Diaphragmatic ultrasound measurement
All the ultrasonographic measurements were made by the same pediatric
intensivist (who was specially trained) using a portable Esaote MyLab
Omega® system equipped with a 4–15 Mhz linear transducer for
diaphragmatic thickness (DT), diaphragmatic thickening fraction (DTF),
and a 6–10 Mhz convex transducer for diaphragmatic excursion (DE),
inspiratory slope (IS), and expiratory slope (ES). We evaluated right
diaphragm since previous studies demonstrated that there was no
difference in sonographic measurements between the two sides and right
diaphragm was easier to assess19,20. All patients were
supine with the head of the bed elevated 30⁰.
Measurements were obtained at the end of the two-hour ERT. First, as in
previous studies21, the linear transducer in B-mode
was placed between the anterior axillary and midaxillary lines, in the
9th and 10th intercostal spaces. The
diaphragm is depicted as a three-layer structure in this image, with two
parallel echoic lines (pleural and peritoneal lines) and a hypoechoic
structure between them (the muscle itself). DT was measured three times,
both at the end of inspiration (DTi) and expiration (DTe). The percent
change in DT between end-expiration and end-inspiration (DTF) was
calculated as (DTi-DTe/Dte) x 100 (Figure 1-A, B).
Second, using the right hepatic lobe as an acoustic window, the 2-5 Mhz
transducer was placed immediately below the right costal margin along
the mid-clavicular line and directed medially, cephalad, and dorsally.
The posterior third of the diaphragmatic muscle was visualized using
this technique. Then, M-mode is used to visualize the diaphragm’s motion
during the respiratory cycle. The diaphragm moves caudally toward the
probe during inspiration; it moves cranially away from the probe during
expiration. Three respiratory cycles were recorded, and the average was
calculated. DE is measured on the vertical axis of the trace from the
baseline to the point of maximum height of
inspiration22 (Figure 1-C, D). Three serial
respiration cycles were recorded for each patient, and mean values for
each diaphragmatic parameter was calculated. Intraobserver variability
of ultrasonic measurements were less than 10%.