Extravascular Lung Water Index (EVLW)
Pulmonary oedema is characterised by an accumulation of fluid in the interstitium of the lung tissue and/or the alveoli. This leads to impaired gas exchange and may even cause pulmonary failure. The amount of the pulmonary oedema can easily be quantified at the bedside by measuring the extravascular lung water index (ELWI).
The usual clinical signs of pulmonary oedema (white-out on the chest x ray, low oxygenation index, decreased lung compliance) are non-specific and only reliable later when the pulmonary oedema may already be advanced.
In the clinical routine, the interpretation of the chest x-ray is most often used to estimate the amount of pulmonary oedema at risk patients. This approach is very complex as the chest x-ray only gives a black & white density image of all components in the chest, including gas volume, blood volume, pleural effusion, bones, muscles, lung tissue, fat, skin oedema and also pulmonary oedema.
Extravascular Lung Water is indexed to the body weight in kg, written as the Extravascular Lung Water Index (ELWI). By indexing to the patient's predicted body weight (PBW), underestimation of lung water, particularly in obese patients, is avoided.
Fig. Examples of chest x rays that do not reflect the level of pulmonary oedema