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Acute mountain sickness is caused by lack of oxygen at higher altitudes. With higher altitudes, the atmospheric pressure decreases leaving fewer oxygen molecules available in the thinner air. In these higher altitudes the rate and depth of breathing increases, this disturbs the balance of gases in the lungs and blood. The blood becomes alkaline, and the distribution of salts (electrolytes) is changed. This alters the fluid distribution of water between tissues and blood, causing the principal problems associated with acute mountain sickness. Problems associated with this illness affect the nervous system, lungs, muscles and heart. Below 7,000 feet effects are few. At 9,000 feet or more effects are common with rapid ascent. Most people can adjust to the changes within a few days up to 10,000 feet. Altitudes beyond 10,000 feet may take days or weeks to acclimate.

Common symptoms may be a dry, continuous cough, shortness of breath at rest which increases during daily activities, sleeping difficulty, rapid pulse, loss of appetite, nausea or vomiting, confusion, fatigue, or coughing up blood. Twenty percent of people have severe headaches. Sometimes the headache is severe enough to awaken one from sleep. The headache can be aggravated by lying down or sitting up, sneezing, straining or lifting.

Additional symptoms include transient vision problems, unilateral (one side) eye drooping, facial swelling, swelling around the eye sockets, and/or unilateral pupil enlargement. Symptoms of confusion, withdrawn behavior or swelling of lower extremities are also possible. A bluish tint to the skin (cyanosis) is common due to lack of oxygen in the blood.

High Altitude Pulmonary Edema.
This is a more serious illness that can follow an episode of acute mountain sickness. It occurs when fluid accumulates in the lungs. Shortness of breath is present with the slightest effort made, a tickling dry cough may turn loose and bubbly with production of phlegm which is pink or blood tinged. High altitude pulmonary edema may worsen quickly and become life threatening within just a few hours.

High Altitude Cerebral Edema
This is the most serious of all complications and needs to be treated promptly. It usually develops within 24 to 96 hours after arriving at higher altitudes. High altitude cerebral edema may be preceded by acute mountain sickness or high altitude pulmonary edema.

Fluid accumulates in the brain causing difficulty walking (ataxia). The ataxia is accompanied by clumsy hand or finger movements. Headaches will be more severe than with acute mountain sickness, hallucinations may develop as the condition progresses. The higher the altitude, the greater the impairment of function and perception will be. This condition can also progress from mild to life threatening very quickly.


Most people recover from acute mountain sickness quickly after being moved to a lower altitude. Increased oxygen to the body helps to relieve symptoms. Mild acute mountain sickness is usually treated by replacing fluids lost during sweating and rapidly breathing dry, thin air. Persons with high altitude pulmonary edema need to be observed closely. Usually bed rest and oxygen therapy are enough. If this doesn't relieve symptoms, the person should be taken to a lower altitude at once. High altitude cerebral edema is a serious condition,. People suffering this should be moved to a lower altitude immediately. Delaying the move will worsen the condition. After descent the condition improves quickly.


It is best to make a climb gradually. Try to take at least two days to reach 8,000 feet and another day for each 1,000 to 2,000 additional feet. Camping midway reduces the risk of acute mountain sickness. Once altitude is reached, avoiding strenuous activity for a day or two will reduce risks. Avoid alcohol and tobacco consumption, extra fluids, salt and medications that cause sleeplessness. Extra sleep is not helpful because it slows the breathing.
When climbing over 8,000 feet symptoms of acute mountain sickness should be carefully watched for. Each person in the party should be evaluated at the end of each day of climbing. Performance, level of fatigue, weakness or shortness of breath, lung function and heart rate should be checked after a few hours of rest.