PaO₂/FiO₂ Ratio (P/F Ratio)
Calculates the ratio of arterial oxygen tension to inspired oxygen fraction. Used to classify severity of hypoxaemic respiratory failure and diagnose ARDS per Berlin criteria.
Score interpretation
P/F ratio ≥ 300: Normal. No ARDS.
→ Monitor if on supplemental oxygen. Address underlying cause.
P/F ratio 200–300 with PEEP/CPAP ≥ 5 cmH₂O: Mild ARDS (Berlin).
→ High-flow nasal oxygen or CPAP. Consider HDU/ICU. Identify precipitant: pneumonia, aspiration, sepsis.
P/F ratio 100–199: Moderate ARDS.
→ ICU admission. Lung-protective ventilation (TV 6 mL/kg IBW). PEEP titration. Prone positioning ≥ 16h/day.
P/F ratio < 100: Severe ARDS.
→ ICU mandatory. Neuromuscular blockade (cisatracurium). Prone positioning. Consider VV-ECMO if refractory.
Interpretation bands for the P/F Ratio. Apply clinical judgement and local guidance.
References
- ARDS Definition Task Force. Acute respiratory distress syndrome: The Berlin Definition. JAMA. 2012;307(23):2526–2533.
Related
Curated clinical cross-links plus same-class fallbacks.
- Acute Asthma in Adults · BTS/SIGN British Guideline on Asthma 2019; NICE NG80
- Pulmonary Embolism Assessment · NICE NG158; ESC 2019 PE Guidelines
- Acute Exacerbation of COPD (AECOPD) · NICE NG115; GOLD 2024
- Spontaneous Pneumothorax (Adult) · BTS Pleural Disease 2023
- Atypical Pneumonia (Legionella / Mycoplasma / Chlamydophila) · BTS 2023; IDSA
- COPD Exacerbation Management · NICE NG115 / GOLD 2024
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.