Serum Bicarbonate and Delirium Risk in Patients With Acute Kidney Injury: A Retrospective Study Using the MIMIC-IV Database

Purpose Serum bicarbonate is widely used to reflect acid–base status and has been linked to adverse outcomes in various diseases. However, its association with delirium in patients with acute kidney injury (AKI) remains poorly defined. This study aimed to explore the association between baseline serum bicarbonate levels and delirium risk in patients with acute kidney injury, and to develop an exploratory risk stratification model based on routinely available clinical variables. Patients and methods: This retrospective study analyzed data from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. Adult patients with AKI who met predefined inclusion and exclusion criteria were enrolled. Univariate and multivariate logistic regression analyses were used to identify factors associated with delirium. A nomogram was constructed based on independent predictors. Model performance was evaluated using the area under the receiver operating characteristic curve (AUC), calibration curves with Hosmer–Lemeshow tests, and decision curve analysis (DCA). Results A total of 26,900 patients with AKI were included, among whom 21.39% developed delirium. Patients were randomly assigned to training and validation cohorts at a 7:3 ratio. Significant differences were observed between patients with and without delirium in demographic characteristics, comorbidities, vital signs, laboratory parameters, and disease severity scores (all P < 0.05). Lower serum bicarbonate levels were independently associated with a higher risk of delirium. The nomogram demonstrated moderate discrimination, with an AUC of 0.753 in the training cohort, and showed good calibration in both cohorts (Hosmer–Lemeshow P > 0.05). DCA indicated favorable clinical utility across a range of threshold probabilities. Conclusion An exploratory nomogram incorporating serum bicarbonate demonstrated moderate discrimination for delirium risk stratification in patients with AKI and may support early risk stratification in clinical practice.