The purpose of this study is to compare two different strategies of intraoperative mean arterial pressure (MAP) and stroke volume index management in high-risk patients undergoing major abdominal and orthopedic surgery (manual versus automated) The investigators hypothesis is that the automated group will spend less time during surgery in hypotension (defined as a MAP<90% of patient's MAP baseline) compared to the manual group.

The maintenance of MAP is essential for organ perfusion pressure. Intraoperative hypotension is a frequent complication both after induction and during maintenance of anaesthesia, ranging from 5% to 75% depending on the chosen definition. Tissue hypoperfusion exposes to the occurrence of a systemic inflammatory response syndrome and is a key determinant of postoperative complications. Persistent intraoperative hypotension has been reported as an important prognostic factor of postoperative morbidity and mortality. Adequate treatment of arterial hypotension is therefore of particular importance during surgery. However, the avoidance of hypotension includes the infusion of vasopressor and/or fluid to optimize perfusion pressure. The manual adjustment of vasopressor administration has been shown to be suboptimal.

Recently, a paper published in the JAMA journal demonstrated that among patients undergoing high-risk surgery, the maintenance of blood pressure within 10% of patient's baseline systolic blood pressure resulted in less postoperative organ dysfunction compared to standard MAP management.

Today, the investigators have an automated clinical decision support system that help ease the administration of both fluid and vasopressors during surgery (individualized fluid and vasopressor administration). The department of the investigators has recently implemented a manual hemodynamic protocol to optimize fluid and vasopressor. The goal is to maintain stroke volume index within 90% of the optimal stroke volume via mini fluid challenge of crystalloid solution (100 ml) following the French guidelines and to maintain MAP within 90 % of patient's baseline MAP. This protocol has been called : Individualized Fluid and vasopressor protocol (because based on patient's values) The purpose of this study is therefore to compare two different strategies of intraoperative mean arterial pressure (MAP) and stroke volume index management in high-risk surgical patients (manual versus automated and decision support guided) The investigators hypothesis is that automated group will spend less time during surgery in hypotension (defined as a MAP<90% of patient's MAP baseline) compared to the manual group because patient's stroke volume and MAP will be better maintained during surgery (within 10% of patient' targets).The decision support system will remind the clinician when to administer a bolus of fluid to maintain stroke volume index within 10% of the optimize stroke volume index value and an automated closed-lopp system will titrate norepinephrine to keep MAP within 10% of patient's MAP target. The study will thus compare an individualized hemodynamic protocol (already in place in our institution) applied manually to a decision support-and closed-loop guided- individualized hemodynamic protocol (intervention group).

Inclusion Criteria:

• All adult patients scheduled for major abdominal and orthopedic surgery equipped with a cardiac output monitoring device.

Exclusion Criteria:

• Patients < 18 years old
• cardiac arrythmia (atrial fibrillation)
• Pregnant woman