The following page summarises the main findings in normal lung, and those so far documented in COVID-19 patients – so far, only from humans. This page will be updated as more information emerges, or more veterinary cases are reported.
What equipment can you use for lung scanning?
Many veterinarians have moved away from cart-based ultrasound to portable ultrasound machines. This equipment is coming into its own right now in the world of human scanning, as doctors re-purpose handheld and laptop-based ultrasound to check patients with suspected COVID-19. The government recently procured 1200 portable machines for the new field hospitals.
Many veterinarians already their ultrasound equipment to check the lungs of their patients, often when performing ‘FAST’ scans to rule out collapsed lung (pneumothorax). In the following, article we discuss the basics of lung ultrasound, and how any portable ultrasound scanner with a convex, microconvex or phased array probe can be adapted for lung scanning. Linear probes can also be used, but provide limited information – usually of the pleura only.
The normal lung
In normal patients, ultrasound cannot pass freely through the lungs because the alveoli are filled with air. This means that all we will see in normal patients are the pleural line and A-lines. We will not see fluid, lung tissue or B-lines in normal patients.
What are A-lines?
In normal patients (as well as in other conditions like asthma and COPD in humans and animals – but not COVID-19), the bright white echogenic pleural line will be reverberated down the screen. This is termed an ultrasound artefact (the A-lines are not ‘real’). Each A line is equidistant from the next.
Another normal finding is lung ‘sliding,’ which can be seen with regular breathing. This is simply the parietal pleura sliding against the visceral pleura (see video below).
The abnormal lung
In diseased lung, sliding is frequently absent, and A-lines are obscured by B-lines.
What are 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.
With pulmonary oedema, B-lines are seen universally, but in some diseases, distribution can be patchy. It is important, therefore, to check the patient from multiple views.
Irregular pleural lines
A thickened and irregular pleura may also be accompanied by lack of sliding. There may also be hypoechoic (dark) regions within the pleura.
Also referred to as ‘lung hepatisation,’ because the lung appears similar to the liver. The alveoli become filled with fluid, allowing the ultrasound energy to pass through without excessive scattering and loss, and return to the probe and create an image.