Association Between Serum Chloride Levels and 365-Day All-Cause Mortality in Critically IV Patients with Gastrointestinal Bleeding: A Retrospective Cohort Study

Abstract Background: Gastrointestinal bleeding (GIB) is a significant clinical emergency with high mortality, particularly among critically ill patients. The role of serum chloride, a crucial electrolyte, in the prognosis of GIB remains unclear. This study aimed to investigate the relationship between serum chloride levels and 365-day all-cause mortality in critically ill patients with GIB. Methods: A retrospective cohort study was conducted using the Medical Information Mart for Intensive Care (MIMIC-IV) database, including patients admitted to the intensive care unit (ICU) with a diagnosis of GIB from 2008 to 2019. Patients were stratified by serum chloride levels within the first 24 hours of ICU admission. The primary outcome was 365-day all-cause mortality. Cox regression models were used to assess the association between serum chloride and mortality, adjusting for confounders. Results: A total of 2355 patients met the inclusion criteria. Elevated serum chloride levels were associated with a lower risk of 365-day all-cause mortality in unadjusted (HR=0.95, 95% CI: 0.94-0.96) and adjusted models (HR=0.97, 95% CI: 0.95-0.99, P=0.005). Non-linearity in the association was observed, with a plateau effect at higher serum chloride levels. Subgroup analyses confirmed the consistency of this association across different patient characteristics. Conclusion: This study reveals a significant inverse association between serum chloride levels and 365-day all-cause mortality in critically ill patients with GIB. Our findings suggest that serum chloride may serve as a prognostic biomarker and could inform clinical decision-making in the management of GIB. Further research is needed to elucidate the underlying mechanisms and to validate these findings in prospective studies.