Calculator for oxygen index \( OI = \frac{FiO_2 \times MAP \times 100}{PaO_2} \), used to quantify oxygenation difficulty and severity of hypoxemic respiratory failure.
Oxygen index incorporates inspired oxygen concentration, mean airway pressure, and arterial oxygen tension into a single value. It is used to describe the degree of support required to achieve a given PaO2.
A rising oxygen index indicates that progressively greater FiO2 and airway pressure support are required to maintain arterial oxygenation. Lower values generally reflect more efficient oxygen transfer at lower support settings.
As a general teaching framework, oxygen index values below about 5 are often relatively reassuring, 5 to 10 suggest increased support needs, 10 to 20 reflect significant oxygenation impairment, and values above 20 indicate severe oxygenation difficulty. Specific clinical thresholds vary by population and institutional use.
Oxygen index should be interpreted with the ventilator mode, lung recruitment state, hemodynamics, disease process, and the broader clinical picture. It is especially useful for trending severity over time rather than as a stand-alone decision point.