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Int Lung, Effusion and Consolidation
To visualize pulmonary edema and effusion you need to use a probe that can penetrate deeper structures and the linear probe may not be your best fit. Use the curvilinear probe (1-8MHz) that allows you to visualize deeper structures at the expense of resolution. You could also use phase array transducers used in cardiac imaging (2-8MHz).
Interstitial Lung Disease and Pulmonary Edema
B-lines
B-lines are reverberation artifacts that appear as hyperechoic vertical lines that extend from the pleura to the edge of the screen without fading. These are vertical in orientation. A few B-lines less than or equal to 2 in each interrogation zone is considered normal. These lines move in synchrony with lung sliding.
These artifacts are characteristic of pulmonary edema or any process that infiltrates the interstitium of the lung. Their presence is strongly correlated with alveolar or interstitial abnormalities seen on CT scan.
We can appreciate B lines in the images below. On the left, multiple B-lines in a single scan segment. On the right, the curtain sign as described in the prior segment. If you look closely between the rib shadows you can observe the pleural line moving. The pleural line looks thin and continuous and you see faint B-Lines that are 2 at most on that segment.
B lines. The normal expected number of B lines is less than 2 per scan line. We appreciate more than that amount on the scan on the left. On the right the Lung curtain with less 2 faint B-lines as the pleural line comes between two rib shadows.
Interstitial Lung Disease
Lung ultrasound is a reliable tool to evaluate diffuse parenchymal lung disease. When 3 or more B-lines are present on the scan consider interstitial lung disease. Depending on the disease process causing this artefact these may be local or general. Remember that B lines are defined as discrete laser-like vertical hyperechoic reverberation artifacts that arise from the pleural line (previously described as ‘‘comet tails’’), extend to the bottom of the screen without fading, and move synchronously with lung sliding.
In patients with diffuse parenchymal lung disease (pulmonary fibrosis), the distribution of B-lines correlates with computed tomography (CT) signs of fibrosis. Bear in mind that the sonographic technique consists of evaluating eight lung regions and that a positive region is defined by the presence of three or more B lines in a longitudinal plane between two ribs. A positive exam for interstitial syndrome involves findings in two or more lung regions.
Lung ultrasound is superior to conventional chest radiography for ruling in significant interstitial syndrome. A negative lung ultrasound is superior to chest X-ray in ruling out significant interstitial syndrome
Sonographic findings that are suggestive of acute respiratory distress syndrome (ARDS) and not cardiogenic pulmonary edema include the following:
1. Anterior subpleural consolidations.
2. Absence or reduction of lung sliding.
3. Areas with normal parenchyma or ‘‘spared areas’’
4. Pleural line abnormalities (irregular thickened fragmented pleural line)
5. Nonhomogeneous distribution of B-lines
Sonographic findings indicative of diffuse parenchymal lung disease (pulm fibrosis) and not cardiogenic pulmonary edema involve:
1. Pleural line abnormalities (irregular, fragmented pleural line)
2. Subpleural abnormalities.
3. B-lines in a nonhomogeneous distribution.
Pulmonary Edema
In this image:
1. More than 3 B lines in this particular scanning plane.
2. The pleural line does not seem disrupted and there is no subpleural abnormalities.
3. If this is a finding throughout the lung the patient is likely experiencing pulmonary edema
Consider ARDS if:
1. Non dependent fields: Bilateral B-lines that non-homogeneous. This means that B-lines are numerous, confluent in another and areas of normal lung (lung sliding and A-lines).
2. Dependent lung fields: B-lines are homogeneous with coalescent B-lines and areas of consolidation especially at the bases. Lung sliding is absent or reduced in areas of coalescent B-lines. The pleural line is also irregular.
ARDS vs Pnuemonia vs Pulmonary Fibrosis
In this image:
1. More than 3 B lines in this particular scanning plane.
2. The B-lines appear confluent and a significant portion of the scanning sector is occupied by this artifact.
3.There is disruption of the pleural line.
4.There is a subpleural abnormality in the middle of the sector being scanned.
Consider ARDS if the findings here correspond to
dependent lung fields: B-lines are homogeneous with coalescent B-lines and areas of consolidation especially at the bases. The pleural line is also irregular.
COVID Pneumonia
In this image:
1. More than 3 B lines in this particular scanning plane.
2. The B-lines appear confluent and a significant portion of the scanning sector is occupied by this artifact. This is sometimes called Waterfall effect.
3. There is disruption of the pleural line and it appears thickened.
4. The is subpleural consolidation.
5. Image collected from a linear probe.
Image courtesy of the POCUS Atlas