Background This randomized trial compared perineural dexamethasone (5 mg) and dexmedetomidine (100 µg) for ultrasound-guided infraclavicular brachial plexus block. We hypothesized that both adjuvants would result in similar durations of motor block and therefore designed the study as an equivalence trial (equivalence margin=3.0 hours).

Methods One hundred and twenty patients undergoing upper limb surgery with ultrasound-guided infraclavicular block (using 35 mL of lidocaine 1%–bupivacaine 0.25% with epinephrine 5 µg/mL) were randomly allocated to receive perineural dexamethasone (5 mg) or dexmedetomidine (100 µg). Patients and operators were blinded to the nature of the perineural adjuvant. After the performance of the block, a blinded observer assessed the success rate (defined as a minimal sensorimotor composite score of 14 out of 16 points at 30 min) as well as the incidence of surgical anesthesia (defined as the ability to complete surgery without local infiltration, supplemental blocks, intravenous opioids, or general anesthesia). Heart rate and blood pressure were recorded before the block as well as during the first 2 hours after its performance. Furthermore, the level of sedation (using the Ramsay Sedation Scale) was recorded in the postanesthesia care unit. Postoperatively, the blinded observer contacted patients with successful blocks to inquire about the duration of motor block, sensory block, and postoperative analgesia.

Results No intergroup differences were observed in terms of success rate and surgical anesthesia. Compared with dexmedetomidine, dexamethasone provided longer durations of motor block (17.4 (4.0) vs 14.3 (3.0) hours; p<0.001; 95% CI 1.7 to 4.5), sensory block (19.0 (4.0) vs 15.0 (3.2) hours; p<0.001; 95% CI 2.6 to 5.4), and analgesia (22.2 (3.6) vs 16.9 (3.9) hours; p<0.001; 95% CI 3.7 to 6.9). Dexmedetomidine resulted in lower heart rate and blood pressure after the performance of the block, as well as an increased level of sedation postoperatively.

Conclusion Compared with dexmedetomidine (100 µg), dexamethasone (5 mg) results in longer sensorimotor block and analgesic durations, as well as a decreased level of patient sedation. Further studies are required to compare dexamethasone and dexmedetomidine using different doses, local anesthetic agents, and approaches to the brachial plexus.

Trial registration number NCT03610893