefits for patients and further promote the use of low dose local anesthetic techniques to anesthesiologists who do not currently use this technique.

Inclusion criteria

• Patients undergoing arthroscopic shoulder surgery at Sunnybrook Health Sciences Centre, Toronto Western Hospital and Women's College Hospital.
• ASA functional status class I to III
• Age 18 to 80 years
• BMI ≤ 35 kg/m2

Exclusion criteria

• Lack of patient consent
• Allergy to dexamethasone or ropivacaine
• BMI > 35 kg/m2
• Contraindications to low dose dexamethasone including peptic ulcer disease, systemic infection, glaucoma, active varicella/herpetic infections, diabetes mellitus
• 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
• Pregnant or nursing females
• Chronic opioid use defined as > 30mg oral morphine or equivalent per day
• Unable to take acetaminophen or celecoxib