Hypoxemia Differential Diagnosis Algorithm by A-a Gradient



Normal A-a Gradient:

 • ↓ Atmospheric pressure

 • Hypoventilation: CNS depression, neuromuscular disease, ↓ chest wall compliance



↑ A-a Gradient:

 • Right-to-Left Shunt: Cardiac, Vascular, Alveolar

 • V/Q Mismatch: ↓Ventilation (↑Shunting), ↓Perfusion (↑Dead space)

 • ↓Diffusion Capacity



Matthew Ho, MD PhD @MatthewHoMD



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