Lung ultrasound must be the first-line image technique in COVID-19 patients

Lung ultrasound (LUS) is a paradigm of Point of Care Ultrasound values. First, it has no “owner” because its use has been developed by different specialties such as Intensive Care Medicine, Emergency Medicine and Internal Medicine. Secondly, its learning curve to acquire a high accuracy is relatively short and it can be performed with any kind of ultrasound machine (old, handheld devices, etc.) [1]. LUS helps in diagnosing any kind of pulmonary disease in many clinical settings and therefore different standardized protocols have been developed [2,3].

The coronavirus disease 2019 (COVID-19) pandemic has confirmed LUS as an outstanding tool in different aspects of patients with SARS-CoV-2 infection management. Its use may reduce the patient's exposure to radiation and minimize the need to moving the patient, thus reducing the incidence of cross-contamination and healthcare workers exposure to the infection [4]. Moreover, it may be used in the emergency department, but also in hospital wards and nursing homes.

Typical findings in patients with COVID-19 pneumonia are the presence of separated or coalescent B lines, the “light beam artifact” (a broad, lucent, band‐shaped, vertical artifact that moves rapidly with sliding, at times creating an “on–off” effect), and subpleural consolidations. Different scores that take into account the number of areas affected and the type of ultrasound findings have been developed. Basically, LUS scores express the degree of lung aeration in these patients [5,6].

LUS has a higher accuracy than chest X-ray for diagnosing or discarding COVID-19 pneumonia with a better sensitivity and negative predictive value [7]. It also has a good accuracy compared to chest CT in diagnosing COVID-19 pneumonia. Current results of the literature report a very high sensitivity (89–100%) for the diagnosis of COVID-19, also establishing extension of lung pneumonitis with a good correlation between the number of disease-positive lung zones and the presence of relevant disease burden on CT scan. LUS also provides clues for alternative diagnosis [8,9].

It has been also demonstrated that LUS gives significant prognostic information in relation to morbidity (the need for mechanical ventilation) and mortality with one ultrasound examination or with serial studies. This is crucial for many reasons such as hospital admission or discharge decision or patient´s allocation during hospital stay. Moreover, treatment intensity could be influenced by this information [10], [11], [12], [13].

Another important aspect of LUS in COVID-19 is the Information that provides about lung sequelae in patients with persistent respiratory symptoms. The evidence about this clinical scenario is scarce. In 96 hospitalized patients, Hernandez-Píriz et al. found that almost 70% of them showed a complete resolution of lesions on lung ultrasound at three months [14]. In 352 patients who recovered from COVID-19 pneumonia, Clofent et al. found that LUS score was strongly correlated with the High-Resolution CT Warrik score. The presence of a score > 3 discriminated patients with relevant interstitial lung sequelae, concluding that a normal LUS examination may rule out the presence of significant sequelae, avoiding the need for additional diagnostic tests such as high-resolution computed tomography (HRCT) [15].

In this issue of the European Journal of Internal Medicine, Barbieri et al. evaluate the diagnostic accuracy of LUS compared to chest CT scan in 232 patients who were hospitalized due to COVID-19 and underwent a three-month follow-up. LUS and chest CT showed a high agreement in identifying residual pathological findings, using cut-off values of 3 (sensitivity 91%, specificity 49%) and 7 (sensitivity 65%, specificity 79%). The results suggest that LUS is very sensitive in identifying pathological findings compared to CT and it could replace it in selected cases, limiting the use of expensive, unsafe, and not always available methods, such as chest CT [16].

With all the existing evidence, we can conclude that LUS examination should be considered as a "gate-keeper" in diagnosing COVID-19 pneumonia, establishing its prognosis and evaluating residual fibrosis, particularly in younger patients or in limited-resource settings. Efforts should be made by the healthcare community to promote its use in primary care, emergency departments, hospital wards and in outpatient clinics to diagnose, treat and follow-up patients who suffer or have suffered from COVID-19 pneumonia.

Declaration of Competing Interest

The authors declare not to have any conflict of interest related to this study.