Time-course of experimental ventilator-induced lung injury : a CT scan study

Introduction High volumes/pressures induce lung lesions indistinguishable from ALI/ARDS. Objective We wished to investigate time course of experimental lung injury with CT scan. Methods Two piglets (25 kg) were ventilated with a level of strain (TV/FRC) of 3 (~44 ml/Kg), which is known to induce experimental Ventilator-Induced Lung Injury. Blood gases, lung mechanics and CT scan data were acquired every 3 hours or when needed. Quantitative lung CT scan analysis was performed to compute lung weight and edema. We also derived the amount of intra-tidal opening and closing. Discussion Table 1 shows the main physiological variables during the course of the study. The quantity of tissue opening and closing tended to increase during the course of experiment with the worsening of clinical conditions (Opening and closing tissue(g)=474±221*PaO2/FiO2,r2=0.96). The development of edema was related to an increase in overall lung volume (lung volume increase(ml)=98±0.62*Lung edema(g),r2=0.62) without a corresponding decrease in FRC. Conclusions VILI, once initiated, proceeds rapidly, leading to widespread lung damage. The development of anatomical lung damage observable at CT scan preceded the impairment of mechanics and gas exchange. We may speculate that the application of PEEP could reduce the opening and closing fraction and the increase in global strain due to lung collapse, delaying the progression of VILI.