The COVID-19 pandemic continues to develop rapidly, particularly in the United States and Europe. Imaging procedures are an essential component of care for patients with symptoms. Besides computed tomography (CT) and X-ray imaging, lung ultrasound (LUS) has become an emerging tool for assessing COVID-19 patients.
The clinical spectrum of COVID-19 ranges from mild respiratory complaints to severe lung failure. A rapid and reliable distinction has to be made between SARS-CoV-2-related pneumonia and other lung conditions. COVID-19 is primarily diagnosed on the basis of a real-time polymerase chain reaction (RT-PCR) assay of throat swabs or sputum [1]. On suspicion of COVID-19, existing CT or X-ray imaging is standard. But where emergency rooms and intensive care units are already confronted with COVID-19 patients or are preparing for a sharp increase, LUS is gaining importance – particularly as it is predestined to be used at the bedside in the form of point-of-care ultrasound (PoCUS).
Characteristics of COVID-19 that can be visualized with LUS
SARS-CoV-2 infections primarily affect the smallest alveoli at the periphery of the lung. As a rule the lesions are located close to the pleura and thus in an area that can be visualized very well by ultrasound. In LUS, diagnosis is based on artifacts – which are apparent, interfering phenomena in the X-ray, CT or MRT image. For COVID-19, the following characteristic artifacts have been found [2, 3]:
- The echo-rich horizontal line corresponding to the visceral pleura (pleura line) appears thickened and irregular
- B-lines with varying patterns, including focal, multifocal, and confluent lines
- Consolidation (accumulations of fluid and/or tissue in pulmonary alveoli preventing gas exchange) with varied patterns, including small multifocal, non-translobar and translobar lines
- Appearance of A-lines during the recovery phase
- Pleural effusions are rare
LUS from A to B
The most important artifacts for evaluation are A-lines and B-lines [4]. In a normal ultrasound image, A-lines appear as parallel horizontal repetition lines of the pleura. They appear with intact lung tissue and normal lung sliding (the movement of the lung at the chest wall in time with the breath). If there is no lung sliding, an abnormal collection of air in the pleural space (pneumothorax) is likely. B-lines run vertically and indicate accumulations of fluid. Multiple B-lines point to pulmonary edema.
PoCUS in practice
At the end of March, a team at the University Policlinic in Rome published the case of a 52-year-old man who had been suffering from fever, coughing, weakness, headache, muscle ache, and sensitivity to light for a week. Since he had been in contact with people from Bergamo, at that time a high-risk region in Italy, there were strong suspicions of COVID-19. As in previous studies, here too the typical COVID-19 signs were evident in the LUS [5]. The SARS-CoV-2 infection was confirmed by throat swab.
Thanks to a wireless portable ultrasound system, it was possible to do the examination as a PoCUS in the emergency department. The risk of contamination could be minimized throughout the process: the examination in the isolation room was done by a physician and a nurse adhering to the infection prevention and control arrangements. The wireless ultrasound probe and the portable console were in a sterile cover. Only the physician had direct patient contact, with the nurse only using the console. Subsequently the probe and the console were disinfected and again put in a sterile cover [5].
Standards and recommendations: work in progress
There is still a lack of sufficient findings on the use of LUS with COVID-19 patients to be able to summarize them in standards and recommendations. Nevertheless, things are also moving on this topic in the scientific community. The World Federation for Ultrasound in Medicine & Biology (WFUMB), for example, has produced a detailed position paper on how it is feasible to do safe ultrasound examinations as part of efforts to monitor infection in the SARS-CoV-2 pandemic [6].
The development of suitable examination protocols is at the center of this endeavor. They are based on the established BLUE protocol (bedside lung ultrasonography), which were developed for acute dyspnea. Thus, the 6-zone BLUE protocol enables the assessment of acute respiratory failure [7]. For patients with COVID-19 there exists a modification of the BLUE protocol, which considers the six zones along the anterior and posterior axillary line on both sides of the thorax, thus resulting in a 12-zone protocol [8].
From Italy there has been a proposal for standardization to improve the use of ultrasound with COVID-19 patients [9]. It covers 14 zones on the front and back and left and right side of the thorax that should be scanned with ultrasound for ten seconds each. At the same time there are detailed technical recommendations designed to assure optimal results.
DEGUM, the German society for ultrasound in medicine, and its Austrian and Swiss counterparts ÖGUM and SGUM, have developed a standardized lung examination protocol [10], which is identical to the 12-zone protocol mentioned above. This protocol sheet enables typical findings to be recorded for both lungs and allocated to the ultrasound points. An evaluation of the protocol in a clinical trial is to follow shortly.
About the Author
Matthias Manych, a biologist based in Berlin, works as a freelance scientific journalist, editor, and author specializing in medicine. His texts appear primarily in specialized journals, but also in newspapers and online.