Pulmonary and extrapulmonary acute respiratory distress syndrome are different

Acute respiratory distress syndrome (ARDS) can be derived from two pathogeneticpathways: a direct insult on lung cells (pulmonary ARDS (ARDSp)) or indirectly(extrapulmonary ARDS (ARDSexp)). This review reports and discusses differences inbiochemical activation, histology, morphological aspects, respiratory mechanicsand response to different ventilatory strategies between ARDSp and ARDSexp. InARDSp the direct insult primarily affects the alveolar epithelium with a localalveolar inflammatory response while in ARDSexp the indirect insult affects thevascular endothelium by inflammatory mediators through the bloodstream.Radiological pattern in ARDSp is characterised by a prevalent alveolarconsolidation while the ARDSexp by a prevalent ground-glass opacification. InARDSp the lung elastance, while in ARDSexp the chest wall and intra-abdominalchest elastance are increased. The effects of positive end-expiratory pressure,recruitment manoeuvres and prone position are clearly greater in ARDSexp.Although these two types of acute respiratory distress syndrome have differentpathogenic pathways, morphological aspects, respiratory mechanics, and different response to ventilatory strategies, at the present, is still not clear, if thisdistinction can really ameliorate the outcome.