Low-dose ketamine infusion reduces postoperative hydromorphone requirements in opioid-tolerant patients following spinal fusion: A randomised controlled trial.

Background: The current opioid epidemic highlights the urgent need for effective adjuvant therapies to complement postoperative opioid analgesia. Intra-operative ketamine infusion has been shown to reduce postoperative opioid consumption and improve pain control in opioid-tolerant patients after spinal fusion surgery. Its efficacy for opioid-naïve patients, however, remains controversial. Objective: We hypothesised that low-dose ketamine infusion after major spinal surgery reduces opioid requirements in opioid-tolerant patients, but not in opioid-naïve patients.

Design: Randomised placebo-controlled study. Setting: Single-centre, tertiary care hospital, November 2012 until November 2014. Patients: A total of 129 patients were classified as either opioid-tolerant (daily use of opioid medications during 2 weeks preceding the surgery) or opioid-naïve group, then randomised to receive either ketamine or placebo; there were thus four groups of patients. All patients received intravenous hydromorphone patient-controlled analgesia postoperatively. Intervention: Patients in the ketamine groups received a ketamine infusion (bolus 0.2 mg kg over 30 min followed by 0.12 mg kg h for 24 h). Patients in the placebo groups received 0.9% saline. Main outcome measures: The primary outcome was opioid consumption during the first 24 h postoperatively. The secondary outcome was numerical pain scores during the first 24 h and central nervous system side effects.

Results: Postoperative hydromorphone consumption was significantly reduced in the opioid-tolerant ketamine group, compared with the opioid-tolerant placebo group [0.007 (95% CI 0.006 to 0.008) versus 0.011 (95% CI 0.010 to 0.011) mg kg h, Bonferroni corrected P < 0.001]. There was no difference in hydromorphone use between the opioid-naïve groups (0.004 and 0.005 mg kg h in the opioid-naïve ketamine and placebo group, respectively, P = 0.118). Pain scores did not differ significantly between the opioid-tolerant ketamine group and the opioid-naïve groups. There was no significant difference in side effects among groups.

Conclusion: Postoperative low-dose ketamine infusion reduces opioid requirements for the first 24 h following spinal fusion surgery in opioid-tolerant, but not in opioid-naïve patients. Trial registration: NCT03274453 with clinicaltrials.gov.