Prone Positioning and Abdominal Binding on Lung and Muscle Protection in ARDS Patients During Spontaneous Breathing

Study protocol will have three steps. The first step is a multimodal description to characterize ICU acquired weakness and ventilator-induced diaphragm dysfunction in prolonged mechanically ventilated ARDS patients at spontaneous breathing onset. The second step is a crossover clinical trial to test different ventilatory approaches oriented to improve physiological variables related to lung injury and diaphragm performance. The third step is a randomized controlled trial to test the effect of the previous ventilatory approaches on lung inflammatory response and biomarkers of lung and muscular injury. FIRST STEP: A multimodal physiological description will be performed in pressure support ventilation mode at spontaneous breathing onset. The assessments will include conventional electromyography; electrical activity of the diaphragm; ultrasound of respiratory and non-respiratory muscles; respiratory flow; tidal volume; airway, esophageal and gastric pressures; and hemodynamic and electric impedance tomography monitoring at the end of 2-hours of spontaneous breathing period. SECOND STEP: A controlled randomized crossover trial will assign patients to three strategies of 2-hours period on pressure support ventilation mode: A.- Control group: supine at 45º, B.- Thoracoabdominal binding: supine at 45º plus thoracoabdominal binding, C.- Prone positioning (without thoracoabdominal binding). These strategies will be performed under standard positive end-expiratory pressure (PEEP) (ARDSNet strategy) and individualized PEEP (obtained at the lowest combination of collapse and overdistension according to electrical impedance tomography), applied in random order. Therefore, each patient will receive the six approaches, with washout periods of 15-minutes in assisted/controlled ventilation. THIRD STEP: Patients will be randomized to one of the three ventilatory strategies previously defined, A.- Control group: supine at 45º, B.- Thoracoabdominal binding: supine at 45º plus abdominal binding, C.- Prone positioning. These three strategies will be applied under standard PEEP (ARDSNet strategy). Between crossover and pilot randomized controlled trial, the patients will remain under moderate sedation in pressure support ventilation mode receiving an individualized PEEP level.