A-a oxygen gradient

Distinguishes hypoxemia from hypoventilation (normal A-a) vs V/Q mismatch / shunt / diffusion limitation (elevated A-a).

Formula

PAO₂ = (FiO₂ × (Pb − 47)) − (PaCO₂ / 0.8)
A-a gradient = PAO₂ − PaO₂
Normal (room air, sea level) ≈ age/4 + 4 mmHg

Interactive form coming soon

The calculation function is live in the codebase. Interactive form UI is being added — formulas above are reference-grade and ready to use at the bedside.