The FloTrac/Vigileo is a minimal invasive device assessing flow based hemodynamic parameters by pulse contour analysis based on the radial artery pressure signal. This method gained popularity as it is minimally invasive compared to esophageal Doppler or pulmonary artery catheter insertion and provides continuous beat-to-beat data. The previous study with 110 patients found that that GDHT guided by stroke volume variation (SVV) using the FloTrac/Vigileo device was associated with a reduced length of hospital stay and a lower incidence of POGD in major abdominal oncological surgery. However, no difference was found in the incidence of postoperative complications between the two groups, lack of statistical power could be a limitation to demonstrate the true association. Therefore, further prospective trials are needed to address this issue. The use of early and efficient therapeutic strategies able to detect and to treat potential triggers of organ failures, such as tissue hypoperfusion, is particularly important. If hypoperfusion is not adequately managed, tissue hypoxia could occur, resulting from an impairment of the adaptive mechanisms of myocardial contractile function, under the influence of inflammatory mediators, and the peripheral tissues will then increase their oxygen extraction (O2ER). AS such, GDHT guided by O2ER may be appropriate to monitor GDHT strategies because it reflects the balance between oxygen delivery and consumption. Therefore, the investigators performed this single-center, randomized, controlled trial to investigate whether GDHT guided by SVV using FloTrac/Vigileo monitor and GDHT guided by O2ER would reduce incidence of postoperative complication and shorten the length of hospital stay, compared with a standard conventional fluid therapy in low-to-moderate risk patients undergoing major laparoscopic gastrointestinal oncological surgery.