Lung Ultrasound in COVID-19

A combination of clinical presentation with positive reverse transcriptase polymerase chain reaction (PCR) testing is the current standard to diagnose Coronavirus Disease 2019 (COVID-19).^{1, 2} Challenges to this approach include lack of specificity of signs and symptoms, and limitations of PCR testing including test availability, delays in obtaining test results, and false negative test results early in the clinical course.^{1, 3}

Chest computed tomography (CT) scans have high sensitivity (98%) for detecting pulmonary infiltrates compared to PCR testing (78%) in COVID-19.¹ However, CT scans are costly, require extensive disinfection, lack portability, and expose patients to radiation. The American College of Radiology explicitly recommends against routine use of CT scans in COVID-19 patients. Lung ultrasound (LUS) has shown strong correlation with chest CT scans for diagnosing and monitoring COVID-19 lung disease.¹ Its portability, ease of disinfection, and immediate availability of results are major advantages in COVID-19.

This article describes common LUS findings, diagnostic accuracy of LUS compared to CT scans, different LUS protocols and scoring systems, and potential use for prognostication in COVID-19.

Diagnostic Accuracy

LUS has comparable diagnostic accuracy as chest CT scans for severe COVID-19 lung disease.³ In an observational study of suspected COVID-19 patients, LUS had a sensitivity of 92%, specificity of 71%, positive likelihood ratio of 3.1, and negative likelihood ratio of 0.1 compared to chest CT scans, and no significant difference was seen in sensitivity and specificity of LUS versus chest CT scan. Another study demonstrated similar sensitivity (89%) for LUS in patients suspected of COVID-19 presenting to an emergency department.⁵

LUS Findings in COVID-19

The posterior and lower lung zones are most often affected in COVID-19.² New or worsening infiltrates in the anterior zones may herald clinical deterioration.⁶ LUS findings in COVID-19 typically extend to the periphery, making them easily visualizable with ultrasound. LUS patterns have been progressively described as follows (see images):^{1, 2}

• mild to moderate (early): Irregular and thickened pleural line; discrete B-lines alternating with normal lung with A-lines (“skipped lesions”); small consolidations (~1 cm).
• severe (progressive): Confluent or fused B-lines; large consolidations.
• critical (advanced): Extensive confluent B-lines and consolidations in upper and anterior lung zones; bilateral interstitial pattern with consolidations ± air bronchograms in the posterobasal lung zones.

Pleural effusions and lymphadenopathy are only seen in 7-9% of COVID-19 patients.¹ A smooth pleural line with discrete B-lines in the upper lung lobes is suggestive of cardiogenic pulmonary edema, while an isolated lower lobe consolidation with dynamic air bronchograms is more likely bacterial pneumonia.^{2, 4}