A 56-year-old woman was transferred to the ED after high-energy thoracic trauma with multiple bilateral rib fractures resulting from a car accident. Because of bilateral hemopneumothorax, bilateral chest tubes were placed and mechanical ventilation was started. As the patient recovered, weaning from mechanical ventilation was initiated. Drainage stopped and chest tubes were removed a few days later. During a weaning trial, a severe flail chest that impaired respiratory efforts became apparent. Surgical stabilization of the chest cage was made with titanium clips. Finally, the patient was successfully weaned from the ventilator. Ten days later, respiratory failure gradually developed. On physical examination, no crepitation or collection was found near the surgical incision. On the auscultation of the left hemithorax, breath sounds were absent. A chest radiograph study showed opacification of the left hemithorax (Fig 1). Further evaluation with chest ultrasonography (US) was performed (Video 1).