P/F Ratio
P/F Ratio - a deterministic tool in Sophie Well's Clinical Math & Conversions group.
Open the P/F Ratio → Runs in your browser. No signup, no tracking.
What this is
Compute the PaO2 / FiO2 ratio - the oxygenation index from the ARDS Berlin Definition (JAMA 2012). Enter the arterial PaO2 in mmHg and the FiO2 as a decimal (0.21 - 1.0) and Sophie Well returns the P/F value plus the Berlin band: mild (200-300), moderate (100-200), or severe (<=100), with PEEP/CPAP >=5 cmH2O assumed for the ARDS definition.
When to use it
Use this on any intubated or high-FiO2 patient to classify oxygenation severity, track response to PEEP/proning/paralytics, or screen for ARDS enrollment criteria. P/F is sensitive to FiO2 changes and to altitude; in non-intubated patients on nasal cannula or HFNC the SpO2/FiO2 ratio or the ROX index are more appropriate substitutes.
References
ARDS Definition Task Force. Berlin Definition. JAMA. 2012;307(23):2526-2533.
Worked example: P/F 180 (Moderate ARDS)
Sophie Well is a reference and educational tool. Not medical, legal, or financial advice. Does not replace clinician judgment, professional billing review, or legal counsel.