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Cornell Pediatrics

Base Excess & Calculated Bicarbonate

Calculate the serum bicarbonate from the serum pH and pCO2.

Input pH 
Input pCO2 
   
   
HCO3 =
Base Excess =

 

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

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