Pulmonary and extrapulmonary acute respiratory distress syndrome: myth or reality?

The pathogenesis of acute respiratory distress syndrome has been explained by the presence of a direct (pulmonary) or indirect (extrapulmonary) insult to the lung parenchyma. Evidence indicates that the pathophysiology of acute respiratory distress syndrome may differ according to the type of the insult. This article presents a brief overview of the differences between pulmonary and extrapulmonary acute respiratory distress syndrome, and discusses the interactions between lung functional, morphological aspects, and response to different therapies, both in experimental models and in patients with acute respiratory distress syndrome.

Many researchers recognize that experimental pulmonary and extrapulmonary acute respiratory distress syndrome are not identical when considering morpho-functional aspects, the response to positive end-expiratory pressure and recruitment manoeuvre, prone position and other adjunctive therapies. Contradictory results have been reported in different clinical studies, however, which may be attributed to the difficulty of classifying acute respiratory distress syndrome in one or the other category, and being confident of the onset, the phase and the severity of acute respiratory distress syndrome in all patients.

Heterogeneous acute respiratory distress syndrome patients are still considered to suffer from one syndrome, and are treated in the same way. Understanding the range of different pathways that lead to pulmonary dysfunction makes it possible to better target clinical treatment.