Neonatal RDS and LUS, is the debate still open?
Dear Editor,
we read the letter to the editor “B-lines score: artifacts as a sign of
neonatal specific disease?” by Quarato et al. and we are pleased by the
interest aroused by our article “Neonatal lung ultrasonography score
after surfactant in preterm infants: A prospective observational study”
published on your journal1. This study included
preterm neonates with respiratory distress syndrome (RDS), requiring
non-invasive ventilation and surfactant. The aim of our citated study
was to asses changes of a validated neonatal lung ultrasonography score
(nLUS) after surfactant treatment. Our data demonstrate a lowering of
the nLUS 2h and 12h after surfactant treatment.
In their letter to the editor Quarato et al. expressed criticism about
the nLUS score validation and about the utility of the Lung Ultrasound
(LUS) as a diagnostic tool. They conclude that “LUS can be used only
for diagnosing minimal pleural effusion and, at least, as complementary
imaging, in addiction to chest radiographs (CR), for monitoring the
reduction of subpleural pneumonitic consolidations under therapy”.
Our citated study hasn’t focused on validation of the nLUS score or on
LUS as a diagnostic tool for neonatal RDS, so we don’t get how Quarato’s
concerns can be addressed to our paper. Nevertheless, finding the debate
about nLUS or LUS in the neonatal field an occasion to promote an
improving in the care of the preterm babies, we will discuss objections
raised in Quadrato’s work, point by point.
First of all: Quarato et al. claim that B-lines can be present in a
normal lung. Coalescent B-lines wouldn’t distinguish neonatal RDS from
fibrosis, severe fluid overload due to congenital heart disease or renal
failure. Moreover, B-lines are present in hydropneumothorax, subpleural
cysts, blebs, emphysema, minimal pleural effusion and residual cavity of
pneumectomy. This leading to the conclusion that we should not use LUS
in management of neonatal RDS.
In our neonatal intensive care unit (NICU) RDS is managed following
European Consensus Guidelines on the Management of Respiratory Distress
Syndrome - 2019 Update2 and we agree with the
statement “LUS may be a useful adjunct to clinical decision making,
with RDS lungs having a specific appearance that can be differentiated
from other common neonatal respiratory disorders and it has potential to
reduce X-ray exposure”2. We assert that after a
clinical suspicion of a specific disease, laboratory and instrumental
tests, including LUS, are tools that can be used by the neonatologist
both to confirm the diagnosis and to exclude other pathological
conditions. Surfactant, in a neonate of few hours of life, is
administrated considering gestational age and FiO2 and
guidelines, in selected situation, don’t exclude a clinical diagnosis,
not requiring instrumental tests, to guide the
therapy2. Clearly, diagnosis as fluid overload due to
renal or heart disease, fibrosis, residual cavity of pneumectomy are not
a usual differential diagnosis of the neonatal RDS and should be
considered because of pre-postnatal clinical history or specific
physical/laboratory signs (eg. congenital heart disease suspicion won’t
be formulated by CR or LUS but by cyanosis unresponsive to oxygen
therapy or blood gas analysis showing low PaO2 with a
normal or low PaCO2).
Another point by Quarato et al. was the intra and inter-operator
variability of the nLUS. They also stated that some artifacts used to
produce the score could be due to the type of probe used or to the
inappropriate set-up of the sonographer. Furthermore, the nLUS is
criticised as it would investigate not more than 70% of pleural
surface.
It is known the nLUS has been validated in a previous
study3 and neonatal LUS agreement between operators
has been tested too4,5. Previous validation of the
score was the reason for us to use it in our study. Both type of probe
and ultrasound machine settings are defined in the “method” section of
our study. We don’t deny some limits of the nLUS, like not resulting
from a complete study of the pleural surface. The decision not to extend
LUS study to the posterior hemithorax has been motivated with the NICU
setting, being neonates requiring intensive care instable. Moreover,
concerns about the setting of the sonographer are not realistic, as it
should be clear that LUS has to be performed only by trained operators
(eg. an image like fig.1b presented by Quarato et al should be
immediately recognised as inadequate by the physician and cannot be
stored in the clinical records or used to take a clinical decision).
Furthermore, it is a Quarato et al. opinion that LUS is not able to
manage a specific disease like RDS. The authors motivated this position
reporting a review by Hiles et al6. They also
nominated some guidelines in order to present no international
acknowledgement for recommending LUS for the diagnosis of neonatal RDS.
The review presented by Quarato et al, focused on chest x-ray vs LUS, is
quite outdated, being published on 2016 and missing some studies like
these7-9. A more recent review and
meta-analysis10 state that “LUS, particularly LUS
score, can be used accurately to determine the need for surfactant
replacement treatment or mechanical ventilation in infants with
respiratory distress treated with nCPAP support”. About the nominated
guidelines, authors decided not to cite them. So, it could be our
mistake, but we couldn’t find (not even in one of them) the paragraphs
focusing on the neonatal RDS. In our NICU, anyway, LUS is performed
following these guidelines11 and
protocol12, which are focused on the neonate’s
disease. Differential patterns of LUS referring to the RDS are
presented, being specific for the detection of: transient tachypnea of
the newborn, RDS, meconium aspiration syndrome, pneumonia, atelectasis,
pneumothorax, pleural effusion and normal lung.
A sentence about surfactant replacement treatment not being cause of
changes on the neonatal lung visible on LUS is reported by Quarato et
al. The sentence was due to an interesting study of Cattarossi et
al13, published in 2010. Key message is that
surfactant resolves regional alveolar aeration, but it does not affect
total lung fluid content. We shared this message in our study. For this
reason, we analysed not only nLUS, but also LUS patterns changes 2h and
12h after surfactant administration. We showed how LUS patterns don’t
change immediately after surfactant therapy. As stated in “conclusion”
section of our study, this data could be due to a wide nLUS variation
(0-18) that permits to detect even little changes in lung fluids,
undetectable performing a global analysis of LUS patterns. Another
possibility is that nLUS changes with an increase in aeration of the
lung, being this situation demonstrated, in adult, in positive end
expiratory pressure induced lung recruitment14.
We thank Quarato et al. to have focused on nLUS and LUS, giving us the
opportunity to discuss about them. We want to remark a data taken from a
study demonstrating the reduction of radiation exposure in “A.Béclère
Medical Center”, Paris, France, with the use of LUS in NICU from
201415. The average number of chest X-rays per baby
and the mean radiation dose per baby were calculated before the
introduction of LUS. Chest X-ray entrance surface dose was 28, 30 and 32
µGy for babies weighing less than 1500 g, 1500-2500 g and more than 2500
g, respectively. The Reduction of radiation exposure should be a goal in
a NICU setting, because of the vulnerability of premature patients even
to radiation. Both the nLUS and LUS represent interesting subjects in
the neonatal research field. Nevertheless, we consider LUS a tool in the
ordinary evaluation of a neonate clinically diagnosed with RDS,
according to the most recent European guidelines2.
- Perri A, Tana M, Riccardi R, et al. Neonatal lung ultrasonography
score after surfactant in preterm infants: A prospective observational
study. Pediatr Pulmonol . 2020;55(1):116-121.
doi:10.1002/ppul.24566
- Sweet DG, Carnielli V, Greisen G, et al. European Consensus Guidelines
on the Management of Respiratory Distress Syndrome - 2019
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in Neonates Treated With Continuous Positive Airway
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