DISCUSSION
Point-of-care LUS has gained significant popularity in emergency
settings recently. The earliest studies emphasized that LUS was a
valuable tool to identify bronchiolitis and it reduced the need for CXR.
Moreover, LUS was in agreement with clinical scores to predict the
severity of the disease. Lung ultrasound was found to be an accurate
device for both diagnosis and management in emergency departments ³ˉ⁵´
¹⁰ˉ¹². We have reported that sonographic scores had significant
agreement with clinical scores to predict the disease severity and the
need for respiratory support, consistent with previous studies. However,
clinical scores may vary individually as non-objective parameters.
Performing LUS for bilateral anterior and posterior chest areas to
obtain echographic scores may be difficult and time-consuming as infants
may not stay calm during the whole period of assessment. For this
reason, these scoring tools may not be rapid, practical, or objective
enough to accurately quantify the severity of the disease and guide
management in the emergency department.
Diaphragm ultrasound (DUS) has also been used in adult and pediatric
intensive care units in order to identify weaning success from
mechanical ventilator, diaphragm paralysis after cardiac/thoracic
operations, or normal values for healthy individuals. In these studies,
TF, EXC, and TEE were found to be good predictors for successful weaning
or diaphragmatic fatigue in particular ¹⁵ˉ¹⁷. There are few such studies
involving the pediatric population, unfortunately.
To our knowledge, there is one study evaluating DUS parameters in
infants with bronchiolitis. Buonsenso et al. ²¹ concluded that clinical
score was correlated with echographic score. The IS values differed
significantly between echographic score groups and patients needing
respiratory support had higher IS values, supporting our findings. They
also reported that EXC was lower in the moderate echographic group
compared with the mild group, but there was no statistically significant
difference between the mild and normal group. In our study, IS, ES, and
EXC values were higher in the moderate-severe group than the mild group
for both clinical and echographic scores. Because there were no patients
with normal echographic scores, we could not compare that category.
Buonsenso et al. ²¹ did not conclude any correlation between respiratory
rate and diaphragm parameters, although we found IS to have a
significant correlation with respiratory rate at admission. This
discrepancy may be related to the different numbers of patients in the
two studies (61 versus 104). Although TF was found to be a valuable
predictor for extubation success from mechanical ventilator in previous
studies, it did not differ between bronchiolitis severity groups in
either of these studies. Buonsenso et al. ²¹ also concluded that
patients with lower TF values required respiratory support, in contrast
to our findings, wherein we considered IS and TEE for predicting the
need for respiratory support. In their study, 25 of 61 patients required
respiratory support, 5 of whom were in the mild group, 15 in the
moderate group, and 5 in the severe group, although all 6 patients who
received HFNC oxygen therapy were in the severe group. Measurements were
evaluated at admission in both studies. We could repeat the measurement
of diaphragm parameters of 2 patients in 2 hours after starting HFNC
oxygen therapy; IS, ES, EXC, TEI, and TEE were all decreased as the
respiratory support reduced the work of breathing, but this difference
was not observed for TF. The number of patients for this observation is
too low for a firm conclusion, but this may have been related to the
pathophysiology of bronchiolitis. El-Mogy et al. ²⁸ concluded that
diaphragm thickness increased and excursion decreased at higher levels
of continuous positive airway pressure (CPAP), although there were no
significant differences found among diaphragmatic dimensions for levels
of either nasal CPAP or high-flow therapy. To our knowledge, there is no
study evaluating the effects of HFNC oxygen therapy on DUS parameters
among children. In comparison with a study that evaluated normal TEE and
EXC measurements in healthy children, our measurements were lower than
those among the age group of 1-12 months, suggesting that bronchiolitis
causes diaphragmatic dysfunction. Nevertheless, our EXC measurements
were also lower than those in a study that evaluated bronchiolitis
patients ²¹. We think that measurement in a semi-recumbent or supine
position could change EXC values. In an adult study aiming to show
changes in diaphragmatic function during breathing control in healthy
participants, EXC values before the test were similar to our findings.
Diaphragm excursion measurements differed in various studies,
interestingly ¹⁹´²⁹.
Our study has some limitations. First, there were few patients in the
severe bronchiolitis group according to both mRDAI and BUS values, so we
had to compare diaphragm parameters between mild and moderate-severe
groups. Second, we could only repeat the examination of DUS after
starting HFNC oxygen therapy for 2 of 6 patients; if we had been able to
perform the examination for all 6 patients, we could have obtained more
useful information.
In conclusion, there was agreement between the clinical and sonographic
severity scores, so lung ultrasound was considered valuable for the
evaluation of bronchiolitis. To our knowledge, this is the first study
evaluating ES measurements with DUS in bronchiolitis patients. To
determine the severity of the disease, IS and ES measurements were both
qualified as reliable predictors. Additionally, IS values provided
convenient information about the length of stay in the hospital.
Diaphragm ultrasound appears to be an objective and useful tool to help
the physician make decisions about the evaluation and management of
bronchiolitis in emergency settings.