Brown Sound: Lung Ultrasound for COVID-19
INTRODUCTION
SARS-CoV-2/COVID-19 is a novel coronavirus first identified in Wuhan, China in late 2019. There are many types of human coronavirus which cause mild symptoms, but COVID-19 is a new disease which has caused a global pandemic. In COVID-19 infection, there are specific findings seen on point-of-care lung ultrasound (LUS) which correlate to computed tomography findings. Thus, LUS may have an important role in the screening, diagnosis, and prognosis of patients presenting with an influenza like illness (ILI).
Why consider using lung ultrasound?
COVID-19 patients present with a wide range of symptoms of highly variable severity, making it difficult to diagnose based on clinical presentation only. Patients often present with few or no respiratory symptoms, but already have a developing or significant pneumonia. The sensitivity of chest x-ray (CXR) for lung pathology is poor,[1] with one study of 3423 patients showing a sensitivity of 43.5% to detect lung opacity compared to lung CT.[2] CT scan is a more sensitive and accurate test for lung pathology, including COVID-19 pneumonia, but the CT scanner is a finite resource in most hospital systems. CT scanners require disinfection after a patient under investigation (PUI) enters the room, putting it out of commission for an extended period of time depending on the institution. Additionally, radiologists will be required to read an increasing number of these scans as the number of potential patients with COVID-19 pneumonia rises. Point-of-care lung ultrasound is a bedside tool which can be used to quickly evaluate a patient for signs of pneumonia and can be interpreted in real time.
What are the characteristic COVID-19 LUS findings?
Scattered, non-confluent, b-lines (“skip lesions”)
Subpleural consolidations
Irregular pleural line (thickened, ratty, discontinuous) [3,4]
Check out examples here, on the Butterfly Network’s COVID-19 page. Below is a table from Peng et al comparing lung ultrasound findings to lung CT findings.[5]
So, how should we be using lung ultrasound?
LUS can be used as a tool for evaluating potential COVID-19 patients or managing patients with known COVID-19 infection. It is important to recognize that LUS does not diagnose COVID-19, but there are some classic LUS findings which suggest a COVID-19 diagnosis in the right clinical context. Imagine the following case scenarios below.
Case 1
A young patient with no PMH presented with cough, nausea, and dyspnea. Vital signs were significant for a fever and mild tachypnea, but no hypoxia.
Management: A young, healthy person with a normal lung ultrasound should be discharged and instructed to self-quarantine at home for 14 days. On the other hand, some physicians are admitting non-hypoxic patients, who have abnormal LUS findings consistent with COVID-19, because there is anecdotal evidence that abnormal LUS findings precedes clinical deterioration.[6] With an abnormal LUS, you may be more likely to admit and treat or, if discharged, to track them closely, with primary care follow-up, home pulse oximetry, or telemetry medicine.
Case 2
An older patient with a PMH of hypertension, congestive heart failure, diabetes, and chronic kidney disease presented with cough, nausea, and dyspnea. The patient was tachycardic, tachypneic, and hypoxic to 88% on room air. The CXR is abnormal, with possible basilar airspace disease, albeit unchanged from prior.
Management: With a normal LUS, the post-test probability of COVID-19 is lower, warranting a broadened differential diagnosis. In this case, a point-of-care cardiac ultrasound could provide important information about systolic function and evaluate for possible RV strain. Regarding disposition, self-quarantine at home may be safe in a non-hypoxic, but high-risk patient with a normal LUS; however, hypoxia and a concerning LUS should trigger admission, with viral testing per institutional guidelines.
Disinfection
It is important to remember that ultrasound machines can be carriers of COVID-19 fomites and need to be disinfected thoroughly after being used for a PUI. Consider using single use packets of gel, covering machines in any room with risk of aerosolization, and using sterile probe covers on known COVID-19 patients. Remove everything you will not need to use from the ultrasound machine before entering the room. We recommend wiping down the entire ultrasound system including probes, cart and wires after use on a PUI.
Take-Aways
LUS should be used to inform clinical decision making. Avoid educational scans.
Know the findings of COVID-19 on LUS: non-confluent b-lines (skip lesions), subpleural consolidations, and an irregular pleural line.
Sterilize every ultrasound unit after use on a PUI.
Faculty Reviewer: Kristin Dwyer, MD
References
Swaminathan A, Stone M, Avila J. Lung Ultrasound and COVID-19. EM:RAP 2020 March 27th Breaking News [Podcast]. Available from: https://www.emrap.org/episode/emrap2020march9/emrap2020march1
Self WH, Courtney DM, McNaughton CD, Wunderink RG, Kline JA. High discordance of chest x-ray and computed tomography for detection of pulmonary opacities in ED patients: implications for diagnosing pneumonia. Am J Emerg Med. 2013; 31(2):401-405.
Huang Y, Wang S, Liu Y, Zhang Y, Zheng C, Zheng Y, Zhang C, Min W, Zhou H, Yu M, Hu M. A Preliminary Study on the Ultrasonic Manifestations of Peripulmonary Lesions of Non-Critical Novel Coronavirus Pneumonia (COVID-19). SSRN. 2020.
Butterfly Network: Fighting COVID 19 Together [Internet]. New York: Butterfly Network. 2020 [accessed 2020 Mar 29]. Available from: http://www.butterflynetwork.com/covid-19
Peng Q, Wang X, Zhang L. Findings of lung ultrasonography of novel corona virus pneumonia during the 2019–2020 epidemic. Intensive Care Med. 2020.
Under Pressure, One Italian Doctor Triages by Ultrasound [Internet]. Medscape Medical News. 2020. [accessed 2020 Apr 1]. Available from: https://www.medscape.com/viewarticle/927470