The aorta is the largest blood vessel in the body and carries blood from the heart to the rest of the body.  The normal aorta in the chest, called the thoracic aorta, is about 2-3cm wide.  However, it can enlarge and balloon out to form an ‘aneurysm’.  This is serious because the wall of the blood vessel weakens and will eventually rupture causing massive internal bleeding and death.  Thoracic aortic aneurysms affect eight per cent of people and cause 5,000 deaths in the UK each year.  They are most common in people over the age of 65 years, and 80 per cent of people will die unless they get urgent medical help from a specialist hospital.

Thoracic aortic stenting, also called TEVAR, is keyhole surgery that is offered to patients when the thoracic aorta reaches 6cm in width.  A small cut is made in a blood vessel in the groin through which a tube, called a stent, is inserted and positioned at the location of the aneurysm.  This effectively seals off the aneurysm with the stent supporting the weakened aorta and acting as an artificial blood vessel for the blood to flow through.

TEVAR is a life-saving procedure but can lead to brain damage.  Mr Gibbs and his team have found that up to 13 per cent of patients can suffer a stroke after TEVAR. During clinic follow-up appointments, the team also found that 88 per cent of patients had memory problems. When the team carried out brain MRI scans in all patients after surgery they found that 81 per cent had evidence of damage to parts of the brain that control our ability to walk and talk, and our memory.

Using a unique machine called transcranial doppler ultrasound (TCD) that monitors the blood flow to the brain during TEVAR, the team found that the cause of damage to the brain was air bubbles being released from the stent as it opens inside the aorta. These air bubbles are able to travel to the brain and stop the blood flow to important areas of the brain. The stents are manufactured in room air conditions and normally, air is flushed out before the stents are used in patients, with sterile salty water, called saline.  However, it is clear that some air remains in the stent which can travel to the brain during surgery to cause damage.

Carbon dioxide is a gas that is found naturally in the air that we breathe out.  The team used carbon dioxide to flush air out of the stents before use and found that only 30 per cent of patients had evidence of brain damage on MRI scans. In order to fully determine the protective effect of carbon dioxide, the team now need to carry out a study called a randomised controlled trial.

This project will investigate how effective carbon dioxide is at removing air from stents and preventing brain damage, stroke and memory problems by comparing it directly with saline flushing.  Patients who have agreed to take part will have a brain MRI scan, clinical examination to look for stroke and memory tests before surgery.  Half of the patients will receive stents that have been flushed with saline and the other half stents that have undergone carbon dioxide flushing.  After surgery, patients will have another brain scan and be examined for stroke.  At their routine six-week and six-month hospital follow-up visits, the memory tests will be repeated.

If successful, this project will make thoracic aortic stenting safer by reducing the risk of stroke and memory problems, which affect quality of life and have a huge impact on family and carers.  The findings will tell us the best way to remove air from the stents and whether it can stop patients developing these complications.  Carbon dioxide flushing is simple and inexpensive, and the results of this study will be easy to translate into routine clinical practice to benefit patients.