bilevel (non‐invasive ventilation or CPAP) ≥ 5 cmH2O via full‐face mask: PaO2/FiO2 ≤ 300 mmHg or SpO2/FiO2 ≤ 264;
mild ARDS (invasively ventilated): 4 ≤ OI < 8 or 5 ≤ OSI < 7.5;
moderate ARDS (invasively ventilated): 8 ≤ OI < 16 or 7.5 ≤ OSI < 12.3;
severe ARDS (invasively ventilated): OI ≥ 16 or OSI ≥ 12.3.