I have never personally experienced altitude sickness, but anyone planning to visit a destination more than 6,000 to 8,000 feet above sea level should be aware of the potential risk involved.

Travelers can be exposed to high elevations whether flying, driving or even hiking. High-altitude airports include Denver, Colo., at 5,280 feet; Cuzo, Peru, at 11,00 feet; La Paz, Bolivia, at 11,300 feet; and Lhasa, Tibet, at 12,500 feet.

Lack of oxygen causes altitude sickness. As the altitude increases, the air becomes “thinner” as the oxygen in the atmosphere decreases. When you breathe less oxygen into your lungs, the amount in your blood decreases.

Individuals vary in their susceptibility to altitude sickness and, unfortunately, there is no screening test. Prior experience with altitude sickness can be an indicator, but is not foolproof. Travelers with underlying medical conditions such as congestive heart failure, myocardial ischemia (angina), sickle cell-disease or any pulmonary disease should contact their physician — or better yet a physician who is familiar with altitude illness — before visiting high-altitude destinations. (Interestingly, the risk of newly diagnosed ischemic heart disease in previously healthy explorers does not seem to increase at high altitudes.)

Altitude sickness is divided into three distinct syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE).

AMS is the most common form, occurring at altitudes of as little as 4,000 to 6,000 feet. Most often it’s the result of abrupt ascents greater than 9,000 feet. The onset of this illness is delayed by six to 12 hours after reaching the altitude, and occasionally symptoms may not appear until 24 to 48 hours after an ascent. The higher the altitude, the greater the effect. Some of the first signs and symptoms are headache, light-headedness, weakness, trouble sleeping, loss of appetite, fatigue, upset stomach, rapid pulse, shortness of breath with exertion, nausea and vomiting.

HACE is a progressive form of AMS that includes the accumulation of fluid in the brain. In addition to the AMS symptoms, you will see lethargy, confusion and a difficult or unsteady gait. Immediate descent is required when this life-threatening malady strikes.

HAPE can occur with HACE or alone, and involves the accumulation of fluid in the lungs. Initially, you will see increased shortness of breath with exertion, accompanied by a dry cough. HAPE eventually progresses to shortness of breath during rest, chest tightness and a productive (wet) cough with blood-tinged sputum. Again, immediate descent is mandatory.

The most effective treatment for any of these three high-altitude syndromes is to descend to lower altitudes. If you are experiencing only mild symptoms, you may be able to stay at your destination and allow your body time to adjust to the altitude; in that case, do not exercise at all until your symptoms disappear. For the severe symptoms of HACE and HAPE, the descent must begin immediately. Helicopter evacuation may be needed unless there is a rapid improvement in medical condition. Physical exertion, even when it is for descent, can be harmful for travelers with HAPE.

If you will be traveling to high-altitude destinations, it is worth bringing along a Gamow bag — a small portable hyperbaric chamber, made of nylon fabric, that can be pressurized via a foot pump. The pressure created inside the Gamow bag increases the oxygen pressure in the body and can rapidly improve a person’s condition. While Gamow bags can cost thousands of dollars, they can be rented for a few hundred.

Plan a sensible itinerary that allows your body time to adjust to the reduced oxygen level at higher altitudes. If you are healthy, you can probably safely travel from sea level to 8,000 feet in the span of a few days. Once at 8,000 feet, do not ascend more than another 1,000 feet per day.

Medications to prevent or treat severe high-altitude illness include: acetazolamide, dexamethasone, nifedipine and oxygen, which also needs to be prescribed by a physician. Acetazolamide enhances the body’s ability to cope with altitude by increasing the rate and depth of breathing and also acts as a mild diuretic to remove excess water from the body. Dexamethasone is used only in HACE victims to assist with descent. Nifedipine is used in the treatment of HAPE, and works by lowering the pressure in the pulmonary blood vessels, thereby decreasing fluid in the lungs. Oxygen is extremely useful, especially in the treatment of HAPE.

Have an enjoyable but safe trip when traveling to high altitudes, but do not ignore the signs of high-altitude sickness. Studies have shown that travelers on organized group treks to high-altitude locations suffer higher death rates than do hikers climbing alone — an unfortunate statistic that can be attributed to the effects of peer pressure, real or imagined. I will never forget watching a television show about a group of trekkers who had just reach the summit of Mount Everest. I found out later that half the group had died on the mountain, stricken by symptoms associated with altitude sickness. When you have the symptoms of high-altitude sickness, you must take immediate measures to save your life. For more information, visit http://www.nlm.nih.gov/medlineplus.

Prevention Is the Best Medicine

When traveling at high altitudes:

Avoid strenuous activity for the first day or two after arrival.
Drink extra fluids and eat light meals that are high in carbohydrates.
Avoid alcohol.
Avoid sedatives.
Plan a gradual descent, with rest days throughout.
Talk to your doctor about medications that can help prevent the symptoms of altitude sickness.