Low-Dose Ketamine Infusions for Highly Opioid-Tolerant Adults Following Spinal Surgery: A Retrospective Before-and-after Study

Managing acute-on-chronic pain in opioid-tolerant individuals is complex and challenging; exploring new analgesia regimens for this population is essential. Ketamine is an N-methyl D-aspartate antagonist that blocks transmission of painful stimuli and could be a useful medication for this patient population. A new low-dose ketamine protocol as an adjunct to conventional pain therapy was implemented in a major urban Level 1 trauma center in Canada. A retrospective before-and-after chart review was conducted to explore the research question, “What is the effect of low-dose ketamine continuous intravenous infusions on pain of highly opioid-tolerant adults following spinal surgery?”. All patients had spine surgery, used a minimum of 100 mg daily oral morphine equivalent preoperatively and were followed postoperatively by the hospital's Acute Pain Service. Data from individuals treated with conventional therapy during the year prior to protocol implementation were compared with data from patients who received conventional therapy plus ketamine post implementation. Outcome measures included pain scores and daily opioid consumption on postoperative days 0 through 5, time to ambulation, time to discharge, and adverse effects. There were no statistically significant differences between conventional therapy and conventional therapy plus ketamine. Ketamine may still be of benefit to patients with acute-on-chronic pain, although this was not evident in this study. Future research using more robust assessment tools to determine effectiveness of ketamine is required.