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] Overall, it is useful for evaluating the extent of damage to the lungs.[1] 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 (i.e., 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]
History
editThe Horowitz index was first proposed in a 1974 paper by Joel H. Horovitz and two co-authors, Charles Carrico and G. Tom Shires.[1][2] 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.[2] 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
editThe Horowitz ratio has used in scoring systems to grade severity in diseases such as acute respiratory distress syndrome (ARDS), sepsis, and community-acquired pneumonia.[3][4][5][6][7][8]
ARDS
editThe Horowitz index plays a major role in the diagnosis of ARDS.[3] Three severities of ARDS are categorized based on the degree of hypoxemia using the Horowitz index, according to the Berlin definition. The Horowitz index also correlates to mortality in ARDS.
| ARDS Severity | PaO2/FiO2 | Mortality |
|---|---|---|
| Mild | 200-300 | 27% |
| Moderate | 100-200 | 32% |
| Severe | <100 | 45% |
*Table adapted from Ranieri et al.[3]
Sepsis
editThe Horowitz index is used in multiple severity scoring systems in sepsis. These include the SOFA, APACHE IV, SAPS-II and SAPS-III scoring systems.[4][5][6][7]
Community-Acquired Pneumonia
editIn patients with community-acquired pneumonia, the Horowitz index is used in the SMART-COP score. This score predicts the need for additional respiratory support in community-acquired pneumonia.[8] This score can help medical providers determine a patient's need for admission to an intensive care unit (ICU) or further intensive respiratory support or vasopressor medications. Further support or admission to the ICU should be considered in patients <50 years old with a Horowitz index <333 mmHg or >50 years old with Horowitz index <250 mmHg.[8]
See also
editReferences
edit- ^ 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. PMID 27618274. S2CID 10481304.
- ^ a b Joel H. Horovitz, Charles J. Carrico and G. Tom Shires (March 1974). "Pulmonary Response to Major Injury". Archives of Surgery. 108 (3): 349–355. doi:10.1001/archsurg.1974.01350270079014. PMID 4813333.
- ^ a b c ARDS Definition Task Force; Ranieri, V. M.; Rubenfeld, G. D.; Thompson, B. T.; Ferguson, N. D.; Caldwell, E.; Fan, E.; Camporota, L.; Slutsky, A. S. (2012-06-20). "Acute Respiratory Distress Syndrome: The Berlin Definition". JAMA. 307 (23): 2526–2533. doi:10.1001/jama.2012.5669. ISSN 0098-7484. PMID 22797452.
- ^ a b Vincent, J. -L.; Moreno, R.; Takala, J.; Willatts, S.; De Mendonça, A.; Bruining, H.; Reinhart, C. K.; Suter, P. M.; Thijs, L. G. (July 1996). "The SOFA (Sepsis-related Organ Failure Assessment) score to describe organ dysfunction/failure: On behalf of the Working Group on Sepsis-Related Problems of the European Society of Intensive Care Medicine (see contributors to the project in the appendix)". Intensive Care Medicine. 22 (7): 707–710. doi:10.1007/BF01709751. ISSN 0342-4642.
- ^ a b Zimmerman, Jack E.; Kramer, Andrew A.; McNair, Douglas S.; Malila, Fern M. (May 2006). "Acute Physiology and Chronic Health Evaluation (APACHE) IV: Hospital mortality assessment for today's critically ill patients*". Critical Care Medicine. 34 (5): 1297–1310. doi:10.1097/01.CCM.0000215112.84523.F0. ISSN 0090-3493. PMID 16540951. S2CID 34985998.
- ^ a b Le Gall, J. R. (1993-12-22). "A new Simplified Acute Physiology Score (SAPS II) based on a European/North American multicenter study". JAMA: The Journal of the American Medical Association. 270 (24): 2957–2963. doi:10.1001/jama.270.24.2957. PMID 8254858.
- ^ a b Vazquez, Guillermo; Benito, Salvador; Rivera, Ricardo (2003). "Simplified Acute Physiology Score III: a project for a new multidimensional tool for evaluating intensive care unit performance". Critical Care. 7 (5): 345. doi:10.1186/cc2163. PMC 270708. PMID 12974964.
- ^ a b c Charles, Patrick G.P.; Wolfe, Rory; Whitby, Michael; Fine, Michael J.; Fuller, Andrew J.; Stirling, Robert; Wright, Alistair A.; Ramirez, Julio A.; Christiansen, Keryn J.; Waterer, Grant W.; Pierce, Robert J.; Armstrong, John G.; Korman, Tony M.; Holmes, Peter; Obrosky, D Scott (August 2008). "SMART-COP: A Tool for Predicting the Need for Intensive Respiratory or Vasopressor Support in Community-Acquired Pneumonia". Clinical Infectious Diseases. 47 (3): 375–384. doi:10.1086/589754. ISSN 1058-4838. PMID 18558884.