Alveolar gas equation

Abstract

The alveolar gas equation for calculating PAO2 is essential to understanding any PaO2 value and in assessing if the lungs are properly transferring oxygen into the blood. Is a PaO2 of 28 mm Hg abnormal? How about 55 mm Hg? 95 mm Hg? To clinically interpret PaO2 one has to also know the patient's PaCO2, FIO2 (fraction of inspired oxygen) and the PB (barometric pressure), all components of the equation for PAO2: