Ultrasound examination
Our ultrasound examination was performed using a Philips ClearVue 350
portable system with an L12–4 MHz linear transducer by a single
well-trained pediatric emergency fellow. Lung ultrasound evaluation was
performed using the methodology previously described by Copetti et al.
¹⁸. Diaphragm ultrasound was performed when the patient looked calm, was
not coughing, and was not crying. Subjects were imaged in the supine
position. If the infiltration was unilateral, the pathological side was
evaluated, while if the lungs were bilaterally affected, then the mean
of the right and left side measurements was calculated. The average
values of three consecutive cycles were recorded. The transducer was
positioned between the 9th and 10thintercostal spaces in the mid-axillary/mid-clavicular line in the
coronal plane. First, the 2-dimensional mode was used to achieve the
best view between the two echogenic parallel lines of the pleura and the
peritoneum. Then M-mode imaging was used to obtain all DUS parameters.
During M-mode, a normally functioning diaphragm is detected as an
echogenic line that moves freely during inspiration and expiration.
During inspiration, the normal diaphragm moves caudally toward the
transducer, as an upward flexion. During expiration, the diaphragm moves
cephalad, away from the probe, as downward flexion. The diaphragm
excursion was measured on the vertical axis, tracing from the baseline
to the point of the maximum height of inspiration on the graph.
Diaphragm thickness (TD) was determined by measuring the vertical
distance between the midpoints of the pleural and peritoneal layers at
the end of inspiration and expiration ¹⁹. The thickening fraction was
calculated as (TEI – TEE)/TEE, where TEI is diaphragm thickness at the
end of inspiration and TEE is diaphragm thickness at the end of
expiration, and it was recorded as a percentage. The speed of
diaphragmatic contraction (IS) and relaxation (ES) and the total
duration time of the respiratory cycle were recorded (Figure 1).