Horowitz index
Pulmonology
Also known as: PaO2/FiO2 ratio · P/F ratio · Horowitz-Index · Horowitz-Quotient · PaO2/FiO2-Quotient · Horowitz indeksi · PaO2/FiO2 oranı · Horowitz index (PaO2/FiO2 ratio)
What it is for
The Horowitz index (also PaO2/FiO2 ratio or P/F ratio) is the arterial partial pressure of oxygen (PaO2) divided by the fraction of inspired oxygen (FiO2, written as a decimal, e.g. 0.21 for room air). A lower value means worse oxygenation for the oxygen given.
Classification
| Category | Description |
|---|---|
| Units | usually PaO2 in mmHg; in kPa the value is about 7.5 times smaller (300 mmHg ≈ 40 kPa). |
| ARDS thresholds (Berlin and global definition, PEEP ≥5 cmH2O) | mild >200 to ≤300 mmHg; moderate >100 to ≤200 mmHg; severe ≤100 mmHg. |
| Surrogate | the SpO2/FiO2 ratio (pulse oximetry) may replace it when no blood gas is available, valid only with SpO2 ≤97%; the global ARDS definition uses SpO2/FiO2 ≤315 as its threshold. |
| Altitude | above 1000 m the global ARDS definition adjusts the ratio by multiplying it by barometric pressure / 760. |
| Not the same as | the oxygenation index (OI), which also includes mean airway pressure. |
Source
A New Global Definition of Acute Respiratory Distress Syndrome
Am J Respir Crit Care Med 2024;209:37-47 (Matthay MA et al.)
DOI: 10.1164/rccm.202303-0558WS
PMID: 37487152
- Edition
- Definition as used in the 2023 global ARDS definition and the Berlin definition (2012)
- Checked on
Summary of the published classification in our own words. Not a substitute for the original publication.
A question about this classification?
Medelix answers clinical questions from guidelines and studies – every statement with its source.