Calculator Inputs
Formula Used
If FiO₂ is entered as a percentage, the calculator first converts it to a fraction.
The Berlin-compatible oxygenation band is shown only when PEEP or CPAP is at least 5 cmH₂O. Even then, ARDS requires clinical findings beyond this ratio.
How to Use This Calculator
- Enter the measured arterial oxygen tension as PaO₂ in mmHg.
- Enter FiO₂ as either a fraction or a percentage.
- Add PEEP or CPAP if you want a Berlin-compatible oxygenation band.
- Click Calculate Ratio to display the results above the form.
- Use the export buttons to save the calculated summary as CSV or PDF.
- Review the interpretation beside the ratio, but confirm decisions clinically.
Example Data Table
| Case | PaO₂ (mmHg) | FiO₂ | PEEP (cmH₂O) | P/F Ratio | Interpretation | Berlin-Compatible Band |
|---|---|---|---|---|---|---|
| Room Air Review | 100 | 21% | 0 | 476.2 | Preserved oxygenation | Not assignable |
| Ventilated Mild Loss | 85 | 40% | 5 | 212.5 | Moderate oxygenation reduction | Mild Berlin-compatible band |
| Ventilated Moderate Loss | 70 | 60% | 8 | 116.7 | Severe oxygenation reduction | Moderate Berlin-compatible band |
| Ventilated Severe Loss | 55 | 80% | 10 | 68.8 | Critical oxygenation reduction | Severe Berlin-compatible band |
Frequently Asked Questions
1. What does the PaO₂/FiO₂ ratio show?
It shows how efficiently oxygen moves from inspired gas into arterial blood. Lower values suggest worse oxygenation and can help summarize respiratory severity.
2. Why does FiO₂ need the correct unit?
The formula uses FiO₂ as a fraction. Entering 40 instead of 0.40 without choosing percent makes the ratio inaccurate.
3. Is this calculator enough to diagnose ARDS?
No. ARDS diagnosis also needs timing, imaging findings, and an explanation that is not fully due to cardiac failure or fluid overload.
4. Why is PEEP or CPAP optional?
The ratio itself can be calculated without it. PEEP or CPAP is used here only to decide whether a Berlin-compatible oxygenation band can be displayed.
5. What if the ratio is above 400?
That usually reflects relatively preserved oxygenation, especially near room air. Clinical context, shunt, sampling timing, and ventilation settings still matter.
6. Can this be used for trends?
Yes. Repeating the same measurement method over time helps compare oxygenation before and after ventilator, positioning, or oxygen changes.
7. Does a low ratio always mean severe lung injury?
No. Sampling error, transient instability, secretion burden, perfusion issues, altitude, and ventilator settings can affect the result.
8. What can the export buttons save?
The CSV export saves key inputs and outputs. The PDF export captures the visible result summary for documentation or review.