Background and aims Dexmedetomidine has demonstrated benefits in sedation and post-operative pain control without respiratory depression. a loading dose (1 ug/kg) and infusion is commonly used, which may cause dose-dependent heavy sedation and hypotension in the post-anesthetic care unit (PACU).We hypothesized that a single dose (0.5 ug/kg) for sedation during spinal anesthesia will reduce opioid consumption without side effects after total knee arthroplasty (TKA).

Methods 54 patients undergoing spinal anesthesia for TKA were randomized to receive normal saline (NS, n = 27) or 0.5 ug/kg dexmedetomidine (DG, n=27) intravenously prior to spinal anesthesia. the primary outcome was morphine consumption in the first 24 hours following surgery. Secondary outcomes were a numeric rating scale for pain, motor and sensory blockade regression, intra-/post-operative side-effects and length of stay in the PACU.

Results The mean (SD) morphine consumption after 24 hours in DG was 35.4 mg (13.6) vs 47.2 mg (19.5) in NS group (mean difference 11.8 mg; 95% CI 2.631–21.028; P <0.01). More patients in DG experienced hypotension intraoperatively (24 vs. 17; p = 0.02) and in PACU (22 vs. 15; p=0.04) compared to NS group. There were no significant differences in pain scores at 6, 12, and 24 hours, time to motor and sensory blockade regression, bradycardia, post-operative side effects and length of stay in the PACU.

Conclusions A reduced single dose dexmedetomidine was associated with a significant decrease in morphine use in the first 24 hours and no difference in length of stay in the PACU following TKA. a single dose of dexmedetomidine in patients receiving spinal anesthesia can produce effective intraoperative sedation and postoperative analgesic effects without significant side effects and may offer a more effective dosing strategy compared to infusion regimens.