High inspired oxygen concentrations (FiO2) are claimed to cause resorption atelectasis increasing the risk for perioperative hypoxemia and postoperative pulmonary complications. Pediatric physicians are still reluctant to accomplish low FiO2 strategies in children. We investigated the association between lung ultrasound score (LUS) and arterial oxygenation (PaO2/FiO2 ratio)in anesthetized mechanically ventilated children undergoing non-abdominal surgery using different FiO2 fractions.