1. What is the P/F Ratio?

The P/F Ratio (PaO2/FiO2 ratio) is a clinical indicator used to assess pulmonary function and oxygenation status. It's particularly useful in diagnosing and monitoring acute respiratory distress syndrome (ARDS) and other respiratory conditions.

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 (0-1)

Explanation: The ratio compares the oxygen level in arterial blood to the concentration of oxygen being inhaled, providing a measure of how efficiently the lungs are oxygenating the blood.

3. Importance of P/F Ratio Calculation

Details: The P/F Ratio is crucial for diagnosing ARDS severity, guiding ventilator management, monitoring treatment response, and assessing prognosis in critically ill patients with respiratory failure.

4. Using the Calculator

Tips: Enter PaO2 in mmHg and FiO2 as a decimal fraction (e.g., 0.21 for room air, 1.0 for 100% oxygen). Both values must be 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 impairment, 200-300 moderate impairment, and <200 severe impairment (consistent with ARDS).

Q2: How does P/F Ratio differ from A-a gradient?
A: While both assess oxygenation, P/F Ratio is simpler and doesn't require calculation of alveolar gas. A-a gradient provides information about gas exchange efficiency but requires more variables.

Q3: When should P/F Ratio be measured?
A: It should be measured in patients with respiratory distress, those on mechanical ventilation, or when monitoring oxygenation status in critical care settings.

Q4: Are there limitations to P/F Ratio?
A: Yes, it can be affected by factors like positive end-expiratory pressure (PEEP), patient position, and cardiac output. It should be interpreted in clinical context.

Q5: How does altitude affect P/F Ratio?
A: At higher altitudes, PaO2 decreases due to lower atmospheric pressure, which will lower the P/F Ratio even with normal lung function.