Association Between Serum Anion Gap and Risk of Postoperative Delirium in Patients Undergoing Gastric Surgery in ICU: A Retrospective Study From the MIMIC‐IV Database

Background: This study aimed to investigate the association between serum anion gap (AG) levels and postoperative delirium (POD) incidence in intensive care unit (ICU) patients undergoing gastric surgery. Methods: We conducted a retrospective study using data from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. Patients who underwent gastric surgery were included to investigate the potential association between serum AG and POD risk. Restricted cubic spline (RCS) regression was used to evaluate nonlinear relationships, and receiver operating characteristic (ROC) curves were used to assess predictive performance. Subgroup and sensitivity analyses were performed to verify the reliability and consistency of the results. Results: Among the 2467 ICU patients who underwent gastric surgery, elevated serum AG levels were independently associated with increased POD risk. The RCS analysis revealed a nonlinear positive correlation between serum AG levels and the risk of POD. ROC curve analysis indicated that serum AG levels had a statistically significant but limited predictive value for POD, with an area under the curve (AUC) of 0.606 (95% CI: 0.584-0.628). Both subgroup and sensitivity analyses confirmed the robustness of these findings. Conclusions: This study establishes an independent association between serum AG and increased POD risk in ICU patients following gastric surgery, suggesting that serum AG may serve as a biomarker of physiological vulnerability for POD.