Tissue hypoxia is one of the most important factors leading to the development of multiorgan failure. Patients presenting for emergent major abdominal surgery might suffer from organ hypoperfusion. Thus, early detection of the imbalance between oxygen supply and demand may improve the outcome. The investigators believe that hypoperfusion of the abdominal organs will cause a decrease of the saturation in the hepatic vein and in the IVC.

Inclusion Criteria:

• All consecutive patients presenting for emergency surgery due to acute abdomen pain
• Older than 18 years old
• Not pregnant

Exclusion Criteria:

• Age < 18
• Pregnancy
• Major coagulopathy
• Permanent pacemaker

Patients before emergent high risk abdominal surgery