Breathing and ventilation
Oxygenation index (OI and OSI)
OI, OSI, P/F and S/F ratios, with PARDS severity from PALICC-2.
For education. Check against your unit's guidance and a second clinician before use.
%
From the ventilator. Needed for OI and OSI.
cmH₂O
OSI and S/F only count when SpO₂ is 97% or less.
%
Enter FiO₂ and a PaO₂ or SpO₂.
Before you use this
- Diagnosing PARDS also needs new lung changes on imaging, onset within 7 days of a known cause, and hypoxaemia not fully explained by heart failure or fluid overload.
- On non-invasive support (full face mask CPAP or BiPAP of at least 5 cmH₂O), PALICC-2 uses P/F of 300 or less, or S/F of 250 or less.
How this is calculated
- OI = (FiO₂ × mean airway pressure in cmH₂O × 100) ÷ PaO₂ in mmHg
- OSI = (FiO₂ × mean airway pressure in cmH₂O × 100) ÷ SpO₂
- P/F ratio = PaO₂ ÷ FiO₂; S/F ratio = SpO₂ ÷ FiO₂ (FiO₂ as a fraction, e.g. 0.4)
- kPa are converted to mmHg by multiplying by 7.5.
- PALICC-2 severity for invasively ventilated children: mild to moderate if OI 4 to under 16 (or OSI 5 to under 12); severe if OI 16 or more (or OSI 12 or more).
Sources
Checked by PICUlearn, 21 Sept 2026.