Standard bicarbonate is the concentration of bicarbonate in the plasma from blood which is equilibrated with a normal PaCO2 (40 mmHg) and a normal pO2 (over 100 mmHg) at a normal temperature (37°C). Usually, it is obtained by solving the Henderson-Hasselbalch equation to get a bicarbonate value when the pH is known and PaCO2 is 40mmHg

This bicarbonate level represents the metabolic contribution to the change in bicarbonate. It was introduced in 1957 by Jorgensen and Astrup. In essence, this is what the bicarbonate should be if all the non-metabolic influences were corrected. It answer the question, "how much would my patient's bicarbonate be if I were ventilating them properly?".

Calculation of the standard bicarbonate

The equation for standard bicarbonate incorporates the actual base excess value.

equation for the standard bicarbonate

The utility of the standard bicarbonate stems from its rejection of the temperature and of the normal influence on buffering which results from changes in oxygen and carbon dioxide concentration. With these variables out of the picture, the only remaining influences on bicarbonate are metabolic. The standard bicarbonate can therefore be said to represent the buffering capacity of the blood more accurately than the actual bicarbonate. Obviously, in states of vigorous health the actual bicarbonate and the standard bicarbonate are more or less identical. However, the greater the respiratory acid-base disturbance, the greater the difference between these two values.


Device-specific information in all these ABG pages refers to the ABG machine used in my home unit.

Other machines may have different reference ranges and different symbols.

For my ABG analyser, one can examine this handy operations manual.

There is also an even more handy reference manual, but one needs to be an owner of this equipment before one can get hold of it. Its called the "989-963I ABL800 Reference Manual"

Ole Siggaard-Andersen's website was an excellent source of information for this topic.

Jørgensen, K., and P. Astrup. "Standard bicarbonate, its clinical significance, and a new method for its determination." Scandinavian Journal of Clinical & Laboratory Investigation 9.2 (1957): 122-132.

Schwartz, William B., and Arnold S. Relman. "A Critique of the Parameters Used in the Evaluation of Acid-Base Disorders: Whole-Blood Buffer Base and Standard Bicarbonate Compared with Blood pH and Plasma Bicarbonate Concentration." New England Journal of Medicine 268.25 (1963): 1382-1388.