Purpose: Dexamethasone prolongs the duration of interscalene block, but the benefits of higher doses and perineural vs intravenous administration remain unclear.
Methods: This factorial design, double-blinded trial randomized 280 adult patients undergoing ambulatory arthroscopic shoulder surgery at a single centre in a 1:1:1:1 ratio. Patients received ultrasound-guided interscalene block with 30 mL 0.5% bupivacaine and 4 mg or 8 mg dexamethasone by either the perineural or intravenous route. The primary outcome (block duration measured as the time of first pain at the surgical site) and secondary outcomes (adverse effects, postoperative neurologic symptoms) were assessed by telephone. In this superiority trial, the predetermined minimum clinically important difference for comparisons between doses and routes was 3.0 hr.
Results: The perineural route significantly prolonged the mean block duration by 2.0 hr (95% confidence interval [CI], 0.4 to 3.5 hr; P = 0.01), but 8 mg of dexamethasone did not significantly prolong the mean block duration compared with 4 mg (1.3 hr; 95% CI, -0.3 to 2.9 hr, P = 0.10), and there was no significant statistical interaction (P = 0.51). The mean (95% CI) block durations, in hours, were 24.0 (22.9 to 25.1), 24.8 (23.2 to 26.3), 25.4 (23.8 to 27.0), and 27.2 (25.2 to 29.3) for intravenous doses of 4 and 8 mg and perineural doses of 4 and 8 mg, respectively. There were no marked differences in side effects between groups. At 14 postoperative days, 57 (20.4%) patients reported neurologic symptoms, including dyspnea and hoarseness. At six months postoperatively, only six (2.1%) patients had residual symptoms, with four (1.4%) patients' symptoms unlikely related to interscalene block.
Conclusion: Compared with the intravenous route, perineural dexamethasone prolongs the mean interscalene block duration by a small amount that may or may not be clinically significant, regardless of dose. However, the difference in mean block durations between 8 mg and 4 mg of dexamethasone is highly unlikely to be clinically important, regardless of the administration route.
Trial registration: www.clinicaltrials.gov (NCT02426736). Registered 14 April 2015.