Reduced atmospheric pressure and a lower concentration of oxygen at high altitude are the causes of this illness. It affects the nervous system, lungs, muscles, and heart. Symptoms can range from mild to life-threatening.

In most cases the symptoms are mild, but in severe cases fluid collects in the lungs (pulmonary edema) causing extreme shortness of breath and further decreasing oxygenation. Swelling may also occur in the brain (cerebral edema), causing confusion, coma, and, if untreated, death.

The likelihood and severity of altitude illness is greater with increasing rate of ascent, higher altitude attained, and higher levels of exertion.

Approximately 20% of people will develop mild symptoms at altitudes between 6,300 to 9,700 feet, but pulmonary and cerebral edema are extremely rare at these heights. However, above 14,000 feet, a majority of people will experience at least mild symptoms, while approximately 10% and 1.5%, respectively, of un-acclimatized people staying at this altitude will develop pulmonary or cerebral edema.

Symptoms generally associated with mild to moderate altitude illness include:

• Headache
• Difficulty sleeping
• Loss of appetite
• Nausea or vomiting
• Fatigue
• Dizziness or light-headedness
• Rapid pulse (heart rate)
• Shortness of breath with exertion

Symptoms generally associated with more severe altitude illness include:

• Cough
• Shortness of breath at rest
• Chest tightness or congestion
• Bluish discoloration of the skin
• Coughing up blood
• Inability to walk in a straight line, or to walk at all
• Decreased consciousness or withdrawal from social interaction
• Confusion

• Gray or pale complexion (cerebral edema)

Listening to the chest with a stethoscope (auscultation) reveals crackles in the lung fields in patients with pulmonary edema.

A chest X-ray may be performed.

The mainstay of treatment for all forms of altitude illness is to descend to lower altitude as rapidly and safely as possible. Supplemental oxygen should also be administered, if available.

Hospitalization may be required for severe illness.

Acetazolamide (Diamox) may be used to stimulate breathing, speed acclimatization, and diminish the milder symptoms of acute mountain sickness. Do not consume alcoholic beverages while taking Diamox, and drink sufficient fluids since Diamox increases urination.

Pulmonary edema is treated with oxygen, nifedipine (a high-blood pressure medication also effective for this disorder), and in severe cases, mechanical ventilation.

For cerebral edema, administration of the steroid drug dexamethasone (Decadron) may be helpful.

Most cases are mild, and symptoms improve promptly with a return to lower altitude. Severe cases may result in death due to respiratory distress or brain swelling (cerebral edema).

In remote locations, emergency evacuation may not be possible, or treatment may be delayed. These conditions could adversely affect the outcome.

• Pulmonary edema
• Coma
• High altitude cerebral edema (brain swelling)

Call your health care provider if symptoms of acute mountain sickness develop, even if symptoms resolved when returning to a lower altitude.

Call the local emergency number (such as 9-1-1) or seek emergency medical assistance if severe difficulty breathing develops, if consciousness is decreased, if coughing up blood, or if other severe symptoms are present. If unable to contact emergency help, descend immediately, as rapidly as is safely possible.

Education of mountain travelers before ascent is the key to prevention. Basic principles include: gradual ascent, stopping for a day or two of rest for each 2,000 feet (600 meters) above 8,000 feet (2,400 meters); sleeping at a lower altitude when possible; and learning how to recognize early symptoms so you can return to lower altitude before worsening symptoms occur.

Mountaineering parties traveling above 9,840 feet (3,000 meters) should carry an oxygen supply sufficient for several days.

Acetazolamide (Diamox) helps to speed acclimatization and reduce minor symptoms. Therapy should start one day before the ascent and continue one to two days into the excursion. This measure is recommended for those making a rapid ascent to high altitudes.

Those susceptible to anemia (particularly women) should consult a doctor regarding an iron supplement to correct the condition before traveling in high altitudes. Anemic persons have a reduced red blood cell count, and therefore, a lower amount of oxygen carried in the blood.

Drink sufficient fluids, avoid alcohol, and eat regularly. Foods should be relatively high in carbohydrates.

People with underlying cardiac or pulmonary (lung) diseases should avoid high altitudes.