MedLecturesMadeEasy's video: A-a gradient hypoxemia

The normal alveolar-arterial (A-a) oxygen gradient is 5-10 mm Hg An increased A-a gradient indicates a barrier to O2 transfer. Hypoxia without O2 barrier does not change A-a gradient: Low PAO2 (high elevation) Hypoventilation: brainstem respiratory depression (eg, drugs [opioids], obesity-hypoventilation syndrome) peripheral neuropathy (eg, critical illness polyneuropathy, Guillain-Barre syndrome) muscle weakness (eg, critical illness myopathy, hypophosphatemia, myasthenia gravis) Cause of hypoxemia A-a Gradient Examples Low PAO2 Unchanged High altitude, hypoxic gas mixture Hypoventilation Unchanged Opioid overdose, neuromuscular disorder Shunt (right-to-left) Increased Atelectasis, pneumonia, VSD or ASD Dead space ventilation Increased Pulmonary embolism, venous air embolism Diffusion defect Increased Cystic fibrosis, interstitial lung disease