B-lines are a vertical “comet-tail” artifact seen on lung ultrasound. They represent interstitial edema or increased lung water in thickened subpleural interlobular septa. In other words, B-lines represent fluid in the lungs (e.g., pulmonary edema, heart failure, etc.).
When performing lung ultrasound, I use a high-frequency linear probe and begin with the anterior and lateral chest views while the patient is positioned supine. Normal lung fields should demonstrate horizontal A-lines, while B-lines are identified as hyperechoic vertical lines extending from the pleural line to the far field. The presence of three or more B-lines in a single intercostal space is typically considered abnormal.
Furthermore, the number and distribution of B-lines can offer insights into the severity of the condition. Few B-lines may suggest mild interstitial syndrome, while numerous B-lines in multiple lung zones may indicate severe pulmonary edema.
