Analytic calculation of physiological acid-base parameters in plasma

Abstract

Analytic expressions for plasma total titratable base, base excess (ΔCB), strong-ion difference, change in strong-ion difference (ΔSID), change in Van Slyke standard bicarbonate (ΔVSSB), anion gap, and change in anion gap are derived as a function of pH, total buffer ion concentration, and conditional molar equilibrium constants. The behavior of these various parameters under respiratory and metabolic acid-base disturbances for constant and variable buffer ion concentrations is considered. For constant noncarbonate buffer concentrations, ΔSID = ΔCB = ΔVSSB, whereas these equalities no longer hold under changes in noncarbonate buffer concentration. The equivalence is restored if the reference state is changed to include the new buffer concentrations.