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Hypercarbia: alveolar gas equation

Alveolar Gas Equation

pAO2 = FiO2 (Patm – pH20) – paCO2/RQ

It is important to note than any increase in CO2 must result in a decrease in the pAO2. As an example, if FiO2 is 0.21 at sea level (pH2O is 47 mm Hg and RQ is 0.8), as PaCO2 rises from 40 to 60 mm Hg, PAO2 decreases from 100 to 75 mm Hg.