Rouby (Paris, France) put forward a new classification for ARDS based on computed tomography findings. He observed that patients can be split into three groups, depending on the appearance of the upper lobes. In group 1 the upper lobes are normal, and positive end-expiratory pressure (PEEP) is of little benefit and results in significant over-distension. Survival in this group is approximately 60%. In group 2 the upper lobes are abnormal, PEEP is of dramatic benefit, but survival is only approximately 25%. In group 3 there are mixed/patchy abnormalities, the effects of PEEP are less predictable, but, as in group 1, survival is approximately 60%.