ASSOCIATION BETWEEN SERUM BICARBONATE AND 28 DAY MORTALITY IN SEPTIC SHOCK PATIENTS: A COHORT STUDY

Abstract

Background: Septic shock is a life-threatening manifestation of sepsis characterized by profound circulatory, cellular, and metabolic abnormalities that contribute to high morbidity and mortality despite advances in critical care. Metabolic acidosis is frequently encountered in septic shock owing to tissue hypoperfusion, impaired oxygen utilization, and lactate accumulation. Serum bicarbonate, a routinely available biochemical parameter, reflects the metabolic component of acid-base balance and may serve as a simple, cost-effective prognostic biomarker. Early identification of patients at increased risk of adverse outcomes using readily available laboratory indices could facilitate timely risk stratification and optimize critical care management. However, the prognostic significance of serum bicarbonate levels in predicting short-term mortality among patients with septic shock remains an area of ongoing investigation. Aim: To evaluate the association between admission serum bicarbonate levels and 28-day mortality among adult patients with septic shock admitted to the intensive care unit of a tertiary care teaching hospital. Materials and Methods: A prospective cohort study was conducted over 24 months (January 2024 to December 2025) in the Department of Critical Care Medicine of a tertiary care teaching hospital. A total of 180 consecutive adult patients fulfilling the Sepsis-3 criteria for septic shock were enrolled after obtaining informed consent from the patient or legally authorized representative. Demographic characteristics, comorbidities, source of infection, clinical examination findings, hemodynamic parameters, Sequential Organ Failure Assessment (SOFA) score, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, laboratory investigations including serum bicarbonate, arterial blood gas analysis, serum lactate, renal function tests, and inflammatory markers were recorded at admission. Patients were followed for 28 days, and outcomes were categorized into survivors and non survivors. Statistical analysis was performed using SPSS version 26.0. Continuous variables were expressed as mean ± standard deviation, categorical variables as frequencies and percentages, and independent predictors of mortality were identified using multivariable logistic regression. A p-value <0.05 was considered statistically significant. Results: The mean age of the study population was 58.9 ± 15.2 years, with males accounting for 61.1% of participants. The overall 28-day mortality rate was 34.4%. Non-survivors demonstrated significantly lower admission serum bicarbonate levels than survivors (17.3 ± 3.8 mmol/L vs. 22.6 ± 3.5 mmol/L; p<0.001). Patients with serum bicarbonate levels below 20 mmol/L had significantly higher mortality, greater vasopressor requirements, higher serum lactate concentrations, and increased SOFA and APACHE II scores. Multivariable logistic regression identified low serum bicarbonate, elevated serum lactate, higher SOFA score, and acute kidney injury as independent predictors of 28-day mortality. Admission serum bicarbonate exhibited good discriminatory ability for predicting mortality and demonstrated significant clinical utility as an early prognostic marker. Conclusion: Lower admission serum bicarbonate levels are significantly associated with increased 28-day mortality among patients with septic shock. Routine assessment of serum bicarbonate at ICU admission provides valuable prognostic information and may complement established severity scoring systems for early risk stratification, individualized management, and prognostic assessment in critically ill patients with septic shock.