Hypercarbia: alveolar gas equation

Alveolar Gas Equation

pAO₂ = FiO₂ (P_atm – 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.