Alternative Names high altitude cerebral oedema, altitude sickness, high-altitude mountain sickness, altitude anoxia, high altitude pulmonary oedema
Definition Acute mountain sickness is a disorder caused by lack of oxygen at high altitudes. It can affect any person who climbs too rapidly above an elevation of around 2500 metres. Symptoms are more likely to occur if a person climbs from sea level to above 2500 metres. It can also occur at lower altitudes.
What is going on in the body? As altitude increases, the atmospheric pressure decreases. There are fewer oxygen molecules available. This decrease in oxygen availability affects the body in many ways. The rate and depth of breathing increase. This disturbs the balance between gases in the lungs and the blood. This increases the alkalinity in the blood, and causes changes in the distribution of potassium and sodium in the cells. As a result, water is distributed differently between the blood and the tissues. These changes are the main case of mountain sickness.
What are the signs and symptoms of the condition? The signs and symptoms of acute mountain sickness include:
shortness of breath
rapid heart rate
fatigue
dizziness
headache
bluish colouration of skin, lips and fingernails
difficulty sleeping
loss of appetite
nausea and vomiting
confusion
cough
facial swelling
pupils different sizes
decreased level of consciousness
problems with vision
What are the causes and risks of the condition? Acute mountain sickness can happen with steady climbs to higher altitudes. It can be prevented by climbing gradually and getting used to midway altitudes. Some people will have symptoms after rapid climbs from sea level to 2500 to 3300 metres. Climbers from sea level to 4600 metres almost always have symptoms. There are no tests to determine if a person is likely to get acute mountain sickness.
This condition is more common in younger people. Individuals with history of acute mountain sickness and those with lung diseases are more prone to this condition.
What can be done to prevent the condition? The best way to prevent acute mountain sickness is to climb short distances when climbing to higher elevations. For example, if a person plans to travel from sea level to the mountains, it would be wise stop at a lower elevation for a couple nights. After getting used to the higher elevation, the person then can travel to the full elevation. Other preventive measures are to avoid tobacco, alcohol and medications that cause sleepiness. Drinking extra fluids and eating light, high starch meals are recommended. Heavy exertion should be avoided but complete rest is not recommended. Light outdoor activity is suggested. Extra sleep is not helpful, since sleeping slows breathing.
How is the condition diagnosed? Diagnosis is made by a physical examination along with a history of climbing to a high elevation. A physical examination can show fluid buildup. A neurological examination may show changes in pupils, decreased level of consciousness, and droopy eyelids.
What are the long-term effects of the condition? Once a person goes to a lower elevation, symptoms should improve. Severe cases can result in death. Once a person starts developing signs of acute mountain sickness, he or she should immediately get to a lower elevation and be given oxygen.
What are the risks to others? Acute mountain sickness is not a contagious disease. If a person become too ill to get down from a very high elevation, those attempting to move him or her to a lower elevation need to be careful to avoid injury to themselves.
What are the treatments for the condition? Temporary relief from acute mountain sickness can be achieved by taking 10 to 12 deep breaths every 4 to 6 minutes. This can cause the "blowing off" of too much carbon dioxide from the body. Acetazolamide and dexamethasone can reduce the severity of acute mountain sickness. For more severe acute mountain sickness, oxygen breathed through a mask that covers the nose and mouth is helpful. If severe symptoms persist, even with oxygen, a person should go to a lower altitude for prompt relief. A person may only need to go down 700 to 900 metres to gain relief. If a person develops fluid buildup surrounding the lungs, diuretics, such as frusemide or hydrochlorothiazide, can be given to help get rid of the excess fluid.
What are the side effects of the treatments? The side effects of treatment with drugs such as acetazolamide can be:
tingling in the lips and fingertips
lowering of vision
changes in taste
These symptoms go away when the drug is stopped. Water pills or diuretics such as frusemide can cause a decrease in blood potassium.
What happens after treatment for the condition? Most people recover very quickly once they go down to a lower elevation. There is an increased risk of more problems should a person return to high elevation. If a person plans to mountain climb, it is important to plan trips carefully to allow for time at several elevations. People should also avoid alcohol and tobacco. A few people who have buildup of fluid in brain tissues may have lingering problems. These may require follow-up even after they have returned to lower elevation.
How is the condition monitored? When climbing, especially in elevations above 2500 metres, a person should look for signs of acute mountain sickness. Symptoms may not be obvious in young, ambitious, physically fit climbers. Each party member should be evaluated at the end of each day's climb after the person has rested for several minutes. The following things should be evaluated:
performance
level of fatigue
weakness or shortness of breath
lung function
heart rate
Author: James Broomfield, MD Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
