Portable ultrasound devices are ideally suited for lung ultrasound, as they can be more easily disinfected between patients than full sized trolley-based machines. Machines like the Apogee 2300 and Apogee 1000 Lite have been at the forefront of lung imaging in China during the outbreak, and we will begin to see an increase in interest and demand across Europe. The Apogee 2300 has been extensively used to assess the lung, as well as to provide guidance during intubation and to avoid puncture injuries in patients in critical shock. This is the machine we have used to illustrate this article.
The most common findings so far reported in COVID-19 patients are:
- Consolidated lung
- An irregular pleural line
The best transducer types for lung ultrasound are phased array and convex probes. Linear probes can also be used, but will lack penetration much further than the pleura.
Normal lung ultrasound findings
In normal patients (as well as in other conditions like asthma and COPD – but not COVID-19), the bright white echogenic pleural line will be reverberated down the screen. Each A line is equidistant from the next.
In normal patients, lung ‘sliding’ can be seen with regular breathing. This is the parietal pleura sliding against the visceral pleura.
- B-lines: In patients with interstitial pneumonia and diffuse alveolar damage, B-lines will be seen. There are vertical lines which arise from the pleural line, and extend all the way down the screen, obscuring A-lines. Their number increases with decreasing air content. At least 3 B-lines must be seen between a single rib space for a positive diagnosis. See Gargani (2011) for example images. With pulmonary oedema, B-lines are seen universally, but a characteristic of Covid-19 appears to be its patchy distribution. It is important, therefore, to check the patient from multiple views.
- Thickened and irregular pleural lines have been reported in COVID-19 patients, which may also be accompanied by lack of sliding. There may also be hypoechoic (dark) regions within the pleura.
- Consolidated areas of lung have also been reported. This is also referred to as ‘lung hepatisation,’ because the lung appears similar in density to the liver. The alveoli become filled with fluid, allowing the ultrasound energy to pass through without excessive scattering and loss, returning to the probe to create an image.
Pleural effusions are less common in Coronavirus patients. If you discover pleural effusions, first consider an alternative diagnosis.
Gargani, L. (2011). Lung ultrasound: a new tool for the cardiologist. Cardiovascular Ultrasound, 9.