The concentration of H + in blood plasma is one of the most finely regulated variables of the human physiology; acute changes of this concentration result in serious cellular and general consequences. An advanced understanding of the acid-base physiology is essential to the management of "acute" patients, and is as important as the exact understanding of the cardiac and pulmonary physiology. Stewart's approach to acid-base balance has come to the identification of three independent variables that regulate pH in blood plasma: carbon dioxide, relative concentration of strong ions, and total weak acid concentrations. All changes in blood pH occur through changes in these three variables.