Altitude Illness Acute Mountain Sickness

Overview, Causes, & Risk Factors

Acute mountain sickness, or AMS, is a mild, self-limiting form of altitude illness. Altitude illnesses are caused by lack of oxygen as a person climbs to higher altitudes. A more severe form of altitude illness, known as high-altitude cerebral edema or HACE, has much more serious consequences.

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 imbalance 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. This change in distribution causes the effects of altitude illness.

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 8,000 to 10,000 feet. Climbers from sea level to 14,000 feet almost always have symptoms. AMS is more common in younger adults than in older people. Individuals with history of AMS and those with lung diseases are more prone to this condition.

Symptoms & Signs

What are the signs and symptoms of the condition?

The following are normal symptoms of exposure to a high altitude:

  • abnormal breathing patterns at night
  • frequent awakening at night
  • shortness of breath with physical activity
  • unusual or memorable dreams
  • urinating large amounts
  • Acute mountain sickness is characterized by a headache plus at least one of the following symptoms:

  • dizziness or lightheadedness
  • fatigue
  • insomnia
  • loss of appetite
  • nausea or vomiting
  • weakness
  • Diagnosis & Tests

    How is the condition diagnosed?

    Diagnosis of AMS begins with a history and physical exam. The healthcare provider may order a cranial CT scan or cranial MRI to look for swelling in the brain.

    Prevention & Expectations

    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 of nights. After getting used to the higher elevation, the person then can travel to the full elevation.

    The following measures can be helpful in avoiding AMS:

  • avoiding medicines that cause drowsiness, such as sleeping pills
  • avoiding smoking and alcohol
  • drinking extra fluids
  • eating light meals with plenty of starch, or complex carbohydrates
  • taking gingko biloba, an antioxidant made from plants
  • 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.

    When climbing, especially in elevations above 8,000 feet, a person should look for signs of AMS. Symptoms may not be obvious in young, 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 factors should be evaluated:

  • heart rate
  • level of fatigue
  • lung function
  • performance
  • shortness of breath
  • weakness
  • What are the long-term effects of the condition?

    Once a person goes to a lower elevation, symptoms should improve. Acute mountain sickness usually resolves within 5 days if the person gets to a lower altitude and receives oxygen. If the person stays at the higher altitude, there is a risk of HACE and death.

    What are the risks to others?

    Acute mountain sickness is not contagious and poses no risk to others.

    Treatment & Monitoring

    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. Two medicines, acetazolamide and dexamethasone, can reduce the severity of AMS. Oxygen breathed through a mask that covers the nose and mouth is helpful. Other medicines may be given to relieve headache or nausea.

    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 2,000 to 3,000 feet to gain relief. If a person develops fluid buildup surrounding the lungs, water pills may be given to help get rid of the excess fluid. More aggressive treatment will be started if the person develops HACE.

    What are the side effects of the treatments?

    Acetazolamide may cause tingling in the lips and fingertips. It can also cause changes in taste and vision. These symptoms go away when the medicine is stopped. Dexamethasone can cause increased bleeding or risk of infection. Water pills can cause salt imbalances.

    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. 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?

    Any new or worsening symptoms should be reported to the healthcare provider.

    Article type: xmedgeneral