Patients with exacerbation in chronic obstructive pulmonary disease (COPD) or asthma do not have interstitial syndrome

Hence, in acute admitted patients with dyspnoea, LUS can be used as a tool to differentiate between cardiogenic and pulmonary causes of dyspnoea

In an emergency department, the by far most common cause for interstitial syndrome is cardiogenic pulmonary edema

Hence, in this setting FLUS with signs of interstitial syndrome, one should suspect cardiogenic pulmonary edema

In patients who have been admitted for a while in an intensive care unit (ICU), many diseases and conditions may cause interstitial syndrome

Hence, LUS with signs of interstitial syndrome, is a less specific finding in this setting

In patients with acute respiratory failure to an intensive care unit, the finding of interstitial syndrome is however most often due to cardiogenic pulmonary edema

Despite these limitations FLUS can still as an efficient tool to rule-out these conditions

Supplementary use of other kinds of point-of-care sonography such as focus assessed transthoracic echocardiography (FATE) can be of further use to differentiate between cardiogenic and non-cardiogenic causes of interstitial syndrome

The finding of interstitial syndrome is a powerful diagnostic tool in diagnosis of pulmonary edema

FLUS is very sensitive for detecting interstitial oedema. Consequently, a FLUS examination with no signs of interstitial syndrome can be used to rule out conditions such as cardiogenic pulmonary oedema

Any condition with universally increased density in the lungs may cause universally multiple B-lines and therefore the interstitial syndrome

In adults the following conditions have been described as causes of interstitial syndrome:

– Cardiogenic pulmonary edema
– Non-cardiogenic pulmonary edema (e.g. fluid overload, renal failure)
– Interstitial lung diseases
– Viral pneumonia
– Bacterial pneumonia
– ARDS
– Acute chest syndrome
– Drowning / near-drowning
– Lung contusion

Using the scanning technique described in the examination technique module, with two anterior, two lateral and three posterior scanning zones, the criteria for IS is the presence of both of the following:*

1: A positive scanning zone is defined by the presence of three or more B-lines in a longitudinal plane between two ribs

2: When scanning the anterior and lateral zones, two or more of the zones have to be positive on each side

* Volpicelli, G., et al., “International evidence-based recommendations for point-of-care lung ultrasound”, Intensive Care Med, 2012, 38(4): p. 577-91

Multiple B-lines can in some diseases be seen almost universally when scanning both lungs. This finding is often referred to as the interstitial syndrome (IS)

As an example of a setting where focal B-lines still can be clinical useful, would be in a patient with clinical suspicion of pneumonia

A lobar pneumonia with resulting increased density of the lobe, with corresponding B-lines would confirm the clinical suspicion

If the density further increases and the lung tissue is filled with fluid and secretions the pattern will change to that of lung consolidation

The finding of focal B-lines is not neccesarily a sign of lung disease

Still, if used together with patient history and physical findings in clinical examination, the finding of focal B-lines may still be useful

The occurrence of multiple, isolated B-lines can both be normal and a pathological sign

In studies approx. 25% of patients with normal chest imaging have multiple B-lines in the lower lateral intercostal space

The presence of focal areas with multiple B-lines can also be seen in any disease with a localised increased density of the lung tissue such as pneumonitis, atelectasis, pulmonary contusion, pulmonary embolism, pleural disease and malignancy