The purpose of this study is to evaluate the effectiveness of using the personal preoperatively assessed cardiac output in high-risk patients to guide perioperative administration of fluids and vasoactive drugs on predefined postoperative complications.

Inclusion Criteria:

• Patients ≥ 18 years undergoing a major abdominal procedure (including general, urological, gynaecological, and vascular) with an expected duration of surgery ≥ 90 min or presumed blood loss exceeding 1,000 mL (e.g., intrabdominal vascular surgery) and ≥ 1 of the following high-risk criteria:
• acute or chronic renal impairment (serum creatinine ≥ 1.3 mg/dL)
• predefined risk factors for cardiac or respiratory complications
• Immunodeficiency due to a therapy (e.g., immunosuppressants, chemotherapy, radiation, long-term or high-dose steroids)
• Immunodeficiency due to specific diseases (e.g., leukaemia, lymphoma, AIDS)
• severe liver impairment (biopsy proven liver cirrhosis plus 1 of the following: portal hypertension or history of upper gastrointestinal bleeding due to portal hypertension or previous episodes of hepatic insufficiency/hepatic encephalopathy/hepatic coma
• Age ≥ 80 years

Exclusion Criteria:

• Age <18 years
• Pregnancy
• surgery for palliative treatment
• emergency procedure
• refusal of consent
• participation in another randomized controlled trial
• failure to meet inclusion criteria