Tag Archives: Lung

Performance of lung ultrasound: Let’s talk numbers

The diagnostic accuracy of lung ultrasound for common pathologies such as pleural effusion, pulmonary edema, pneumothorax, and pneumonia is superior to chest radiograph and is comparable to chest CT scan. In addition, POCUS is helpful to evaluate the progress of lung pathology and response to treatment over time.

In ESRD patients on dialysis, lung ultrasound greatly outperforms the physical exam findings that we commonly rely on to ensure adequate ultrafiltration. It’s time to upgrade our physical exam!

B-lines in the lung: numbers to remember and scanning Zones

In routine clinical practice, 4 standard sonographic lung zones are evaluated on each side delineated using the parasternal line, anterior and posterior axillary lines and a horizontal line about the level of 3rd-4th intercostal space. Experts recommend scanning at least 1 posterior zone (posterior to posterior axillary line) on each side as well in supine patients when monitoring response to diuretic or ultrafiltration therapy.

Visualization of occasional B-lines, especially in the dependent zones of the lung is not abnormal. The presence of three or more B-lines per “rib interspace” in a longitudinal plane is abnormal and constitutes “B-pattern”. Generally, the observable distance between the lines should be no more than 7 mm.

B-pattern in two or more sonographic lung zones bilaterally is suggestive of “interstitial syndrome”, as demonstrated in Figure 1. This term encompasses pulmonary edema of various causes, interstitial pneumonia and diffuse parenchymal lung disease (e.g. fibrosis). In case of diffuse B-line pattern, whether you are dealing with pulmonary edema or fibrosis largely depends on the clinical context. However, findings such as irregular, fragmented pleural line, sub pleural abnormalities appearing as small hypoechoic areas and nonhomogeneous distribution of B-lines favor fibrosis. On the other hand, “focal” B-line pattern may be seen in pneumonia, atelectasis, pulmonary contusion, pulmonary embolism, pleural disease and malignancy.

There are several scoring systems, primarily described for research purposes, based on various scanning approaches. Commonly described scanning zones are illustrated in Figure 2. When evaluating an acutely dyspneic patient, examining 2 anterior zones might be enough, while more comprehensive approach is needed in chronically volume overloaded patients (e.g. CHF patient in the clinic, patient on maintenance hemodialysis etc.). Also note that the studied chest zones could include more than 1 rib interspace with a number of possible probe positions.

28-zone lung US from Clin J Am Soc Nephrol. 2016 Nov 7; 11(11): 2005–2011

Pleural effusion: The ‘Spine sign’

Spine sign: visualization of the vertebral bodies in the thoracic cavity above the diaphragm – indicative of pleural effusion.

In the absence of pleural effusion, the spine is obscured by air in the lung, and is cut off at the diaphragm. Because fluid is a good transmitter of sound waves, spine is seen when there is fluid around the lung.

Sometimes, pleural effusion may be noticed incidentally on abdominal scans. Below image shows transverse section of the liver with anechoic area in the posterior aspect, which corresponds to lung/pleural area; black = fluid. In such cases, go up and scan in the above mentioned coronal plane to confirm your findings.

Lung ultrasound: A and B-lines

Lung ultrasonography can be used alone or in conjunction with limited echocardiography and sonographic assessment of the inferior vena cava to determine a patient’s volume status in day-to-day nephrology practice. B-lines seen on lung ultrasound provide semi-quantitative estimation of extravascular lung water, which is particularly important in critically ill patients and those with cardiorenal syndrome.

In normal aerated lung, hyperechoic, horizontal lines arising at regular intervals from the pleural line can be seen, which are called A-lines. These are reverberation artifacts that arise when the ultrasound beam reflects off of the pleura and, instead of entering the probe, partially reflects off of the probe face back to the pleura again before getting back to the machine. This double-length pathway is interpreted and displayed as if the source of the echo lies at two times the distance between pleura and skin because, the distance at which a particular structure is displayed on the screen depends on how long the echoes returning from that structure take to reach the probe. Multiple reverberations result in multiple A-lines, at multiples of the pleural depth. In short, if you see A-lines, the lungs are filled with air.

B-lines are defined as discrete laser-like vertical hyperechoic artifacts that arise from the pleural line and extend to the bottom of the screen without fading, move synchronously with lung sliding and erase A-lines. They used to be called “comet tails” and “lung rockets” in the past, and this terminology is obsolete now. B-line formation is incompletely understood but they are believed to be a subtype of reverberation artifact, called the ring-down artifact.

Here is my full post on introduction to lung ultrasound on the Renal Fellow Network.

Here is a short video explaining why we should perform lung POCUS in dialysis patients.