Dynamic parameters like pulse pressure variation have been shown to be accurate predictors of fluid responsiveness. Hemodynamic optimization based on fluid management and stroke volume optimization have been shown to improve patient outcomes, especially for moderate and high risk abdominal surgical patients. A novel closed-loop fluid administration system based on multi-parameter hemodynamic monitoring have been described recently. This prospective, randomized, surgeon and patient blinded study aims at comparing the cardiac output provided by either this closed-loop system or the anesthesiologist team in high-rish surgical patient elected for abdominal surgery at Pierre Bénite University Hospital, Hospices Civils of Lyon, France. Primary endpoint is the mean indexed cardiac output during surgery per group. We will also compare hemodynamic parameter (cardiac output, stroke volume, blood pressure heart rate…) and patient's outcomes (morbidity, mortality, transfusion rate, hospital length of stay) between groups

Inclusion Criteria:

• Elective major abdominal surgery
• Patient physical status ASA 2-4
• General anesthesia with positive pressure ventilation
• High risk surgical patient with a per operative Vigileo® cardiac output monitoring decided a priori.

Exclusion Criteria:

• Pregnant female
• Intraoperative hyperthermic chemotherapy procedure
• Patient physical status ASA more than 4
• Patient with allergy to hydroxyethyl starch
• Cardiac arrhythmia
• ventilation with tidal volume inferior 7mL/Kg