Inspiratory-expiratory variation of pleural line thickness in neonates with and without acute respiratory failure

Background There are relatively few data about the ultrasound evaluation of pleural line in patients with respiratory failure. We measured the pleural line thickness during different phases of the respiratory cycle in neonates with and without acute respiratory failure as we hypothesized that this can significantly change. Methods Prospective, observational, cohort study performed in an academic tertiary neonatal intensive care unit recruiting neonates with transient tachypnoea of the neonate (TTN), respiratory distress syndrome (RDS) or neonatal acute respiratory distress syndrome (NARDS). Neonates with no lung disease (NLD) were also recruited as controls. Pleural line thickness was measured with high-frequency ultrasound at end-inspiration and end-expiration by two different raters. Results Pleural line thickness was slightly but significantly higher at end-expiration (0.53 [0.43–0.63] mm) than at end-inspiration (0.5 [0.4–0.6] mm; p = 0.001) for the whole population. End-inspiratory (NLD: 0.45 [0.38–0.53], TTN: 0.49 [0.43–0.59], RDS: 0.53 [0.41–0.62], NARDS: 0.6 [0.5–0.7] mm) and -expiratory (NLD: 0.47 [0.42–0.56], TTN: 0.48 [0.43–0.61], RDS: 0.53 [0.46–0.65], NARDS: 0.61 [0.54–0.72] mm) thickness were significantly different (overall p = 0.021 for both), between the groups although the absolute differences were small. The inter-rater agreement was optimal (ICC: 0.95 (0.94–0.96)). Coefficient of variation was 2.8% and 2.5% for end-inspiratory and end-expiratory measurements, respectively. These findings provide normative data of pleural line thickness for the most common forms of neonatal acute respiratory failure and are useful to design future studies to investigate possible clinical applications.