DISCUSSION
To our knowledge, this is the first multicenter national study assessing
LUS findings and their prognostic role in a relatively large cohort of
children with microbiologically confirmed SARS-CoV-2 infection. Overall,
we found that children with higher LUS scores and with subpleural
consolidations have a significantly higher risk of being hospitalized or
require oxygen support after initial assessment in the PED.
Our study confirms, on a larger populations, what initially suggested by
smaller pediatric cohorts from Italy, Turkey and Spain, showing that
children with LRTI during SARS-CoV-2 infection can have a cohort of LUS
findings such as vertical artifacts and subpleural
consolidations.13-22 Authors from four different
hospitals in Italy, in particular, found vertical artifacts and
subpleural consolidations to be the most common findings, while pleural
effusions were more rare and more described in children with MIS-C.
However, cohorts were mostly limited to less than 50 patients. In
general, these LUS artifacts are in line with what we have learnt from
the past decade of LUS practice in pediatrics. Although the initial role
of LUS has mostly been detecting pneumonia in children, its role has
significantly evolved. 8 The better understanding of
different semeiotic LUS patterns and of their physical mechanismsled
authors to investigate if specific LUS patterns may better discriminate
different lung conditions. 23 For example,
pediatricians from Rome found LUS patterns (like large consolidations,
complicated effusions, fix or liquid bronchograms) as more predictive of
bacterial or more severe pneumonia. 24, 25Similarly,
two independent teams investigated if some LUS patterns may be more
associated to viral or bacterial pneumonia, both finding that small
subpleural consolidations and vertical artifacts are more frequent in
viral LRTIs, while large consolidations with bronchograms more in
bacterial etiologies. 26, 27 Therefore, our findings
that vertical artifacts and small subpleural consolidations are more
frequent in Covid-19 pneumonia is in line with what expected from
previous LUS literature in adults with Covid-19 or children with other
viral conditions. 8
Our multicenter study allowed us to include a larger number of patients
and provide information about prediction of severity, but also
subanalyses according to age groups. Unsurprisingly, our study found
that children with higher LUS scores of subpleural consolidations had a
higher risks of needing hospitalization or oxygen support. These
findings are in line with a few pediatric studies which included very
small number of children with severe disease, but also confirm studies
from adults with Covid-19.13-19 In adults, several
studies have documented how LUS performed in the ED can predict
hospitalization, ventilation support and deaths.10-12Our findings are not unexpected in light of recent understanding of the
physical bases of LUS. 23 In particular, there is
growing agreement in literature that vertical artifacts represent
peripheral lung abnormalities that generate acoustic traps, eventually
seen as vertical lines on LUS. As these abnormalities represent areas of
dysventilation and possibly altered gas exchange, it is not unsurprising
that those children with more abnormalities on LUS may have a higher
risk of developing more severe disease. Similar evidence is already
available from other pediatric respiratory conditions like acute
bronchiolitis, where several studies have documented that children with
higher LUS score have a higher risk of hospitalization, respiratory
support and intensive care unit admission.28
In our study, we performed subanalyses according to age groups. In
general, we found that lung involvement was more significant in children
older than 1 year of age, which is in line with a well-established
although not yet fully understood gradient of more severe disease
according to increasing age.1 Some authors have
suggested that better innate immunity in the upper airways might have
contributed to lesser degree of LRTIs in children. 29In our cohort, children younger than 1 year of age had, in fact, less
frequently vertical artifacts and subpleural consolidations, supporting
this hypothesis. However, this age groups may also have been protected
by maternal antibodies, since maternal vaccinations have started during
the study period, although we did not collect this information.30 Conversely, when we divided our cohorts in children
younger than 5 years, 5-11 and older than 12 years of age (which
reflects the different age groups that have had access to vaccination),
the characteristics of LUS patterns were similar, suggesting that
children younger than 5 years of age have a similar rate of LRTI
involvement than older one. These data may have clinical implications,
as can provide further information to both healthcare workers and
parents about the decision of vaccinating or not younger children, a
still debated topic.31
Our study has limitations to address. The most important limit is the
low number of children with critical Covid-19 that required mechanical
ventilation. However, such a severe outcome is very rare and would
require significantly larger populations, a limit difficult to overcome,
even with multicenter studies. Also, our study did not include
populations at higher risk of more severe Covid-19, including children
with comorbidities, black and latino communities, therefore our findings
may not be generalized to different epidemiological contexts. Also,
these data refer to pre-omicro era, and therefore more studies are
needed understand the impact of LUS in these cohorts. Last, we did not
included a cohort of vaccinated children, therefore we have not been
able to evaluate the impact of vaccination on the development of LRTI
during Covid-19 in children.
In conclusion, this national study on children with Covid-19 confirmed
that LUS is able to detect Covid-19 low respiratory tract involvement,
which is characterized by pleural line irregularities, vertical
artifacts and subpleural consolidations. Importantly, children with
higher LUS score have a higher risk of required hospitalization or
oxygen support, further supporting LUS a valid and safe point-of-care
first level tool for the assessment of children with Covid-19. Further
studies will be needed to understand how vaccinations and new variants
may determine a different degree of LRTI in children with Covid-19.