Travelers whose itineraries will take them above an altitude of 1,829 to 2,438 meters (6,000 to 8,000 feet) should be aware of the risk of altitude illness. Travelers are exposed to higher altitudes in a number of ways: by mountain climbing or trekking in or to high-altitude destinations such as Cusco, Peru (3,000 meters [11,000 feet]); La Paz, Bolivia (3,444 meters [11,300 feet]); or Lhasa, Tibet (3,749 meters [12,500 feet]). Travelers with underlying medical conditions, such as congestive heart failure or pulmonary insufficiency, should be advised to consult a doctor familiar with high-altitude illness before undertaking such travel. The risk of ischemic heart disease does not appear to be increased at high altitudes, but having a heart attack in a remote area increases the problems of obtaining appropriate treatment.
Travelers vary considerably in their susceptibility to altitude illness, and there are currently no screening tests that predict whether someone is at greater risk of getting altitude illness. Past experience is the most reliable guide; susceptibility to altitude illness appears to be genetic, and is not affected by training or physical fitness.
Altitude illness is divided into three syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). AMS is the most common presentation of altitude illness and, while it can occur at altitudes as low as 1,219 to 1,829 meters (4,000 to 6,000 feet), most often occurs in abrupt ascents to over 2,743 meters (9,000 feet). The symptoms resemble an alcohol hangover: headache; profound fatigue; loss of appetite; nausea; and, occasionally, vomiting. The onset of AMS is delayed, usually beginning at least 6 to 12 hours after arrival at a higher altitude.
HACE is considered a severe progression of AMS. In addition to the AMS symptoms, lethargy becomes profound, confusion can manifest, and ataxia will be demonstrated during the tandem gait test. The tandem gait test. having the traveler walk a straight line while placing the heel of the front foot against the toe of the rear foot. is the best test for determining whether HACE is present. A traveler who falls off the line while trying to do the tandem gait test has HACE by definition, and immediate descent is mandatory.
HAPE can occur by itself or in conjunction with HACE. The initial symptoms are increased breathlessness with exertion, and eventually increased breathlessness at rest. The diagnosis can usually be made when breathlessness fails to resolve after several minutes of rest. At this point, it is critical to descend to a lower altitude.
The main point of instructing travelers about altitude illness is not to prevent any possibility of getting altitude illness, but to prevent deaths from altitude illness. The onset of symptoms and clinical course are slow enough and predictable enough that there is no reason for someone to die from altitude illness unless trapped by weather or geography in a situation in which descent is impossible. The three rules that travelers should be made aware of to prevent death from altitude illness are:
Learn the early symptoms of altitude illness and recognize when personally
suffering from them.
Never ascend to sleep at a higher altitude when experiencing any of the symptoms
of altitude illness.
Descend if the symptoms become worse while resting at the same altitude.
Studies have shown that travelers who are on organized group treks to high-altitude
locations are more likely to die of altitude illness than travelers who are
by themselves. This is most likely the result of group pressure (whether perceived
or real) and a fixed itinerary. The most important aspect of preventing severe
altitude illness is to refrain from further ascent until all symptoms of altitude
illness have disappeared.
Children are as susceptible to altitude illness as adults, and young children who cannot talk can show very nonspecific symptoms, such as loss of appetite and irritability. There are no studies or case reports of harm occurring to a fetus if the mother travels briefly to a high altitude during pregnancy. However, most authorities recommend that pregnant women stay below 3,658 meters (12,000 feet) if possible.
Three medications have been shown to be useful in the prevention and treatment of altitude illness. Acetazolamide (Diamox®) can prevent AMS when taken prior to ascent, and can speed recovery if taken after symptoms have developed. The drug appears to work by acidifying the blood, which causes an increase in respiration and thus aids in acclimatization. The standard dose is 250 milligrams (mg) BID (bis in die, that is, . twice daily. ), usually starting the day prior to ascent. Anecdotal observations support the use of 125 mg BID as being equally effective with fewer side effects. Allergic reactions to acetazolamide are extremely rare, but the drug is related to sulfonamides, and should not be used by sulfa-allergic travelers.
Dexamethasone has been shown to be effective in the prevention and treatment of AMS and HACE. The drug prevents symptoms, but there is no evidence that it aids acclimatization. Thus, there is a risk of a sudden of symptoms if the traveler goes off the drug while ascending. It is preferable for the traveler to use acetazolamide to prevent AMS while ascending, and to reserve the use of dexamethasone to treat severe symptoms. The dosage is 4 mg every 6 hours.
Nifedipine has been shown to prevent and ameliorate HAPE in people who are particularly susceptible to HAPE. The dosage is 10 mg every 8 hours.
For the majority of travelers, the best way to avoid altitude illness is to plan a gradual ascent. If this is not possible, acetazolamide may be used prophylactically, and dexamethasone and nifedipine may be carried for emergencies.