PF Ratio Calculator
PaO2/FiO2 Ratio
Enter your arterial oxygen partial pressure (PaO2) and fractional inspired oxygen (FiO2) to instantly calculate your PF Ratio. Assess lung function and determine ARDS criteria.
Calculate PaO2/FiO2
Find your clinical PF ratio instantly
Measured via arterial blood gas (ABG) test.
Percentage of oxygen being delivered (Room air is 21%).
Your PaO2/FiO2 Ratio
What Is The PaO2/FiO2 Ratio?
The PaO2/FiO2 ratio (or PF ratio) is widely used in intensive care units and clinical settings to objectively assess a patient's lung function and oxygenation status. It represents the ratio between the partial pressure of oxygen in arterial blood (PaO2) and the fractional inspired oxygen (FiO2).
A healthy individual breathing normal room air (21% oxygen) typically has a PaO2 of roughly 90-100 mmHg. Therefore, a normal PF ratio sits comfortably around 400 to 500 mmHg. When lungs are damaged—such as in pneumonia or Acute Respiratory Distress Syndrome (ARDS)—oxygen transfer into the blood is impaired, causing the PF ratio to drop significantly.
How to Interpret Your PF Ratio Results
| PF Ratio (mmHg) | Clinical Classification | Description |
|---|---|---|
| ≥ 400 | Normal | Healthy oxygenation status. Lungs are efficiently transferring oxygen to the blood. |
| 200 – 300 | Mild ARDS | Also historically known as Acute Lung Injury (ALI). Indicates mild impairment in gas exchange. |
| 100 – 200 | Moderate ARDS | Significant oxygenation deficit. Patients typically require closer monitoring and respiratory support. |
| ≤ 100 | Severe ARDS | Critical impairment in lung function. Usually requires mechanical ventilation and intensive care. |
PaO2 (Arterial Oxygen)
This is the measurement of oxygen dissolved in the blood plasma, indicating how well oxygen moves from the lungs into the blood. It is obtained via an Arterial Blood Gas (ABG) test.
FiO2 (Inspired Oxygen)
FiO2 is the concentration of oxygen that a person inhales. Room air naturally contains about 21% oxygen (0.21). If a patient is on supplemental oxygen or a ventilator, this number will be higher.
Why the Ratio Matters
Looking at PaO2 alone can be misleading if a patient is receiving supplemental oxygen. The ratio standardizes the oxygenation assessment by factoring in how much oxygen assistance the patient is receiving.
Clinical Limitations
While the PF ratio is highly useful, it is just one diagnostic tool. Altitude, positive end-expiratory pressure (PEEP), and other physiological factors must also be evaluated by a physician.
Supporting Recovery Through Nutrition & Health
- 1Consult Your Doctor Immediately — The PF ratio is a clinical metric. If you or a loved one are experiencing severe shortness of breath or low PF ratios, immediate medical evaluation and ICU care is required.
- 2Protein for Muscle Preservation — During recovery from severe respiratory illnesses (like ARDS or severe pneumonia), the body undergoes heavy metabolic stress. Adequate protein intake is vital to prevent muscle wasting.
- 3Manage Carbohydrate Intake — Digesting carbohydrates produces more carbon dioxide (CO2) than digesting fats. For patients with severely compromised lungs, clinical dietitians sometimes adjust macronutrient ratios to reduce the respiratory burden.
- 4Hydration is Key — Proper hydration helps thin out mucus secretions in the lungs, making it easier for the body to clear airways and improve overall gas exchange.
- 5Vitamins and Antioxidants — Supporting the immune system post-illness requires a diet rich in vitamins C, D, and Zinc. Focus on anti-inflammatory foods to aid systemic recovery.
Post-Recovery Diet Planning With Expert Help
Recovering from respiratory distress takes a toll on your body. Our certified dietitians create personalised, healing Indian meal plans designed to rebuild your strength, optimize immunity, and support your long-term health.