A-a Gradient (PA-aO2) (A-aDO2) Alveolar-arterial O2 Tension …

Normal = 10 – 25 mm Hg (room air) = 30 – 50mm Hg (100% O2). Increases with age and FIO2. PaO2 is calculated at FIO2 0.5 breathed x 20 min to get PaO2 …