What is the base excess theory of the pathophysiology of metabolic acidosis?

Updated: Oct 05, 2018
  • Author: Antonia Quinn, DO; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

Unfortunately, the Henderson/Hasselbalch equation is not linear; pCO2 adjusts pH as part of the normal respiratory compensation for acid/base derangements. This nonlinearity of Henderson-Hasselbalch prevents this equation from quantifying the exact amount of bicarbonate deficit in a metabolic acidosis. This observation led to the development of a semiquantitative approach, base excess (BE).

BE = (HCO3 – 24.4 + [2.3 X Hgb + 7.7] X [pH – 7.4]) X (1 – 0.023 X Hgb)

Base excess attempts to give a quantitative amount of bicarbonate (mmol) that is required to be added or subtracted to restore 1 L of whole blood to a pH of 7.4 at a pCO2 of 40 mm Hg. To standardize BE for hemoglobin, the following formula was developed with improved in vivo accuracy, the standardized base excess (SBE):

SBE = 0.9287 X (HCO3 – 24.4 + 14.83 X [pH – 7.4])


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