Horowitz index
| Horowitz index | |
|---|---|
| LOINC | 50982-8, 50984-4, 50983-6, 50985-1, 50986-9 |
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.[1] It is also utilized to assess pulmonary disease course and guide therapy and in the evaluation of donor lungs in lung transplantation.[1] 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.
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.[1]
The Horowitz index plays a major role in the diagnosis of acute respiratory distress syndrome (ARDS). Three severities of ARDS are categorized based on the degree of hypoxemia using the Horowitz index, according to the Berlin definition.[2]
History
The Horowitz index was first proposed in a 1974 paper by Joel H. Horovitz and two co-authors, Charles Carrico and G. Tom Shires.[1][3] The reason for the spelling with w is unclear.
In this study, the authors utilized the PaO2/FiO2 ratio to compare patients treated with varying inspired oxygen concentrations. One of the major reasons for the use of this ratio is that it is simple to calculate in critically ill patients. These patients often have arterial blood gas samples taken, which allows providers to measure the PaO2.
Uses
The Horowitz ratio has used in scoring systems to grade severity in diseases such as acute respiratory distress syndrome (ARDS), sepsis, and community-acquired pneumonia.[2]
See also
References
- ^ a b c d John R. Feiner, Richard B. Weiskopf (2017). "Evaluating Pulmonary Function: An Assessment of PaO2/FiO2". Critical Care Medicine. 45 (1): e40 – e48. doi:10.1097/CCM.0000000000002017.
- ^ a b The ARDS Definition Task Force* (2012-06-20). "Acute respiratory distress syndrome: The berlin definition". JAMA. 307 (23): 2526–2533. doi:10.1001/jama.2012.5669. ISSN 0098-7484. PMC 3408735. PMID 22797452.
- ^ Joel H. Horovitz, Charles J. Carrico and G. Tom Shires (March 1974). "Pulmonary Response to Major Injury". Archives of Surgery. 108 (3): 349–355.
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