Dexmedetomidine, an alpha 2 receptor agonist, prolongs nerve block duration when administered in conjunction with peripheral nerve blocks. We hypothesised that sedation with dexmedetomidine could also significantly prolong the analgesic duration of brachial plexus block (BPB) during orthopaedic surgery on the upper extremities.

One hundred and two patients received upper extremity surgery under BPB. The patients were randomly sedated with dexmedetomidine (D group) or midazolam (M group) following BPB using 25 mL of local anaesthetics (1:1 mixture of 1% lidocaine and 0.75% ropivacaine). Adequate sedation was evaluated with the modified Ramsay Sedation Scale. Primary outcome was measured as the time the patient first requested analgesic via a patient-controlled analgesia device. Total opioid consumption during the first 24 post-operative hours was also measured as secondary outcomes.

Time to first request for analgesia (mean ± standard deviation) was significantly longer in the D group (616.9 ± 158.2 min) than in the M group (443.7 ± 127.2 min) (P < 0.001, Mean difference [95% CI] 173.2 [114.8–231.5] min). Total opioid consumption were significantly lower in the D group (fentanyl equivalent, 280.0 μg [171.3;374.0] vs. 363.9 μg [208.3;570.1], P = 0.01). Although patients in the D group showed deeper sedation over time (P < 0.001), PACU stay time was only slightly extended in D group (5.2 [1.2–9.2] min). Perioperative complications did not differ in the two groups.

Sedation with dexmedetomidine not only prolongs analgesic duration of BPB, but also reduces total opioid consumption during the first 24 post-operative hours.