Acute mountain sickness is an illness that can affect mountain climbers, hikers, skiers, or travelers at high altitudes, usually above 8,000 feet (2,400 meters).
Acute mountain sickness is caused by reduced air pressure and lower oxygen levels at high altitudes.
The faster you climb to a high altitude, the more likely you will get acute mountain sickness.
You are at higher risk for acute mountain sickness if:
- You live at or near sea level and travel to a high altitude
- You have had the illness before
Your symptoms will also depend on the speed of your climb and how hard you push (exert) yourself. Symptoms range from mild to life-threatening. They can affect the nervous system, lungs, muscles, and heart.
In most cases, symptoms are mild. Symptoms of mild to moderate acute mountain sickness may include:
- Difficulty sleeping
- Dizziness or light-headedness
- Loss of appetite
- Nausea or vomiting
- Rapid pulse (heart rate)
- Shortness of breath with exertion
Symptoms that may occur with more severe acute mountain sickness include:
Exams and Tests
The health care provider will examine you and listen to your chest with a stethoscope. This may reveal sounds called crackles (rales) in the lung. Rales may be a sign of fluid in the lungs.
Tests that may be done include:
- Blood tests
- Brain CT scan
- Chest x-ray
- Electrocardiogram (ECG)
Early diagnosis is important. Acute mountain sickness is easier to treat in the early stages.
The main treatment for all forms of mountain sickness is to climb down (descend) to a lower altitude as rapidly and safely as possible. You should not continue climbing if you develop symptoms.
Extra oxygen should be given, if available.
People with severe mountain sickness may need to be admitted to a hospital.
Acetazolamide (Diamox) may be given to help you breathe better. It can help reduce mild symptoms. This medicine can make you urinate more often. Make sure you drink plenty of fluids and avoid alcohol when taking this drug. This medication works best when taken before reaching a high altitude.
If you have fluid in your lungs (pulmonary edema), treatment may include:
- A high blood pressure medicine called nifedipine
- Beta agonist inhalers to open the airways
- Breathing machine in severe cases
- Medicine to increase blood flow to the lungs called phosphodiesterase inhibitor (such as sildenafil)
Dexamethasone (Decadron) may help reduce swelling in the brain (cerebral edema).
Portable hyperbaric chambers allow hikers to simulate conditions at lower altitudes without actually moving from their location on the mountain. These devices are very helpful if bad weather or other factors make climbing down the mountain impossible.
Most cases are mild. Symptoms improve quickly when you climb down the mountain to a lower altitude.
Severe cases may result in death due to lung problems or brain swelling, called cerebral edema.
In remote locations, emergency evacuation may not be possible, or treatment may be delayed. This can have a negative affect on your outcome.
The outlook depends on the rate of descent once symptoms begin. Some individuals are more prone to developing altitude-related sickness and may not respond as well.
- Coma (unresponsiveness)
- Fluid in the lungs (pulmonary edema)
- Swelling of the brain (cerebral edema), which can lead to seizures, mental changes, or permanent damage to the nervous system
When to Contact a Medical Professional
Call your provider if you have or had symptoms of acute mountain sickness, even if you felt better when you returned to a lower altitude.
Call 911 or your local emergency number if you or another climber have any of the following symptoms:
- Severe breathing problems
- Altered level of alertness
- Coughing up blood
Climb down the mountain right away and as safely as possible.
Keys to preventing acute mountain sickness include:
- Climb the mountain gradually
- Stop for a day or two of rest for every 2,000 feet (600 meters) of climb above 8,000 feet (2,400 meters)
- Sleep at a lower altitude when possible
- Learn how to recognize early symptoms of mountain sickness
If you are traveling above 9,840 feet (3,000 meters), you should carry enough oxygen for several days.
If you plan on quickly climbing to a high altitude, ask your provider about a medicine called acetazolamide (Diamox). This drug helps your body get used to higher altitudes more quickly, and reduces minor symptoms. It should be taken the day before you climb, and then for the next 1 to 2 days.
If you are at risk for a low red blood cell count (anemia), ask your provider if an iron supplement is right for you. Anemia lowers the amount of oxygen in your blood. This makes you more likely to have mountain sickness.
- Drink plenty of fluids
- Avoid alcohol
- Eat regular meals, high in carbohydrates
You should avoid high altitudes if you have heart or lung disease.
High altitude cerebral edema; Altitude anoxia; Altitude sickness; Mountain sickness; High altitude pulmonary edema
Hackett PH, Roach RC. High-altitude medicine. In: Auerbach PS, ed. Wilderness Medicine. 5th ed. Philadelphia, PA: Elsevier Mosby; 2007:chap 1.
Schoene RB, Swenson ER. High altitude. In: Mason RJ, Murray JF, Broaddus VC, Nadel JA, eds. Textbook of Respiratory Medicine. 4th ed. Philadelphia, PA: Elsevier Saunders; 2005:chap 65.
Wright A, Brearey S, Imray C. High hopes at high altitudes: pharmacotherapy for acute mountain sickness and high-altitude cerebral and pulmonary oedema. Expert Opin Pharmacother. 2008;9(1):119-127. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18076343
Yaron, M, Paterson RD, Davis DB. High-altitude medicine. In: Marx JA, Hockberger RS, Walls RM, et al., eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 44.
Update Date 1/12/2015
Updated by: Jacob L. Heller, MD, MHA, Emergency Medicine, Virginia Mason Medical Center, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.