Base Excess and Beyond: Evolving Concepts in Acid-base Analysis

Base excess (BE), a marker used to detect metabolic acid-base disturbances, is also known to predict mortality in critically ill patients; the traditional concept, originally based on the Henderson-Hasselbalch model, has been further refined through integration with the Stewart approach, enabling a more comprehensive and mechanistic evaluation of acid-base disturbances. However, the increasingly complex mathematical formulations required for this integration demand extensive calculations, which can hinder bedside assessment. To address this, the BE formula has been simplified and integrated into the Stewart concept, resulting in a more reliable, detailed, and rapid bedside evaluation. Additionally, the term "alactic BE" was introduced to distinguish metabolic acidosis caused by retention of fixed acids from that caused by lactic acid accumulation, particularly in patients with renal failure. This review discusses the concept of BE and its evolution over the years.