Examining Use of Low-Dose Ketamine Infusions During the Postoperative Period: A Retrospective Study Comparing Opioid-Tolerant and Nonopioid-Tolerant Patients.

Ketamine is a well-known anesthetic that has been used since the 1970s. Despite its ubiquitous use as a postoperative analgesic, no studies have described dosing differences between opioid-tolerant (OT) and nonopioid-tolerant (NOT) patients or determined optimal dosing. The primary aim of this study was to assess whether OT and NOT patients had significant differences in ketamine infusion dosing requirements. We also aimed to measure the overall incidence of psychotomimetic adverse effects associated with low-dose ketamine infusions. We hypothesized that NOT patients would have lower ketamine infusion dosing requirements and a higher incidence of psychotomimetic adverse effects compared with OT patients. We performed a retrospective chart review and showed that the percentages of OT and NOT patients experiencing psychotomimetic adverse effects were similar (15.5% vs 15.3%; P=.93) and that increasing age was the only factor associated with increased odds of experiencing a psychotomimetic adverse effect potentially associated with ketamine (odds ratio, 1.29 [95% CI, 1.11-1.50]; P=.001). Optimal subanesthetic ketamine infusion dosing could not be established, and further research in this area may be warranted.