Enter Respiratory Values
Use the fields below to calculate oxygenation index, compare it with a prior reading, estimate oxygen saturation index, and review supporting metrics.
Example Data Table
| Scenario | FiO2 (%) | MAP (cmH2O) | PaO2 (mmHg) | Calculated OI | Interpretation |
|---|---|---|---|---|---|
| Case A | 40 | 10 | 100 | 4.00 | Low / near-normal impairment |
| Case B | 60 | 14 | 75 | 11.20 | Moderate impairment |
| Case C | 80 | 18 | 60 | 24.00 | Severe impairment |
| Case D | 100 | 22 | 55 | 40.00 | Critical impairment |
Formula Used
OI = (FiO2 fraction × Mean Airway Pressure × 100) ÷ PaO2
P/F Ratio = PaO2 ÷ FiO2 fraction
OSI = (FiO2 fraction × Mean Airway Pressure × 100) ÷ SpO2
Variable guide:
- FiO2 fraction is the oxygen percentage divided by 100.
- Mean Airway Pressure reflects average airway pressure during ventilation.
- PaO2 is arterial oxygen partial pressure from a blood gas.
- SpO2 can be used to estimate OSI when arterial oxygen is unavailable.
How to Use This Calculator
- Enter FiO2 as a percentage, not a decimal fraction.
- Enter mean airway pressure from the ventilator record.
- Enter PaO2 from the most relevant arterial blood gas.
- Optionally enter SpO2 to estimate oxygen saturation index.
- Add prior OI and hours between readings to evaluate direction of change.
- Press the calculate button to show the result above the form.
- Review the graph, interpretation bands, and urgency note.
- Use the CSV or PDF buttons to save the result summary.
Frequently Asked Questions
1. What does oxygenation index measure?
It measures how much oxygen concentration and airway pressure are required to achieve arterial oxygenation. Higher values usually mean worse oxygenation efficiency and greater respiratory support burden.
2. Why is mean airway pressure included?
Mean airway pressure reflects the ventilator pressure load across the breathing cycle. Oxygenation index uses it because oxygenation can worsen even when FiO2 stays unchanged.
3. What units should I enter?
Enter FiO2 in percent, mean airway pressure in cmH2O, PaO2 in mmHg, and SpO2 in percent. Mixing units will distort the result.
4. Is a higher oxygenation index always worse?
In general, yes. A rising oxygenation index means more pressure and oxygen are needed for a given PaO2. Clinical meaning still depends on diagnosis, timing, and protocol.
5. Why does the calculator also show P/F ratio?
The P/F ratio is a familiar oxygenation marker and helps compare severity using a simpler method. Seeing both values adds context during trend review.
6. When is oxygen saturation index useful?
OSI is helpful when arterial blood gas data are unavailable or delayed. It uses SpO2 instead of PaO2, so it is convenient but less direct.
7. Can I use this for adults, children, and neonates?
The math works across populations, but interpretation thresholds can vary by age group, diagnosis, and local protocol. Always compare with the correct clinical standard.
8. Can this calculator replace bedside judgment?
No. It is a structured support tool for calculation and trending. Final assessment should include examination, gas analysis, imaging, ventilator settings, and clinician judgment.