Pulmonary barriers to oxygen transport in chest trauma.

The pathodynamics of respiratory insufficiency are based upon the impairment of movement of O2 from the atmosphere to the pulmonary capillary blood. In blunt chest trauma the mechanisms can be clarified in terms of mechanical barrier phenomena. Two barriers are identified. The first is the mass or gross lung-thorax complex and is determined by integrity of the chest wall and ventilation of the lungs. Impairments are manifested by reduced PaO2. The second is the micro complex of the alveolocapillary membrane. The disturbance is a combination of VA/Q alterations and increased diffusion barrier block and is manifested by reduced PaO2 and increased A-aDO2. These are summarized in Table 5. The degree of alteration in PaO2, and especially in A-aDO2, can distinguish between flail (loss of chest wall integrity) and flail plus contusion (VA/Q and a-c block). Management of chest wall-lung gross problems is well established and relatively successful. The micro barrier disturbance is more complex and difficult.