UCSF

Introduction: Patients on chronic opioid therapy (COT) who are admitted for a planned surgical procedure may experience inadequately controlled pain in the post-anesthesia care unit (PACU) due to drug tolerance. This is disruptive for not only patients but PACU nurses and can lead to increased utilization of hospital resources and extend PACU and hospital length of stay. Pain management may be optimized in this group using low-dose intravenous (IV) ketamine. However, in a pilot study, we found that administration of this medication occurred 114 minutes (range 14 minutes to 394 minutes) after admission to the PACU, with resultant sub-optimal pain management and delays in PACU throughput. We hypothesize that identifying patients in the preoperative phase who may benefit from this therapy could reduce administration delays and improve pain management. However, specific patient-level variables that may be useful to screen for are largely unknown. Purpose: Examine demographics, opioid use history, mental health diagnosis, and/or surgical service type associated with the administration of low-dose IV ketamine in the PACU. Methods: Retrospective study in 6,419 consecutive adult patients (≥18 years) presenting for a scheduled surgical procedure between Jan 1, 2020, and Dec 31, 2021. The outcome variable was the administration of a low-dose IV ketamine infusion in the PACU. Hypothesized patient predictors were obtained from the electronic health record. A stepwise regression model was used to identify statistically significant variables. Results: In 6,419 consecutive patients, 90 (1.4%) received low-dose IV ketamine in the PACU. Significant variables in the final stepwise model included: age of 55-71 years (p=0.029); history of opioid or substance use disorder (p<0.001); outpatient opioid prescription (p=0.025); outpatient methadone prescription (p=0.049); and morphine milligram equivalency (MME) ≥90/day (p<0.001). Conclusion: Two variables had the highest odds ratio associated with low-dose IV ketamine in the PACU. Patients with an MME ≥90/day were 13.26 times more likely to have received low-dose IV ketamine in the PACU and those with SUD/OUD were 4.02 times more likely to have received low-dose IV ketamine in the PACU. Implications for Practice and Future Research: Nurses should consider evaluating patients in the preoperative phase of care for MME ≥90/day and those with SUD/OUD, as these appear to be important predictors of low-dose IV ketamine in the PACU. However, a larger patient cohort of patients who received low-dose IV ketamine in the PACU is needed to further develop and test a preoperative screening tool.