Wet B-lines are made by water and decreased by diuretics, which cannot modify dry B-lines made by connective tissue. The number and spatial extent of B-lines on the antero-lateral chest allows a semi-quantitative estimation of EVLW (from absent, ≤5, to severe pulmonary oedema, 30 B-lines). Increasing EVLW accumulation changes the normal, no-echo signal (black lung, no EVLW) into a black-and-white pattern (interstitial sub-pleural oedema with multiple B-lines) or a white lung pattern (alveolar pulmonary oedema) with coalescing B-lines.
Lung ultrasound shows B-lines, comet-like signals arising from a hyper-echoic pleural line with a to-and-fro movement synchronized with respiration. In pulmonary congestion however, the presence of both air and water creates a peculiar echo fingerprint.
