PaO₂/FiO₂ ratio (P/F)
- Category: Respiratory
- Version: v1.1.1
- Reviewed: Reviewed 6 Sep 2026
- Validation: Validation pending
P/F = PaO₂ in mmHg ÷ FiO₂ as a fraction from 0.21 to 1.0. A PaO₂ entered in kPa converts at 1 kPa = 7.50062 mmHg. The ratio is displayed rounded to a whole number, but the bands are matched against the unrounded ratio. Bands follow the Berlin (2012) ARDS severity strata: ≤ 100 severe, > 100 to ≤ 200 moderate, > 200 to ≤ 300 mild, and > 300 above the ARDS oxygenation threshold.
The Berlin bands are adult bands and require PEEP or 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.
| Result | Interpretation |
|---|---|
| ≤ 100 | ≤ 100 — Corresponds to the severe category in the Berlin ARDS definition (with PEEP or CPAP ≥ 5 cm H₂O). |
| >100 to 200 | > 100 to ≤ 200 — Corresponds to the moderate category in the Berlin ARDS definition (with PEEP or CPAP ≥ 5 cm H₂O). |
| >200 to 300 | > 200 to ≤ 300 — Corresponds to the mild category in the Berlin ARDS definition (with PEEP or CPAP ≥ 5 cm H₂O). |
| > 300 | > 300 — Above the Berlin ARDS oxygenation threshold. Interpret in the full clinical context. |
References
- ARDS Definition Task Force; Ranieri VM, et al. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526–2533.PMID 22797452DOI 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 36661420DOI 10.1097/PCC.0000000000003147
Reproduction rights
Freely reproducible.Arithmetic ratio; Berlin/PALICC-2 numeric thresholds are facts, not copyrightable expression (pf-sf.md IP status).
Independent clinical validation: pending
Two independent clinical validators will be named here once review is complete.
- 2026-08-10v1.0.0Initial releaseInitial published text.
- 2026-09-03v1.1.0Formula correctionGrades the exact PALICC-2 and Berlin cut-points correctly. The arithmetic behind these indices is binary and the thresholds are decimal, so a value that IS the cut-point did not compute to it: an OI of exactly 16 evaluates to 15.999999999999998 from a mean airway pressure of 24, FiO2 0.60 and PaO2 90; an OSI of exactly 12 to 11.999999999999998; a P/F of exactly 100 to 100.00000000000001. Compared raw, all three placed the patient one band TOO MILD, the under-triage direction and never the reverse, while the page printed the rounded figure beside the milder label and appeared to contradict itself. The band matcher now treats a value within a millionth of a millionth of a bound as being on it, which is four orders above the floating-point residue and far below any difference a clinician draws. NO OTHER VALUE MOVES: a number genuinely below a cut-point still bands below it. Found 2026-09-03 by an independent recompute of every calculator from its published source; the same defect as the PRISM 14-day age term, in a different unit. On this score a patient at the Berlin severe threshold of 100, or at the moderate threshold of 200, was graded one band milder.
- 2026-09-06v1.1.1ClarificationAdded a one-line description for the catalogue card. No rule, threshold or reference changed.
Other respiratory scores
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.