Evolutive acid-base derangements in critically ill patients: epidemiological aspects, association with mortality and metabolic acidosis prediction

Objective:  To assess the prevalence and evolution of acid-base disturbances at intensive care unit admission and throughout hospitalization and their association with intensive care unit mortality.

Methods:  A retrospective epidemiological study was conducted, analyzing consecutive patients admitted to a single intensive care unit.

Results:  Metabolic acidosis, either isolated or combined with other disturbances, was the most prevalent disorder (58.0%), followed by respiratory alkalosis (37.6%), respiratory acidosis (25.7%), and metabolic alkalosis (12.8%). Multivariate analysis demonstrated that metabolic alkalosis combined with respiratory alkalosis was independently associated with reduced mortality (OR 0.427, 95%CI 0.194 - 0.869). Higher standard base excess at intensive care unit admission was correlated with lower mortality (OR 0.973, 95%CI 0.956 - 0.990). Maximum pCO₂ variation during hospitalization showed no significant association with mortality. However, greater standard base excess improvement was independently linked to reduced mortality in patients with intensive care unit stays exceeding 5 days. Additionally, disease severity markers and younger age were predictive of metabolic acidosis both at admission and during hospitalization.

Conclusion:  Metabolic acidosis was the most common acid-base disorder at intensive care unit admission, with lower standard base excess levels associated with increased mortality. Standard base excess improvement during prolonged intensive care unit stays correlated with improved survival. Disease severity indicators were predictive of metabolic acidosis upon admission and throughout hospitalization.

Keywords:
Acid-base imbalance; Metabolic acidosis; Acidosis, respiratory; Alkalosis, respiratory; Mortality; Critical illness; Prevalence; Alkalosis; Hospitalization; Intensive care units