Base Excess & Calculated Bicarbonate

Calculate the serum bicarbonate from the serum pH and pCO₂.

The calculations above are based on the Henderson-Hasselbalch equation:

pH = pK + log	[HCO3-]
	[CO2]

Replacing pK = 6.1, and [CO₂] = 0.03 * pCO₂, and removing the logarithms to get

HCO₃ = 0.03 * pCO₂ * 10 ^{(pH - 6.1)}

In conjunction with the Siggaard-Anderson equation:

B.E. = 0.9287 (HCO₃ - 24.4 + 14.83 (pH - 7.4))

or

B.E. = 0.9287 * HCO₃ + 13.77 * pH - 124.58

The end result is:

B.E. = 0.02786 * pCO₂ * 10 ^{(pH - 6.1)} + 13.77 * pH - 124.58

See further the great online tutorial on Acid-Base Balance by Dr. Alan W. Grogono, MB, BS, MD, FRCA. Retired Professor and former Chair, Department of Anesthesiology, Tulane University School of Medicine.

Siggaard-Andersen O. An acid-base chart for arterial blood with normal and pathophysiological reference areas. Scan J Clin Lab Invest. 27:239-245, 1971.

Created: January 7, 2000
Revised: January 3, 2001