Monitoring and optimizing tissue oxygenation (StO2) in high-risk surgery and/or high-risk surgical patients may decrease the risk of postoperative complications.

Tissue hypoxia occurs frequently during high-risk surgery in high-risk patients. The investigators want to see if an algorithm aimed at optimizing intraoperative tissue oxygenation reduces perioperative complications as well as length of stay in the intensive care unit (ICU LOS), 28-day mortality, and the duration of mechanical ventilation in these patients.

Inclusion Criteria:

. Major elective surgery

• Aged over 65 years with moderate functional limitation of one or more organ systems
• ASA classification III or IV, i.e. severe cardiac, vascular, respiratory or metabolic illness resulting in severe functional limitation
• Routine use of arterial and central venous lines
• Planned postoperative stay on ICU or PACU

Exclusion Criteria:

• Refusal of consent
• acute myocardial ischemia prior to enrolment
• patients receiving palliative treatment only
• disseminated malignancy
• patients unlikely to survive more than 6 hours
• emergency surgery
• transplantations
• neurosurgical patients
• patients undergoing extensive liver surgery requiring low CVP management