Respiratory distress syndrome (RDS) is a common problem in preterm infants. This condition is caused by deficiency of pulmonary surfactant in an immature lung and is related to morbidity and mortality in preterm infants. The incidence of RDS increases with the decreasing of gestational age (GA). The National Institute of Child Health and Human Development Neonatal Research Network reports a 93 percent incidence of RDS in a cohort of extremely preterm infants (GA 28 weeks or below)1. Although the risk is lower, RDS occurs even in a significant number of late preterm infants2. Diagnosis of RDS is based on clinical manifestations, arterial blood gas and chest X-ray findings. Chest X-ray is considered a first-line imaging test for diagnosis of RDS2. Chest X-ray findings, however, are not related to the respiratory prognosis3 .

Recently, lung ultrasonography (LUS) has been used in critically ill patient and it has become an important tool for neonatologists4. Specific LUS patterns have been described for typical neonatal respiratory conditions such as RDS5, transient tachypnea of the newborn (TTN)6, meconium aspiration syndrome (MAS)7, and pneumothorax8,9.As reported in The Consensus Conference on lung ultrasound, both LUS and chest X-ray are accurate in the diagnosis of RDS and TTN in neonates10.

Surfactant replacement therapy is crucial in the management of RDS. Recent guidelines recommend to treat affected babies with early nasal continuous positive airway pressure (nCPAP) and early selective surfactant administration10. The European Association of Perinatal Medicine and the American Academy of Pediatrics advise surfactant administration when oxygen requirement increases despite early nCPAP treatment11,12. Some studies have recently highlighted the usefulness of LUS in predicting neonatal intensive care unit admission or the need for mechanical ventilation13,14 or nCPAP failure15. Many scores based on LUS findings have proved their reliability in adult critical care16,17. In the neonatal field few studies presented chest X-ray derived scores18 or directly compared LUS with chest ray. There are no data, to our knowledge, that compare the accuracy of LUS with chest X-ray in predicting the need for surfactant administration in infants with RDS18-20.

Basically, each lung was divided into 3 areas (upper anterior, lower anterior, and lateral) and examined using a linear microprobe through both transverse and longitudinal scans. For each lung area, a 0- to 3-point score was given (total score ranging from 0-18). The LUS score encompassed signs typical of TTN and RDS21-22 . and described the total spectrum of possible conditions (a normal aerated lung, an interstitial pattern, an alveolar pattern, and consolidation). In details, the LUS score was assigned as follows:0 indicates A-pattern (defined by the presence of the only A-lines); 1, B-pattern (defined as the presence of ≥3 well-spaced B-lines); 2, severe B pattern (defined as the presence of crowded and coalescent B lines with or without consolidations limited to the subpleural space); and 3, extended consolidations. A-lines represent reflection of pleura due to ultrasound diffusing through an airfilled lung; B-lines are due to fluid filling the interstitium (and the alveolar space if they become confluent)23,24.