Lung Ultrasound, PEEP and Overdistension (LUPO)

The investigators suppose that lung sliding could be reduced in the same lung region moving from less ventilated to overinflated condition. This is supported by theoretical arguments by some authors but so far it has not been demonstrated. The investigators suppose that speckle tracking applied to LUS is able to demonstrate a reduction or abolition in pleural sliding when lung tissue is overinflated by higher PEEP after lung recruitment maneuver. The overinflation is diagnosed by Electric Impedance Tomography (EIT) and mechanical respiratory measurements (reduction in compliance as ratio between tidal volume over difference between plateau pressure and PEEP) and localized by EIT.