Perineural dexmedetomidine decreases the onset time of bupivacaine 0.5%–epinephrine–dexamethasone for infraclavicular block: a randomized trial

Background This randomized trial compared three admixtures of local anesthetic for ultrasound (US)-guided infraclavicular block (ICB): adrenalized bupivacaine 0.5%- dexamethasone 4 mg (group D0) versus adrenalized bupivacaine 0.5%- dexamethasone 4 mg- dexmedetomidine 0.67 µg/kg (group D1) versus adrenalized bupivacaine 0.5%, dexamethasone 4 mg- dexmedetomidine 1.33 µg/kg (group D2). We hypothesized that the D2 group would display a 30%-shorter onset time than the D1 group, which in turn would display a 30%-shorter onset time than the D0 group. Methods After obtaining ethics committee approval, we recruited 104 patients undergoing upper limb surgery distal to the elbow. All subjects received 35 mL of bupivacaine 0.5%+epinephrine 5 µg/mL+perineural dexamethasone 4 mg. Patients were randomized to one of three perineural doses of dexmedetomidine (0 µg/kg, 0.67 µg/kg, or 1.33 µg/kg). The primary outcome was the onset time, defined as the time required to reach a minimal score of 14 points on a 16-point sensorimotor scale. The sensorimotor block was assessed every 5 min for 1 hour. Secondary outcomes included the incidence of surgical anesthesia, the duration of analgesia as well as sensorimotor block, and the occurrence of adverse events possibly related to dexmedetomidine (ie, bradycardia, hypotension, and oxygen desaturation). Results Compared with the D0 group, both D1 and D2 groups resulted in shorter median onset times (20 12.5–25.0 vs 25 17.5–30.0 min; p=0.038 and 15 (15.0–20.0) vs 25 (17.5–30.0) min; p=0.003, respectively). No statistical differences were found between the D1 and D2 groups. However, tests of trend were significant for onset time (p<0.001), thereby suggesting a dose-dependent increase in the observed effect over the three doses of dexmedetomidine. Compared with its D0 counterpart, the D2 group displayed a longer mean duration of motor block (26.4 (6.6) vs 23.0 (4.9) hours; p=0.030). No other differences in analgesic or block duration were found among the three groups. The incidences of surgical anesthesia (97.1–100%) and adverse events were similar for all three groups. Conclusion Compared with control (dexmedetomidine 0 µg/kg), perineural dexmedetomidine 0.67 µg/kg and 1.33 µg/kg decrease the onset time of bupivacaine 0.5%–epinephrine (5 µg/mL)–perineural dexamethasone (4 mg) for US-guided ICBs. Although no intergroup differences in onset were found between the 0.67 µg/kg and 1.33 µg/kg doses, there was a statistically significant directional trend, which suggested a possible dose-dependent effect. Future trials are also required to determine the optimal dose of perineural dexmedetomidine.