How will they save my babies brain while they do heart surgery?

The brain is what the body is all about and over time there has been a greater and greater appreciation that although the heart could be fixed often the brain suffered sometimes severe damage in the process leading to a poor quality of life for the child. Many new techniques have been developed to try to protect the brain during and after surgery.

Chill it!! Whether the child's heart is stopped during surgery of put on bypass, cooling the brain (literally packing it in ice) as well as the body seems to help the brain survive the surgery better. Quick cooling should be better no? Actually not. One famous heart surgeon in the Boston area was known for both his skill and speed so they would cool the babies down quickly and then warm them up fast. The surgical team was perplexed about why this superior surgeon's babies had more brain damage than his less skilled and slower resident fellows until they discovered the difference was the slow cooling/rewarming necessary for the slower resident surgeons.
Avoid anemia! anemia is low blood counts particularly the red blood cells that carry the dissolved  oxygen to the brain. The bloods job is to carry the oxygen around the body and just the right amount is just that - just right. Too much blood and it thickens and clots blocking blood getting to the brain( a stroke) and too little and the brain is short on the oxygen that it loves. The babies blood count will be carefully monitored to keep it just right.
Prevent air from getting where it shouldn't be!  Blood carries dissolved oxygen but air bubbles - like those in a fish tank are much too big and get stuck in the small blood vessels leading to the brain. The tiny strokes that these can cause can lead to long term problems with learning, speech and intellect. The bubbles can be microscopic and can come from anywhere- the bypass machine, IV tubing, or the heart that is open to the outside air as the surgeon operates. To avoid this some surgeons actually pour carbon dioxide (think of the cloud of smoke at the last KISS concert you went to) over the heart as they work on it. They will also have someone look with a special scope called a echo at the babies heart to make sure the bubbles are gone before they reconnect the heart and get it pumping again.

Watch the brain during surgery! this is done with a variety of special instruments. Transcranial dopplers that can listen to the blood flow to the brain and EEG that can look at the electrical activity of the brain.

Monitoring chemicals in the blood after surgery. close monitoring of the acidity of the blood (pH), oxygen levels and blood pressure can ensure that the brain is getting the best possible environment to recover

Home monitoring: despite all of this about 1/3 of babies die after the first surgery before they get the second surgery. This has been greatly reduced in some centers by having home monitoring program that acts like an early warning system. Parents are supplied with an Oximeter to check the babies oxygen levels every morning and a scale to weigh the baby to look for early heart failure. Anything that is abnormal is called to the heart team immediately otherwise they check in by phone every two weeks.