The purpose of this study is to determine whether the early identification and more precise intervention of goal-directed intraoperative plasma volume expansion and catecholamine therapy using arterial pressure based cardiac output (APCO) measurement in addition to normal vital signs will improve postoperative organ function, in particular renal function, in patients undergoing major abdominal surgery.

Inclusion Criteria:

• Patient is scheduled for elective major abdominal surgery and has two or more risk factors according to the Lee classification scheme.
• Patient can sign informed consent before surgery.
• Patient is able to comply with the study procedure.
• Patient must require an indwelling radial or a femoral artery catheter.
• Patient must be 20 years old or older.
• Patient must be 40kg or heavier.
• Patients height and weight can be accurately obtained prior to study start.

Exclusion Criteria:

• Emergency surgery.
• Patients with aortic or mitral valve regurgitation.
• Renal insufficiency requiring hemodialysis.
• Liver dysfunction (alanine/aspartate aminotransferase >40 U/L).
• Patient with contraindications for the placement of radial, femoral or other arterial cannulae.
• Patient being treated with an intraaortic balloon pump.
• Female patients with a known pregnancy.
• Patient is currently participating in an investigational drug or another device study that has not completed the primary endpoint or that clinically interferes with the study endpoints.