PaO₂/FiO₂ Ratio (P/F Ratio) — Oxygenation Index

Calculates the ratio of arterial oxygen tension to fraction of inspired oxygen (PaO₂/FiO₂), the primary metric for classifying ARDS severity and assessing oxygenation failure in mechanically ventilated and spontaneously breathing patients. The P/F ratio provides a normalized measure of oxygenation independent of the level of oxygen supplementation.