Treffpunkt Stewart

[Acid-base balance and Stewart concept : Guide to routine daily use]

In 1981 the Canadian Peter Stewart presented a new concept for the interpretation of the acid-base balance. Rehm et al. published the first German language article on this topic. In 2007 the works of Deetjen and Lichtwarck-Aschoff as well as Funk presented both the physiological and clinical foundations of the Stewart concept as well as algorithms to interpret the acid-base status more precisely. Furthermore, since 2004 many other publications on the Stewart concept have been published, which have sometimes been controversially discussed and has not yet found its way into the everyday interpretation of blood gas analysis. This gap is intended to be filled by this work. It introduces a simple, practical algorithm and provides an approach to understanding the acid-base balance and the Stewart concept, which assumes that the plasma ions determine the pH value and the base excess (BE) in the plasma.

Acid-base analysis: a critique of the Stewart and bicarbonate-centered approaches

When approaching the analysis of disorders of acid-base balance, physical chemists, physiologists, and clinicians, tend to focus on different aspects of the relevant phenomenology. The physical chemist focuses on a quantitative understanding of proton hydration and aqueous proton transfer reactions that alter the acidity of a given solution. The physiologist focuses on molecular, cellular, and whole organ transport processes that modulate the acidity of a given body fluid compartment. The clinician emphasizes the diagnosis, clinical causes, and most appropriate treatment of acid-base disturbances. Historically, two different conceptual frameworks have evolved among clinicians and physiologists for interpreting acid-base phenomena. The traditional or bicarbonate-centered framework relies quantitatively on the Henderson-Hasselbalch equation, whereas the Stewart or strong ion approach utilizes either the original Stewart equation or its simplified version derived by Constable. In this review, the concepts underlying the bicarbonate-centered and Stewart formulations are analyzed in detail, emphasizing the differences in how each approach characterizes acid-base phenomenology at the molecular level, tissue level, and in the clinical realm. A quantitative comparison of the equations that are currently used in the literature to calculate H+concentration ([H+]) is included to clear up some of the misconceptions that currently exist in this area. Our analysis demonstrates that while the principle of electroneutrality plays a central role in the strong ion formulation, electroneutrality mechanistically does not dictate a specific [H+], and the strong ion and bicarbonate-centered approaches are quantitatively identical even in the presence of nonbicarbonate buffers. Finally, our analysis indicates that the bicarbonate-centered approach utilizing the Henderson-Hasselbalch equation is a mechanistic formulation that reflects the underlying acid-base phenomenology.

Das Säure-Basen-Modell nach Stewart

In addition to paCO(2), Stewart's acid base model takes into account the influence of albumin, inorganic phosphate, electrolytes and lactate on acid-base equilibrium. It allows a comprehensive and quantitative analysis of acid-base disorders. Particularly simultaneous and mixed metabolic acid-base disorders, which are common in critically ill patients, can be assessed. Stewart's approach is therefore a valuable tool in addition to the customary acid-base approach based on bicarbonate or base excess. However, some chemical aspects of Stewart's approach remain controversial.