A commonly used anaesthetic could cause changes in the brain linked to Alzheimer's, a US study suggests.
Anaesthetists say special care is taken when dealing with elderly patients
The anaesthetic isoflurane is linked to cell death.
The researchers said the Journal of Neuroscience findings from cell tests suggested caution was needed regarding the anaesthetic's use for the elderly.
Alzheimer's experts said work was needed to check if similar effects occurred in patients, and anaesthetists urged caution over the study.
Alzheimer's disease is a progressive, degenerative and irreversible brain disorder.
It is characterised by the formation of plaques made of amyloid beta protein, which kills brain cells.
More than 41,000 people in the UK are currently affected by the condition.
Some studies have suggested that general anaesthesia might increase the risk of developing Alzheimer's disease.
It also is known that a small number of surgical patients experience a form of dementia after their operation.
But there has been no evidence of a direct link between anaesthesia and the risk of dementia.
The team from the Massachusetts General Hospital carried out tests on brain cells.
They found isoflurane boosts the activity of an enzyme called capase, which plays a major part in causing cells to die - a process called apoptosis - and in the development of amyloid protein.
Dr Zhongcong Xie, of the Massachusetts General Institute for Neurodegenerative Disease who led the research, said: "Our studies have shown that isoflurane may induce a vicious cycle of apoptosis, amyloid-beta generation, and further rounds of apoptosis.
"If future studies support these findings, they suggest that caution be used in choosing this anaesthetic for elderly patients, who already are at increased risk for Alzheimer's and for postoperative cognitive dysfunction."
The team plan to carry out further research to assess if the same effects would be seen in patients.
Dr Susanne Sorensen, head of research at the UK's Alzheimer's Society, said: "Around 10% of people who are given anaesthetic for major surgery experience 'post-operative cognitive decline.'
"This involves lasting problems with their memory and attention, but it is not yet clear whether this decline may increase a person's risk of Alzheimer's disease."
She said the study had raised interesting questions, and added: "It is crucial that more work is now done to establish whether this same reaction can occur in the human brain. "
Dr Keith Myerson, a spokesman for the Royal College of Anaesthetists: "We take this report very seriously, but we would advise caution in extrapolating these findings to humans."
He added: "We know it's important to maintain blood flow to the brain when dealing with elderly patients and monitor blood pressure carefully.
"It's also important that the level of carbon dioxide in the blood is not allowed to drop too low."