First Protocol on How to Use Lung Ultrasound to Triage COVID-19

Liam Davenport

April 09, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's  Coronavirus Resource Center.

The first protocol for the use of lung ultrasound to quantitively and reproducibly assess the degree of lung involvement in patients suspected of having COVID-19 infection has been published by a team of Italian experts with experience of using the technology on the front line.

Particularly in Spain and Italy — where the pandemic has struck hardest in Europe — hard-pressed clinicians seeking to quickly understand whether patients with seemingly mild disease could be harboring more serious lung involvement have increasingly relied upon lung ultrasound in the emergency room.

Now Libertario Demi, PhD, head of the ultrasound laboratory, University of Trento, Italy, and colleagues have developed a protocol, published online March 30 in the Journal of Ultrasound Medicine, to standardize practice.

Their research, which builds on previous work by the team, offers broad agreement with industry-led algorithms and emphasizes the use of wireless, handheld ultrasound devices, ideally consisting of a separate probe and tablet, to make sterilization easy.

Firms such as the Butterfly Network, Phillips, Clarius, GE Healthcare, and Siemens are among numerous companies that produce one or more such devices, including some that are completely integrated.

Not Universally Accepted

However, lung ultrasound is not yet universally accepted as a tool for diagnosing pneumonia in the context of COVID-19 and triaging patients.

The National Health Service in England does not even mention lung ultrasound in its radiology decision tool for suspected COVID-19, specifying instead chest X-ray as the first-line diagnostic imaging tool, with CT scanning in equivocal cases.

But Giovanni Volpicelli, MD, University Hospital San Luigi Gonzaga, Turin, Italy, who has previously described his experience to Medscape Medical News, says many patients with COVID-19 in his hospital presented with a negative chest X-ray but were found to have interstitial pneumonia on lung ultrasound.

Moreover, while CT scan remains the gold standard, the risk of nosocomial infection is more easily controlled if patients do not have to be transported to the radiology department but remain in the emergency room and instead undergo lung ultrasound there, he stressed.

Experts Share Experience of Lung Ultrasound in COVID-19

In developing and publishing their protocol, Demi, senior author of the article, and other colleagues from the heavily affected cities of Northern Italy, say their aim is "to share our experience and to propose a standardization with respect to the use of lung ultrasound in the management of COVID-19 patients."

They reviewed an anonymized database of around 60,000 ultrasound images of confirmed COVID-19 cases and reviewers were blinded to patients' clinical backgrounds.

For image acquisition, the authors recommend scanning 14 areas in each patient for 10 seconds, making the scans intercostal to cover the widest possible surface area.

They advise the use of a single focal point on the pleural line, which they write, optimizes the beam shape for observing the lung surface.

The authors also urge that the mechanical index (MI) be kept low, as high MIs sustained for long periods "may result in damaging the lung."

They also stress that cosmetic filters and modalities such as harmonic imaging, contrast, doppler, and compounding should be avoided, alongside saturation phenomena.

What Constitutes Intermediate Disease?

Once the images have been taken, they are scored on a 0-3 scale for each of the 14 areas, with no weighting on any individual area.

A score of 0 is given when the pleural line is continuous and regular, with the presence of A-lines, denoting that the lungs are unaffected.

An area is given a score of 3 when the scan shows dense and largely extended white lung tissue, with or without consolidations, indicating severe disease.

At both ends of this spectrum, there is agreement between the Italian protocol and an algorithm developed by the Butterfly Network.

However, the two differ when it comes to scoring intermediate cases. On the Butterfly algorithm, the suggestion is to look for B-lines, caused by fluid and cellular infiltration into the interstitium, and to weigh that against the need for supplementary oxygen.

The Italian team, in contrast, says a score of 1 is given when the pleural line is indented, with vertical areas of white visible below.

A score of 2 is given when the pleural line is broken, with small to large areas of consolidation and associated areas of white below.

Demi told Medscape Medical News that they did not refer to B-lines in their protocol as their visibility depends entirely on the imaging frequency and the probe used.

"This means that scoring on B-lines, people with different machines would give completely different scores for the same patient."

He continued: "We prefer to refer to horizontal and vertical artifacts, and provide an analysis of the patterns, which is related to the physics of the interactions between the ultrasound waves and lung surface."

In response, Mike Stone, MD, Legacy Emanuel Medical Center, Portland, Oregon, and director education at Butterfly, said there appears to be wide variation in lung findings that "may or may not correlate with the severity of symptoms."

He told Medscape Medical News it is "hard to know exactly if someone with pure B-lines will progress to serious illness or if someone with some subpleural consolidations will do well."

A Negative Ultrasound Is the Most Useful

Volpicelli believes that, in any case, any patient with an intermediate pattern will require further diagnosis, such as other imaging modalities and blood exams, and the real role of lung ultrasound is in assessing patients at either end of the spectrum.

"In other words, there are situations where lung ultrasound can be considered definitive," he told Medscape Medical News. "For instance, if I see a patient with mild signs of the disease, just fever, and I perform lung ultrasound and see nothing, lung ultrasound rules out pneumonia."

"This patient may have COVID-19 of course, but they do not have pneumonia, and they can be treated at home, awaiting the result of the swab test. And this is useful because you can reduce the burden in the emergency department."

Volpicelli continued: "On the other hand, there are patients with acute respiratory failure in respiratory distress. If the lung ultrasound is normal, you can rule out COVID-19 and you need to use other diagnostic procedures to understand the problem."

"This is also very important for us because it's crucial to be able to remove the patient from the isolation area and perform CT scan, chest radiography, and all the other diagnostic tools that we need."

Are Wireless Machines Needed? Not Necessarily

With regard to the use of wireless technology, the Italian team says that "in the setting of COVID-19, wireless probes and tablets represent the most appropriate ultrasound equipment," as they can "easily be wrapped in single-use plastic covers, reducing the risk of contamination," and making sterilization easy.

Stone suggests that integrated portable devices, however, are no more likely to cause cross-contamination than separate probes and tablets, as they can fit within a sterile sheath as a single unit.

Volpicelli, for his part, doesn't like what he sees as undue focus on wireless devices for lung ultrasound in the COVID-19 protocols.

He is concerned that recommending them as the best approach may be sending out the wrong message, which could be very "dangerous" as people may then think they cannot perform this screening with standard ultrasound machines.

For him, the issue of cross-contamination with standard lung ultrasound machines is "nonexistent. Cleaning the machine is quite easy and I do it hundreds of times per week."

He does acknowledge, however, that if the lung ultrasound is performed under certain circumstances, for example when a patient is using a continuous positive airway pressure (CPAP) machine, "the risk of having the machine contaminated is a little bit higher."

"In these situations...we have a more intensive cleaning procedure to avoid cross-contamination."

He stressed: "Not all centers have wireless machines, whereas a normal machine is usually in all hospitals."

"The advantages of using lung ultrasound [in COVID-19] are too great to be limited by something that is not important in my opinion," he concluded.

Stone is director of education at the Butterfly Network. No other conflicts of interest were declared.

J Ultrasound Med. Published online March 30, 2020. Full text

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