This project will evaluate fluid balance and edema formation in children with congenital heart disease in need of a surgical procedure, The Fontan procedure. Surgery will make the child end up with a univentricular heart with one-chamber circulation ( Fontan circulation). This project will evaluate if these children has increased micro vascular leakage before surgery due to their congenital heart defect. The project will also investigate if the edema formation seen during cardiac surgery with the use of Cardio-Pulmonary Bypass (CPB) and hypothermia is caused by capillary leakage of plasma protein.

The study hypothesis are

1. Edema developed during heart surgery is caused by reduced colloid osmotic pressure gradient through the capillary membrane.
2. The degree of micro vascular leakage in open-heart surgery is related to duration of CPB and hypothermia.
3. Fontan circulation cause peripheral edema related to elevated central venous pressure and is not caused by increased micro vascular leakage of plasma proteins.

Inclusion Criteria: Diagnosis of Congenital heart defect in need of Fontan procedure -

Exclusion Criteria: No parental consent

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Children with congenital heart defect scheduled for Fontan surgery