1. What is the P/F Ratio?

The PaO2/FiO2 (P/F) ratio is a clinical indicator of pulmonary gas exchange and is commonly used to assess the severity of acute respiratory distress syndrome (ARDS). It compares arterial oxygen partial pressure (PaO2) to the fraction of inspired oxygen (FiO2).

2. How Does the Calculator Work?

The calculator uses the P/F ratio formula:

Where:

• \( PaO_2 \) — Partial pressure of arterial oxygen (mmHg)
• \( FiO_2 \) — Fraction of inspired oxygen (decimal from 0.21 to 1.0)

Explanation: The ratio provides a simple way to assess oxygenation status while accounting for varying levels of supplemental oxygen.

3. Importance of P/F Ratio

Details: The P/F ratio is crucial for diagnosing and classifying 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, 1.0 for 100% oxygen). All values must be valid (PaO2 > 0, FiO2 between 0.21-1.0).

5. Frequently Asked Questions (FAQ)

Q1: Why use P/F ratio instead of just PaO2?
A: The ratio accounts for varying oxygen concentrations, making it more meaningful than PaO2 alone when patients receive supplemental oxygen.

Q2: What are normal P/F ratio values?
A: Normal is generally >300 mmHg. Values below 300 suggest impaired oxygenation.

Q3: When should P/F ratio be calculated?
A: For patients with suspected ARDS or acute hypoxemic respiratory failure, especially those receiving oxygen therapy.

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

Q5: How does altitude affect P/F ratio?
A: At higher altitudes, normal PaO2 is lower, so expected P/F ratios are proportionally lower as well.