Tehran University of Medical Sciences Archives of Anesthesiology and Critical Care 2423-5849 0 0 2026 09 12 1691 1691 Reza Akhondzadeh Pain Research Center, Department of Anesthesiology, Imam Khomeini Hospital, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Fatemeh Javaherforooshzadeh Pain Research Center, Department of Anesthesiology, Imam Khomeini Hospital, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Nelia Reza Gholi Dehkordi Pain Research Center, Department of Anesthesiology, Imam Khomeini Hospital, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Alireza Olapour Pain Research Centre, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran Kamran Mahmoodi Pain Research Center, Department of Anesthesiology, Imam Khomeini Hospital, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. 2026 07 17 2026 08 01 Background: The optimal adjuvant for epidural anesthesia in orthopedic surgery remains controversial. Although epidural use has declined in some ERAS protocols, it remains valuable for prolonged procedures, patients with contraindications to spinal anesthesia, and resource-limited settings. No randomized trial has directly compared dexmedetomidine (Dex) and magnesium sulfate (MgSO4) as epidural adjuvants specifically in lower limb orthopedic procedures. We compared their efficacy as adjuvants to bupivacaine. Methods: We randomized 100 ASA I-II patients who received epidural bupivacaine (15 mg) to either MgSO4 50 mg or dexmedetomidine 5 µg. The primary outcome was the sensory block duration, and we also assessed sensory onset time and motor block parameters, analgesic requirements, pain scores, time to first mobilization, and adverse events as secondary outcomes. Results: Group D demonstrated significantly longer sensory block duration (mean difference 64 minutes; 95% CI [47,81]; p<0.001), approaching the 60-minute clinically significant threshold. Group D had faster sensory onset (mean difference −4.2 minutes; p<0.001) and lower 24-hour pethidine requirement (mean difference −35 mg; p=0.003). An exploratory observation was sensory prolongation without a statistically significant motor block increase (225 vs. 210 min, p=0.12), suggesting a potential sensory-sparing effect requiring validation. Group D had lower pain scores at 6 and 12 hours (p<0.001), and shorter time to first mobilization (median 8.5 vs. 11.2 hours; p=0.02), and magnified benefits in the trauma subgroup (n=40, post-hoc). Bradycardia was more common in Group D (8% vs. 2%; p=0.04), but other adverse events were comparable. Conclusion: Dexmedetomidine provides a longer sensory block, faster onset, superior analgesia, reduced opioid consumption, and earlier mobilization compared to MgSO4 as an epidural adjuvant for lower limb orthopedic surgery, but with a higher bradycardia risk. The sensory-sparing effect and trauma subgroup benefit require prospective validation. https://aacc.tums.ac.ir/index.php/aacc/article/view/1691