Respiratory Failure

    • A-a gradient = PAO2 – PaO2: normal (on room air) = “4 + age/4” or “2.5 + (0.2 × age)”
    • Hypoxemia + nl A-a gradient: problem is ↓ PiO2/FiO2 or ↑ PaCO2 (ie, hypoventilation)
    • Hypoxemia + ↑ A-a gradient: problem is either
      • R → L shunt, anatomic (congenital heart dis) or severe pathophys (alveoli filled w/ fluid; eg, PNA, pulm edema); cannot overcome w/ 100% O2 b/c of sigmoidal Hb-O2