Surgical operations involving general anaesthetic may damage mental ability by starving the brain of oxygen, researchers fear, after conducting tests on climbers as they scaled Mount Everest.
Up to one fifth of people develop hypoxia, or oxygen deficiency, after surgery, which can lead to symptoms such as wheezing, confusion, high blood pressure and even heart failure and death.
But research from City, University of London and University College London suggests that the condition can also have a significant impact on brain function, with the effects lasting for at least 11 days after oxygen deprivation.
The landmark study, which monitored 198 climbers who scaled Everest, where there is only one third the amount of oxygen that there is at sea level, found significant cognitive decline after the teams descended.
In particular, tasks associated with speech and language, learning, planning, focusing and organising were severely affected, with performance falling by nearly 20 per cent on tests taken before and after the ascent. The effects were still present when the climbers returned to Kathmandu, 11 days later.