PaO₂/FiO₂ ratio (P/F)

Independent clinical validation: pending

Two independent clinical validators will be named here once review is complete.

Validator slot open 1

Validator slot open 2

How it is calculated

P/F ratio = PaO₂ ÷ FiO₂, with PaO₂ in mmHg (kPa is converted using 1 kPa = 7.50062 mmHg) and FiO₂ as a fraction from 0.21 to 1. A single dimensionless value is returned; it is displayed rounded to a whole number, but the interpretation bands are matched against the unrounded ratio. Bands follow the Berlin (2012) adult ARDS severity strata: ≤ 100 severe, > 100 to ≤ 200 moderate, > 200 to ≤ 300 mild, and > 300 above the ARDS oxygenation threshold.

Limitations and notes

The Berlin bands are validated in adults and require PEEP/CPAP ≥ 5 cm H₂O. In children, PALICC-2 grades invasive-ventilation severity by oxygenation index (OI/OSI) rather than P/F, and uses P/F on non-invasive support. Berlin mortality figures are population associations, not individual predictions.

Accepted input ranges

Arterial oxygen tension (PaO₂) — 10–700 mmHg
Fraction of inspired oxygen (FiO₂) — 0.21–1 fraction

References

ARDS Definition Task Force; Ranieri VM, et al. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526–2533.PMID 22797452 DOI 10.1001/jama.2012.5669
Emeriaud G, et al. Executive Summary of the Second International Guidelines for the Diagnosis and Management of Pediatric ARDS (PALICC-2). Pediatr Crit Care Med. 2023;24(2):143–168.PMID 36661420 DOI 10.1097/PCC.0000000000003147

Version and changelog

v1.0.0 · Respiratory

2026-07-25 v1.0.0 — Initial release: P/F ratio with Berlin severity bands.

Important

For use by qualified health professionals as an informational and educational aid. It supports clinical judgment and does not replace it. Verify every result independently before making a clinical decision. This is not a medical device.