You have now learned how to:

Obtain the:

Can pleural fluid be confirmed or excluded?

The following signs confirm a pleural fluid collection:

Normal ultrasonographic image
The medial border of the pleural cavity being the thoracic spine and mediastinum is normally not seen with ultrasonography because the ultrasound waves do not travel through the aerated lung tissue.

When fluid is present
With pleural fluid replacing aerated lung tissue in the phrenicomediastinal recess, the mediastinum and the thoracic spine become visible and can be seen as a medial border of the cavity – above the diaphragm.

This is called the ‘spine sign’.

Visualising pleural fluid
In most cases, a pleural fluid collection is clearly visible as a black border just above the diaphragm, often with consolidation of the basal part of the lung.

Positioning is key
Remember that fluid follows gravity.

If no fluid is seen in a patient in the Trendelenburg position, fluid can still be hidden in the apical part of the pleural cavity – try repositioning the patient to a horizontal or semi-upright position.

Rule in
Pleural fluid collection can be ruled in by ‘spine sign’ or visible fluid.

Rule out
Significant amounts of fluid in the pleura can be ruled out by ‘lung curtain’ and absence of ‘spine sign’, when the patient is positioned correctly.

Remember that fluid is dependent upon gravity and is found at the lowest point accessible.

In a patient in the Trendelenburg position, the fluid is found in the apical part of the pleural cavity and not in the basal part above the diaphragm.

Where air is present, the image is obscured
In the normal aerated lung without pleural fluid, the lung is expanding in caudal direction with deep inspiration. The expanded lung interspaces between the transducer and the diaphragm making the diaphragm disappear in the ultrasound screen – this is called the ‘curtain sign’.

The curtain sign rules out significant amounts of pleural fluid in the phrenicocostal sinus.

With pleural fluid collection the consolidation of the lung and the fluid between the lung and the diaphragm prevent the lung curtain.

Not even in healthy patients can the curtain sign always be seen if the breathing is shallow.

Asking the patient to take a deep breath is often necessary when assessing for curtain sign.

What are B-lines?
As mentioned previously, B-lines are hyperechoic vertical artefacts visually originating from the pleural line that continue to the bottom edge of the screen.

B-lines represent air-water interfaces in the lung tissue closest to the pleura and single B-lines can be seen in healthy people especially in the basal part of the lungs.

B-lines and pulmonary edema
Pathological amounts of B-lines (> 2 in each intercostal view) are seen with any condition that causes increased water in the lung tissue and can be found localised in pneumonia etc.

In contrast to localised lung disease, pulmonary edema involves the lungs globally and bilaterally and multiple B-lines can therefore be found when pulmonary edema is present.

Are signs of pulmonary edema present or can pulmonary edema be excluded?

The following ultrasonographic signs are suggestive of pulmonary edema:

High sensitivity
Multiple B-lines (>2 in each intercostal view) in more than one view bilaterally is very sensitive of pulmonary edema (98-100%).

Specificity high, but not as high
Unfortunately, diffuse multiple B-lines can also be found in e.g. pulmonary fibrosis and ARDS, and the finding is thus less specific unless combined with other findings (i.e. signs of decreased left ventricular function and pleural fluid collection as discussed later).

However, the absence of multiple B-lines generally ‘rules out’ pulmonary edema.

Ok, I got it! But how to do the examination?
– Look at the video on the next page