Acute Mountain Sickness: Causes, Symptoms, and Diagnosis

Acute Mountain Sickness: Causes, Symptoms, and Diagnosis

Acute mountain sickness is an illness that can affect mountain climbers, hikers, skiers, or travellers at high altitude (typically above 8,000 feet or 2,400 meters). It occurs from lower air pressure and oxygen levels at high altitudes that leave your body unable to take in enough oxygen for proper functioning.

It is also commonly sometimes known as High altitude cerebral edema; Altitude anoxia; Altitude sickness; Mountain sickness; High altitude pulmonary edema.


Acute mountain sickness is due to a combination of reduced air pressure and lowers oxygen levels at high altitudes.

The faster you climb to a high altitude, the more likely you will get acute mountain sickness. Your symptoms will also depend on the speed of your climb and how hard you push (exert) yourself.

Some people are more prone to altitude sickness and can develop severe complications such as fluid on the lungs -- called high altitude pulmonary edema -- but that’s rare at altitudes below 10,000 feet. Unfortunately, we don’t know how to predict who will develop life-threatening altitude problems; researchers are studying genetic patterns to see if they can uncover common gene mutations that could better predict risk


Symptoms range from mild to life-threatening and can affect the nervous system, lungs, muscles, and heart.

In most cases, the symptoms are mild. Symptoms generally associated with mild to moderate acute mountain sickness include:

  • Difficulty sleeping
  • Dizziness or light-headedness
  • Fatigue
  • Headache
  • Loss of appetite
  • Nausea or vomiting
  • Rapid pulse
  • Shortness of breath

Symptoms generally associated with more severe acute mountain sickness include:

  • Bluish discolouration of the skin (cyanosis)
  • Chest tightness or congestion 


  • Cough
  • Coughing up blood

Decreased consciousness or withdrawal from social interaction

  • Gray or pale complexion
  • Inability to walk in a straight line, or to walk at all
  • Shortness of breath at rest


How does the body acclimatize?

Within a few days, you’ll increase your breathing rate to take in more oxygen. Other systems in your body adjust as well; for instance, your kidneys will excrete more bicarbonate in the urine in order to accommodate your faster breathing rate. That will cause you to urinate more frequently. After several weeks, your body will produce more red blood cells to become more efficient at transporting oxygen.



Early diagnosis is important. Acute mountain sickness is easier to treat in the early stages.

You should not continue climbing if you develop symptoms.

Going to a lower altitude is the best remedy. Acetaminophen, ibuprofen, or another over-the-counter pain reliever can be used to treat headaches, but it may not work in severe cases. 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 improve breathing and reduce mild symptoms. This drug can cause increased urination. Make sure you drink plenty of fluids and avoid alcohol when taking this drug.

If you have fluid in your lungs (pulmonary edema), treatment may include:

  • Oxygen
  • A high blood pressure medicine called nifedipine
  • A type of drug called a phosphodiesterase inhibitor (such as sildenafil)
  • Lung inhalers beta-agonists


A breathing machine, in severe cases

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.

Outlook (Prognosis)

Most cases are mild, and symptoms improve promptly when you climb down the mountain to a lower altitude.

Severe cases may result in death due to lung problems or brain swelling.

In remote locations, an emergency evacuation may not be possible, or treatment may be delayed. This can have a negative effect on your outcome.

Possible Complications

  • Coma
  • Fluid in the lungs (pulmonary edema)
  • Swelling of the brain


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) 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 travelling 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 doctor about a medication 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 anaemia, ask your doctor if an iron supplement is right for you. Anaemia lowers the amount of oxygen in your blood.

While climbing:

  • Drink plenty of fluids
  • Avoid alcohol
  • Eat regular meals, high in carbohydrates

You should avoid high altitudes if you have heart or lung disease.

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