Variability in lung collagen amounts after prolonged support of acute respiratory failure

In order to identify correlates of fibrosis in acute respiratory failure, autopsies were performed on 16 patients who died after an episode of more than two weeks' duration, and the left lower lung lobe was obtained for biochemical measurements. The average amount of lobar collagen in one group of patients was nearly three times that in another group. Both groups had been mechanically ventilated for the same length of time and could not be distinguished by primary diagnosis. However, the group with increased collagen had received nearly twice the level of positive end-expiratory pressure and had received an inspired oxygen fraction of more than 0.4 for twice as long as the normal collagen group. Examination of complications and other aspects of therapy did not reveal clearcut differences between the groups. Examination of the same clinical data in a group of patients who had survived an episode of similar duration indicated that survivors differed from the high collagen group in inspired oxygen levels.