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High Altitude Illness and Acute Mountain Sickness

How to recognize, prevent and treat symptoms of high altitude illness

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Updated September 04, 2013

Exercise at High Altitude

Exercise at High Altitude

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Altitude illness or acute mountain sickness (AMS) refers to the various symptoms that often develop when you travel to high altitude. Most people who experience altitude illness who notice symptoms once they reach about 8000 feet. Even if you are physically fit, you may develop acute mountain sickness if you don't gradually adjust to the altitude with proper acclimatization. Acclimatization is a process in which the body slowly adapts to higher altitude. This process typically takes several days. But depending upon the altitude and the individual, it may take weeks to fully acclimate.

Acclimatization to Altitude
Although the concentration of oxygen is the same at sea level and at altitude, when you travel to higher altitude, the number of oxygen molecules per breath decreases due to a drop in the barometric pressure. In order to get adequate oxygen for activity, you have to breathe more or adjust to having less oxygen. Even with a faster breathing rate, it is difficult to get adequate oxygen to the working muscles and you may find that you fatigue much sooner at altitude than at sea level. At altitude, most people will notice a faster hear rate, a faster breathing rate, shortness of breath upon mild exertion, increased urination, and even trouble sleeping.

When traveling to high altitude, your body also undergoes some complicated changes in fluid balance during acclimatization. One of these changes is an increase in the number of red blood cells to carry oxygen. You may also notice more frequent urination. Other changes also take place to help your body adapt to this change in altitude.

Altitude Illness
The problem of altitude illness starts when acclimatization does not keep pace with your ascent to high altitude. This often happens when you ascend too quickly or go from sea level to high altitude in a day. It's helpful to follow some basic guidelines if you plan to travel to high altitude.

Preventing Altitude Illness
The best way to prevent altitude illness is by making a slow, gradual ascent to altitude and give yourself time to acclimatize. Rates of acclimation are not the same for everyone. So it is difficult to determine the amount of time you will require. Some general guidelines include the following:

  • Avoid flying directly into high altitude. Start at or below 10,000 feet and walk up gradually.
  • Climb high and sleep low. This is the climber's golden rule. Once you reach 10,000 feet, avoid increasing your sleeping elevation more than 1000 feet per night.
  • For every 3000 feet you ascend, spend two nights at the same elevation.
  • Eat a high carbohydrate diet (70% of calories) while at altitude.
  • Avoid alcohol.
  • Stay hydrated. Remember that acclimatization often results in fluid loss and dehydration occurs more quickly at high altitude, so it's important to replenish loss fluids.

Recognizing Altitude Illness
After ascending to 8000 feet or more, you may notice symptoms of altitude illness. These include:

  • A headache is often the first warning sign of altitude illness.
  • Dizziness
  • Loss of appetite
  • Shortness of breath
  • Trouble sleeping
  • Nausea
  • Vomiting
  • Fatigue or weakness
Most symptoms of altitude illness tend to be worse at night. For the majority of people, the symptoms won't interfere with daytime activity and disappear in a couple of days as you acclimate.

If your symptoms increase or persist the best treatment is to descend to lower altitude. Certain medications can help treat altitude illness; however, these are temporary solutions that only treat the symptoms.

If left untreated, altitude illness can progress into the very severe and life-threatening conditions called high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). These two conditions are recognized by changes in a person's level of consciousness, coordination, and severe breathlessness. They are medical emergencies that require immediate descent and medical attention.

Taking a trip to a high altitude can be a wonderful experience if you know how to do it safely. For more information about traveling to high altitude, see Preventing Altitude Illness During Active Vacations.

Source:

High Altitude Medicine & Biology Volume 8, Issue 2, June 2007.

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