1. What is a PF Ratio Calculator?

Definition: This calculator computes the ratio of arterial oxygen partial pressure (PaO₂) to fractional inspired oxygen (FiO₂), known as the PF ratio.

Purpose: It helps medical professionals assess a patient's lung function and oxygenation status, particularly in critical care settings.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( PF \) — PF ratio (mmHg/unitless)
• \( PaO_2 \) — Arterial oxygen partial pressure (mmHg)
• \( FiO_2 \) — Fraction of inspired oxygen (0-1)

Explanation: The PaO₂ value from an arterial blood gas is divided by the FiO₂ (expressed as a decimal) the patient is receiving.

3. Clinical Importance of PF Ratio

Details: The PF ratio is used to:

• Diagnose and classify ARDS (Acute Respiratory Distress Syndrome)
• Monitor respiratory status in critically ill patients
• Guide oxygen therapy and ventilator management

4. Using the Calculator

Tips:

• Enter PaO₂ in mmHg (from arterial blood gas)
• Enter FiO₂ as a decimal (0.21 for room air, 1.0 for 100% oxygen)
• Normal PF ratio is >300 mmHg

5. Frequently Asked Questions (FAQ)

Q1: What is a normal PF ratio?
A: A normal PF ratio is >300 mmHg. Values ≤300 indicate impaired oxygenation.

Q2: How is PF ratio used in ARDS diagnosis?
A: ARDS is classified by PF ratio:

• Mild ARDS: 200-300 mmHg
• Moderate ARDS: 100-200 mmHg
• Severe ARDS: <100 mmHg

Q3: When should I calculate PF ratio?
A: Calculate when assessing oxygenation in patients receiving supplemental oxygen or mechanical ventilation.

Q4: What are limitations of PF ratio?
A: It doesn't account for PEEP levels, patient effort, or other factors affecting oxygenation.

Q5: How does altitude affect PF ratio?
A: At higher altitudes, normal PaO₂ is lower, so expected PF ratio decreases proportionally.