1. What is the PF Ratio?

Definition: The PF ratio (PaO₂/FiO₂ ratio) is a measure of oxygenation used to assess the severity of acute respiratory distress syndrome (ARDS).

Purpose: It helps clinicians evaluate lung function and determine the appropriate treatment for patients with respiratory failure.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( PF \) — PF ratio (mmHg/unitless)
• \( PaO_2 \) — Arterial oxygen partial pressure (mmHg)
• \( FiO_2 \) — Fraction of inspired oxygen (0-1, unitless)

Explanation: The ratio compares the oxygen level in arterial blood to the concentration of oxygen being inhaled.

3. Importance of PF Ratio

Details: The PF ratio is critical 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 the PaO₂ value from arterial blood gas analysis and the FiO₂ (0.21 for room air up to 1.0 for 100% oxygen). Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal PF ratio?
A: A normal PF ratio is typically >300 mmHg when breathing room air (FiO₂ 0.21).

Q2: Why is the PF ratio important in ARDS?
A: It provides an objective measure of oxygenation impairment independent of ventilator settings.

Q3: How does FiO₂ affect the PF ratio?
A: Higher FiO₂ values will decrease the PF ratio if oxygenation remains the same.

Q4: When should I use this calculator?
A: When assessing patients with respiratory distress or when ARDS is suspected.

Q5: What are limitations of the PF ratio?
A: It doesn't account for PEEP levels and may be affected by other factors like cardiac output.