The purpose of the study is to determine whether it is possible to manage the flow of blood through blood vessels using varying levels of carbon dioxide during cardiac surgery, and what effect this has on how well the major organs of the body work.

A great number of studies have shown that MAPCAs are a real issue for these patients, who require far higher blood flows than previously suggested. However, the optimal method of CPB is still unknown. Recent research by Sakamoto et al., showed that a raised carbon dioxide (pCO2) increased brain blood flow in cyanotic patients, suggesting a noticeable decrease in aorto-pulmonary blood shunting. However, the mechanism of this action is not understood and it is unclear if this observation is an associated or causative one. Whilst the vasoconstrictive (narrowing of vessels) effect of hypoxia has been well documented, with and without high carbon dioxide, there are no reports indicating that pCO2 alone increases the narrowing of blood vessels in the lung. We hypothesize that a rise in pCO2 could cause a shift in blood flow from pulmonary to systemic circulation, either through direct constricting action on MAPCA vessels, or through a vasoconstriction of blood vessels in the lung. Furthermore, we predict the phenomenon could potentially be used to optimize the method of treatment, ensuring that vital organs receive the correct amount of blood flow during the surgical correction of these rare congenital heart diseases.

Inclusion Criteria:

• Patients whose parents/guardians are willing and able to provide written informed consent for participation in the study
• Patients undergoing elective TCPC surgery
• MRI proven presence of MAPCA vessels
• Patients between 1 day and 5 years of age

Exclusion Criteria:

• Emergency surgery
• Documented history of cognitive impairment (may have an effect on biochemical markers of cerebral injury)
• Documented history of major organ dysfunction