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Overview

Altitude sickness, also known as 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 2,500 metres (approximately 8,000 feet). If untreated, the condition can result in death. Another, rarer, type of altitude sickness caused by prolonged exposure to high altitude is chronic mountain sickness, also known as Monge's disease.

Symptoms

The early symptoms of altitude sickness include drowsiness, general malaise, and weakness, especially during physical exertion. More severe symptoms are headache, insomnia, persistent rapid pulse, nausea and sometimes vomiting, especially in children. Extreme symptoms include confusion, psychosis, hallucination, symptoms resulting from pulmonary edema (fluid in the lungs) such as persistent coughing, and finally seizures, coma and death.

Causes

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 known for certain. 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 about 2% of those who are adjusting to altitudes of about 3000 m (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
• rales (crackling noises heard in the lungs).

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 ~2700 m (9,000 feet). Symptoms include:

• headache
• fatigue
• visual impairment
• bladder dysfunction
• bowel dysfunction
• loss of coordination
• paralysis on one side of the body
• confusion
• slowed reflex response

Descent to lower altitudes may save those afflicted with HACE.

Treatment

Once symptoms appear the person who is suffering must be taken to a lower altitude immediately. Descending is the absolute treatment of choice. For serious cases of AMS, a portable plastic pressure bag inflated with a foot pump can be used to reduce the effective altitude by as much at 1,500 meters (5,000 feet).

The mainstay of treatment of AMS is rest, fluids, and mild analgesics: acetaminophen (paracetamol), aspirin, or ibuprofen. These medications will not cover up worsening symptoms. The natural progression for AMS is to get better, and often simply resting at the altitude at which you became ill is adequate treatment. Improvement usually occurs in one or two days, but may take as long as three or four days. Descent is also an option, and recovery will be quite rapid.

A frequent question is how to tell if a headache is due to altitude. Altitude headaches are usually nasty, persistent, and frequently there are other symptoms of AMS; they tend to be frontal (but may be anywhere), and may worsen with bending over. However, there are other causes of headaches, and you can try a simple diagnostic/therapeutic test. Dehydration is a common cause of headache at altitude. Drink one liter of fluid, and take some acetaminophen or one of the other analgesics listed above. If the headache resolves quickly and totally (and you have no other symptoms of AMS) it is very unlikely to have been due to AMS.

Prevention

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 (10,000 feet), most climbers and high altitude trekkers follow the "golden rule" - Climb High, Sleep Low. For high altitude climbers, the way to acclimatize is to stay a few days at base camp, slowly climb up to a higher camp, stay there for one night initially, then return to base camp. People seem to do best when they climb during the day but return to a lower altitude to sleep. 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 the climber is used to that altitude, the process is repeated 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 (10,000 feet) to 4,500 metres (15,000 feet) in one day, but one should then descend back to 3,300 metres (11,000 feet) to sleep. This process cannot be rushed, and this explains why climbers need to spend days (or even weeks at times) acclimatizing before attempting to climb a high peak.

Acetazolamide may help speed up the acclimatization process in some people. This medicine forces the kidneys to excrete bicarbonate, the base form of carbon dioxide; this re-acidifies the blood, balancing the effects of the hyperventilation that occurs at altitude in an attempt to get oxygen. It is also used to treat mild cases of altitude sickness. Drinking plenty of water will also help in acclimatization to replace the fluids lost through heavier breathing. Patients can sometimes control mild altitude sickness by consciously taking ten to twelve rapid large breaths every five minutes. If overdone, this can blow off too much carbon dioxide and cause tingling in the extremities of the body. Other treatments include injectable steroids to reduce pulmonary edema, and inflatable pressure vessels to relieve and evacuate severe mountain-sick persons.