Patient reaction time slowed by 0.3 milliseconds per surgery

Many families have stories of how repeated surgeries and hospitalisation impacted the reaction time and memory of elderly relatives; however the exact biological reason and impact is still unknown.

A new University of Sydney led study has now revealed multiple surgeries have a small effect on memory, reaction time, task-switching and problem solving for older patients with each additional surgery. The study also found brain MRIs of people who had surgeries also showed physical differences in areas of the brain responsible for memory.

It is the first study of its kind to investigate the impact of multiple, complex surgeries on brain health, using brain imaging techniques such as MRIs in a large population.

The international team examined data from almost half a million adults in the United Kingdom who underwent surgeries, ranging from day surgery to heart bypass operations, with diagnostic procedures and neurosurgery excluded.

As part of the study, patients then underwent brain MRIs and cognitive function testing for signs of neurodegeneration.

The study found with each additional surgery, patients’ overall reaction time slowed by 0⋅3 milliseconds. Cognitive flexibility, problem solving, and the ability to remember pictures and numbers also decreased with each additional surgery.

People who had surgeries were also found to have a smaller hippocampus, the area of the brain responsible for memory and learning. They also had more evidence of brain damage associated with blocked blood vessels, compared to those who did not undergo repeated surgeries.

“The results suggest that the cognitive decline per surgery may seem small, but those changes and losses in neurodegeneration really start to add up after multiple surgeries,” says lead researcher Dr Jennifer Taylor from the University of Sydney’s Faculty of Medicine and Health.

“We found that surgeries are safe on average but also that the burden of multiple surgeries on the brain health of older patients should not be underestimated,

“This is a reminder to medical professionals to consider all treatment options and be cautious in recommending major surgery for older and more vulnerable patients. If surgery is the best or only treatment option, patients should be reassured that the cognitive harm from each surgery is small on average. Nonetheless, careful attention in perioperative care is required to prioritise brain health and recovery.”

Published in The Lancet Healthy Longevity, the researchers examined the impact of surgical and medical hospital admissions on cognition, using a large population- based sample of British adults from UK Biobank from 2006- 2023.

UK Biobank is the world’s most comprehensive source of health data available for research, housing a vast and continuously growing dataset of biological, health and lifestyle information collected over 15 years from half a million UK volunteers.

Data was pooled from 46,706 people, who all underwent detailed magnetic resonance imaging (MRI) and detailed cognition tests.

Participants were tested on their reaction time, memory and ability to think flexibly, by answering a series of language of mathematics questions.

This study continues work from the same research team who previously found both major surgery (including cardiac, thoracic, vascular, and intracranial surgeries), and hospital admissions are associated with cognitive decline among older patients.

The researchers say future work should focus on understanding the biological inner workings of neurodegeneration. One hypothesis suggests inflammation could be the reason for delayed cognitive recovery after surgery, and understanding how this leads to brain damage will be a key next step.

“This paper represents a critical milestone for our field, defining the importance of research into perioperative brain health. We are already testing potential therapeutics in clinical trials as we strive to advance safe anaesthesia and perioperative care,” said senior author Professor Robert Sanders from the University of Sydney.