Risk factors for ventilator-induced-lung injury develop three to five times faster after a single episode of lung injury

Abstract

Introduction Mechanical ventilator breaths provided to deeply sedated patients have an abnormal volume distribution, encouraging alveolar collapse in dependent regions and promoting alveolar overdistention in non-dependent regions. Collapse and overdistention both start with the first breath and worsen over time, driving ventilator-induced lung injury (VILI). This is exacerbated when the lung is already injured or has increased heterogeneity. Our study investigated the impact of a single episode of lung injury on lung mechanics and the risk factors for ventilator-induced injury, compared with non-injured lungs. Methods Two groups of pigs were sedated and ventilated using lung-protective volume-controlled mode at 8 mL/kg, positive end-expiratory pressure (PEEP) 5 cmH~2~O, with respiratory rate and FiO2 set to maintain normal blood gas values. Animals in one group were ventilated for 50 h (50-Hour MV group, n=10). Animals in the second group had lung injury induced using oleic acid and were ventilated for 12 h post-injury (LI MV group, n=6). Both groups were compared with a never-ventilated control group (NV, n=6). Lung mechanics and injury were measured using electrical impedance tomography, esophageal pressure monitoring and tissue histology. Results End-expiratory lung-volume loss was greater in the 50-Hour MV group (P\<0.05). Plateau pressure, driving pressure and lung injury score were higher in the LI MV group, (P\<0.05). Conclusion Risk factors for VILI developed three- to five-times faster in the group with injured lungs, demonstrating that a single lung-injury episode substantially increased the risk of VILI, compared with normal lungs, despite using a lung-protective mechanical ventilation protocol.