PaO2/FiO2 Ratio (P/F)

Calculate PaO2/FiO2 ratio and classify ARDS severity by Berlin 2012 criteria.

For educational and clinical reference. Not a substitute for medical judgment. See the medical disclaimer.
P/F Ratio
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ARDS Class (Berlin)
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References

  1. ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526-2533.

How to use

  1. Enter PaO2 (mmHg) and FiO2 (as 0.4 or 40 — auto-detected).
  2. P/F ratio and ARDS classification appear instantly.
  3. Berlin requires PEEP ≥ 5 cmH₂O for ARDS classification.

Frequently asked questions

Formula?

P/F ratio = PaO2 / FiO2 (FiO2 as a fraction, e.g., 0.5 for 50%).

Berlin ARDS classification?

Mild ARDS: 200 < P/F ≤ 300. Moderate: 100 < P/F ≤ 200. Severe: P/F ≤ 100. Requires PEEP ≥ 5 cmH₂O.

P/F vs A-a gradient?

P/F is simpler and used in ARDS criteria; A-a gradient requires FiO2 and barometric pressure calculations and is more useful at room air.

What about altitude?

Berlin criteria recommend altitude correction: P/F × (PB / 760) for elevations > 1000 m.

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