The addition of perineural dexamethasone may significantly prolong the duration of interscalene block over IV administration of the adjuvant, but this benefit likely is not enough to overcome the potential for adverse effects. Researchers found little difference between 4- and 8-mg doses of dexamethasone on block prolongation.
“Although interscalene block is known to provide effective analgesia for shoulder surgery, it has limited duration—often less than 12 hours,” said Darren W. Holland, MD, a resident at the University of Manitoba, in Winnipeg, who worked under the guidance of lead author Thomas Mutter, MD. “Dexamethasone is known to prolong the analgesic duration of interscalene block by as much as twofold compared to local anesthetic alone, and these effects have been seen with both intravenous and perineural administration.
“The issue with perineural dexamethasone is that there is a theoretical risk of neurotoxicity,” Dr. Holland continued. “So with that downside in mind, novel routes and higher doses should certainly be justified by significant benefit in order to accept this risk.” Nevertheless, previous research on the topic has been insufficiently powered, a drawback that prevents researchers from making strong conclusions regarding the optimal dose and route of administration of dexamethasone used as an adjunct.
The investigators conducted the factorial, randomized superiority trial of 280 adult patients, all of whom were undergoing arthroscopic shoulder surgery at the institution between June 2015 and July 2016. After random assignment in a 1:1:1:1 fashion, all patients received preoperative ultrasound-guided interscalene block with 30 mL of 0.5% bupivacaine plus 4- or 8-mg dexamethasone via the perineural or IV route. Patients with diabetes mellitus, chronic opioid use, or contraindications to interscalene block or dexamethasone were excluded. All relevant parties were blinded to the intervention group.
“Care for these patients was at the discretion of the attending anesthesiologist,” Dr. Holland said, “with a few exceptions. We required that dynamic ultrasound was used with an in-plane approach, the block solution could not be altered and dexamethasone could not be given other than as determined by randomization.”
Higher Incidence of Neurologic Symptoms
Patients were assessed at multiple time points, and the trial’s primary outcome was block duration. Secondary outcomes, including adverse effects, quality of recovery markers and postoperative neurologic symptoms, were assessed by telephone follow-up or chart review.
In presenting the study during the Residents’ Competition of the 2017 annual meeting of the Canadian Anesthesiologists’ Society (abstract 260987), Dr. Holland noted that the perineural route significantly prolonged block duration by 2.0 hours (95% CI, 0.4-3.5; P=0.01), representing less than 10% prolongation over the IV route, regardless of the dexamethasone dose. Moreover, 8 mg of dexamethasone did not significantly prolong block duration over 4 mg (1.3 hours; 95% CI, –0.3 to 2.9 hours; P=0.10), regardless of administration route.
No significant interaction and no remarkable differences in secondary outcomes between groups were observed. “The one thing that we did find that was unexpected was that the incidence of persistent neurological symptoms was higher than expected,” Dr. Holland said. “In our study it was 16%, where we would expect, based on previous literature, that the incidence would be between 10% and 12%.” These symptoms resolved by six months in all but five patients.
“So we conclude that perineural dexamethasone marginally prolongs block duration compared to IV administration,” Dr. Holland said. “What’s more, 8 mg of dexamethasone was not significantly different from 4 mg, regardless of the route. No other significant benefits of the perineural route were found. So our conclusion is that clinicians should strongly consider the risks of administered perineural dexamethasone given its limited analgesic benefit and theoretical risks of neurotoxicity.”
Dr. Holland’s audience raised several questions about the trial, beginning with dexamethasone dose. Stephan K.W. Schwarz, MD, PhD, a professor of anesthesiology, pharmacology and therapeutics at the University of British Columbia, in Vancouver, and one of the competition’s judges, said, “Your results are consistent with those of previous studies that demonstrate prolongation of peripheral nerve blockade with systemic [IV] dexamethasone. Yet among the issues that this raises is that if there is a perineural site of action—as opposed to a systemic site of action—the possibility exists that the doses required perineurally for target tissue concentrations might be very small. Yet you used the same doses—4 mg and 8 mg—for both routes, and many clinicians may consider a perineural bolus of 4 mg or 8 mg to be high.”
“In its own way, we were using the IV route as the control, and wanted a similar dose for the perineural route,” Dr. Holland said. “We found that both 4 mg and 8 mg were the mo st commonly used perineural doses in the previous literature, going up to as much as 10 mg. So it wasn’t outside the realm of previous studies. And both 4 mg and 8 mg are commonly used intravenously as well.”
Given these results, Dr. Holland found little reason to continue research into the benefits of adjuvant perineural dexamethasone in these blocks. “Given this marginal benefit, I would hesitate suggesting that perineural dexamethasone administration should continue to be investigated, without question,” he concluded.