🫁 P/F Ratio (PaO₂/FiO₂, Berlin ARDS)
Calculate the PaO₂/FiO₂ (P/F) ratio for ARDS severity under the Berlin definition.
P/F Ratio (PaO₂/FiO₂, Berlin ARDS)
PaO₂ (mmHg)
FiO₂ (fraction)
When to use
Grade hypoxaemia and classify ARDS severity.
How it works
P/F = PaO₂ ÷ FiO₂ (fraction). ≤ 300 mild, ≤ 200 moderate, ≤ 100 severe ARDS, measured on PEEP ≥ 5 cmH₂O.
Key points
- The Berlin definition requires PEEP/CPAP ≥ 5 cmH₂O.
- At altitude, multiply by (barometric pressure / 760).
- Lower ratios indicate worse oxygenation.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.