Differential Effects of Intrathecal Dexmedetomidine and Fentanyl Added to Bupivacaine: A Comparative Study

Background: Intrathecal adjuvants are commonly used to enhance the efficacy of spinal anesthesia. Dexmedetomidine, an α2-adrenergic agonist, and fentanyl, an opioid, have shown benefits in prolonging sensory and motor blockade when added to bupivacaine. Objective: To compare the efficacy and safety of intrathecal dexmedetomidine versus fentanyl as adjuvants to bupivacaine in patients undergoing elective lower limb or lower abdominal surgeries. Methods: Seventy patients aged 18–65 years, classified as ASA I or II, were randomly assigned into two groups of 35 each. Group D received 3 mL of 0.5% hyperbaric bupivacaine + 5 µg dexmedetomidine, while Group F received 3 mL of 0.5% hyperbaric bupivacaine + 25 µg fentanyl intrathecally. Parameters assessed included onset and duration of sensory and motor block, hemodynamic changes, postoperative analgesia, and side effects. Results: The onset of sensory and motor block was faster in Group D (sensory: 3.2 ± 0.6 min vs. 4.1 ± 0.7 min, p < 0.05; motor: 4.5 ± 0.8 min vs. 5.6 ± 0.9 min, p < 0.05). Duration of sensory block was longer in Group D (190 ± 25 min) compared to Group F (150 ± 20 min, p < 0.01). Postoperative analgesia was prolonged in Group D (mean analgesia: 240 ± 30 min vs. 180 ± 25 min, p < 0.01). Hemodynamic parameters were comparable, with mild bradycardia in 2 patients in Group D. No major adverse events were reported. Conclusion: Intrathecal dexmedetomidine as an adjuvant to bupivacaine provides faster onset, longer duration of sensory and motor block, and prolonged postoperative analgesia compared to fentanyl, with minimal side effects. Dexmedetomidine is an effective alternative to fentanyl for spinal anesthesia.