Analytic calculation of physiological acid-base parameters in plasma

Analytic expressions for plasma total titratable base, base excess (Delta C-B), strong-ion difference, change in strong-ion difference (Delta SID), change in Van Slyke standard bicarbonate (Delta VSSB), 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, Delta SID = Delta C-B = Delta VSSB, 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.