Bedside Ultrasound to Monitor Lung Function and Blood Flow in Newborns Treated With Surfactant

The ULISSES study (Point-of-Care Ultrasonography for Assessing Lung Aeration and Pulmonary Vascular Resistance Dynamics After Surfactant Administration in Neonates With Respiratory Distress Syndrome) is a prospective, multicenter, non-interventional (observational) study involving approximately 200 preterm neonates across 10-12 tertiary-level neonatal intensive care units (NICUs) in Poland. The study is designed to evaluate real-world practices related to the use of point-of-care lung ultrasound (LUS) in the decision-making process for surfactant therapy in neonates with Respiratory Distress Syndrome (RDS). The investigation is aligned with evolving European neonatal care guidelines that recommend incorporating LUS findings alongside traditional oxygen thresholds (FiO₂) when determining surfactant need. All enrolled neonates will undergo a baseline lung ultrasound within the first 6 hours of life, prior to surfactant administration. LUS scoring will follow a validated 5-point scale (0-4) per lung quadrant, resulting in a total score between 0-16. A second LUS examination will be performed between 24 and 30 hours after surfactant administration to assess treatment response and identify any asymmetry in lung aeration, defined as a side-to-side LUS score difference ≥2 points. In a subset of centers that routinely conduct neonatal hemodynamic assessments, echocardiographic evaluation of the main pulmonary artery (MPA) and ascending aorta (AA) diameters will be carried out. The MPA-to-AA ratio will serve as a surrogate marker of pulmonary vascular resistance and potential pulmonary hypertension. A ratio \>1.3 will be considered indicative of clinically significant pulmonary arterial hypertension, consistent with published literature. The surfactant treatment (product: Curosurf) will be administered per standard clinical practice, including both LISA (Less Invasive Surfactant Administration) and INSURE (INtubation, SURfactant administration, Extubation) methods. The mode of surfactant delivery and timing of administration will be recorded, as will any need for redosing. Comprehensive clinical data-including gestational age, birth history, comorbidities, oxygenation parameters (SpO₂/FiO₂), and level and duration of respiratory support-will be collected through the neonatal hospital stay. Respiratory support will be categorized into escalating classes from spontaneous breathing to mechanical ventilation, to allow stratified analysis of post-surfactant respiratory outcomes. The study will also explore associations between post-treatment lung ultrasound asymmetry, mode of surfactant delivery, and the presence of pulmonary comorbidities using multivariable logistic regression modeling. All data will be collected in accordance with good clinical practice and applicable data protection regulations. As a non-interventional study, ULISSES is intended to provide evidence on the integration of bedside imaging into neonatal care, without altering routine clinical management. The planned study duration is from end-July 2025 to December 2026.