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PF Ratio Calculator Merck

PF Ratio Formula:

\[ PF = \frac{PaO_2}{FiO_2} \]

mmHg
(0.21-1.0)

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1. What is the PF Ratio?

Definition: The PF ratio (PaO₂/FiO₂ ratio) is a measure of lung function that assesses oxygenation efficiency.

Purpose: It helps clinicians evaluate respiratory status and classify the severity of hypoxemia, particularly in ARDS (Acute Respiratory Distress Syndrome).

2. How Does the Calculator Work?

The calculator uses the formula:

\[ PF = \frac{PaO_2}{FiO_2} \]

Where:

Explanation: The arterial oxygen level is divided by the fraction of inspired oxygen to standardize oxygenation assessment across different oxygen delivery methods.

3. Clinical Interpretation of PF Ratio

Normal: > 400 mmHg
Mild impairment: 300-400 mmHg
Moderate impairment: 200-300 mmHg
Severe impairment (ARDS): ≤ 200 mmHg

4. Using the Calculator

Tips: Enter the PaO₂ value from arterial blood gas (mmHg) and the FiO₂ (0.21 for room air to 1.0 for 100% oxygen).

5. Frequently Asked Questions (FAQ)

Q1: Why is the PF ratio important?
A: It standardizes oxygenation assessment regardless of the oxygen delivery method, allowing for consistent clinical evaluation.

Q2: What's the normal range for PF ratio?
A: A normal PF ratio is >400 mmHg. Lower values indicate worsening oxygenation.

Q3: How is this different from SpO₂/FiO₂ ratio?
A: The SpO₂/FiO₂ ratio uses pulse oximetry instead of arterial blood gas, but PF ratio is more accurate when ABG is available.

Q4: When is PF ratio most clinically useful?
A: Primarily for assessing and monitoring ARDS severity and response to treatment.

Q5: Does this calculator account for altitude?
A: No, the calculator assumes sea level conditions. At higher altitudes, normal ranges may differ.

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