Acid-Base Disorders and Their Correlation with Disease Severity in Critically Ill Patients: A Prospective Observational Study

Abstract

Background: Acid-base disorders are highly prevalent in critically ill patients and have been associated with adverse clinical outcomes. This study aimed to determine the prevalence and distribution of acid-base disorders in critically ill patients, evaluate their correlation with disease severity scores (APACHE II and SOFA), and identify independent predictors of ICU and hospital
mortality. 

Methods: A prospective observational study was conducted over 18 months in a tertiary-care, multi-specialty ICU. Adult patients (age ≥18 years) admitted with a primary or secondary acid-base disorder were enrolled. Arterial blood gas (ABG) analysis, serum electrolytes, lactate, and other biochemical markers were recorded at admission. Disease severity was assessed using the Acute Physiology and Chronic Health Evaluation II (APACHE II) and Sequential Organ Failure Assessment (SOFA) scores. Logistic regression and Pearson correlation analyses were performed. 

Results: A total of 333 patients were enrolled. Metabolic acidosis was the most prevalent disorder (n=112, 33.6%), followed by respiratory acidosis (n=74, 22.2%) and mixed disorders (n=63, 18.9%). Serum lactate demonstrated the strongest positive correlation with both APACHE II (r=+0.762, p<0.001) and SOFA scores (r=+0.789, p<0.001). Arterial pH was the most powerful negative correlate of mortality (r=-0.741, p<0.001). On multivariate logistic regression, mixed acid-base disorders conferred the highest odds of ICU mortality (OR 11.62, 95% CI 4.28–31.58, p<0.001). The combined predictive model achieved an AUC of 0.923 (95% CI 0.893–0.953).

Conclusion: Acid-base disorders are closely and independently correlated with disease severity and mortality in critically ill patients. Mixed disorders carry the gravest prognosis. Arterial pH, serum lactate, and anion gap are the most robust prognostic biochemical markers. Routine and systematic ABG interpretation should be integral to ICU management protocols.