When we operate on the heart we stop the heart and use a heart-lung bypass machine to pump the blood around the body. At the moment it is normal for the blood to be cooled down during the operation (‘hypothermic perfusion’). It is then warmed to a normal temperature again at the end of surgery.

This technique (sometimes called “whole body cooling”) is standard practice at the Bristol Children’s Hospital. We now think that it could be better to keep the blood at normal body temperature during the operation (‘normothermic perfusion’) instead of cooling it. Research on adults who need heart surgery has shown that it might be even better to leave blood at its normal temperature and not cool it down. The effects of the two techniques on younger people have not yet been directly compared so we do not know which is best.

The reason for this study is to compare the two temperatures used (hypothermic and normothermic) and look at their effects on the heart and other organs in detail. We will also look at whether the blood temperature used during the operation has an effect on memory and language skills and physical and social development at 3 months and 1 year post-operation.