1. What is the PF Ratio?

The PF Ratio (PaO₂/FiO₂ Ratio) is a clinical indicator used to assess pulmonary gas exchange and the severity of lung injury. It's commonly used in critical care settings to evaluate respiratory function and diagnose conditions like Acute Respiratory Distress Syndrome (ARDS).

2. How Does the Calculator Work?

The calculator uses the PF Ratio formula:

Where:

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

Explanation: The ratio compares the oxygen level in the blood (PaO₂) to the amount of oxygen being delivered (FiO₂), providing a measure of how efficiently the lungs are oxygenating the blood.

3. Importance of PF Ratio Calculation

Details: The PF Ratio is crucial for diagnosing and classifying the severity of respiratory conditions, particularly ARDS. It helps guide treatment decisions, monitor patient progress, and determine the need for advanced respiratory support.

4. Using the Calculator

Tips: Enter PaO₂ in mmHg (typically from arterial blood gas analysis) and FiO₂ as a decimal between 0.21 (room air) and 1.0 (100% oxygen). Both values must be valid and within physiological ranges.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal PF Ratio?
A: A normal PF Ratio is typically greater than 400 mmHg. Lower values indicate impaired gas exchange.

Q2: How is PF Ratio used in ARDS diagnosis?
A: ARDS is classified as mild (PF Ratio 200-300), moderate (PF Ratio 100-200), or severe (PF Ratio < 100) when measured with PEEP ≥ 5 cm H₂O.

Q3: When should PF Ratio be measured?
A: PF Ratio should be calculated when there's clinical concern for respiratory failure, especially in patients receiving supplemental oxygen or mechanical ventilation.

Q4: Are there limitations to PF Ratio?
A: Yes, PF Ratio can be affected by factors like positive end-expiratory pressure (PEEP), patient effort, and technical aspects of blood gas measurement. It should be interpreted in clinical context.

Q5: How does PF Ratio differ from Oxygenation Index?
A: Oxygenation Index incorporates mean airway pressure and is often used in pediatric populations, while PF Ratio is simpler and more commonly used in adults.