1. What is the Horowitz PF Ratio?

The Horowitz PF Ratio (PaO₂/FiO₂ ratio) is a measure of pulmonary gas exchange used to assess the severity of acute respiratory distress syndrome (ARDS). It provides a simple way to evaluate oxygenation status independent of ventilator settings.

2. How Does the Calculator Work?

The calculator uses the Horowitz PF Ratio formula:

Where:

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

Explanation: The ratio compares the oxygen level in arterial blood (PaO₂) to the concentration of oxygen being inhaled (FiO₂).

3. Importance of PF Ratio Calculation

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 PaO₂ in mmHg and FiO₂ as a decimal between 0.21 (room air) and 1.0 (100% oxygen). Both values must be valid (PaO₂ > 0, 0.21 ≤ FiO₂ ≤ 1.0).

5. Frequently Asked Questions (FAQ)

Q1: What is a normal PF ratio?
A: A normal PF ratio is typically >300 mmHg. Values below 300 suggest impaired oxygenation.

Q2: How does PF ratio differ from oxygenation index?
A: The oxygenation index incorporates mean airway pressure, making it more useful in mechanically ventilated patients.

Q3: When should PF ratio be measured?
A: PF ratio should be measured when ARDS is suspected and after any significant change in ventilator settings.

Q4: Are there limitations to PF ratio?
A: The ratio can be affected by altitude, PEEP levels, and the patient's position. It's less reliable at very high FiO₂ levels.

Q5: How does PF ratio guide treatment?
A: Lower PF ratios indicate more severe ARDS and may prompt more aggressive interventions like higher PEEP or prone positioning.