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).