How to Use Oxygenation Index Calculator
Enter mean airway pressure in cmH2O, FiO2 as a decimal, and arterial PaO2 in mmHg. The Oxygenation Index Calculator combines ventilator pressure, oxygen concentration, and arterial oxygenation into one number.
FiO2 should be typed as a fraction, not a percent. Room air is about 0.21, 60% oxygen is 0.60, and 100% oxygen is 1.0.
A higher OI means that more airway pressure and inspired oxygen are needed to achieve the measured PaO2. The timing of the blood gas and ventilator settings should match.
Formula & Theory — Oxygenation Index Calculator
The Oxygenation Index Calculator uses the following formula or scoring rule:
OI = (MAP × FiO2 × 100) ÷ PaO2Oxygenation index rises when MAP rises, FiO2 rises, or PaO2 falls. This makes it different from the PF ratio because it includes ventilator pressure as part of the oxygenation burden.
Multiplying FiO2 by 100 converts the fractional oxygen concentration into the conventional OI scale.
OI is commonly interpreted in context with diagnosis, ventilator mode, blood gas timing, and trends rather than a single isolated measurement.
Use Cases for Oxygenation Index Calculator
The Oxygenation Index Calculator is useful in specific situations such as:
- reviewing respiratory failure severity trends
- teaching the difference between OI and PF ratio
- checking calculations from ventilator settings and arterial blood gas values
- comparing oxygenation before and after ventilator adjustments