Serum Bicarbonate: Reconsidering the Importance of a Neglected Biomarker in Predicting Clinical Outcomes in Sepsis

Background Despite being an important pathophysiological component, information on the predictive value of serum bicarbonate level in sepsis is limited. Study design and method This is a single-centered retrospective study involving 4176 patients admitted to the medical ICU (MICU) with a diagnosis of sepsis. Patients were divided into two groups based on the presence or absence of chronic kidney disease (CKD) on admission: CKD and non-CKD, respectively. Each group was then divided into three sub-groups based on serum bicarbonate level at presentation (in mEq/l)- low (<22), normal (22-28), and high (>28). We compared the clinical outcomes between the sub-groups in each group, with in-hospital mortality as the primary endpoint. Secondary endpoints included vasopressor-free days, ventilator-free days, ICU-free days, and hospital-free days. Result In both the CKD and non-CKD groups, low serum bicarbonate was associated with significantly increased in-hospital mortality. There was no difference in the mortality between the sub-groups with normal and high serum bicarbonate. When adjusted for other known predictors of mortality, the association of low serum bicarbonate with increased in-hospital mortality was statistically significant only in the patient group with a Sequential Organ Failure Assessment (SOFA) score of ≥9. Additionally, the SOFA score had a better predictive value for in-hospital mortality, ICU-free days, and ventilator-free days when the serum bicarbonate level was <22. Interpretation Serum bicarbonate is a good predictor of clinical outcomes in sepsis and can be used along with other markers of sepsis to predict clinical outcomes.