Kidney Function Modifies the Effect of Intraoperative Opioid Dosage on Postoperative Delirium

BACKGROUND There are few studies demonstrating how kidney function affects the risk of developing delirium in older adult surgical patients administered opioids. This study determined whether baseline kidney function influences the relationship between morphine equivalent dose and the development of delirium on postoperative day (POD) 2 in patients with hip fracture. METHODS This retrospective study analyzed emergency department (ED) estimated glomerular filtration rate (eGFR), perioperative serum creatinine, intravenous morphine equivalents, and POD2 delirium assessment by the Confusion Assessment Method in 652 patients aged 65 years or older without preoperative delirium. ED eGFR was used to divide subjects into groups by presence or absence of chronic kidney disease (CKD), and associations of opioid dose with POD2 delirium were compared using multivariable logistic regression. RESULTS POD2 delirium incidence was 29.8% (N = 194). Intraoperative and postanesthesia care unit (PACU) morphine equivalent dosage as well as ED eGFR were similar comparing patients with and without POD2 delirium. Age, American Society of Anesthesiologists status, and dementia were associated with delirium on POD2. The odds of POD2 delirium increased significantly with increase of intraoperative opioid in patients with CKD (odds ratio = 1.6; 95% confidence interval = 1.2–2.2), but not in patients without CKD (P‐interaction = .04). PACU or POD1 opioid doses were not associated with POD2 delirium after covariate adjustment. CONCLUSION This study suggests that incremental increases in intraoperative opioids combined with CKD increase odds of POD2 delirium after hip fracture repair, compared with patients without CKD.