Tidal changes on CT and progression of ARDS

Cereda, Maurizio; Xin, Yi; Hamedani, Hooman; Bellani, Giacomo; Kadlecek, Stephen; Clapp, Justin; Guerra, Luca; Meeder, Natalie; Rajaei, Jennia; Tustison, Nicholas J; Gee, James C; Kavanagh, Brian P; Rizi, Rahim R

used in our previous study. 12 Rats received different ventilator settings without randomisation, because our aim was to induce variability in injury trajectory rather than to test treatment strategies. We could not separate the effects of baseline injury severity from those of ventilator management because both PEEP and V T each affect CT images, critical care and these were not standardised during imaging. We chose this design because colocalisation with future injury requires that inflation is measured with ventilation settings identical to those being employed; future studies will address the predictive independence of high-risk inflation. The experimental model, acid aspiration, involves direct epithelial injury 38 and intratracheal injection, which could explain the centrifugal injury propagation. 12 The study is also limited by the short duration of the experiments and by the fact that injury progression was assessed through deterioration of imaging, C dyn and oxygenation, but lung inflammation was not directly measured. However, histology confirmed disseminated injury in rats with severe radiological and functional worsening, in our previous rat study following a similar injury protocol. 12 Furthermore, deterioration of lung compliance indicates the onset of ventilator-induced injury. 39 The correlation between high-risk inflation and mortality in the patients could be related to the 'pulmonary' 38 source of ARDS in seven of nine subjects (table 3) and may be different in other patterns of injury (eg, sepsis), where bacterial spreading, endothelial damage 38 or systemic inflammation may affect propagation. We selected patients who were imaged once within a week of endotracheal intubation, aiming to study early ARDS, 40 in whom ventilator settings were not standardised during or after imaging; thus, the impact on unstable inflation of a shorter (or longer) duration and the effects of ventilator management after imaging are unknown. Finally, extrapulmonary factors may explain patient mortality, although this seems unlikely given the similarity of the severity of illness scores between survivors and non-survivors (table 3) .