1. What is the P/F Ratio?

The P/F Ratio (PaO2/FiO2 ratio) is a clinical measurement used to assess pulmonary gas exchange and oxygenation status. It's particularly useful in evaluating patients with respiratory distress and diagnosing acute respiratory distress syndrome (ARDS).

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 lung efficiency in oxygen transfer.

3. Importance of P/F Ratio Calculation

Details: The P/F Ratio is crucial for diagnosing and classifying the severity of respiratory conditions, particularly ARDS. It helps guide treatment decisions and monitor response to therapy in critically ill patients.

4. Using the Calculator

Tips: Enter PaO2 in mmHg and FiO2 as a fraction between 0.21 and 1.0. Both values must be valid positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal P/F Ratio?
A: 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 is FiO2 determined?
A: FiO2 is the fraction of oxygen in inspired air. Room air is 0.21 (21%), while supplemental oxygen can increase this up to 1.0 (100% oxygen).

Q3: When should P/F Ratio be measured?
A: It should be measured when assessing patients with respiratory distress, hypoxemia, or suspected ARDS, and to monitor response to oxygen therapy or mechanical ventilation.

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 P/F Ratio differ from other oxygenation indices?
A: P/F Ratio is simpler than other indices like the Oxygenation Index (OI) or Alveolar-arterial gradient, but provides a quick assessment of oxygenation efficiency.