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.