The evaluation of the lung by ultrasound is an adjunct tool to the
clinical assessment. Among different hallmarks at lung ultrasound,
B-lines are well known artifacts which are not correlated to
identifiable structures but can be used as an instrument for
pathological classification. Multiple B-lines are the sonographic sign
of lung interstitial syndrome with a direct correlation between the
number of B-lines and the severity of the interstitial involvement of
lung disease. In neonatology and paediatrics, the quantitative
assessment of B-lines is questionable as opposed to in adult medical
care. Counting B-lines is an attempt to enrich the clinical assessment
and clinical information, and not simply arrive at a dichotomous answer.
A semiquantitative or quantitative B-lines assessment was shown to
correlate with fluid overload and demonstrated prognostic implications
in specific neonatal and paediatric conditions. In neonatology, the
count of B-lines is used to predict the need for admission in neonatal
intensive care unit and the need for exogenous surfactant treatment. In
paediatrics, the B-lines count has the role of quantifying hypervolemia
in infants and children receiving dialysis. B-lines as predictors of
length of stay in the paediatric intensive care unit after cardiac
surgery, as a marker of disease severity in bronchiolitis, or as an
indicator of lung involvement from SARS-CoV-2 infection are speculative
and not yet supported by solid evidence. Lung ultrasound with the
quantitative B-lines assessment is promising. The current evidence
allows to use the quantification of B-lines in a limited number of
neonatal and paediatric diseases.