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By Dr. Jeff Hersh / Daily News Correspondent
Q: What is mountain sickness and what is the cause?
A: Although oxygen remains at about 21% of the air we breathe, even at high altitude, the air is 'thinner' (fewer molecules per volume), so the total amount of oxygen we inhale is lower. This means that the body becomes relatively deprived of oxygen (hypoxic) at high altitude, and that is what causes the symptoms of mountain sickness. The most common form of mountain disease, acute mountain disease (AMS), is the most benign form. The most serious diseases in the mountains are called high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE).
Although the severity of the symptoms manifests itself differently from one person to the other, they usually depend on the severity of the hypoxia and its rapidity. This is because the body can acclimate (compensate) to the lower oxygen availability in many ways. For example, we can breathe more quickly (so that even though there is less oxygen per breath, there are more breaths per minute), the oxygen transport capacity of blood can increase (red blood cells, red blood cells, carry oxygen and therefore the amount of red blood cells can increase), oxygen carried by red blood cells can be more easily transferred into the body tissues, as well as through other mechanisms compensatory.
The diagnosis of MAM is made when the patient has a headache, accompanied by gastrointestinal symptoms (loss of appetite or nausea / vomiting) or constitutional symptoms (weakness, fatigue, dizziness or vertigo).
The symptoms of HAPE result from the accumulation of fluid in the lungs and include progression of symptoms of SMA to shortness of breath (even at rest), wheezing, coughing with foamy sputum (which may be white or even pink / red blood) and ultimately respiratory failure. The symptoms of HAPE may appear gradually during ascent or quickly, especially after sleeping at high altitude.
HACE – the most severe form of mountain sickness – the symptoms are due to swelling of the brain and begin with changes of confusion and cries. The walk then becomes weakened and the climber can not follow the group. The brain can continue to swell and the mountaineer can become lethargic and even fall into a coma. HACE should be treated immediately. untreated, death will occur.
The specifics of hypoxia at the origin of mountain sickness are not completely understood, but the maximum altitude reached and the rate of climb are known risk factors.
Mountain sickness, of any type, usually occurs only at altitudes above about 8,000 feet. At altitudes of 8,000 to 10,000 feet (altitude of many ski resorts), symptoms of ADS are common and affect up to 25 people.
More severe hypoxia can occur with exercise or even with sleep, although acclimation is possible. The rapid ascent (eg by plane) at these altitudes will cause symptoms of SMA in up to three quarters of people, and some will develop a HAPE or even an HACE (less than 2% of climbers) .
Above 18,000 feet, compensatory mechanisms are usually overloaded and the most severe symptoms become more common.
The best way to avoid MAM is to minimize the rate of ascent, leaving time for acclimation.
All people who climb at high altitude should stay warm, ensure adequate hydration and avoid alcohol.
People flying at high altitude (more than 8,000 feet) should plan to rest for the first two days.
Mountaineers should attempt to plan their ascent to avoid increasing their sleep altitude by no more than 1,000 feet per day; it is the mountaineer's rule to "climb high, sleep low".
For mountaineers with mild symptoms of ADS, a 24-hour rest period without further ascents (to allow for acclimation) may be effective in resolving symptoms. If the symptoms disappear, the climber can then start climbing again.
If symptoms persist or worsen, or if the patient has severe symptoms (such as HAPE or HACE), an immediate descent is indicated. A descent as little as 1,000 to 2,000 feet is often effective in improving symptoms. Oxygen therapy can also be beneficial. A portable hyperbaric chamber can be used to treat patients with ADS who, for whatever reason, are unable to get off.
The best way to think about symptoms in a person at altitude is as follows: Always badume that symptoms come from mountain sickness; if symptoms occur, stop climbing until they disappear; and if the symptoms are severe or worsen, get off immediately.
In addition to following these guidelines, there are medications that can prevent / minimize altitude sickness. Acetazolamide can be effective in improving acclimation. For patients with HACE and whose descent may be delayed, steroid dexamethasone may be beneficial, but it should not be used as an alternative treatment for descent or use of a hyperbaric chamber.
The AMS usually resolves itself completely and quickly with the descent. The HAPE also has good results if it is recognized early and treated with a descent, then with oxygen and other treatments as needed. More than half of the mountaineers who develop HACE coma die, and many survivors suffer from permanent disabilities.
Jeff Hersh, Ph.D., M.D., can be contacted at [email protected]
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