Is general anaesthesia linked to memory loss and Alzheimer's disease?
Hello everyone,
Most people have either had a major operation or know someone who has – in fact an estimated 230 million major surgical procedures under general anaesthesia are carried out each year. Waking up from surgery can be disorienting, but could it also lead to higher risk of memory loss and Alzheimer’s disease? We asked 5 experts in anaesthesiology, Alzheimer’s Disease and medicine, ‘Is general anaesthesia linked to memory loss and Alzheimer's disease?’, here is what they said…
EXPERT CONSENSUS
Is general anaesthesia linked to memory loss and Alzheimer's disease?
‘Uncertain’ according to 5 experts
What is general anaesthesia and what is it used for?
The word ‘anaesthesia’ means ‘loss of sensation’. General anaesthesia (GA) is a state of controlled unconsciousness. It is used to carry out surgical procedures that would be too painful or dangerous to perform if you were conscious. An alternative anaesthesia, called regional anaesthesia, is used for operations where certain parts of the body are made numb, but the patient remains conscious.
GA is achieved through a mixture of medications, including those to keep you asleep, relieve pain and relax your muscles. The correct combination of these medications are delivered by an anaesthetist before the operation, and then GA is carefully maintained during the surgery before the patient is woken up again.
Why is it difficult to study the effects of general anaesthesia?
Dr James Cory-Wright, a medical doctor from Royal Berkshire Hospital NHS Foundation Trust in the UK, says “This is a tricky question to answer because general anaesthesia (GA) rarely occurs in the absence of surgery, so it is difficult to design studies to investigate whether GA in isolation is linked to memory loss and Alzheimer’s disease (AD). To complicate things further there are different types of GA including inhalation anaesthesia and total intravenous general anaesthesia (TIVA).”
Due to this difficulty, most studies looking at the effect of GA also look at the effects of surgery, and whether GA and surgery together can be linked to memory loss and AD.
Is general anaesthesia (and surgery) linked to memory loss?
Professor Lisbeth Evered, an expert in anaesthesiology and Alzheimer’s Disease from St Vincents Hospital Melbourne in Australia, says “There is a large body of evidence demonstrating that some older people suffer objectively defined cognitive decline following anaesthesia and surgery.”
Dr Cory-Wright says “there is good evidence that the combination of GA and surgery results in short-term effects on memory, termed post-operative cognitive decline (POCD), which is common in the elderly population with an incidence of 30% at 1 week in one study. This link between surgery involving GA and POCD has been recognised as far back as 1887, with an article published in the BMJ titled ‘Insanity following the use of anesthetises in operations’. ” He goes on to explain that POCD risk increases with age along with other factors such the length and type of operation.
Dr Roderic Eckenhoff, an expert in anaesthesiology from Pennsylvania University in the USA, says “Anaesthesia by itself is unlikely to accelerate AD or memory loss in humans. Most data from animals suggests only a transient effect. However, considering both anaesthesia and surgery, the data do suggest a longer lasting effect in those patients with pre-existing vulnerabilities.”
Is general anaesthesia (and surgery) linked to Alzheimer’s Disease?
Professor Evered says “There is animal evidence of Alzheimer's disease-type neuropathological changes associated with gaseous anaesthetics, but none of this work has been replicated in humans.”
Dr Cory-Wright agrees, saying “large observational studies investigating this have yielded mixed results. A well-designed study in Denmark looked at cognitive function in twins and found that GA and surgery did not lead to higher dementia risk and that other factors such as underlying disease were far more important. Another study with over 11 years of follow-up, looked specifically at whether POCD was linked to AD also found no evidence.”
How might anaesthesia affect memory?
Dr Cory-Wright says “There are multiple proposed mechanisms by which GA and surgery cause POCD. Animal studies have shown that some inhalational anaesthetic agents can directly cause neuronal cell death as well as AD-like changes in the brain such as accumulation of brain plaques.”
He goes on to say that “meta-analyses have found that whether you have general or regional anaesthesia does not affect your chance of getting POCD. This suggests that, while GA may play a role, other factors such as the surgery and being admitted to hospital may be more instrumental in the cause of POCD.”
How might surgery affect memory?
Dr Cory-Wright says “Surgery itself causes inflammation which can open the blood-brain barrier, resulting in the influx of pro-inflammatory chemicals into the brain. This affects neuronal signalling and the brain itself. Other proposed mechanisms by which GA and surgery cause POCD include low blood pressure and oxygen levels during the operation as well as pain and sleep disturbances afterwards.”
Is more research needed?
Dr Evered says we “need to know if the memory changes which occur in association with anaesthesia and surgery are the same as memory changes in the community like mild cognitive impairment and dementia or AD.” Dr Cory-Wright agrees and says “It is well known that GA and surgery are linked to short-term effects on memory and GA may well play a role in this. However, it is unclear whether GA is linked to AD and more research is needed in this area.”
The takeaway:
General anaesthesia and surgery is linked to short-term effects on memory, particularly in older adults. There is not strong evidence that general anaesthesia is linked to permanent memory loss or Alzheimer’s Disease.
May the facts be with you!
Eva
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