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The Speed of Sound

The Speed of Sound

Tracing COVID-19 by ‘Light Beams’ in the Lungs

Butts, Christine MD

doi: 10.1097/01.EEM.0000695600.51452.d6
    COVID-19, lungs, ultrasound
    COVID-19, lungs, ultrasound:
    Note the pleural line (arrow), which appears even and regular, and the repeating horizontal lines extending into the lung parenchyma in this low-frequency image of a normal lung. These A lines indicate a normally aerated lung. Visit http://bit.ly/SpeedofSoundVideos to see a video of this image.
    Figure
    Figure

    Testing was not widely available when I wrote about using ultrasound for patients with known or suspected COVID-19 a few months ago. (“Ultrasound a Potential Tool for Detecting COVID-19,” EMN. 2020;42[6]:13; https://bit.ly/3dnCxDf.) Obtaining results where I work took as long as 10 days. Since then, testing has improved, and trying to determine which patients with respiratory symptoms are infected with the coronavirus is much more straightforward, and the goals of using ultrasound have shifted.

    Ultrasound findings of the coronavirus include B lines, which indicate interstitial edema. The pleural line may appear irregular, as opposed to a normal, smooth, and even line. Consolidation may be seen and ranges in size from small subpleural lesions to large areas. Consolidation typically appears as a hypoechoic area with an irregular border, and it often takes on a tissue-like appearance, with a texture similar to the liver or spleen. Bright areas within the consolidation, representing air within the bronchioles, may also be seen, as may pleural effusions, though they are less common.

    Figure
    Figure:
    Note the pleural line (arrow), which appears irregular and indistinct, in this low-frequency image of a lung affected by COVID-19. Instead of A lines, they are vertical, bright B lines, indicating interstitial edema. Visit http://bit.ly/SpeedofSoundVideos to see a video of this image, which demonstrates the “light beam” effect, where the B lines appear and disappear.

    The recognition of these signs alone, however, may not be as clinically useful. Many patients presenting with mild symptoms may demonstrate a degree of lung involvement when evaluated by ultrasound. These findings, in my experience, however, are not necessarily correlated with clinical progression. Are there signs (or lack of) that can help us feel confident that our patients won't significantly worsen and can be safely discharged? Once a COVID-19 diagnosis is established and the patient is hospitalized or placed on mechanical ventilation, are there any signs we can use to guide treatment?

    A recent paper by Volpicelli, Lamorte, and Villen looked at what's new in lung ultrasound during the COVID-19 pandemic. (Intensive Care Med. 2020;1; https://bit.ly/3hp3okM.) These authors, drawing on their experience with the pandemic in Italy, described a phenomenon that they deemed a “light beam” artifact, which was seen in patients with ground glass opacities on chest CT. These artifacts are similar to B lines, but they appear to move with respiration, giving an on-off effect caused by the B lines appearing and then disappearing.

    They also discussed using ultrasound to estimate the percentage of lung involvement by identifying the areas that demonstrate signs typical of COVID-19. Finding only a few B lines in one region of the lung, for example, is not as significant as finding multiple signs in multiple areas. The authors speculated that patients with more significant involvement are at higher risk for needing ventilatory support. They also suggested that looking at the progression or improvement in the severity of involvement of the lung zones can be used to guide treatment. Specifically, they describe guiding proning patients based on their findings.

    No doubt we're only at the beginning of understanding this disease. I'll come back to this topic in a few more months with another update.

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    Dr. Buttsis the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans. Follow her on Twitter@EMNSpeedofSound, and read her past columns athttp://bit.ly/EMN-SpeedofSound.

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