Altitude sickness
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Altitude sickness (also: acute mountain sickness (AMS) or altitude illness) is a pathological condition that is caused by lack of adaptation to high altitudes. It commonly occurs above 2,440 metres (8,000 feet). The symptoms are headaches, fatigue, shortness of breath, nausea, unsteadiness and dizziness, loss of appetite, insomnia, weakness and sometimes even seizures and coma.
Different people have different susceptibilities to altitude sickness. For some otherwise healthy people symptoms can begin to appear at around 1,500 metres (5,000 feet) above sea level. This is the altitude of Mexico City and Denver, Colorado. Diets high in carbohydrates may make people suffering AMS feel better. The carbohydrates seem to liberate more energy and oxygen compared to their lipid counterparts.
The most serious symptoms of altitude sickness are due to edema (fluid accumulation in the tissues of the body). At very high altitude, humans can get either high-altitude pulmonary edema (HAPE), or high altitude cerebral edema (HACE). These syndromes are potentially fatal. The physiological cause of altitude-induced edema is not conclusively established. For those suffering HAPE or HACE, dexamethasone may provide temporary relief from symptoms in order to keep descending under their own power.
HAPE occurs in ~2% of those who are adjusting to altitudes of ~10,000 feet or more. It can be life threatening. Symptoms include fatigue, dyspnea, headache, nausea, dry cough without phlegm, pulmonary edema, fluid retention in kidneys, and rales. Descent to lower altitudes alleviates the symptoms of HAPE.
HACE is a life threatening condition that can lead to coma or death. It occurs in about 1% of people adjusting to altitudes above 9,000 feet. Symptoms include headache, fatigue, visual impairment, bladder dysfunction, bowel dysfunction, loss of coordination, paralysis on one side of the body, confusion, and slowed reflex response. Descent to lower altitudes may save those afflicted with HACE.
Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 metres (9,800 feet), most climbers and high altitude trekkers follow the "golden rule" - Trek/Climb High, Sleep Low. For high altitude climbers, the way to acclimatise is to stay a few days at base camp, climb up to a higher camp (slowly), stay there for one night initially, then return to base camp. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body "get used" to the oxygen level there. Once you are used to that altitude, you then repeat the process with a camp placed at higher elevations. The general rule of thumb is to not ascend more than 300 metres (1,000 feet) per day to sleep. That is, one can climb from 3,000 to 4,500 metres (14,765 feet) in one day, but one should then descend back to 3,300 metres (10,825 feet) to sleep. This process cannot be rushed, and this explains why you need to spend days (or even weeks at times) acclimatising before attempting to climb a high peak.
Acetazolamide may help some people in speeding up the acclimatization process and can treat mild cases of altitude sickness. Drinking plenty of water will also help in acclimatization to replace the fluids lost through the heavier breathing.
The only real cure once symptoms appear is to take the sufferer to a lower altitude. For serious cases of AMS, a Gamow bag can be used to reduce the effective altitude by as much at 1,500 meters (5,000 feet). A Gamow bag is a portable plastic pressure bag inflated with a foot pump.
External links
- Merck Manual entry on altitude sickness (http://www.merck.com/pubs/mmanual/section20/chapter281/281a.htm)
- University of Buffalo Reporter article on research into the cause of altitude sickness (http://www.buffalo.edu/reporter/vol29/vol29n30/n1.html)
- http://www.ismmed.org/np_altitude_tutorial.htm
- High Altitude Pathology Institute (http://www.altitudeclinic.com)de:Höhenkrankheit