The base excess is defined as the number of mEq of acid needed to titrate 1 liter of blood to a pH of 7.4 at pCO2 of 40 mm Hg and at 37 C. It is useful in determining the metabolic component in mixed respiratory and metabolic disorders. There are two versions - in vivo base excess and in vitro base excess. The in vitro base excess can be calculated from the Siggaard-Andersen formula.
