GIVING elderly patients certain general anaesthetics could increase their risk of developing Alzheimer's disease and other memory and attention problems.
The suggestion arises from recent test tube and animal experiments. They also indicate that anaesthetists need to log more carefully the combinations and doses of the anaesthetics they give to patients, to allow the risks to be properly assessed.
The link between surgery and cognitive problems was first noted during the 1950s, but it was never clear whether postoperative cognitive dysfunction (POCD) was the result of the surgery itself or the anaesthetics, says Pravat Mandal of the University of Pittsburgh Medical School in Pennsylvania. It has been suggested that heart bypass surgery in particular could make the protective blood-brain barrier leaky, allowing immune tissue or unwanted debris into the brain.
Now animals studies and test tube experiments are beginning to show that certain anaesthetics reduce the rate at which brain cells are born and develop, a factor that seems to be important to normal memory function. They may also directly affect the rate at which beta amyloid proteins bind together. This could be worrying, as the formation of clumps or "plaques" of these proteins is characteristic of Alzheimer's disease and may contribute to brain cell death.
Last week at the annual meeting of the Society for Neuroscience in Atlanta, Georgia, Mandal revealed that the inhaled anaesthetics halothane and isoflurane encourage clumping of beta amyloid protein, as does the commonly used intravenous
anaesthetic propofol, at least at higher concentrations. The findings back up a previous study in which Mandal used NMR spectroscopy to show that halothane interacts directly with a pocket in the beta amyloid protein, changing its shape and encouraging neighbouring proteins to bind. Just 6 hours of exposure to halothane is sufficient to trigger protein clumping similar to that seen
Contact: Claire Bowles