Physicochemical Models of Acid-Base.

Physicochemical models have played an important role in understanding, diagnosing, and treating acid-base disorders for more than 100 years. This review focuses on recent complex models, solved using computers, and shows how these models provide new understanding and diagnostic approaches in acid-base disorders. These advanced models use the following physicochemical principles: (1) chemical equilibrium, (2) conservation of mass, (3) electroneutrality, and (4) osmotic equilibrium to describe the steady-state distribution of H2O and ions in the four major body-fluid spaces, cells, interstitium, plasma, and erythrocytes, and show how this distribution is changed by fluid infusions and losses through renal and gastrointestinal physiological processes. Illustrations of model use with a new comprehensive diagnostic approach are the understanding of an important clinical situation, saline acidosis, and the diagnosis of a patient with diabetic ketoacidosis. This new approach predicts a patient's whole-body base excess and partitions this value into 10 individual values, producing the disorder. These data and other data produced by the diagnostic model described in this review provide much more extensive insight than previous approaches.