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 curve V/Q mismatch where “shunt-like” areas (↓ V & nl Q) cause unoxygenated blood to mix with oxygenated blood; can be overcome w/ ↑ O2 delivery Diffusion limitation: generally seen with exercise/↑CO

• Workup of acute hypoxemia

• Approach to oxygenation, hypoxemia, and hypoxemic respiratory failure

• Chemical Causes of Cellular Hypoxia

• Etiologies of High elevated PaCO2