- Alveolar gas equation
The alveolar pO

_{2}is not routinely measured but is calculated from blood gas measurements by theAlveolar gas equation :$p\_AO\_2\; =\; p\_IO\_2\; -\; p\_ACO\_2/R\; +\; F\; ,$

where:

* R is theRespiratory quotient (normally about 0.8)* p

_{A}O_{2}is the Alveolar pO_{2}* p

_{I}O_{2}is the Inspired pO_{2}, 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

_{A}CO_{2}is the Alveolar pCO_{2}(assumed to be equal to the measured arterial pCO_{2})* F is a correction factor (usually less than 2 mmHg)

**External links*** [

*http://vam.anest.ufl.edu/simulations/alveolargasequation.php Free interactive model of the simplified and complete versions of the alveolar gas equation (AGE)*]

* [*http://www.surgery.ucsf.edu/eastbaytrauma/Protocols/Formulas%20pages/formulasaalvgasequation.htm Formula at ucsf.edu*]

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