Tidal Volume Challenge and Reliability of Plethysmography Variability Index

Tidal volume (VT) will be increased from 6 to 8 ml/kg of for one minute and hemodynamic variables, including PVI with 8 ml/kg tidal volume ventilation (PVI8) will be recorded.

After these two baseline hemodynamic measurements, volume expansion will be performed for 10 min using an infusion of balanced crystalloid solution (6ml/kg of predicted body weight).