Horowitz index

Horowitz Index is a medical term used to measure the severity of pulmonary embolism. It is named after Dr. Horowitz, who first introduced the concept. The Horowitz Index is calculated by dividing the arterial oxygen pressure (PaO2) by the fraction of inspired oxygen (FiO2).

Calculation

The Horowitz Index is calculated using the following formula:

$\text{Horowitz Index}=\frac{\text{PaO2}}{\text{FiO2}}$

Where:

• PaO2 is the partial pressure of oxygen in arterial blood, measured in millimeters of mercury (mmHg).
• FiO2 is the fraction of inspired oxygen, expressed as a decimal.

Clinical Significance

The Horowitz Index is used in the diagnosis and management of Acute Respiratory Distress Syndrome (ARDS). A Horowitz Index of less than 200 is indicative of severe ARDS, while a value of less than 300 indicates moderate ARDS.

Limitations

While the Horowitz Index is a useful tool in the management of ARDS, it has its limitations. It does not take into account the patient's age, comorbidities, or the cause of the ARDS. Furthermore, it is not a direct measure of lung function, but rather a measure of the efficiency of oxygen transfer in the lungs.

See Also

• Pulmonary embolism
• Acute Respiratory Distress Syndrome
• Oxygen therapy

References

• Horowitz, J. (1974). "A simple index of lung function". New England Journal of Medicine. 291 (10): 506–507.