Comparison of Small Dose Ketamine and Dexmedetomidine Infusion for Postoperative Analgesia in Spine Surgery--A Prospective Randomized Double-blind Placebo Controlled Study

Background: High doses of opioids are frequently used to treat postoperative pain after spine surgery. This leads to opioid-related side effects like nausea, vomiting, respiratory depression, etc. The current study is an attempt to find a safe analgesic adjuvant, which will afford opioid sparing property.

Method: Sixty-six patients undergoing spine surgery were randomized into 1 of the 3 groups-group K (ketamine bolus 0.25 mg/kg followed by infusion of 0.25 mg/kg/h with midazolam bolus 10 μg/kg and infusion of 10 μg/kg/h mixed in the same infusion pump), group D (dexmedetomidine bolus 0.5 μg/kg followed by 0.3 μg/kg/h infusion), and group C (normal saline). Study drugs were started in the postoperative period and continued for 24 hours. Pain-free period, pain scores, rescue analgesic (morphine) requirements, and side effects were noted for 48 hours postoperatively.

Result: Mean pain-free periods in the ketamine group (860 min) and the dexmedetomidine group (580 min) were longer than in the saline group (265 min) (P<0.002) during the observation period of 48 hours. There was a significant decrease in the rescue analgesic requirement in both ketamine and dexmedetomidine group (P<0.05) (cumulative morphine requirement at 24 h-group C 15.64±9.31 mg, group D 6.89±5.88 mg, group K 2.45±2.06 mg; at 48 h-group C 21.09±12.88 mg, group D 7.98±7.72 mg, group K 2.59±1.97 mg). Hemodynamics were maintained within normal range in all the groups. Patients in ketamine and dexmedetomidine groups were sedated, but none required assistance for maintaining airway patency. Few patients in the ketamine group had nausea, dizziness, and diplopia, but the difference was insignificant in comparison with other groups (P>0.05).

Conclusions: Infusion of low-dose ketamine and dexmedetomidine both provide good postoperative analgesia with minimal side effects. Both of the tested analgesic regimes can be used safely and effectively for postoperative pain relief in patients after spine surgery.