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PaO2/FiO2 Oxygenation Assessment & ARDS Severity HUD
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Understanding the PaO2/FiO2 Ratio
The P/F Ratio is a clinical tool used to quantify the severity of hypoxemia and lung injury. It is the primary metric used in the Berlin Criteria to diagnose Acute Respiratory Distress Syndrome (ARDS).
Berlin Criteria Classification
- Normal: Ratio > 400 mmHg
- Mild ARDS: 201 - 300 mmHg (with PEEP ≥ 5)
- Moderate ARDS: 101 - 200 mmHg
- Severe ARDS: ≤ 100 mmHg
Clinical Utility FAQs
Can I use SpO2 instead of PaO2?
When an ABG is not available, clinicians often use the S/F ratio (SpO2/FiO2). While useful for screening, the P/F ratio remains the gold standard for formal ARDS diagnosis.
Why is PEEP important for the ratio?
Per the Berlin definition, the P/F ratio must be assessed while the patient is on at least 5 cmH2O of Positive End-Expiratory Pressure (PEEP) to ensure the hypoxemia is not simply due to atelectasis.
Professional References
- 1. ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012.
- 2. Oh's Intensive Care Manual. 8th Edition.
Dr. Nikhil Mahajan, PT
CLINICAL RESOURCE