Evaluating the Influence of IV Ketamine on Postoperative Opioid Use for Surgical Patients at a Tertiary Care Centre.

Background: Subanesthetic doses of ketamine have been shown to improve the efficacy of opioids, increase pain control, and exemplify opioid-sparing effects when used as postoperative analgesia for adults.

Objectives: To determine, for surgical patients, the impact of IV ketamine infusions on opioid use in hospital, overall and within 24 h before discharge, as well as pain scores.

Methods: A retrospective matched cohort study was conducted, in which surgical patients exposed to ketamine were compared with those not exposed to ketamine, among admissions from January 1, 2018, to February 28, 2020. Patients were matched for age, surgical service, and sex.

Results: A total of 104 patients were included in the study. Overall, there was no significant difference in mean total opioid use in hospital for patients exposed and not exposed to ketamine (171.7 mg versus 115.5 mg oral morphine equivalent [OME], p = 0.09), nor was there any difference in opioid use in the 24 h before discharge (28.2 mg versus 18.2 mg OME, p = 0.14). Patient-reported pain scores did not differ between groups. More patients in the ketamine group experienced hallucinations than in the group not exposed to ketamine (5 versus 0, p = 0.024).

Conclusions: Overall, subanesthetic doses of IV ketamine used postoperatively in surgical patients did not decrease opioid use or patient-reported pain. More patients who received ketamine had documented hallucinations. These results will help guide postoperative analgesia practice and strategies to reduce opioid use.