Alameda County Medical Center / Highland General Hospital

Trauma Service

---

Formulas and calculations

 

Alveolar Gas Equation
PAO2	= PIO2  -  (PaCO2 / R)
	= FIO2 (Patm  -  pH2O)  -  (PaCO2 / R)
where: PAo2 = alveolar partial pressure of oxygen  PIO2  = inspired partial pressure of oxygen PaCO2 = arterial partial pressure of carbon dioxide FIO2 = fraction of inspired oxygen Patm = atmospheric pressure (at sea level = 760 mm Hg) PH20 =  partial pressure of water in alveolus, 100% saturated (at seal level = 47 mm Hg) R = respiratory quotient (normally 0.8)