Horowitz index
The Horowitz index or Horovitz index (also known as the Horowitz quotient or the P/F ratio) is a ratio used to assess lung function in patients, particularly those on ventilators. Overall, it is useful for evaluating the extent of damage to the lungs. The simple abbreviation as oxygenation can lead to confusion with other conceptualizations of oxygenation index.
| Horowitz index | |
|---|---|
| LOINC | 50982-8, 50984-4, 50983-6, 50985-1, 50986-9 |
The Horowitz index is defined as the ratio of partial pressure of oxygen in blood (PaO2), in millimeters of mercury, and the fraction of oxygen in the inhaled air (FiO2) — the PaO2/FiO2 ratio. This is calculated by dividing the PaO2 by the FiO2.
Example: patient who is receiving an FiO2 of .5 (ie, 50%) with a measured PaO2 of 60 mmHg has a PaO2/FiO2 ratio of 120.
In healthy lungs, the Horowitz index depends on age and usually falls between 350 and 450. A value below 300 is the threshold for mild lung injury, and 200 is indicative of a moderately severe lung injury. A value below 100 is a criterion for a severe injury.