Lung water, aeration and function in late preterm/term neonates: subgroup analysis of the ULTRAS study.

Abstract

We aimed to study the pathophysiology of late preterm and term neonates with respiratory failure, without lung inflammation, and identify features associated with surfactant treatment. Ancillary subgroup analysis of a prospective multicenter cohort study. Forty-eight neonates were enrolled. Extravascular lung water (estimated as thoracic fluid content (TFC)), lung ultrasound score (LUS) and extended LUS (eLUS), transcutaneous partial pressure of carbon dioxide (PtcCO₂) and O₂ (PtcO₂), fraction of inspired oxygen (FiO₂), preductal peripheral hemoglobin saturation (SpO₂) and derived metrics (SpO₂/FiO₂, oxygenation index (OI) and oxygen saturation index (OSI)) were assessed. TFC was similar between neonates treated (13.2 [10.7-16.6] KOhm^-1/Kg) and not treated with surfactant (15.6 [12.9-19.7] KOhm^-1/Kg, p = 0.197). Lung aeration was better in neonates who did not need surfactant (LUS = 6 [4-8]; eLUS = 11 [9-16]) than in those who did (LUS = 10 [10-12], p < 0.001; eLUS = 19 [17-20], p < 0.001). PtcCO₂ was similar between groups. Oxygenation was better in neonates who did not receive surfactant (PtcO₂/FiO₂ ratio = 281 [211-346]; SpO₂/FiO₂ ratio = 445 [388-462]; OI = 2.1 [1.6-2.6]; OSI = 1.3 [1.3-1.5]) than in those who did (PtcO₂/FiO₂ = 168 [110-244], p = 0.003; SpO₂/FiO₂ = 233 [183-288], p < 0.001; OI = 3.9 [2.5-5.4], p = 0.002; OSI = 2.6 [2.2-3.3], p < 0.001). Late preterm and term neonates with respiratory failure treated with surfactant show decreased lung aeration associated with impaired oxygenation likely due to surfactant insufficiency rather than excessive extra-vascular lung water. Late preterm and term neonates receiving surfactant show decreased lung aeration and impaired oxygenation, likely due to surfactant insufficiency, rather than to excessive extra-vascular lung water. This helps characterising respiratory failure in late preterm and term neonates and identifying those who are at risk of surfactant insufficiency and need closer monitoring.