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.