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Oxygenation index (OI) and oxygen saturation index (OSI)

Also called OI, OSI, PARDS severity, PALICC-2

Mean airway pressure-adjusted oxygenation indices with PALICC-2 paediatric ARDS severity bands for invasively ventilated children.

cmH₂O
%

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Formula and scoring

OI = mean airway pressure (cmH₂O) × FiO₂ (%) ÷ PaO₂ (mmHg). OSI = mean airway pressure × FiO₂ (%) ÷ SpO₂. PALICC-2: OI < 16 or OSI < 12 mild/moderate; OI ≥ 16 or OSI ≥ 12 severe.

Exam and ward pearls

  • OI accounts for ventilator pressure, unlike P/F – the same P/F at higher mean airway pressure means sicker lungs.

When not to rely on it

  • FiO₂ enters as a percentage (60, not 0.6). PALICC-2 bands apply to invasively ventilated children; adult ARDS uses P/F or S/F.

Source

  1. Emeriaud G, et al. Executive summary of the Second International Guidelines for the Diagnosis and Management of Pediatric Acute Respiratory Distress Syndrome (PALICC-2). Pediatr Crit Care Med. 2023;24(2):143-68. doi:10.1097/PCC.0000000000003147 · PMID 36661420

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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