Expected PCO2 =

Baseline PCO2 + ((Measured bicarbonate - 24) x 0.6)

Default value for Baseline PCO2 is 40.

Interpretation: if the patient's PCO2 is lower than the expected result, the patient has a superimposed respiratory alkalosis. If it is higher, the patient has a superimposed respiratory acidosis.

Limit of compensation is 55. Thus, any result (expected PCO2) higher than 55 should be converted to 55.