Integration of acid-base and electrolyte disorders.

Copyright © 2014 Massachusetts Medical Society. This review describes a method of analyzing acid–base disorders that incorporates insights from the traditional, bicarbonate-centered model and the Stewart (or strong ion) model (Table 1).1-6 Acid–base balance and electrolyte homeostasis are intricately connected at the cellular level and in clinical disorders. This article emphasizes the integration of the principles of mass balance and electroneutrality — which are prominently featured in the strong ion model (also known as the physicochemical model) — for interpretation of acid–base phenomena. Most acid–base abnormalities can be diagnosed and interpreted with the use of the traditional approach. Why, then, should the strong ion theory be incorporated into teaching about acid–base balance? Although the Stewart model is not primarily a mathematical expression of a confirmed reality, it is relevant because it is a powerful construct that can shed light on an important biologic system. Included in this article are several case vignettes that show the explanatory power of the strong ion approach in clinical practice. Some of these examples have been presented in a companion article on the physiological approach to acid–base balance by Berend et al.7 Other cases that are interpreted with a strong ion approach are included in the Supplementary Appendix, available with the full text of this article at NEJM.org. The more complex chemistry of the hydrogen-ion concentration in intracellular and extracellular fluid compartments is beyond the scope of this article.