Fluid Loading in Abdominal Surgery: Saline Versus Hydroxyethyl Starch (FLASH Study)

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)