Like any form of inflammation, acute lung injury during ARDS represents a complex process in which multiple cellular signalling pathways can propagate or inhibit lung injury. Death has traditionally been attributed to the underlying disease, the presence of sepsis and the failure of vital organ systems other than the lung. The association of ARDS with multiple system organ dysfunctions is not inevitable, but it certainly is common. It is postulated that local injury to the lungs (pneumonia, trauma, aspiration, gas inhalation) could set up a secondary diffuse inflammatory response resulting in damage to other organs.