Causes of death on Mount Everest examined

Most deaths during expeditions to the summit of Mount Everest occur during descents from the summit in the so-called death zone, U.S. researchers said.

Paul Firth of Massachusetts General Hospital said thousands of climbers have attempted to reach the summit of 8,850-meter, or 29,000-foot, Mount Everest since the 1920s. The international research team, which included investigators from three British hospitals and the University of Toronto, reviewed available expedition records including the Himalayan Database.

Of a total of 212 reported deaths on Everest from 1921 to 2006, 192 occurred above Base Camp, the last encampment before technical — roped — climbing begins, Firth said.

The study, scheduled to be published in the British Medical Journal, found the factors most associated with the risk of death were excessive fatigue, a tendency to fall behind other climbers and arriving at the summit later in the day. Many developed symptoms such as confusion, a loss of physical coordination and unconsciousness, which suggest high-altitude cerebral edema, a swelling of the brain that results from leakage of cerebral blood vessels.

Symptoms of high-altitude pulmonary edema, which is involved in most high-altitude-related deaths, were surprisingly rare.

We also were surprised at how few people died due to avalanches and ice falls in recent years — those usually happen at lower altitudes, and overwhelmingly people died during summit bids above 8,000 feet — and that during descents, the mortality rate for climbers was six time that of sherpas, Firth said.