BÀI SOẠN VỀ SIÊU ÂM CHẨN ĐOÁN: Role of Lung Ultrasound in Patients with Severe COVID-19 in Low and Middle-Income Countries [LMICs]

In LMICs, what is the role of lung ultrasound in patients with severe COVID-19? Rationale.

Chest imaging can be essential in the diagnosis and management of patients with COVID-19. Published reports to date have focused mainly on standard chest x-ray (CXR) and chest computed tomography (CT). Abnormalities are very often present on CXR images of COVID-19 patients44; consolidations and ground-glass opacities have been reported in 47% and 33%, respectively. Not all patients with COVID-19 have abnormalities on chest CT images.45 Patchy ground-glass opacities, typically in a bilateral and peripheral locations, and consolidations have been most commonly described.46–48 In light of the high sensitivity of an abnormal scan, CT has even been suggested as a primary diagnostic tool for COVID-19.49,50 Challenges with access to CT and, at times, even simple CXR may preclude the usefulness of these imaging techniques in LMICs.

Lung ultrasound (LUS) is increasingly recognized as a chest imaging tool with a strong potential to guide management of critically ill patients and may represent a useful tool in patients with COVID-19. Search results. MEDLINE, Embase, and Web of Science were searched until May 2020. The search used combinations of MeSH terms and free-text words, including “COVID–19,” “coronavirus,” “SARS–CoV–2,” “‘radiography,” “chest radiography,” “CT,” “chest CT,” “CT,” “chest CT,” “ultrasound,” “LUS,” and “lung ultrasonography.” Several studies were found but none reporting data from LMICs.

Evidence. For the diagnosis of pneumonia from causes other than COVID-19, LUS has been found to be superior to standard CXR, and it approaches chest CT in terms of diagnostic accuracy.51–53 Lung ultrasound had a better diagnostic yield than CXR in the early diagnosis of H1N1 2009 viral pneumonia.54 Experience with LUS in patients with COVID-19 is rapidly growing, with the consistent finding that nearly all COVID-19 patients have an abnormal LUS.55

Four major findings are frequently described in COVID-19 patients (Figure 1), although the sensitivity and specificity of the following findings remain uncertain.56

1. focal, multifocal, or confluent B-lines (in 97% of cases);

2. pleural thickening (in 50% of cases);

3. subpleural and pleural consolidations (in 40% of cases); and

4. rarely, pleural effusions (in 16% of cases).57–61 A patchy distribution of multiform clusters alternating with “spared areas” (regions of normal lung parenchyma) is often observed.62

One LUS finding of particular usefulness in COVID-19 is the “light beam,” a broad, lucent, band-shaped, vertical artifact that moves rapidly with sliding (see https:// link.springer.com/article/10.1007/s00134-020-06048-9), which may correspond to early ground-glass alterations on a chest CT scan. The precise diagnostic accuracy of this sign is currently being tested in a prospective study.63 Early reports suggest that the extent of LUS findings correlate with severity of lung injury in COVID-19.45 In one review of LUS in patients with COVID-19, the relative number and distribution of B-lines and consolidations approximated other parameters of clinical severity, including oxygen saturation, need for supplemental oxygenation, and respiratory rate.64 The WHO clinical management guidelines suggest that LUS be used to assist in COVID-19 diagnosis and identify or exclude pulmonary complications.1 Potentially useful scoring systems for patients with COVID19 are summarized in Table 2. A scoring system to quantify the degree of lung injury in patients with COVID-19 has been proposed for both ventilated and non-ventilated patients (Figure 1).65 In invasively ventilated patients, early quantification of the severity of lung involvement by LUS in patients with COVID-19 can be estimated by using the “LUS score,” 66 which has been extensively tested in ARDS patients.67,68 The dynamic changes in aeration can then potentially be quantified by reassessing the LUS score (Figure 2). A previous study in Rwanda proposed the use of LUS combined with pulse oximetry to diagnose ARDS (from causes other than COVID19) in a cohort of primarily non-ventilated patients.69 This approach was externally validated in invasively ventilated patients in the Netherlands,70 but its performance in COVID19 ARDS remains to be established. To our knowledge, there are currently no published studies comparing LUS with RT-PCR for the diagnosis of COVID-19. However, multiple studies looking at diagnosis (NCT0435180, NCT04370275, NCT04393402, NCT04338568, NCT04322487, and NCT04377035) or prognosis (NCT04379544, NCT04384055, and NCT04370249) are currently underway as of November 5, 2020. One of these studies is being performed in Turkey (NCT04399681). Availability, feasibility, affordability, and safety. Data on the availability of ultrasound devices in LMICs remain limited. In a recent multicenter observational study in 54 Asian ICUs, 54% of centers reported having a dedicated chest radiography apparatus versus 79% an ultrasound apparatus,71 and a hospital CT was available in 96% of centers. A bedside ultrasound machine was reported to be available sometimes in Haiti.72 Lung ultrasound studies in LMICs are still performed less frequently than abdominal and cardiac ultrasound.73 However, with the availability of smaller and cheaper devices and a growing body of evidence, wider use of LUS can be foreseen.74,75 Although cost-effectiveness studies in LMICs are lacking, LUS has been shown to reduce the use of CXR and chest CT in resource-rich ICUs, with less radiation exposure and lower costs.76,77 An important advantage of LUS is that it can be performed with most available ultrasound machines and probes. It remains an operator-dependent technique but can be taught readily to non-experts with little formal ultrasonography training. In an international, multicenter study across 10 ICUs, performance of 25 supervised LUS examinations resulted in sufficient acquisition of skills by non-experts for the assessment of the “LUS score.” 78 In more resource-restricted settings, a study of 20 participants in Ghana demonstrated good retention of cardiorespiratory ultrasonography principles 9– 11 months after participants received a training program.79 Point-of-care ultrasound training intervention in a resource restricted setting in Rwanda resulted in high numbers of diagnostic quality studies over long-term follow-up,80,81 although remote quality assurance feedback was found an effective educational tool in Uganda.

An important limitation of LUS is that it cannot detect lesions that are intrapulmonary and do not reach the pleural line.82 Usefulness of LUS via telemedicine is proposed, but direct evidence is still lacking.83

Recommendations and suggestions (Table 1).

1. In LMICs, where availability of standard CXR and CT is limited, we suggest using LUS to detect abnormalities to identify patients with possible COVID-19 (weak recommendation, low quality of evidence);

2. In LMICs, we recommend against the use of LUS to exclude COVID-19 (UG best practice statement);

3. In LMICs, we suggest using LUS in combination with clinical parameters to monitor progress of the disease and responses to therapy in COVID-19 patients (weak recommendation, low quality of evidence).

LMICs= Low and Middle-Income Countries