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PaO₂ / FiO₂ Ratio

Assess oxygenation status and classify ARDS severity

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Educational Use Only: This tool is for educational purposes only. It does not replace clinical judgment or medical advice.

Enter Values

PaO₂ (Arterial Oxygen Pressure)(mmHg)

mmHg

FiO₂ (Fraction of Inspired Oxygen)((0.21-1.0 or 21-100%))

(0.21-1.0 or 21-100%)

How to measure:

• PaO₂: From arterial blood gas analysis

• FiO₂: Set oxygen concentration (21% = room air, 100% = pure oxygen)

• Formula: P/F Ratio = PaO₂ ÷ FiO₂

• Normal: >400 mmHg (on room air ≈ 400-500)

ARDS Classification (Berlin Definition):

• Normal: > 400 mmHg

• Mild ALI: 300-399 mmHg

• Mild ARDS: 201-300 mmHg

• Moderate ARDS: 101-200 mmHg

• Severe ARDS: ≤ 100 mmHg

Clinical Significance:

The P/F ratio is a key indicator of oxygenation efficiency and lung function. It helps classify severity of acute respiratory distress syndrome (ARDS) and guides treatment decisions.

Lower ratios indicate more severe impairment and may require advanced interventions such as high PEEP, prone positioning, or ECMO therapy.

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