Prevalence of Delirium After Abdominal Surgery and Association With Ketamine: A Retrospective, Propensity-Matched Cohort Study

IMPORTANCE: Delirium is a common postoperative complication for older patients in the ICU. Ketamine, used primarily as an analgesic, has been thought to prevent delirium.

OBJECTIVE: Determine the prevalence and association of delirium with low-dose ketamine use in ICU patients after abdominal surgery.

DESIGN: Single-center, retrospective, propensity-matched cohort study.

SETTING: Eight hospital academic medical center.

PATIENTS: Cohort comprising 1836 patients admitted to the ICU after abdominal surgery between June 23, 2018 and September 1, 2022.

MAIN OUTCOMES AND MEASURES: Propensity score matching (PSM) with a 3:1 ratio between no-ketamine use and ketamine use was performed through a greedy algorithm (caliper of 0.005). Outcomes of interest included: delirium (assessed by Confusion Assessment Method-ICU), mean pain score (Numeric Pain Scale or Critical Care Pain Observation Tool score as available), mean opioid consumption (morphine milligram equivalents), length of stay (d), and mortality.

RESULTS: Prevalence of delirium was 47.71% (95% CI, 45.41-50.03%) in the cohort. Of 1836 patients, 120 (6.54%) used low-dose ketamine infusion. After PSM, the prevalence of delirium was 56.02% (95% CI, 51.05-60.91%) in all abdominal surgery patients. The ketamine group had 41% less odds of delirium (odds ratio [OR] = 0.59; 95% CI, 0.37-0.94; p = 0.026) than patients with no-ketamine use. Patients with ketamine use had higher mean pain scores (3.57 ± 2.86 vs. 2.21 ± 2.09, p < 0.001). In the subgroup analysis, patients in the ketamine-use group 60 years old or younger had 64% less odds of delirium (OR = 0.36; 95% CI, 0.13-0.95; p = 0.039). The mean pain scores were higher in the ketamine group for patients 60 years old or older. There was no significant difference in mortality and opioid consumption.

CONCLUSIONS AND RELEVANCE: Low-dose ketamine infusion was associated with lower prevalence of delirium in ICU patients following abdominal surgery. Prospective studies should further evaluate ketamine use and delirium.