How is P/F ratio calculated and what are the Berlin ARDS thresholds?

P/F = PaO2 (mmHg) / FiO2 (as decimal, e.g., 0.40). Berlin definition (requires PEEP >=5 cmH2O): Mild 200 < P/F <=300 (mortality 27%); Moderate 100 < P/F <=200 (mortality 32%); Severe P/F <=100 (mortality 45%). P/F <150 used as threshold for prone positioning and cisatracurium in most protocols.

Can SpO2/FiO2 (S/F ratio) substitute for P/F ratio?

S/F ratio correlates well with P/F: S/F 235 approximately equals P/F 200 (mild-moderate ARDS threshold); S/F 148 approximately equals P/F 100 (moderate-severe threshold). S/F is useful for screening in absence of arterial blood gas, particularly in low-resource settings or during weaning from oxygen. However, P/F remains the standard for Berlin definition classification.

P/F Ratio ARDSnet Classification Calculator

Calculate PaO2/FiO2 (P/F) ratio and classify ARDS severity: mild (200 to 300 mmHg), moderate (100 to 200 mmHg), severe (<100 mmHg) per Berlin definition, with PEEP correction requirement.

⚕ Clinical Disclaimer: These calculators are for educational and reference purposes only. Always verify results with qualified clinical judgment and current clinical guidelines. Do not use as a sole basis for medical decisions.

How to Use

Enter the values for the scenario you are assessing. Calculate PaO2/FiO2 (P/F) ratio and classify ARDS severity: mild (200 to 300 mmHg), moderate (100 to 200 mmHg), severe (<100 mmHg) per Berlin definition, with PEEP correction requirement. Use the p/f ratio ards class result to inform your calculation.

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