A man presented with fractures of 4th to 10th ribs and respiratory distress after a Road Traffic Accident (A). He is diagnosed to have flail chest and a PaO2, of

Flail chest occurs when three or more contiguous ribs are fractured in at least two locations. Paradoxical movement of this free-floating segment of chest wall may be evident in patients with spontaneous ventilation, due to the negative intrapleural pressure of inspiration. The decreased compliance and increased shunt fraction caused by the associated pulmonary contusion that is typically the source of postinjury pulmonary dysfunction. Pulmonary contusion often progresses during the first 12 hours. Resultant hypoventilation and hypoxemia may require presumptive intubation and mechanical ventilation. Ref: Cothren C., Biffl W.L., Moore E.E. (2010). Chapter 7. Trauma. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.