Brain swelling causes most Everest deaths
A brain swelling condition related to low oxygen levels in the air may be the cause of most Mount Everest deaths, say researchers.
An international team led by Dr Paul Firth of Massachusetts General Hospital studied the 212 reported deaths from 1921 to 2006 on Mount Everest, the highest on earth.
Hazards awaiting those who dare to climb the 8850 metre Himalayan mountain include extreme cold, strong winds, changing weather, treacherous climbs and avalanches. Oxygen content in the air is only a third of that at sea level.
"Nobody was attacked by any Yeti or anything else," says Firth, whose findings appear in the British Medical Journal.
He says that while the cause of some deaths could not be determined with certainty, many appeared to have been the result of high-altitude cerebral oedema.
In this condition, low oxygen levels cause cerebral blood vessels to leak fluid into surrounding brain tissue, triggering swelling. Confusion and loss of coordination follow.
Many deaths occurred above 8000 metres in an area dubbed 'the dead zone', particularly among people who already reached the summit and were climbing back down.
"Of the guys who died up at 8000 meters, a large number of them were developing neurological symptoms. In other words, they were getting confused, comatose or they were having a loss of coordination," says Firth.
This seemed consistent with high-altitude cerebral oedema, he says. "If you go too fast and you haven't adapted to the low oxygen levels, then you can get various types of high altitude illness."
Firth says that he expected to find more lung problems in his study, but they were rare.
The researchers speculate that many of the deaths attributed to falls or the person vanishing during the climb may have been due to high-altitude cerebral oedema.
The study showed that 1.3% of mountaineers who climbed above their Everest base camp died.