Diaphragmatic Ultrasound in Neonates with Transient Tachypnea: Comparison with Healthy Controls and Inter-Operator Reliability

<b>Background:</b> The role of diaphragmatic function in transient tachypnea of the newborn (TTN) remains poorly understood. This study aimed to compare diaphragmatic ultrasound parameters between neonates with TTN requiring non-invasive ventilation (NIV) and healthy neonates. Secondary objectives include the relationships between these parameters and gestational age (GA), birth weight (BW), and the evaluation of inter-operator reproducibility. <b>Methods:</b> This prospective observational pilot study involved neonates with GA ≥ 34 weeks with clinical and ultrasound diagnosis of TTN treated with NIV. An equal number of healthy neonates served as controls. Diaphragmatic and lung ultrasound were performed on day 1 (T0) and day 2 (T1) of life. Measurements included end-inspiratory and end-expiratory diaphragmatic thickness (DTi and DTe, respectively), diaphragmatic excursion (DE), and Lung Ultrasound Score (LUS). Inter-operator reproducibility was tested in 31 neonates (62 scans in total). <b>Results:</b> Forty neonates were enrolled (20 TTN, 20 controls). DE was significantly higher in controls compared with TTN neonates (4.6 ± 0.9 mm vs. 5.4 ± 1.3 mm, <i>p</i> = 0.03) and increased from T0 to T1 in the control group (4.6 ± 1.1 mm vs. 5.4 ± 1.3 mm, <i>p</i> = 0.04), while no significant variation was observed in TTN cases. A negative correlation, approaching significance, was found between DE and LUS at T1 (<i>p</i> = 0.05). DTi and DTe increased linearly with GA and BW (<i>p</i> < 0.001). Bland-Altman analysis showed low bias and acceptable limits of agreement between measurements. <b>Conclusions:</b> The underlying pulmonary disease may influence diaphragmatic function in neonates with TTN. The integration of lung and diaphragmatic ultrasound could be useful for monitoring disease progression and follow-up.