Comparison of PVI and RPVI

"PVI and RPVI measurements during variations of the tidal volume (Vt challenge) and a recruitment maneuver in anesthetized and mechanically ventilated patients.~* T0 : Vt 6 mL/kg of predicted body weight (PBW) during 5 minutes~* T1 : Vt 8 mL/Kg of PBW during 5 minutes~* T2 : Vt 10 mL/kg of PBW during 5 minutes~* T3 : Vt 6 mL/kg of PBW during 5 minutes~* T4 : A single recruitment maneuver~Data will be recorded at each step."