1. What is the P/F Ratio?

The P/F ratio (PaO₂/FiO₂ ratio) is a clinical indicator used to assess the severity of lung impairment, particularly in acute respiratory distress syndrome (ARDS). It compares the arterial oxygen partial pressure to the fraction of inspired oxygen.

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 (%)

Explanation: The ratio provides a measure of how effectively the lungs are oxygenating the blood relative to the oxygen concentration being delivered.

3. Importance of P/F Ratio Calculation

Details: The P/F ratio is crucial for diagnosing and classifying ARDS severity, guiding treatment decisions, and monitoring patient response to therapy in critical care settings.

4. Using the Calculator

Tips: Enter PaO₂ in mmHg and FiO₂ as a percentage (21-100%). Both values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are normal P/F ratio values?
A: Normal P/F ratio is typically >400 mmHg. Values between 300-400 indicate mild ARDS, 200-300 moderate ARDS, and <200 severe ARDS.

Q2: When should P/F ratio be measured?
A: P/F ratio should be measured in patients with respiratory distress, suspected ARDS, or those requiring mechanical ventilation to assess oxygenation status.

Q3: Are there limitations to this calculation?
A: The ratio may be affected by factors such as positive end-expiratory pressure (PEEP), patient position, and the timing of blood gas measurement relative to oxygen administration.

Q4: How does P/F ratio differ from oxygenation index?
A: While both assess oxygenation, the oxygenation index incorporates mean airway pressure and may provide a more comprehensive assessment in mechanically ventilated patients.

Q5: Can P/F ratio be used for non-intubated patients?
A: Yes, P/F ratio can be calculated for non-intubated patients receiving supplemental oxygen via various delivery devices.