Using a new type of oxygenator during heart bypass surgery to reduce air bubbles in the blood

Some people experience mild problems affecting their brain after heart surgery. These can include short-term difficulties with thinking, attention, and memory.

1 in 5 people over age 65 who have heart surgery, and 1 in 3 people over age 80 who have heart surgery, experience these problems.

Surgeons believe the brain problems sometimes seen in patients after heart surgery are caused by tiny nitrogen-rich air bubbles in the blood, called gaseous micro-emboli. These tiny air bubbles can get into the blood when it’s circulated in the machine that temporarily takes over the job of the heart and lungs during surgery. This machine is called a heart and lung machine.

An oxygenator is the part of the heart and lung machine that adds oxygen to the blood and removes carbon dioxide. A new type of oxygenator which removes nitrogen has been developed. Using this type of oxygenator may reduce the number of air bubbles in the blood, and therefore in the brain, during heart surgery.

Project aims

We did this project to see if there were any differences in the number of air bubbles circulating to the brain during heart surgery using a hypobaric oxygenator versus the standard oxygenator in the heart and lung machine.

What we did

We carried out an early‑phase randomised controlled trial in patients undergoing heart surgery to test whether a new dual‑chamber oxygenator could reduce the number of gaseous micro‑emboli reaching the brain. To do this, we randomly assigned patients to undergo a procedure where either the new oxygenator or the standard oxygenator were used. During surgery, we continuously measured bubbles in the blood vessels going to the brain using ultrasound.

We stopped the study early, after recruiting only 25 patients. This was because results showed that the new oxygenator did not reduce the number of air bubbles reaching the brain. In fact, patients who received the new device tended to have similar or higher numbers of bubbles, particularly at the start of surgery. There were no clear differences in markers of brain injury, complications, or short‑term outcomes between the two groups, and no patients experienced obvious neurological harm.

Overall, our findings showed that this new oxygenator did not achieve its intended effect of reducing air bubbles in the brain. This highlights the importance of carefully testing new surgical technologies in clinical trials before wider use. It also indicates that further research is needed to understand how best to reduce air bubbles during heart surgery.