Oxygen Saturation Index (OSI)
Independent clinical validation: pending
Two independent clinical validators will be named here once review is complete.
How it is calculated
OSI = (mean airway pressure × FiO₂ × 100) ÷ SpO₂, with MAP in cm H₂O, FiO₂ as a fraction (0.21–1.0), and SpO₂ as a percent; the ×100 factor compensates for FiO₂ being a fraction, so the PALICC rendering MAP × FiO₂% ÷ SpO₂ yields the same number. OSI is only interpretable when SpO₂ ≤ 97% — values above 97% are rejected as out-of-range and never scored. The raw index is banded against the PALICC-2 (2023) invasive-ventilation cutoffs: OSI < 5 is below the oxygenation criterion, 5 ≤ OSI < 12 is mild–moderate, and OSI ≥ 12 is severe. Bands are matched on the unrounded value even though the index is displayed to one decimal place.
Limitations and notes
OSI is the mean airway pressure times FiO₂ times 100, divided by the pulse-oximeter oxygen saturation (SpO₂) — higher OSI means a worse oxygenation defect. It substitutes SpO₂ for the arterial PaO₂ used by the Oxygenation Index (OI), sparing an arterial draw, and is defined only on positive-pressure ventilation, where a mean airway pressure exists (conventional IMV or HFOV). OSI is valid only when SpO₂ ≤ 97%: above ~97% the oxyhemoglobin dissociation curve plateaus and SpO₂ no longer tracks PaO₂, so OSI cannot discriminate severity (Thomas 2010; PALICC-2) — SpO₂ > 97% is rejected as out-of-range, never scored. Interpretation bands here are the PALICC-2 (2023) two-tier scheme for invasively ventilated children: the oxygenation criterion is OSI ≥ 5 and severe is OSI ≥ 12. PALICC 2015 used a three-tier scheme — mild (5 ≤ OSI < 7.5), moderate (7.5 ≤ OSI < 12.3), severe (OSI ≥ 12.3) — and PALICC-2 collapsed the two lower tiers into mild–moderate and moved the OSI severe cutoff from 12.3 (2015) to 12 (2023); this implementation applies the PALICC-2 (2023) edition. The ×100 factor exactly compensates for FiO₂ being a fraction; the PALICC table rendering MAP × FiO₂% / SpO₂ gives the same number — applying both or neither is a 100× error. [NEEDS SOURCE]: the map_awp (5–50 cmH₂O) numeric limits are engineering input-validation bounds, not values from a specific publication. OSI classifies a physiologic defect; it is not an individual-patient outcome prediction.
Accepted input ranges
- Mean airway pressure (MAP) — 5–50 cmH2O
- Fraction of inspired oxygen (FiO₂) — 0.21–1 fraction
- Pulse oximeter oxygen saturation (SpO₂) — 1–97 %
References
- Emeriaud G, López-Fernández YM, Iyer NP, et al; Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2) of the PALISI Network. 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):143–168.PMID 36661420DOI 10.1097/PCC.0000000000003147
- Pediatric Acute Lung Injury Consensus Conference Group. Pediatric acute respiratory distress syndrome: consensus recommendations from the Pediatric Acute Lung Injury Consensus Conference. Pediatr Crit Care Med. 2015;16(5):428–439.PMID 25647235DOI 10.1097/PCC.0000000000000350
- Thomas NJ, Shaffer ML, Willson DF, Shih MC, Curley MAQ. Defining acute lung disease in children with the oxygenation saturation index. Pediatr Crit Care Med. 2010;11(1):12–17.PMID 19561556DOI 10.1097/PCC.0b013e3181b0653d
- Slaughter J, Sites J, Ballard H, Bauer J, Schadler A, Severyn N. Comparison of the oxygenation index and the oxygen saturation index as clinical indicators for neonatal ECMO. Front Pediatr. 2025;13:1586985.PMID 40630719DOI 10.3389/fped.2025.1586985
Version and changelog
v1.0.0 · Respiratory
- 2026-07-25 v1.0.0 — Initial release: OSI split out from the former OI/OSI score, with PALICC-2 (2023) two-tier severity bands and the SpO₂ ≤ 97% OSI validity guard.