Oxygen Saturation Index Calculator

About this calculator

The Oxygen Saturation Index (OSI) is calculated as (FiO2 × mean airway pressure × 100) ÷ SpO2, giving clinicians a way to assess how severely impaired a patient's oxygenation is using only non-invasive measurements — pulse oximetry and ventilator settings — instead of requiring an arterial blood gas draw to get PaO2 for the more traditional oxygenation index (OI).

Neonatal and pediatric intensivists use OSI most often, since arterial lines are harder to place and maintain in small patients, tracking OSI over time to gauge the severity of conditions like acute respiratory distress syndrome (ARDS) and to guide decisions on escalating respiratory support such as high-frequency oscillatory ventilation or extracorporeal membrane oxygenation (ECMO), with rising OSI trends signaling worsening lung function.

This calculator takes your patient's FiO2, mean airway pressure and SpO2 values, and returns the calculated Oxygen Saturation Index.