Spontaneous breathing during mechanical ventilation in an experimental model of acute lung injury: assessment of lung inflammation by PET-CT using two values of positive end-expiratory pressure (PEEP)

Abstract

Patients with Acute Respiratory Distress Syndrome (ARDS) submitted to invasive mechanical ventilation (MV) are usually ventilated with modes that allow spontaneous breathing, which can increase transpulmonary pressure due to the negative pleural pressure caused by the contraction of the diaphragm. In an experimental study of experimental lung injury, the presence of spontaneous breaths increased lung inflammation in the dorsal region (dependent) when compared to animals receiving muscle paralysis (no spontaneous ventilation). This finding is possibly explained by a pendelluft effect (air movement from non-dependent to dependent lung regions) during inspiration, caused by a more negative pleural pressure in the dependent regions. Preliminary data from our laboratory suggests that the use of PEEP values enough to avoid lung collapse in the dependent regions reduces this "pendelluft" effect and may also reduce pulmonary injury.The aim of this study is to evaluate, in pigs with severe lung injury, the effect of spontaneous breathing on lung inflammation during mechanical ventilation for 20 hours. The animals will be randomized to two levels of PEEP: 1) ideal PEEP: PEEP adjusted by electrical impedance tomography that produces minimum pulmonary collapse; and 2) ideal PEEP minus 10 cmH2O (value that determines significant collapse, but allows a proper oxygenation of the animal). The lung inflammation will be evaluated after the induction of lung injury and after 20 hours of MV by Positron Emission Tomography (PET) using Fluorodeoxyglucose (18F-FDG). At the end of the experiment, the inflammation in the lung tissue will be assessed regionally by histological analysis and determination of inflammatory markers. (AU)