Lung Ultrasound in COVID-19 Pneumonia: Prospects and Limitations.

Dear Editor,

Since the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Wuhan, China, chest computed tomography (CT) imaging has been used extensively in the diagnosis and evaluation of patients with the novel coronavirus disease (COVID-19) (1,2). However, recent studies have recommended the use of lung ultrasound in the diagnosis and management of COVID-19. These studies have indicated that point-of-care lung ultrasound (POCUS) could be implemented as a substitute for chest CT scan (3, 4, 5).

Although lung ultrasound has several advantages including the absence of radiation, lower contamination risk, lower cost, and repeatability (6,7), one of its limitations is the relatively lower sensitivity in comparison to chest CT scan (8). Another disadvantage of this imaging modality is that ultrasound cannot usually detect lesions that are deep and intrapulmonary (5,9).

A study reporting the ultrasonographic manifestations of patients with COVID-19 found that the most common findings are B lines, patchy consolidations, and unsmooth pleural lines (9). Similarly, Peng et al. reported that focal B lines are the major ultrasonographic feature of early-stage COVID-19 pneumonia (6). Since these findings are also present in other viral pneumonias (10,11), we believe that lung ultrasonography is not appropriate for the initial diagnosis of COVID-19. Recently, Soldati et al. suggested a scoring system for classifying findings observed on lung ultrasonography in patients with COVID-19 (12). The air bronchogram sign is also seen in some patients with COVID-19; however, this is not a specific sign for this disease (13). Based on published studies, the main finding in the chest CT scan of patients diagnosed with COVID-19 is ground-glass opacity (14), a finding that is difficult to detect via lung ultrasonography. In addition, ground-glass opacity is mainly observed in the posterobasal regions that might not be easy to reach for the radiologist performing the examination due to the patient's position at the bedside. Infiltrations detected by lung ultrasound can be suggestive of pulmonary edema, infarct or lobar pneumonia; nevertheless, a confirmed diagnosis of either of these findings requires a complementary imaging modality such as chest CT. Thus, we believe that the previously published studies might have exaggerated the usefulness and value of lung ultrasonography in the management of COVID-19. We agree that in critically ill hospitalized patients with COVID-19 who are admitted to the intensive care unit, ultrasonography may be helpful. Since these patients are at a greater risk of developing thromboembolic events and pulmonary thromboembolism (15), Doppler ultrasonography could be used for the detection of pulmonary thromboembolism in these patients. Moreover, ultrasonography could be used for assessing COVID-19-related complications, such as pneumothorax in those who are under mechanical ventilation or parapneumonic effusion in patients with superimposed pneumonia. Conclusively, we believe that ultrasonography may be helpful in COVID-19 management; however, its use in COVID-19 diagnosis and screening is limited and so, chest CT scan remains the imaging modality of choice for diagnosing COVID-19. However, in places where chest CT scan is not feasible, lung ultrasound could be used as an alternative in the setting of the current pandemic. Since earlier studies have included a small number of patients, we recommend further large-scale studies to evaluate lung ultrasound in patients with COVID-19 in terms of diagnosis, response to therapy, and prognosis.