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P/F Ratio (PaO₂/FiO₂)

PaO₂ to FiO₂ ratio, with Berlin ARDS oxygenation categories.

For healthcare professionalsRespiratoryv1.0.1

For healthcare professionals / clinical use. Not a self-diagnosis tool.

Your measurements

%

Calculated on your device. Nothing is sent to a server.

Your result will appear here

Enter your measurements, then press Calculate.

Methodology

Berlin definition of ARDS (2012)

P/F = PaO₂ (mmHg) ÷ FiO₂ (fraction)

The ratio is one criterion: ARDS also requires timing, bilateral opacities and exclusion of cardiac failure as the main cause. The 2024 global definition keeps P/F ≤ 300 and also accepts S/F ≤ 315 when SpO₂ is 97% or less.

Who it is for
Adults with an arterial blood gas; Berlin categories need PEEP or CPAP ≥ 5 cmH₂O.
Version
1.0.1

How this calculator works

Where the formula comes from

  • The Berlin Definition (2012) grades ARDS by PaO₂/FiO₂: mild over 200 to 300, moderate over 100 to 200, severe 100 or less (mmHg).[1]
  • In a patient-level analysis of 4,188 patients, mild, moderate and severe ARDS had mortality of 27%, 32% and 45%; the definition's predictive validity for mortality was modest (AUROC 0.577).[1]

Versions and alternatives

  • The 2024 global definition keeps PaO₂/FiO₂ ≤ 300 mmHg, also accepts SpO₂/FiO₂ ≤ 315 when SpO₂ is 97% or less, and includes high-flow nasal oxygen at 30 L/min or more.[2]
  • In resource-limited settings the global definition does not require PEEP, a set oxygen flow or a specific support device.[2]

Sources

  1. ARDS Definition Task Force; Ranieri VM, Rubenfeld GD, Thompson BT, et al. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526–2533. doi:10.1001/jama.2012.5669
  2. Matthay MA, Arabi Y, Arroliga AC, et al. A new global definition of acute respiratory distress syndrome. Am J Respir Crit Care Med. 2024;209(1):37–47. doi:10.1164/rccm.202303-0558WS

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on

Worked example: how to calculate P/F ratio

Inputs

PaO₂ (arterial oxygen)
80 mmHg
FiO₂ (inspired oxygen)
40 %

Result

PaO₂/FiO₂
200 mmHg

Over 100 to 200: Berlin 'moderate' range

Calculation:

80/0.4 = 200

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

  • Depends on PEEP and FiO₂; not interpretable at high altitude without adjustment.

References

  1. ARDS Definition Task Force; Ranieri VM, Rubenfeld GD, Thompson BT, et al. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526–2533. doi:10.1001/jama.2012.5669
  2. Matthay MA, Arabi Y, Arroliga AC, et al. A new global definition of acute respiratory distress syndrome. Am J Respir Crit Care Med. 2024;209(1):37–47. doi:10.1164/rccm.202303-0558WS

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