PŘEHLEDOVÉ ČLÁNKY / REVIEW ARTICLES Imaging of COVID-19 in critical care with a focus on chest ultrasound 62 | ANESTEZIOLOGIE A INTENZIVNÍ MEDICÍNA / Anest intenziv Med. 2023;34(2):61-68 / www.aimjournal.cz For many years, CUS has been thought of as impossible and not feasible due to the very nature of the lungs being air‑containing structures. CUS can be performed at the bedside when needed and waiting for a radiology report is eliminated as clinical information is acquired within a few minutes if not seconds. CUS is a portable, mobile imaging tool with a steep learning curve in contrast to other imaging modalities. Furthermore, the combination of CUS and echocardiography is extremely valuable in the assessment of not only lung pathology, but also in assessing the haemodynamic parameters of a patient. CUS is also excellent in the diagnosis of pleural and diaphragmatic pathologies, guiding thoracentesis and aiding in the evaluation of pulmonary consolidations [1–4]. This reduces serial bedside CXRs, thus reducing unnecessary radiation exposure (for reference, one non‑contrast chest CT (an effective dose of about 8 millisieverts (mSv)) equals about 400 chest anterior‑posterior (AP) CXR examinations as one CXR has an effective dose of about 0.02 mSv). There is also a reduction in the potential side effects of contrast administration during CT, notably hypersensitivity reactions to contrast medium, contrast‑induced nephropathy (CIN), and rarely, contrast‑induced thyroid dysfunction [5–8]. Bedside CXR is limited in diagnosing pulmonary consolidations, small to moderate pleural effusions, small to moderate‑sized pneumothoraces or alveolar‑interstitial syndrome [7–10] due to technical complications which arise when a bedside CXR is performed. The spatial resolution of bedside CXR is compromised by the fact that the patient cannot do a breath hold; thus, there is movement of the thorax. Furthermore, due to film cassette positioning (between the bed and the patient), the x‑ray beam is shortened because of a shorter acquisition distance (3). This leads to suboptimal images which can be challenging to accurately interpret. In critically ill patients who are extensively monitored by a number of invasive devices, CT scanning not only is cumbersome, but transportation to the CT suite and positioning of such patients in the gantry is a task in itself, with a potential for significant respiratory and haemodynamic derangements for the patients [11–13]. The limitations brought on by the aforementioned radiology methods make CUS the go-to method of assessing critically ill patients. COVID-19 pneumonia and ARDS During the worldwide pandemic due to COVID-19, there has been a greater need for accessible, reproducible, and safer means of imaging. In this regard, CUS can be extremely useful (just as it was during the H1N1 pandemic) to evaluate patients at the bedside for the evolution (either progression or regression) of the disease and the efficacy of any supportive treatment initiated for COVID-19 pneumonia, and can confer an easier, dynamic method of assessment since an ultrasound machine is widely available in specialised ICUs. It needs to be stressed, however, that imaging findings related to COVID-19 are not specific to COVID-19 and a definitive diagnosis inevitably involves other methods such as microbiology sampling, serology and bronchoscopy, as similar imaging findings can be seen in cardiac and other pulmonary pathologies, e.g. in cardiac failure, other viral or bacterial pneumonias, and chronic pulmonary diseases [13, 14]. Chest radiographic imaging (CXR and CT) CXR can help to guide therapy after the first 48 hours (hrs) of clinical COVID-19. Nonetheless, CXR performs inferiorly to CUS in terms of diagnosing COVID-19 associated pulmonary findings [1, 2, 4, 5, 15, 16] (Figs. 1 and 2). Changes seen on lung ultrasound and clinical presentation (Fig. 2) precede those seen on CXR and CT (Figs. 1 and 3). Beyond the first 48 hrs, CT has shown far more sensitivity than CXR where discrete lung changes are involved [17]. COVID-19 pneumonia has an evolution, starting off as microvascular damage which then progresses to acute fibrinous and organising pneumonitis (AFOP) or, less commonly, to diffuse alveolar damage (DAD). On CT, it typically has these features: predominantly peripheral ground‑glass opacities (GGOs) with or without consolidations or crazy paving, with a bibasilar predominance [17–21] (Figs. 3 and 4). Fig. 1. Spectrum of COVID-19 lung changes in patients admitted with dyspnoea on oxygen. A normal CXR (A) can be seen, as well as the bilateral interstitial pattern (B) or visible infiltrates (C). Images reproduced with permission from the archives of the Department of Diagnostic Radiology, University Hospital Bulovka, Prague, Czech Republic
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