Alveolar gas equation

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The alveolar pO₂ is not routinely measured but is calculated from blood gas measurements by the Alveolar gas equation:

where:

• R is the Respiratory quotient (normally about 0.8)

• p_AO₂ is the Alveolar pO₂

• p_IO₂ is the Inspired pO₂, equal to about 150 mm Hg (0.21 x 713 mmHg) at sea level. The given pressure at sea level is due to atmospheric pressure (760 mmHg) minus the partial pressure of water vapor (47 mmHg), as alveolar gas is completely saturated with water. The mole fraction of oxygen is about 0.21 in dry atmospheric gas.

• p_ACO₂ is the Alveolar pCO₂ (assumed to be equal to the measured arterial pCO₂)

• F is a correction factor (usually less than 2 mmHg)

[edit] External links

• Free interactive model of the simplified and complete versions of the alveolar gas equation (AGE)
• Formula at ucsf.edu

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