A–a oxygen gradient and P/F ratio

Alveolar–arterial gradient, expected value for age, and PaO₂/FiO₂ ratio.

Previewv0.1.0 · Pending clinical review

Inputs

0 of 4

Age

years

FiO₂

PaO₂

PaCO₂

Atmospheric pressureOptional; 760 at sea level

mmHg

Patient values are shared with every calculator.

When to use

Pearls and pitfalls

A normal gradient with hypoxemia suggests hypoventilation or low inspired oxygen.
Patm is 760 mmHg at sea level; lower at altitude.

Why use

Adds the age-expected gradient and Berlin P/F category.

PAO 2 = FiO 2 \times (Patm - 47) - \frac{PaCO 2}{0.8}

Gradient = PAO 2 - PaO 2

P/F = \frac{PaO 2}{FiO 2}