Use of diffusion-weighted MRI to detect silent brain injury after open heart valve surgery

Around 21,000 people undergo open heart surgery to repair or replace a heart valve each year in the UK. As many as 12,500 of these people will suffer some degree of brain injury as a result of their surgery.

The severity of brain damage can vary. Most people have mild symptoms, such as confusion and memory problems, and many are unaware that they have even suffered a brain injury. Unfortunately, in some people, brain damage can be serious. Up to six in 100 people will have a stroke after their surgery.

As the average age of the surgical population steadily increases, brain damage from open heart surgery may be responsible for an increased burden on healthcare providers with longer hospital stays, longer recovery. slow and progressive dementia quality of life.

Patient undergoing MRI

Patient undergoing MRI

Experts believe brain damage occurs because tiny air bubbles enter the bloodstream when the heart is opened during surgery. These tiny air bubbles travel to the brain and block small blood vessels, preventing blood from flowing to that area and causing damage.

It is believed that blowing carbon dioxide on the heart during surgery (carbon dioxide insufflation) will reduce the amount of air bubbles entering the bloodstream. Carbon dioxide is heavier and more soluble than air, so it must prevent air from entering the surgical wound during surgery and dissolve quickly if it enters the bloodstream.

However, there is currently no definitive evidence to recommend the use of carbon dioxide insufflation. Some UK heart surgery centers use it regularly while others do not use it at all.

Researchers in Bristol are currently conducting a study to determine whether insufflation with carbon dioxide is effective in reducing brain damage. the CO2 study is a multicenter, placebo-controlled, blinded, randomized controlled trial conducted by the Bristol Trials Center, which will assess whether carbon dioxide insufflation protects against brain damage in patients undergoing open heart valve surgery by comparing it to a placebo, medical air, in addition to conventional deaeration techniques.

CO2 study logo

CO2 study logo

This study will use a novel, sensitive imaging technique to identify lesions in the brain called diffusion-weighted imaging (DW MRI). Unlike standard MRI or CT scans, DW MRI detects brain lesions (lesions) within minutes of the lesion occurring, so pre-surgical analysis is not necessary.

Because the technique is so sensitive, it can identify very small lesions that would not be seen using conventional imaging. Many of these small lesions will go away over time, therefore, for optimal identification, scans should be done within a week of surgery.

Neurocognitive function tests can also detect the effects of brain damage after open heart surgery, but these tests are influenced by external factors such as pain relievers and therefore may not reflect true brain damage.

We hope to recruit 704 participants aged 50 and over who are undergoing planned open heart valve surgery across the UK to participate in the study.

Doctor working on computer showing MRI brain scans

Doctor working on computer showing MRI brain scans

© Gorodenkoff /

Participants will undergo a DW brain MRI ideally between 2 to 7 days after surgery. The images will be examined by a clinical neuroradiologist at the Wellcome Center for Integrative Imaging at the University of Oxford who will report the age, number and size of any lesions present.

We will compare the number and size of lesions seen in the images between patients who had carbon dioxide or air blown on their hearts during surgery to determine if there is a difference between the groups. Study participants will also undergo neurocognitive testing before surgery, then 3 days and 3 months after their surgery.

As we begin to open to recruitment following the COVID-19 pandemic, we continue to support centers that are already participating, but also welcome all centers interested in participating. If you have any questions about the study or would like to participate as a recruiting center, please contact us at

This project (17/145/40) is funded by the Efficacy and Mechanism Evaluation (EME) program, a partnership between the Medical Research Council (MRC) and the National Institute for Health Research (NIHR). The views expressed in this publication are those of the authors and not necessarily those of the MRC, NIHR or the Department of Health and Social Affairs.

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