Critical Care

P/F Ratio (PaO₂/FiO₂)

Oxygenation; ARDS severity (Berlin).

Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.

When to use

Use to grade hypoxaemia and ARDS severity (Berlin definition, on PEEP/CPAP ≥5 cmH₂O).

Why use

It is the core oxygenation measure for defining and grading ARDS.

Critical actions

Enter PaO₂ in mmHg (multiply kPa by 7.5) and FiO₂ as a fraction. Berlin ARDS grading assumes PEEP/CPAP ≥5 cmH₂O.

Evidence & references

  1. ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012.

Related calculators

A-a GradientAlveolar-arterial oxygen gradient (kPa).ROX IndexPredicts high-flow nasal oxygen success.

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