Each patient has received both ventilatory modes with same settings (tidal volume- TV, respiratory rate- RR, positive end expiratory pressure- PEEP- and inspired fraction of Oxygen - FiO2). Intra-lung compliance and global inhomogeneity Index (GI) were assessed though Electric Impedance Tomography (EIT) (PulmoVista 500, Draeger Medical, Germany), allowing at least five minutes after change of mode to let adequate time for gas distribution. At the same time, respiratory mechanics measures were obtained in quasi-static conditions after an inspiratory hold manoeuver, ensuring stability of plateau pressure (PPLAT). We assessed resistive (PIP-PPLAT) and elastic components (DeltaP and quasi-static compliance) of working pressure, and mechanical power as a marker of energy dissipation.

Intra-lung Compliance is an EIT- based parameter which shows if, between the two modes of ventilation, there is a net gain or loss of intraprenchimal compliance. This is expressed as percentage change from the first-point Compliance measured. We will compare Compliance in PRVC to RVD in VCV ventilation. VCV is the reference point.

GI is a EIT-derived index to quantify the tidal volume distribution within the lung. We will compare GI in PRVC to RVD in VCV ventilation. VCV is the reference point.