Sonographic Assessment of Postural Lung Recruitment in Pediatric Patients Under General Anesthesia

Anesthesia-induced atelectasis is a well-known entity observed in approximately 68-100% of pediatric patients undergoing general anesthesia. The collapse of dependent lung zones starts with anesthesia induction but can persist for hours or even days after surgery. Lung collapse is a pressure-dependent phenomenon. Each acinus has a critical closing pressure, i.e., the minimum transpulmonary pressure (Ptp) below that the acinus begins to collapse. While airway pressure is homogeneously distributed within all lung units, Pleural pressure increases along the vertical gravitational vector because of the lung's weight. As a consequence, the decreased Ptp in the dependent zones promotes collapse. This means that patients in the supine position suffer from increasing closing pressures in the ventral to dorsal direction. Alveolar recruitment maneuvers recruit collapsed alveoli, increase gas exchange, and improve arterial oxygenation. The investigators hypothesized that in children with anesthesia-induced atelectasis, postural changes have recruiting effects and improve lung aeration assessed by lung ultrasound.