RESUMO
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 0.2âmgâkg over 30âmin followed by 0.12âmgâkgâh for 24âh). Patients in the placebo groups received 0.9% saline. MAIN OUTCOME MEASURES: The primary outcome was opioid consumption during the first 24âh postoperatively. The secondary outcome was numerical pain scores during the first 24âh 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)âmgâkgâh, Bonferroni corrected Pâ<â0.001]. There was no difference in hydromorphone use between the opioid-naïve groups (0.004 and 0.005âmgâkgâh in the opioid-naïve ketamine and placebo group, respectively, Pâ=â0.118). 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 24âh following spinal fusion surgery in opioid-tolerant, but not in opioid-naïve patients. TRIAL REGISTRATION: NCT03274453 with clinicaltrials.gov.