Definition
Pleural fluid collection refers to any accumulation of liquid in the pleural cavity.

Causes
Pleural fluid collection can arise from multiple conditions, including hydrothorax (effusion/transudate), hemothorax (blood), pyothorax (pus), etc.

The most frequent causes are pleural effusion and hemothorax.

Hemothorax is predominantly caused by trauma to the thorax, whereas the causes of pleural effusion are multiple – including heart failure, infection, and malignancies.

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

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:

What is a lung point?
In pneumothorax, the edge of the collapsed lung will appear as a “lung point”.

The lung point represents the transition zone between the area of air-filled pleura and the reunion of the pleural blades.

The lung point moves back and forth in synchrony with the patient’s breathing.

Anterior to the lung point, with air-filled pleura, no lung sliding is seen.

Posterior to the lung point, with contacting pleural blades, normal lung sliding is seen.

Right at the lung point both can be observed as seen on the image to the right.

Lung point and pneumothorax
Lung point is diagnostic of pneumothorax.

Can pneumothorax be confirmed or excluded?

The lung ultrasound signs Lung sliding/lung pulse, B-lines and Lung point are used in diagnosing or excluding pneumothorax. These signs are explained in the following topics.

Use the signs:
Ruling out pneumothorax:

Lung sliding
Lung sliding is a horizontal movement of the bright pleural line in synchrony with the respiratory cycle indicating sliding movement of the visceral pleura against the parietal pleura.

Lung pulse
Lung pulse is a variation of the same phenomenon, but is caused by projection of the heart beats through the lung tissue, causing small frequent movements of the pleural blades.
Lung pulse is only clearly seen when there is no respiration/ventilation.

Pathologies
Absence of lung sliding and lung pulse is seen in any condition causing the visceral and the parietal pleura to be either separated (e.g. pneumothorax) or joined (e.g. pleurodesis).

Presence of lung sliding or lung pulse is 100% specific and rules out pneumothorax at the location of the transducer.

What are B-lines?
B-lines are hyperechoic, laser-like, vertical artefacts that visually originate from the pleural line and continue to the bottom edge of the screen without fading in intensity.

B-lines and pneumothorax
Visualisation of the B-line artefact is only possible when there is no air between the two pleural blades and they are in contact with each other.

The finding of one or more B-lines can be used to rule out pneumothorax.

B-lines also play a role in diagnosing pulmonary edema (discussed later).

Definition
Pneumothorax is the presence of air in the pleural space.

Facts
Loss of contact between the visceral pleura and the parietal pleura and a gradual collapse of the affected lung can result from a continuous leak of air into the pleural space.

The application of ultrasonography allows rapid evaluation for pneumothorax and the sensitivity and specificity are higher than for conventional x-ray.