The U-Shaped Relationship Between Serum Bicarbonate Levels and 28-Day Mortality in Patients With Sepsis: A Retrospective Cohort Study of MIMIC-IV Database.

Background: The elevated mortality rate associated with sepsis is a primary global health concern. The correlation between bicarbonate levels and mortality risk in sepsis remains unclear.

Method: A retrospective cohort study was conducted using data from the MIMIC-IV database, including 12 744 adult sepsis patients. The primary exposure was serum bicarbonate levels, categorized into quintiles. The primary outcome was 28-day mortality, and secondary outcomes included 90-day mortality. Multivariable Cox regression models adjusted for demographic, clinical, and laboratory variables were used to examine the relationship between bicarbonate levels and mortality. Curve fitting and sensitivity analyses were performed to validate the findings.

Results: A U-shaped relationship between serum bicarbonate levels and 28-day mortality was identified. Both low (≤19.0 mEq/L) and high (>26.0 mEq/L) bicarbonate levels were associated with increased mortality risk. Patients with bicarbonate levels between 24.0-26.0 mEq/L had the lowest 28-day mortality. The relationship remained consistent across subgroups, and an inflection point was observed at 25.0 mEq/L. Sensitivity analyses confirmed the robustness of the findings across different data imputations.

Conclusion: This study demonstrates that both low and high serum bicarbonate levels are associated with increased mortality in sepsis patients. The optimal bicarbonate range for minimizing mortality risk appears to be between 24.0-26.0 mEq/L. These findings highlight the importance of monitoring bicarbonate levels in clinical practice, suggesting that maintaining bicarbonate within this range may improve patient outcomes. Further prospective studies are needed to confirm these findings and explore potential therapeutic strategies.