Horovitz quotient

The Horovitz quotient (synonyms: Oxygenation index according to Horovitz , Horovitz index ) is a parameter used mainly in intensive care medicine for lung function , with which the extent of damage to the lungs can be described. It can be determined by a blood gas analysis .

calculation

It is defined as the quotient of the arterial oxygen partial pressure and the concentration of oxygen in the inhaled air (inspiratory oxygen concentration FiO ₂ ).

${\ displaystyle {\ text {Horovitz quotient}} = {\ frac {paO_ {2}} {F_ {i} O_ {2}}}}$

In the English-speaking world ( oxygenation index ), the average ventilation pressure is also included as a factor in this index.

Example: The patient has a paO ₂ of 100 mmHg in the arterial blood gas analysis (BGA). It is oxygenated with 50% oxygen. This results in a quotient of 100 mmHg / 0.5 = 200 mmHg.

interpretation

For people with healthy lungs, the Horovitz quotient is usually between 350 mmHg and 450 mmHg , depending on age (example for a person with healthy lungs in room air: paO ₂ = 90 mmHg; FiO ₂ = 0.21 -> Horovitz quotient = 90 mmHg / 0.21 = 429 mmHg )

The paO ₂ is usually easy to determine using arterial or approximately capillary BGA. In contrast, FiO ₂ can only be measured using a ventilator. If the Horovitz quotient is to be determined in a spontaneously breathing patient, any existing oxygen insufflation should be interrupted for some time so that: FiO ₂ = 0.21 (oxygen concentration in room air)

A value below 300 to 200 mmHg is an indication of slight lung damage, a value between 200 and 100 mmHg for moderate lung damage and a value below 100 mmHg for severe lung damage. This new gradation has been in effect since 2012 and was set out in the Berlin classification . In this, the old classification from 1994, which defined a Horovitz index between 300 and 200 mmHg as acute lung injury (ALI), was replaced.

Individual evidence

Clinical guidelines for intensive care medicine, 6th edition 2005, p. 101

↑ Luterman, A. et al .: Withdrawal from positive end-expiratory pressure. Surgery. 1978 Mar; 83 (3): 328-32.
↑ Ranieri, VM, et al .: Acute respiratory distress syndrome: the Berlin Definition. JAMA. 307 (23): p. 2526-33.

[1] Luterman, A. et al .: Withdrawal from positive end-expiratory pressure. Surgery. 1978 Mar; 83 (3): 328-32.

[2] Ranieri, VM, et al .: Acute respiratory distress syndrome: the Berlin Definition. JAMA. 307 (23): p. 2526-33.