Background This randomized trial compared perineural dexamethasone with combined perineural dexamethasone-dexmedetomidine for ultrasound-guided infraclavicular block. We hypothesized that the combination of perineural adjuvants would result in a longer motor block.

Methods Fifty 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 (2 mg) or combined perineural dexamethasone (2 mg)-dexmedetomidine (50 µg). 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), the onset time (defined as the time required to reach a minimal composite score of 14 points) 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).

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, onset time and surgical anesthesia. Compared with dexamethasone alone, combined dexamethasone-dexmedetomidine provided longer durations of motor block (21.5 (2.7) vs 17.0 (3.9) hours; p<0.001; 95% CI 2.6 to 6.4), sensory block (21.6 (3.6) vs 17.2 (3.6) hours; p<0.001; 95% CI 2.2 to 6.5), and postoperative analgesia (25.5 (9.4) vs 23.5 (5.6) hours; p=0.038; 95% CI 1.0 to 7.7).

Conclusion Compared with perineural dexamethasone (2 mg) alone, combined perineural dexamethasone (2 mg)-dexmedetomidine (50 µg) results in longer durations of sensorimotor block and analgesia. Further studies are required to determine the optimal dosing combination for dexamethasone-dexmedetomidine.

Trial registration number ClinicalTrials.gov identifier: NCT04875039.