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

Background 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. Methods 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 (PtcCO(2)) and O-2 (PtcO(2)), fraction of inspired oxygen (FiO(2)), preductal peripheral hemoglobin saturation (SpO(2)) and derived metrics (SpO(2)/FiO(2), oxygenation index (OI) and oxygen saturation index (OSI)) were assessed. Results 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). PtcCO(2) was similar between groups. Oxygenation was better in neonates who did not receive surfactant (PtcO(2)/FiO(2) ratio = 281 [211-346]; SpO(2)/FiO(2) ratio = 445 [388-462]; OI = 2.1 [1.6-2.6]; OSI = 1.3 [1.3-1.5]) than in those who did (PtcO(2)/FiO(2) = 168 [110-244], p = 0.003; SpO(2)/FiO(2) = 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). Conclusions 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.