Determine the ability of changes in Plethysmographic Variability Index during tidal volume challenge to predict fluid responsiveness

The change of Plethysmographic Variability Index after tidal volume challenge as a predictor of fluid responsiveness, confirmed with the change of SVV using Flotrac advance cardiac output monitor.

To determine whether the patient is fluid responder, Fluid challenge will be performed afterwards to confirm the patient's fluid responsiveness.

We also aim to calculate the least significant change for Plethysmographic Variability Index and Philips PPV system.

Inclusion:

Patients undergoing elective major surgery (estimated > 2-hr) with general anesthesia and mechanical ventilation in supine position

Exclusion:

1. BMI < 18.5 or >30 kg/m2
2. Pregnant patient
3. Allergy to starch solution
4. estimated glomerular filtration rate< 60

Patients undergoing elective major surgery (estimated > 2-hr) with general anesthesia and mechanical ventilation in supine position