For more than 15 years, an alternative view of the universe has been available for acid-base physiology. While conceptually new, this analysis, originally presented by Peter Stewart, is based on the same underlying fundamental principles used in more traditional treatments of acid-base. When properly translated, all approaches are mathematically interchangeable. The difference, however, is that the Stewart approach emphasizes mathematically independent and dependent variables. By this definition, bicarbonate and hydrogen ions are dependent variables and thus represent the effects rather than the causes of acid-base derangements. Neither bicarbonate nor pH can be regulated directly; rather, they are controlled by the independent variables. In blood plasma there are three independent variables: PCO2, weak acids, and the strong ion difference. The strong ion difference is the difference between completely dissociated cations (e.g., Na+) and completely dissociated anions (e.g., Cl–)
Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
Correspondence to John A. Kellum, MD, University of Pittsburgh Medical Center, Division of Critical Care Medicine, 200 Lothrop Street, Pittsburgh, PA 15213-2582; e-mail: Kellumja@anes.upmc.edu
