## 4 Discussion  
Easy-to-access and reliable diagnostic methods, which can accurately guide the management of COVID-19, are vital in non-hospital settings and areas with limited resources [5]. Some studies have noted that LUS could be a first-line diagnostic alternative to conventional chest X-ray and CT scans since there is no exposure to ionizing radiation [4; 6; 13] and should be encouraged to avoid transporting patients and reduce the risk of environmental contamination [21; 22; 23]. Moreover, it could be considered in vulnerable populations, such as pregnant women and children. Previous research has shown that COVID-19 has notable LUS characteristics, such as B-lines or consolidations [11]. These findings correlate well with COVID-19 CT findings, such as ground-glass consolidations and septal thickening [9]. As a result, given that LUS may be able to predict outcomes in COVID-19 patients, it is crucial to ascertain whether clinicians can correctly interpret these results. In this study, several LUS findings demonstrated moderate agreement (e.g., consolidations) and others fair agreement (e.g., individual B-lines and confluent B-lines \(<50\%\)). Therefore, LUS could signify a reliable COVID-19 diagnostic and prognostic tool. Moreover, there was good agreement as to whether an LUS scan was interpreted as normal. In addition, beyond COVID-19, an abnormal LUS scan has prognostic implications for multiple diseases. This study represents the first study to assess inter-observer agreement in LUS findings in COVID-19 obtained with the same device and including practitioners from multiple specialties and centers, who commonly use different portable devices. Our results are similar to other previous studies on inter-rater reliability for LUS outside of COVID-19. Previous investigations have demonstrated moderate to substantial agreement for B-lines [15; 16; 17], while this research shows only moderate to fair agreement for consolidations. This is similar to the results obtained in a previous LUS study with COVID-19 patients [14]. This work shows the importance of working toward a more standardized interpretation protocol. Among the possible solutions, the following options should be considered:  
1. Standardization of the terminology to describe artifacts and signs in LUS is essential. Several definitions of each LUS abnormality can be found in the literature, especially for consolidations, but also regarding pleural abnormalities [1], which were not considered in this study. This group believes that the reliability of findings such as consolidations might improve with a more specific and consensus-based definition. Figure 6: (**a**) Scatter plot with the longitudinal vs transversal total scores per patient. Points and error bars correspond to the average and standard deviation, respectively, of the evaluations obtained from all physicians. The 3 subgroups shown correspond to the classification of the patients based on their severity; (**b**) Bland–Altman plot of the total score per patient (obtained as the average value of all the evaluations) assigned to the videos acquired with longitudinal and transversal probe orientation (“Score difference” indicates longitudinal minus transversal scores). 2. The use of automatic tools to quickly analyze the acquisitions and obtain some quantitative values, such as the percentage of affected pleura (B-lines \(<\) 50% or \(>\)50%) and the size of the consolidations, may be helpful to obtain more consistent results among raters. 3. The length of the acquired videos (3 s in this study) could be extended to provide more information in some cases. 4. Access to additional clinical data about the patients may also help in their evaluation. There are several limitations to this study. Due to its dynamic nature, the use of LUS fundamentally differs from traditional medical imaging practices where an exam is performed by a technologist and interpreted remotely by a physician with limited clinical knowledge of the patient.