The acute respiratory distress syndrome (ARDS) is an acute lung injury that can be triggered by pulmonary (direct lung injury) and extrapulmonary (indirect lung injury) etiologies. Pediatric ARDS (pARDS) occurs in approximately 3% of children admitted to intensive care units (ICUs) and is associated with approximately 17% mortality. The primary etiologies of pARDS have been summarized as pneumonia (35%), aspiration (15%), sepsis (13%), near-drowning (9%), cardiac disease (7%), and other clinical conditions (21%). ARDS manifests as pulmonary inflammation, alveolar edema, and hypoxemic respiratory failure. Mechanical ventilation remains an essential component in the care of patients with ARDS. Many adjunctive treatments rely on pathophysiological considerations. The pathophysiology of ARDS is characterized by inflammatory, proliferative, and fibrotic phases. The different phases induce a ventilation-perfusion mismatch. Inflammation causes surfactant inactivation and depletion. A number of clinical studies have reported clinical benefits following the instillation of exogenous surfactant in pediatric patients with acute respiratory failure. On the other side, prone positioning seem to be a promising intervention in critically ill infants and children with infection-associated acute lung injury. However, data conflict on the use of prone positioning in pediatric patients with acute lung injury.

Turning patients with moderate to severe lung disease into prone position has shown many positive effects. Prolonged intervals of prone positioning have been associated with a decrease in mortality in adult patients with acute respiratory failure. An increase in partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2) has been described after 4 hours in prone position in adult patients with severe acute respiratory failure. Similarly, a decrease of the oxygenation index has been found after 8 hours of prone positioning in adult patients with respiratory failure from coronavirus disease of 2019 (COVID-19) associated acute respiratory distress syndrome. The process of prone positioning appeared safe also in critically ill infants and children. In a randomized control trial, it has been shown that in 90% of prone positioning oxygenation index decreased of more than 10% in children with acute lung injury.

Electrical impedance tomography (EIT) and lung ultrasound (LUS) are two non-invasive methods to monitor aeration and lung function parameters. EIT can quantify regional distribution of ventilation as well as improvement in end-expiratory air content. EIT has been used at bedside in critically ill adult patients to measure effects of prone position and also in infants with respiratory distress syndrome. On the other side, LUS has become an increasingly popular diagnostic bedside tool for lung examination. It is considered reliable and fast to detect various lung-related pathologies, such as pneumonia, atelectasis, pneumothorax, and interstitial syndrome.

The main objective is to determine the short-term effect of prone positioning in infants with infection-associated severe acute respiratory distress syndrome. To accomplish this, oxygenation parameters and measurements from EIT and LUS will be compared in mechanically ventilated infants in prone position versus supine position after surfactant administration.