1. What is the PaO2/FiO2 Ratio?

The PaO2/FiO2 ratio is a measure of oxygenation that compares arterial oxygen partial pressure (PaO2) to the fraction of inspired oxygen (FiO2). It's commonly used to assess the severity of acute respiratory distress syndrome (ARDS) and other lung conditions.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

• \( PaO_2 \) — Partial pressure of arterial oxygen (mmHg)
• \( FiO_2 \) — Fraction of inspired oxygen (0.21 for room air to 1.0 for 100% oxygen)

Explanation: The ratio provides a standardized way to evaluate oxygenation status regardless of the amount of supplemental oxygen being administered.

3. Clinical Significance

Details: The P/F ratio is primarily used to classify ARDS severity:

• Mild ARDS: 200-300 mmHg
• Moderate ARDS: 100-200 mmHg
• Severe ARDS: <100 mmHg

4. Using the Calculator

Tips: Enter PaO2 in mmHg (from arterial blood gas) and FiO2 as a decimal (0.21 for room air, 0.4 for 40% oxygen, etc.). Both values must be valid (PaO2 > 0, FiO2 between 0.21-1.0).

5. Frequently Asked Questions (FAQ)

Q1: What is a normal P/F ratio?
A: Normal is typically >300 mmHg. Values below 300 suggest impaired oxygenation.

Q2: How does this differ from SpO2/FiO2 ratio?
A: SpO2/FiO2 is a non-invasive alternative but less accurate. P/F ratio using arterial blood gas is the gold standard.

Q3: When should P/F ratio be calculated?
A: Primarily for ARDS diagnosis and monitoring, or when assessing oxygenation status in mechanically ventilated patients.

Q4: Are there limitations to this ratio?
A: It doesn't account for PEEP levels or other ventilatory parameters that affect oxygenation.

Q5: How often should it be measured in ARDS patients?
A: Typically with each arterial blood gas analysis to monitor disease progression and response to treatment.