At baseline, in the operating room before the first PLR maneuver, the heart rate, systolic, diastolic and mean arterial pressure, CVP value, CI measured in triplicate with the thermodilution method and the FloTrac derived variables are recorded. These variables include the CO indexed CO and SVV measured by the FloTrac/EV1000. The same variables are recorded at 1, 3 and 5 minutes after the beginning of PLR except CI by thermodilution which is measured again only once, at 3 minutes and EtCO2 which is recorded every 12 seconds. The EtCO2 curve is inspected at baseline and during the PLR maneuver to ensure the changes in EtCO2 were not related to changes in inspired CO2, ventilator or circuit malfunction or increase in airway resistance.