Washington, Dec 10 (ANI): An international research team has conducted the first detailed analysis of deaths during expeditions to the summit of Mount Everest.
The team, led by Massachusetts General Hospital (MGH) investigators, found that most deaths occur during descents from the summit in the so-called "death zone" above 8,000 meters.
They also identified factors that appear to be associated with a greater risk of death, particularly symptoms of high-altitude cerebral edema.
"We know that climbing Everest is dangerous, but exactly how and why people have died had not been studied," said Paul Firth, of the MGH Department of Anesthesia, who led the study.
"It had been assumed that avalanches and falling ice - particularly in the Khumbu Icefall on the Nepal route - were the leading causes of death and that high-altitude pulmonary edema would be a common problem at such extreme altitude. But our results do not support either assumption," he added.
In order to examine the circumstances surrounding all deaths on Everest expeditions, the research team reviewed available expedition records including the Himalayan Database, a compilation of information from all expeditions to 300 major peaks in the world's highest range.
Of a total of reported 212 deaths on Everest from 1921 to 2006, 192 occurred above Base Camp, the last encampment before technical (roped) climbing begins.
Firth and three physician co-authors reviewed records for all deaths and classified them according to available information.
More detailed analysis was conducted on deaths occurring above 8,000 meters during the past 25 years.
Deaths were categorized as traumatic, from falls or external hazards such as avalanches; non-traumatic, from high-altitude illness, hypothermia or other medical causes; or as disappearances.
Expedition participants were classified as either 'climbers,' individuals from outside the Himalayan region, or 'sherpas' - high-altitude porters, most of them ethnic Sherpas or Tibetans, hired to transport equipment and otherwise assist the climbers.
The overall mortality rate for Everest mountaineers during the entire 86-year period was 1.3 percent; while the rate among climbers was 1.6 percent and the rate among sherpas was 1.1 percent.
During the past 25 years, a period during which a greater percentage of mountaineers climbed above 8,000 meters, the death rate for non-Himalayan climbers descending via the longer Tibetan northeast ridge was 3.4 percent, while on the shorter Nepal route it was 2.5 percent.
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 of those who died 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. (ANI)