Oxygen Saturation Index Calculator

About this calculator

The Oxygen Saturation Index (OSI) is a non-invasive substitute for the traditional Oxygenation Index, calculated as (FiO₂ × mean airway pressure × 100) divided by SpO₂. It was developed because the classic Oxygenation Index needs an arterial blood gas to get PaO₂, which requires an arterial line — something not every ventilated patient, especially children, has in place.

Because pulse oximetry (SpO₂) is continuous and non-invasive, OSI lets clinicians in pediatric and neonatal intensive care grade the severity of respiratory failure and monitor it in real time without repeated blood draws. It is incorporated into the Pediatric Acute Lung Injury Consensus Conference (PALICC) criteria for grading ARDS severity in children, with rising OSI thresholds marking mild, moderate and severe disease.

This calculator takes FiO₂, mean airway pressure and SpO₂ and returns the OSI along with its corresponding severity grade.