Intravascular Microaggregates and Pulmonary Embolization in Shock and Surgery

Adult respiratory distress syndrome (ARDS) is a frequent cause of death in intensive care units and probably represents a collection of different conditions. In the complex issue of its aetiology the failure to define terms has led in our opinion to considerable confusion. It is doubtful whether the pulmonary failure that follows viral pneumonia or specific lung infections has the same pathophysiology as that following 3 days after massive blood transfusion, although both may share similar X-ray features and be called “ARDS”. In this chapter “shock” refers to that condition in which there is a failure of the circulation of blood to meet the metabolic needs of the tissues. “Shock lung” is defined here as pulmonary failure without left ventricular failure typified by increased pulmonary arteriovenous admixture and widespread opacification of the lung fields on X-ray, developing as a consequence of and at an interval of hours or days following an episode of shock or severe sepsis. In this way we may concentrate entirely on that variety of ARDS that almost certainly has a common, although possibly multiple, cause that was almost certainly active during the episode of shock. The delay before pulmonary failure develops is a consistent feature of great importance in understanding the pathophysiology.