Assisted Fluid Management (AFM) System and Postoperative Outcome After High-risk Abdominal Surgery

Inclusion Criteria: * Any adult patient (aged 18 years or older) admitted to the operating room for an elective high-risk abdominal surgery (both open and laparoscopically assisted). * Patients must fulfill at least one of the following high-risk criteria: * American Society of Anesthesiologists physical status \> 2 * classification exercise tolerance \< 4 metabolic equivalents as defined by the guidelines of the American College of Cardiology/ American Heart Association * renal impairment (serum creatinine ≥1.3mg/dL or \>115 mmol/l or estimated glomerular filtration rate \< 90 mL/min/1.73 m2 within the last 6 months) or renal replacement therapy * coronary artery disease (any stage) * chronic heart failure (New York Heart Association Functional Classifcation ≥ II) * valvular heart disease (moderate or severe); * history of stroke * peripheral arterial occlusive disease (any stage) * chronic obstructive pulmonary disease (any stage) or pulmonary fibrosis (any stage) * diabetes mellitus requiring oral hypoglycemic agent or insulin; immunodeficiency due to a disease (e.g., HIV, leukemia, multiple myeloma, solid organ cancer) or therapy (e.g., immunosuppressants, chemotherapy, radiation, steroids) * liver cirrhosis (any Child-Pugh class) \-- body mass index ≥30 kg/m2 * current smoking or 15 pack-year history of smoking * All participants must receive clear study information and give signed informed consent Exclusion Criteria: * Patients with preoperative cardiac arrhythmia…