Discussion
In this study, we compared the findings from CXR, which is typically
conducted to evaluate lung expansion in preterm and term infants treated
with HFOV, with that of POCUS, which we performed in our NICU The level
of the right hemidiaphragm, which we assessed for lung expansion using
both CXR and POCUS, was comparable in both methods.
Unlike conventional ventilation, HFOV has a lung protective effect by
keeping hyperinflation at a minimum with low tidal volumes. However,
optimal lung volume must be ensured for effective ventilation and
oxygenation. Many experimental and clinical studies have been conducted
to evaluate optimal lung volume during HFOV. However, even though these
sophisticated devices used in studies provided more exact information
than SaO2 and diaphragm level measurements, they could
not be used in clinical practice due to practical difficulties[5-7,9-13].
Although measuring lung capacity during HFOV is challenging, CXR can be
used for approximation. Chest radiography is one of the most commonly
used imaging modalities in the NICU. CXR, which is mostly performed in
the anteroposterior supine position, is sufficient for the evaluation of
the chest wall, heart, lungs, diaphragm, catheter, and endotracheal
tubes. Because optimizing lung expansion is an important aspect of the
HFOV strategy, CXR should be performed frequently in the early phases of
HFOV, and subsequently at least daily as the patients become more
stable. Furthermore, if a small adjustment in mean airway pressure leads
to a significant increase in the patient’s oxygen requirement, CXR
should be performed to assess lung volume [14]. If
conditions do not improve or deteriorate despite performing lung opening
maneuvers to restore sufficient end-expiratory volume, a CXR should be
taken [15].
The position of the diaphragm and the relative flattening of the
diaphragm are two criteria to consider lung expansion. The right
hemidiaphragm should be located between the lower border of the
8th to 10th ribs for optimal lung
expansion. Although more advanced technologies are needed for more
precise lung volume estimation, CXR, which is routinely employed in all
neonates who require mechanical ventilation, appears to be a more
practical overall strategy [7,13,14]. However,
substantial concerns have recently emerged regarding the harmful
consequences of radiation exposure in diagnostic procedures
(radiography, computed tomography, angiography, etc.) that entail a high
risk of malignancy development. The risk of malignancy may increase
later in life due to both the effect of radiation exposure on cells in
the neonatal period and the fact that children who are growing are more
radiosensitive. Newborns in critical condition are still regularly
subjected to radiographic imaging during the management of pulmonary
diseases. The desire to reduce exposure and various disadvantages of CXR
have highlighted the POCUS in NICU. POCUS has become a more favorable
technology than radiography due to its point-of-care applicability,
diagnostic reliability, faster detection compared to CXR, lack of
radiation damage, repeatability, ability to evaluate disease course and
response to treatment, and low cost [16].
POCUS should become part of the clinical examination and should be
performed by clinicians who can properly interpret the images to avoid
time loss for newborns and should be regarded as an ethical choice
rather than an alternative method to radiography. For the clinicians to
perform POCUS, they should be trained for 6-8 weeks and have evaluated
about 20-30 patients [17,18]. In our study, POCUS
was performed by a neonatologist who had previously been trained and
used ultrasonography in her daily practice.
In this study, we evaluated the extent of lung expansion using
ultrasonography to reduce radiation damage in babies on HFOV in our
unit. With CXR, the right hemidiaphragm was recorded at the median
9th rib (8-11) while with POCUS it was recorded at the
7th (6-8.5) rib. We associated the difference of about two ribs with the
anatomical structure of the chest wall and the rib level of the right
hemidiaphragm being counted posteriorly with CXR and anteriorly with
USG. Such a good correlation of these measurements with each other shows
that lung aeration can be evaluated following adjustments in HFOV using
USG instead of CXR. Furthermore, the measurements taken at different
postnatal ages of patients in our study at different weeks of gestation
and with varied lung pathologies, as well as their correlation with CXR
findings, enhance the method’s clinical applicability regardless of
gestational age and pathology.
Our study is the first in this field as no other studies have been
conducted on this subject so far. However, randomized controlled studies
in larger patient groups are required to routinely employ
ultrasonography in the evaluation of appropriate lung volume, to respond
to patients more promptly, to reduce radiation exposure and time loss,
and to improve this method further.