Background: Intrathecal dexmedetomidine has been reported to potentiate the effect of local anesthetics.

Objective: To compare post-operative analgesic effect of 5 μg dose of dexmedetomidine or 0.2 mg dose of morphine added with intrathecal bupivacaine.

Materials and Methods: Fifty-six patients undergoing hip or knee arthroplasty under spinal anesthesia were randomized into two groups. Each patient received a 12.5 mg dose of bupivacaine for spinal anesthesia. A 0.2 mg dose of morphine or a 5 μg dose of dexmedetomidine was diluted in an equivalent volume and administered intrathecally in the control (M) and intervention (D) group, respectively. Post-operative morphine patient control analgesia (PCA) was used in every patient. The primary objective was to determine the time to the first analgesic requirement. The time to reach the T10 sensory level, time to regression to S1 sensory level and motor levels, the 24-post-operative-hour morphine requirement, verbal numerical rating pain scale, and adverse effects were recorded.

Results: Patients in group M had a significantly longer analgesic duration of the time to the first analgesic requirement; 468.50 and 302.46 minutes in groups M and D, respectively, (p-value 0.006). The morphine requirement during the first 24 post-operative hours was smaller in group M (19.14 mg) than in group D (37.58 mg) (p-value 0.003). Pruritus was significantly higher in group M. Post-operative pain score, nausea and vomiting, and sedation score were not different between the two groups.

Conclusion: Intrathecal dexmedetomidine provided significantly lower post-operative analgesia in 24 hours after hip or knee arthroplasty compared to morphine.