Blood Gas Analysis and Acid-base Disorders

Acid-base physiology is among the most complex topics in clinical medicine. Disturbances of this system are common in the critically ill, and important clinical decisions based on measured acid-base parameters occur on a daily, even hourly basis. Therefore, a sound understanding of acid-base physiology is mandatory for the intensivist. The field is full of complicated concepts and equations that, at times, have only limited applicability to the practicing clinician due to the failure of any current model to faithfully and completely recapitulate the complex buffering process in vivo. The purpose of this chapter is to provide a conceptual introduction to the current approach to acid-base physiology, while de-emphasizing calculations and formulas. The goal is not to know how to derive the commonly used formulas, but rather to understand the meaning of measured and derived acid-base parameters that are used clinically, and how they may—or may not—help in answering three essential questions in the critically ill patient with an acid-base disturbance: