Acid-base balance: The traditional approach

Maintenance of hydrogen ion concentration within a narrow range is essential for normal physiological function. In the first of two articles, we consider the 'traditional approach' to acid-base balance, based upon the bicarbonate/carbon dioxide relationship. The role of the bicarbonate buffer system and the manipulation of its components by the respiratory and renal systems are presented. The bicarbonate buffer system has been central to the understanding and quantitative analysis of acid-base changes in plasma using the Henderson-Hasselbalch equation. Several other buffer systems also play a vital role in hydrogen ion homeostasis by limiting pH changes within various fluid compartments in the body. Manipulation of the partial pressure of carbon dioxide via changes in alveolar ventilation allows the respiratory system to operate a feed-back control system for rapid correction of acid-base disturbances. The traditional approach considers that renal control of acid-base balance primarily involves hydrogen ion secretion and bicarbonate production. These mechanisms, and the renal tubular buffer systems that allow them to operate, are described.