1. What is the P/F Ratio?

The P/F ratio (PaO₂/FiO₂ ratio) is a measure of oxygenation used to assess respiratory function. This calculator provides an approximation using SpO₂ (peripheral oxygen saturation) as a proxy for PaO₂ (arterial oxygen partial pressure).

2. How Does the Calculator Work?

The calculator uses the approximation formula:

Where:

• \( SpO_2 \) — Peripheral oxygen saturation (percentage)
• \( FiO_2 \) — Fraction of inspired oxygen (0.21 for room air to 1.0 for 100% oxygen)

Note: This is an approximation. The actual P/F ratio requires arterial blood gas measurement for precise calculation.

3. Importance of P/F Ratio

Clinical Use: The P/F ratio is used to assess the severity of hypoxemia and classify acute respiratory distress syndrome (ARDS). Lower values indicate more severe impairment.

4. Using the Calculator

Instructions: Enter SpO₂ as a percentage (typically 80-100%) and FiO₂ as a decimal (0.21 for room air up to 1.0 for 100% oxygen).

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this approximation?
A: It provides a reasonable estimate but is less accurate than actual PaO₂ measurement, especially at SpO₂ extremes.

Q2: What are normal P/F ratio values?
A: Normal is >300 mmHg. ARDS is classified as mild (200-300), moderate (100-200), and severe (<100).

Q3: When should I use this calculator?
A: When arterial blood gas results aren't available but SpO₂ monitoring is being used.

Q4: What are the limitations?
A: Accuracy depends on proper SpO₂ measurement and doesn't account for factors like hemoglobin levels or acid-base status.

Q5: Can this replace ABG measurements?
A: No, it's only an approximation. Critical decisions should be based on actual ABG results when available.