Planning a trip to Nepal, or a hike in the Alps or Rockies? If so, have a great trip, but beware of the dangers of high altitude sickness.

What is high altitude sickness
High altitude sickness, also called acute mountain illness, often occurs when exerting oneself 8,000 feet above sea level. The incidence of symptoms ranges from 25 percent at 7,000 feet to 50 percent at 15,000 feet. The disease is more common in those who are young and physically fit, perhaps because they are the most physically active.

Although the cause of high altitude sickness is not completely understood, it appears to be related to lack of oxygen (hypoxia). Oxygen is an essential part of the metabolism and breakdown of sugar (glucose) into energy. In essence, our bodies are like engines that use oxygen as a source of fuel. However, the higher the altitude the less oxygen there is in the atmosphere. Consequently, like an engine running our of fuel, our bodies begin to hesitate, sputter and stall.

As oxygen becomes depleted in higher altitudes our bodies adapt by various physiological mechanisms. Blood vessels begin to dilate in order to bring more blood to the tissues. The heart rate increases, there is retention of fluids and breathing becomes more rapid (hyperventilation).

However, these compensatory mechanisms are limited, and with progressive elevation complications set in. The lungs start retaining fluid (pulmonary edema) and the brain begins to swell (cerebral edema).

What are the symptoms of altitude sickness?

Initial symptoms of high altitude sickness are headache, nausea, poor appetite, difficulty sleeping, cough, shortness of breath, muscle ache and general lethargy. These symptoms can occur anytime during ascent to high altitude, but characteristically occur six to 48 hours after ascent. As the illness progresses, confusion and hallucinations occur, as well as a loss of concentration, coordination and judgment. The late symptoms of high altitude sickness are stupor, coma, respiratory failure and death.

How can altitude sickness be treated?

The simplest and most effective treatment is to immediately descend to a lower altitude. This can easily be done while on a mountain climb. However, if you are on a plateau as in Tibet, this is not a practical solution.

Administration of oxygen will alleviate symptoms. It is also important to stay at rest until symptoms subside. Exertion of any kind will only exacerbate the condition. Medications such as aspirin, paracetamol, acetamenophen or ibufen will help relieve headaches. Acetazolamide, especially if taken early, will help relieve coughing and breathlessness. Steroids, such as dexamethasone, may help to reduce brain swelling. However, they may cause serious side effects and should be given under the direction of a physician.

The symptoms and signs o;f mild high altitude sickness, (such as cough, nausea and headache), usually su;bside within two to three days. However, any deterioration of mental or respiratory function requires urgent medical treatment and evacuation.

How can altitude sickness be prevented?

Physical conditioning at sea level will not prevent high altitude sickness. However, there are several ways to reduce the chances of becoming ill.

First, plan a gradual ascent. During the first two days, limit your climb to below 8,000 feet. Sleeping at an altitude below 8,000 feet is especially important. On the subsequent days, limit your ascent to no more than 2,000 feet per day. If you are flying to a high altitude city such as La Paz, Bolivia, plan to rest the first couple of days. Do not engage in physical activities such as long walks, jogging or sporting activities.