Association of Serum Bicarbonate Level with Mortality in Patients with Acute Kidney Injury: A Retrospective Cohort Study

Abstract

ABSTRACT Background: Metabolic acidosis due to a decreased level of serum bicarbonate in patients with chronic kidney disease is associated with increased mortality, but the association of serum bicarbonate with outcomes in patients with acute kidney injury (AKI) is uncertain. We investigated the association of serum bicarbonate level with mortality in patients with AKI. Methods: The study cohort consisted of 4800 patients diagnosed with AKI at multiple hospitals between September 17, 2013, and April 14, 2014. Smooth curve fitting, threshold effect analysis, and multiple regression analysis were used to assess the relationship between serum bicarbonate and 14-day mortality (primary outcome) and with intensive care unit (ICU) admission, length of hospitalization, and total hospital costs (secondary outcomes). Results: Multiple regression analysis, adjusting for confounding factors, demonstrated a U-shaped association between serum bicarbonate levels and AKI mortality. The lowest mortality rate was observed in patients with a bicarbonate level of 26.9 mmol/L, while greater rates were observed in those with lower and higher levels. Additionally, patients with AKI exhibiting high serum bicarbonate levels (> 26.9 mmol/L) had a significantly lower rate of ICU admission and a shorter hospital stay compared to those with low serum bicarbonate levels (< 26.9 mmol/L). Conclusion: A serum bicarbonate level of 26–29 mmol/L in patients with AKI is associated with a lower 14-day mortality rate, with the lowest rate observed at a serum bicarbonate level of 26.9 mmol/L. Prospective clinical studies are needed to determine whether optimizing the serum bicarbonate level can decrease mortality in this population.