What is High Altitude?

Altitude is defined on the following scale:

High: 8,000 - 12,000 ft (2,438 - 3,658 m)

Very High: 12,000 - 18,000 ft (3,658 - 5,487 m)

Extremely High 18,000+ ft (5,500+ m)

There are no specific factors such as age, sex, or physical condition that correlate with susceptibility to altitude sickness. Most people can go up to 8,000 ft (2,438 m) with minimal effect. If you haven't been to high altitude before, it's important to be cautious. If you have been at that altitude before with no problem, you can probably return to that altitude without problems as long as you are properly acclimatized.

What Causes Altitude Sickness
The concentration of oxygen at sea level is about 21%. As altitude increases, the number of oxygen molecules per breath is reduced. At 12,000 ft (3,658 m) there are roughly 40% fewer oxygen molecules per breath. In order to properly oxygenate the body, your breathing rate (even while at rest) has to increase. This extra ventilation increases the oxygen content in the blood, but not to sea level concentrations. Since the amount of oxygen required for activity is the same, the body must adjust to having less oxygen.

Acclimatization

The major cause of altitude sickness is going too high too fast. Given time, your body can adapt to the decrease in oxygen molecules at a specific altitude. This process is known as acclimatization and generally takes 1-3 days. For example, if you hike to 10,000 ft (3,048 m), and spend several days at that altitude, your body acclimatizes to 10,000 ft (3,048 m). If you climb to 12,000 ft (3,658 m), your body has to acclimatize once again. A number of changes take place in the body to allow it to operate with decreased oxygen.

  • The depth of respiration increases.
  • Pressure in pulmonary arteries is increased, "forcing" blood into portions of the lung which are normally not used during sea level breathing.
  • The body produces more red blood cells to carry oxygen.
Prevention of Altitude Sickness

Prevention of altitude sickness falls into two categories: proper acclimatization and preventive medications. Below are a few basic guidelines for proper acclimatization.
  • Do not over-exert yourself or move higher for the first 24 hours.
  • If you go above 10,000 ft (3,048 m), only increase your altitude by 1,000 ft (305 m) per day and for every 3,000 ft (915 m) of elevation gained, take a rest day.
  • If you begin to show symptoms of moderate altitude illness, don't go higher until symptoms decrease ("Don't go up until symptoms go down").
  • If symptoms increase, go down, down, down!
  • Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least 3-4 quarts per day).
  • Take it easy. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.
  • Avoid tobacco, alcohol and other depressant drugs including barbiturates, tranquilizers, and sleeping pills. These depressants further decrease the respiratory drive during sleep, resulting in a worsening of the symptoms.
  • Eat a high carbohydrate diet (more than 70% of your calories from carbohydrates) while at altitude.

Preventive Medications
  • Diamox (Acetazolamide) allows you to breathe faster so that you metabolize more oxygen, thereby minimizing the symptoms caused by poor oxygenation. This is especially helpful at night when respiratory drive is decreased. Since it takes a while for Diamox to have an effect, it is advisable to start taking it 24 hours before you go to altitude and continue for at least five days at higher altitude. Please read instructions carefully or consult a physician before taking Diamox.
Acute Mountain Sickness (AMS)

AMS is common at high altitudes. At elevations over 10,000 ft (3,048 m), 75% of people will suffer mild symptoms. The occurrence of AMS is dependent upon the elevation, the rate of ascent, and individual susceptibility. Symptoms usually start 12-24 hours after arrival at altitude and begin to decrease in severity around the third day. The symptoms of Mild AMS are headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and a general feeling of malaise. Mild AMS does not interfere with normal activity and symptoms generally subside within 2-4 days as the body acclimatizes. As long as symptoms are mild, ascent can continue at a moderate rate.

Basic Treatment of AMS

The only cure is either acclimatization or descent. Symptoms of Mild AMS can be treated with pain medications for headache and Diamox. Both help to reduce the severity of the symptoms, but remember, reducing the symptoms is not curing the problem. Since it takes a while for Diamox to have an effect, it is advisable to start taking it 24 hours before you go to altitude and continue for at least five days at higher altitude. Possible side effects include tingling of the lips and finger tips, blurring of vision, and alteration of taste. Contact your physician for a prescription.

Moderate AMS

Moderate AMS includes severe headache that is not relieved by medication, nausea and vomiting, increasing weakness and fatigue, shortness of breath, and decreased coordination. Normal activity is difficult, although the person may still be able to walk on their own. At this stage only advanced medications or descent can reverse the problem. Descending even a few hundred ft (70-100 m) may help and definite improvement will be seen in descents of 1,000-2,000 ft (305-610 m). 24 hours at the lower altitude will result in significant improvements. The person should remain at lower altitude until symptoms have subsided (up to 3 days). At this point, the person has become acclimatized to that altitude and can begin ascending again.

Preventive Medications
  • Dexamethasone (a steroid) is a prescription drug that decreases brain and other swelling, reversing the effects of AMS. Dosage is typically 4 mg twice a day for a few days starting with the ascent. This prevents most symptoms of altitude illness. It may be combined with Diamox.