Oxygenation Index Calculator

The oxygenation index, or OI, describes how much oxygen concentration and airway pressure are required to achieve a measured arterial oxygen level in a mechanically ventilated patient. The formula is FiO2 multiplied by mean airway pressure, multiplied by 100, then divided by PaO2. Because mean airway pressure is included, OI reflects the pressure cost of oxygenation and provides different information from the PaO2 to FiO2 ratio alone. A higher result indicates that more respiratory support is being used for the achieved PaO2. PaO2 is the arterial partial pressure of oxygen from a blood gas and is entered in mmHg. FiO2 is the fraction of inspired oxygen set on the ventilator and must be entered as a decimal, such as 0.40 for 40 percent. Mean airway pressure, or MAP, is the average pressure across the respiratory cycle and is usually reported by the ventilator in cmH2O. All three values should represent approximately the same clinical moment because changes in settings or physiology can quickly alter the result. General educational ranges often describe OI below 5 as normal efficiency, 5 to below 15 as mild impairment, 15 to below 25 as moderate impairment, and 25 or more as severe impairment. Thresholds and treatment implications differ by population, institution, disease, and guideline. Neonatal and pediatric teams may use serial OI values in decisions about escalation or extracorporeal support, while adult ARDS assessment often emphasizes other measures as well. A single value should never trigger treatment without clinical interpretation. The index can change because of PaO2, FiO2, MAP, or any combination of them. Increasing pressure may improve PaO2 but can still raise OI if oxygenation does not improve proportionally. This is why trends measured under documented conditions are usually more informative than isolated calculations. Lung compliance, hemodynamics, recruitment, positioning, airway resistance, and blood sampling quality can also affect the clinical picture. This calculator supports arithmetic and education; it does not recommend ventilator changes or diagnose respiratory failure. Mechanical ventilation and severe hypoxemia require trained clinical management. Verify source measurements, follow local protocols, and review unexpected or worsening results promptly with the responsible critical care team. The safest use is to document the calculation alongside the underlying settings and interpret it with the patient's complete respiratory and hemodynamic status.