The primary purpose of the study is to evaluate whether the type of fluid (0.9% saline or 6% Hydroxyethyl starch 130/0.4) in the context of an individualized goal-directed fluid therapy is associated with a difference in morbidity and mortality within the first 14 days in patients at moderate-to-high risk of postoperative complications after abdominal surgery.

Fluid administration is the mainstay treatment for suspected hypovolemia during surgery, but the effects of different crystalloid and colloid solutions on outcome remain poorly explored in surgical patients.

Two recent international multicenter studies (6S and CHEST studies) have shown that, compared to crystalloid solutions, the use of hydroxyethyl starch (HES) could be responsible for higher morbidity, especially renal failure, and mortality in ICU patients, thus leading to a recent restriction of their range of indications.

In contrast, in surgical patients, recent meta-analyses have concluded on the absence of difference in terms of mortality and postoperative renal failure between crystalloids and latest generation HES. Excessive fluid administration during surgery is associated with increased risk of postoperative morbidity, including renal dysfunction and mortality. It has been suggested that, compared with the volume-restoring effects of colloids, crystalloid use may require the administration of higher fluid volumes, which may contribute to poorer outcomes. In the surgical context, clinical trials and meta-analyses have shown that individualized goal-direct fluid administration can reduce postoperative morbidity. Although most GDT studies have used colloid solutions for fluid loading, the effects of the type of fluids are currently unknown and crystalloids are proposed for first-line therapy.

The proposed Flash multicenter study will be conducted to assess if the use of HES or crystalloid solutions during an individualized GDT contribute to outcome differences in patients at moderate-to-high risk of postoperative complications after abdominal surgery. As these fluids are widely used during surgery and because of current concerns about the risks related to the use of HES-based products in ICU patients, the trial will provide important data to clinicians involved in perioperative care.

Inclusion Criteria:

All adult patients who

• Undergo elective or emergency abdominal surgery under general anesthesia
• With an estimated surgical duration greater than or equal to 2 hours
• With moderate-to-high risk of postoperative complications defined by an AKI risk index≥ class 3, as defined by the presence of at least 4 of the following factors: age> 56 years, male gender, intraperitoneal surgery, active congestive heart failure, ascites, hypertension, emergency surgery, mild or moderate renal insufficiency, diabetes mellitus treated by oral or insulin therapy

Exclusion Criteria:

The following patients will not be evaluated for inclusion:

• Age <18 years
• Preoperative acute heart failure
• Preoperative acute coronary insufficiency
• Preoperative severe renal failure (defined by creatinine clearance <30 ml/min or requiring renal replacement therapy)
• Preoperative shock defined by the need for vasoactive amines
• History of allergy with the use of 6% Hydroxethyl starch 130/0.4
• Contraindication to the use of HES: sepsis, burnt patient, renal insufficiency or dialysis, cerebral hemorrhage, ICU patient , hypervolemia, lung edema, dehydration, severe hypernatremia or severe hyperchloremia, severe hepatic insufficiency, congestive heart failure, severe coagulopathy, organ transplant
• Patient's or relative's refusal to participate
• Parturient or breastfeeding woman
• Protected major (guardianship)