Home › Pulmonary & Critical Care › OI

Oxygenation Index (OI)

Oxygenation index = (mean airway pressure × FiO₂ % ) ÷ PaO₂. In ventilated children (PALICC 2015), OI 4–8 is mild, 8–16 moderate and ≥16 severe pediatric ARDS; in neonates, OI >40 is a traditional ECMO threshold.

Mean airway pressure (cmH₂O)
FiO₂ (% or fraction) (%)
PaO₂ (arterial) (mmHg or kPa)

—

Interpretation

Result	Meaning
<4	Below PARDS threshold
4 to <8	Mild PARDS
8 to <16	Moderate PARDS
≥16	Severe PARDS
>40 (neonates)	Traditional ECMO criterion

Formula

OI = (mean airway pressure cmH₂O × FiO₂ %) ÷ PaO₂ mmHg

Clinical pearls

Unlike P/F ratio, OI accounts for the ventilator pressure needed to achieve oxygenation.
When no arterial line is available, the oxygen saturation index OSI = (MAwP × FiO₂ × 100) ÷ SpO₂ can be used (SpO₂ ≤97%).

Examples

oxygenation index mean airway pressure 15 fio2 60% pao2 60 OI for MAP 20 cmH2O, FiO2 1.0, PaO2 8 kPa

FAQ

What is a normal oxygenation index?

Healthy lungs give an OI well under 4; OI ≥4 in a ventilated child meets PALICC oxygenation criteria for pediatric ARDS.

What OI suggests ECMO?

In neonates with hypoxemic respiratory failure, a persistent OI above about 40 has traditionally prompted ECMO referral.

Evidence

Pediatric Acute Lung Injury Consensus Conference Group. Pediatric acute respiratory distress syndrome: consensus recommendations. Pediatr Crit Care Med 2015;16:428–39.

Pulmonary & Critical Care · Reviewed 2026-10-14 · Methodology