Table 1_Association between anion gap and postoperative delirium in patients undergoing open heart surgery.docx

BackgroundOpen heart surgery (OHS) is crucial for treating cardiovascular diseases, but postoperative delirium (POD) is a common and challenging complication. Existing POD prognostic indicators have limitations in clinical application. The relationship between AG and POD in OHS patients remains unclear.
MethodsData from the MIMIC-IV database were used. Patients aged 18 or older who underwent OHS, were admitted to the ICU post-surgery, and had an AG test within the first 24 h after surgery were included. The maximum AG value within 24 h after surgery was the exposure variable, and POD occurrence was the primary outcome. Multivariable logistic regression was applied to explore the relationship between AG and POD. A restricted cubic spline regression model (RCSRM) was used to analyze the correlation shape, and subgroup and interaction analyses were performed. Causal mediation analysis (CMA) was conducted to explore the mediating role of ICU length of stay (LOS) in the relationship between AG and POD.
ResultsWe included 6,429 patients. The overall POD incidence was 13%. Multivariable logistic regressions showed that AG was significantly associated with POD (OR = 1.686, 95% CI: 1.348–2.113, P < 0.001 for group 2; OR = 1.54, 95% CI: 1.161–2.037, P = 0.003 for group 3; OR = 2.005, 95% CI: 1.574–2.558, P < 0.001 for group 4; P for trend <0.001) and ICU LOS (OR = 1.256, 95% CI: 1.066–1.48, P = 0.007 for group 2; OR = 1.281, 95% CI: 1.033–1.585, P = 0.023 for group 3; OR = 1.595, 95% CI: 1.32–1.928, P < 0.001 for group 4). The RCSRM revealed a non-linear relationship between AG and POD (P-overall <0.001, P for non-linear = 0.042). No multiplicative or additive interactions were detected between AG and any subgroup. CMA indicated that ICU LOS mediated 5.392% (95% CI: 0.483%–11.98%; P = 0.034) of the effect of AG on POD.
ConclusionAn elevated AG level within the first 24 h after OHS is significantly associated with an increased risk of POD, and the relationship shows a tendency toward non-linearity. ICU LOS may proportionally mediate the impact of AG on POD development.