Horowitz index

In 1974, Joel H. Horovitz first described the Horovitz Index named after him (Horovitz 1974).

A Horowitz index is the calculation of the oxygenation index (Herold 2020). It is used to assess transpulmonary oxygen transport (Oczenski 2008) and thus provides information about the ability of the lungs to saturate the blood flowing through them with oxygen (Michels 2010).

The Horowitz index is calculated from the formula: O2 = paO2 / FiO2, where (PaO2) stands for the arterial oxygen partial pressure and (FiO2) for the fraction of inhaled oxygen (Herold 2020).

The normal value is > 450 mmHg, a pathological value is defined as < 350 mmHg. In an ALI (acute lung injury), for example, values of < 300 mmHg and in an ARDS (acute respiratory distress syndrome) < 200 mmHg are found (Oczenski 2008).

The Horowitz index is of great importance with regard to hypoxemia due to diffusion disorders or increased shunt volume (Köhler 2010). Otherwise, Köhler considers the index to be rather critical, as pathophysiological correlations could be obscured by the quotient or incorrect conclusions could be drawn as a result.

ECMO therapy:

The Mannheim ECMO algorithm represents an indication for ECMO therapy. It is also based on the Horowitz Index:

Horowitz index: Measure:

- 100 - 200 mmHg = contact ECMO center

- < 100 mmHg = arrange for transfer

- 50 - 100 mmHg = consider ECMO

- < 50 mmHg = immediate criterion for ECMO (Kuhlen 2003)

Differentiation between ARDS and ALI:

The differentiation between ARDS (Acute Respiratory Distress Syndrome) and the milder form ALI (Acute Lung Injury) is also based on the Horowitz Index. If this is < 300, it is referred to as ALI. Only from a value < 200 is it referred to as ARDS (Hecker 2012).

Marker for mortality:

The Horowitz index also serves as a marker for mortality in patients with cardiogenic shock. With an index of < 126, the 30-day mortality rate was 1.8 times higher than with an index > 126 (Scherer 2021).

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