The alveolar-arterial (A-a) oxygen gradient measures the difference between alveolar and arterial oxygen tension. It helps differentiate causes of hypoxemia and assess gas exchange efficiency.
Normal A-a gradient with elevated PaCO₂: Pure hypoventilation — consider CNS depression, neuromuscular disease, or obesity hypoventilation syndrome.
Elevated A-a gradient: Indicates V/Q mismatch, intrapulmonary shunt, diffusion impairment, or pulmonary embolism. The A-a gradient increases with age and with higher FiO₂.
For educational use only. Not a substitute for clinical judgment.
