Pleural line thickness reference values for preterm and term newborns

Background In lung ultrasound (LUS), the pleural line is an artifact whose thickness depends on the underlying lung pathology. To date there are no published studies on normal values of pleural line thickness (PLT) in newborns. Objective The aim of our study is to describe normal PLT values in term newborn (TN) and preterm newborn (PTN). Methods We recruited eupneic TN and PTN, under 34 weeks of gestation, on their first 24 hours of life. Newborns presenting any respiratory distress since birth were excluded. LUS was performed in four areas: upper anterior, lower anterior, lateral and posterior. At each location, we measured PLT and values where compared. Intraobserver and interobserver agreement were assessed using the intraclass correlation coefficient (ICC), and the kappa coefficient. Results We included 23 TN with a median birth weight of 3365 g (interquartile range [IQR] 3100-3575 g) and a median gestational age of 39 weeks (IQR, 38-40 weeks). In the PTN group, 23 patients were included with a median birth weight of 1350 g (IQR, 1150-1590 g) and a median gestational age of 31 weeks (IQR, 30-32 weeks). Median PLT values were less than 1 mm, and there were no significant differences between groups at any locations, with the exception of the left lower anterior field (0.79 mm [IQR, 0.72-0.89 mm] vs 0.68 mm [IQR, 0.62-0.72 mm]). Intraobserver agreement was high: consistency ICC 0.77 (95% confidence interval [CI], 0.32-0.92) and absolute ICC 0.78 (95% CI, 0.34-0.93). Interobserver agreement was high for the definition of thin pleural line as less than 1 mm. Conclusions TN and asymptomatic PTN have similar PLT values. Overall, PLT in healthy newborns should be less than 1 mm.