Predictive Value of 48-hour Anion Gap Fluctuations in ICU Patients with Acute Kidney Injury: An Analysis based on MIMIC Database

Introduction: Increasing anion gap (AG) correlates with both short- and long-term mortality in intensive care unit (ICU) patients with acute kidney injury (AKI). However, the relationship between AG fluctuations and AKI prognosis has been understudied. This study aims to evaluate the predictive value of AG fluctuations within the first 48 hours after ICU admission for renal recovery and 30-day all-cause mortality in AKI patients. Methods: Data were extracted from the Medical Information Mart for Intensive Care (MIMIC-IV, v2.2) database, including AKI patients aged 18 and older. A multifactorial Cox regression model was employed to assess the impact of AG fluctuations within 48 hours of ICU admission on mortality, adjusted using five models. Kaplan-Meier survival curves and curve-fitting analysis were used to illustrate the relationship between AG fluctuations and mortality risk. Results: A total of 15,438 patients with AKI were included, 57.0% of whom were male. The 30-day all-cause mortality rate was 19.19%. Patients were categorized into three groups based on AG fluctuations within the first 48 hours: <3 mmol/L, 3-5 mmol/L, and >5 mmol/L. Cox regression and survival analysis indicated a significantly higher 30-day mortality rate in the >5 mmol/L group (HR = 1.63; 95% CI = 1.50-1.77, P < 0.001), with the worst prognosis. Restricted cubic spline analysis revealed a nonlinear relationship between AG fluctuations and 30-day mortality risk. Discussion: The findings suggest that AG fluctuations during the first 48 hours of ICU admission are closely associated with adverse outcomes in AKI patients. Monitoring AG dynamics may aid clinicians in identifying high-risk patients and enhancing patient management by allowing for timely interventions that may improve prognosis. Conclusion: AG fluctuations within the first 48 hours of ICU admission are a key predictor of renal recovery and 30-day mortality in AKI patients. AG fluctuations greater than 5 mmol/L are significantly associated with increased mortality risk. conclusion: AG fluctuations within the first 48 hours of ICU admission are a key predictor of renal recovery and 30-day mortality in AKI patients. AG fluctuations greater than 5 mmol/L are significantly associated with increased mortality risk.