Low Dose Dexamethasone in Supraclavicular Blocks

Overview

Brachial plexus nerve blocks provide superior analgesia over opioids while avoiding unwanted side effects. Single shot blocks with local anesthetic alone usually do not last the duration of the acute post-surgical pain period. This has led to the exploration of multiple adjuvants to increase the duration of single shot blocks, the most promising adjuvant being dexamethasone. Peri-neural administration is an off-label use of dexamethasone. While no adverse events have been reported in human clinical studies, logic would dictate that we minimize the dose needed to produce the desired effect. Most studies thus far have used peri-neural dexamethasone doses ranging from 4-10 mg. However, Albrecht et al. found no difference in block duration comparing 4 mg and 8 mg doses while Liu et al. reported equivalent block duration using doses of 1, 2 and 4 mg. Recent studies have evaluated whether systemic and peri-neural administrations of dexamethasone are equivalent, which would in turn imply a site of action. Results have been mixed. Four studies concluded peri-neural and intravenous administration are equivalent at prolonging analgesia, though one study had methodological errors, including the administration of intravenous dexamethasone to all patients. All of these studies used dexamethasone doses of 8 to 10 mg. One study where a lower dose (4 mg) was used found that peri-neural administration prolonged block duration whereas intravenous did not. With that, the rationale of our study is to determine if equivalent block-prolonging analgesia can be achieved using low dose (1 mg) dexamethasone given peri-neural or intravenous. Clinical experience at our centre has been that 1 mg dexamethasone added to 20 mL produces similar block duration to that reported in published studies using higher doses.

The investigators will evaluate the block-prolonging efficacy of dexamethasone 1 mg in supraclavicular blocks. The investigators will be answering essentially two questions. First, how long do supraclavicular blocks last when low dose dexamethasone is used as an adjunct. Only one study has looked at doses this low (Liu et al. 2015). Some methodological problems with this study include evaluation of shoulder surgery using supraclavicular blocks, which may or may not cover the posterior port site; use of the endpoint of "time to first analgesic", which may or may not indicate actual block duration; and low numbers powered to 80%, which may yield spurious results. To avoid these issues the investigators chose upper limb surgery, a type of block which will definitely cover the entire surgical site, and an endpoint of time to first pain at surgical site, regardless of whether analgesic is needed. The investigators are also powering to 95% and recruiting higher numbers of patients. The second question evaluates the efficacy of 1 mg of intravenous dexamethasone. The study is powered to address this question, but in doing so is also powered adequately to address the first question. Studies to date have mixed results and methodological errors. No other studies have evaluated this dose of intravenous dexamethasone.