Oxygenation index

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The oxygenation index (OI) is a simple number doctors use in intensive care to see how well someone is oxygenating. It combines FiO2 (the fraction of inspired oxygen), MAP (mean airway pressure), and PaO2 (arterial oxygen). The formula is OI = (FiO2 × MAP) / PaO2 × 100. A lower OI means better oxygenation, since improving oxygen levels or lowering FiO2 and MAP lowers the value. In newborns on life support, a high OI can signal the need for ECMO; for example, an OI above 40 is often used as a threshold.