Altitude
Illness
Travelers whose itineraries will take them above an altitude of
1,829-2,438 meters (6,000-8,000 ft) should be aware of the risk
of altitude illness. Travelers are exposed to higher altitudes
in a number of ways: by flying into a high-altitude city, by driving
to a high-altitude destination, or by hiking or climbing in high
mountains. Examples of high-altitude cities with airports are
Cuzco, Peru (3,000 m; 11,000 ft); La Paz, Bolivia (3,444 m; 11,300
ft); or Lhasa, Tibet (3,749 m; 12,500 ft).
Travelers differ considerably in their susceptibility
to altitude illness, and there are currently no screening tests
that predict whether someone is at greater risk for altitude illness.
Susceptibility to altitude illness appears to be inherent in some
way and is not affected by training or physical fitness. How a
traveler has responded in the past to exposure to high altitude
is the most reliable guide for future trips but is not infallible.
Travelers with underlying medical conditions, such as congestive
heart failure, myocardial ischemia (angina), sickle cell disease,
or any form of pulmonary insufficiency, should be advised to consult
a doctor familiar with high-altitude illness before undertaking
such travel. The risk of new ischemic heart disease in previously
healthy travelers does not appear to be increased at high altitudes.
Three Types of Altitude Illness
Altitude illness is divided into three syndromes:
-
Acute Mountain Sickness (AMS)
AMS is the most common form of altitude illness and, while it
can occur at altitudes as low as 1,219-1,829 m (4,000-6,000
ft), most often it occurs in abrupt ascents to >2,743 meters
(>9,000 ft). The symptoms resemble those of an alcohol hangover:
headache, fatigue, loss of appetite, nausea, and, occasionally,
vomiting. The onset of AMS is delayed, usually beginning 6-12
hours after arrival at a higher altitude, but occasionally >24
hours after ascent.
-
High-Altitude Cerebral Edema (HACE)
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. A traveler who fails the tandem gait test has HACE
by definition, and immediate descent is mandatory.
-
High-Altitude Pulmonary Edema (HAPE)
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. HAPE can be more rapidly fatal
than HACE.
Preventing Death From Altitude Illness
Determining an itinerary that will avoid any occurrence of altitude
illness is difficult because of variations in individual susceptibility,
as well as in starting points and terrain. The main point of instructing
travelers about altitude illness is not to prevent any possibility
of altitude illness, but to prevent the person from dying of 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.
Three rules to prevent death from altitude illness
are-
-
Learn the early symptoms of altitude illness
and be willing to admit that you have them.
-
Never ascend to sleep at a higher altitude
when experiencing any of the symptoms of altitude illness,
no matter how minor they seem.
-
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 and Altitude Illness
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 to a fetus if the mother travels briefly
to high altitude during pregnancy. However, most authorities recommend
that pregnant women stay below 3,658 m (12,000 ft) if possible.
Three Medications to Prevent and Treat Altitude
Illness
-
Acetazolamide (Diamox; Lederle Pharmaceutical,
Pearl River, NY) can prevent AMS when taken before 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.
An effective dose that minimizes the common side effects of
increased urination, along with paresthesias of the fingers
and toes, is 125 mg every 12 hours, beginning the day of ascent.
However, most clinical trials have been done with higher doses
of 250 mg two or three times a day. Allergic reactions to
acetazolamide are extremely rare, but the drug is related
to sulfonamides and should not be used by sulfa-allergic persons,
unless a trial dose is taken in a safe environment before
travel.
-
Dexamethasone has been shown to be
effective in the prevention and treatment of AMS and HACE.
The drug prevents or improves symptoms, but there is no
evidence that it aids acclimatization. Thus, there is a
risk of a sudden onset or worsening of symptoms if the traveler
stops taking 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
symptoms while trying to descend. The dosage for both indications
is 4 mg every 6 hours.
-
Nifedipine has been shown to prevent
and ameliorate HAPE in persons who are particularly susceptible
to HAPE. The dosage is 10-20 mg every 8 hours.
Newer medications have recently been tried to help
prevent AMS and HAPE. In two small trials, gingko biloba,
an herbal remedy, was shown to reduce the symptoms of AMS when taken
before ascent. Gingko has not yet been compared with acetazolamide,
although a study is planned. Inhaled salmeterol (a beta-adrenergic
agonist) was demonstrated to help prevent HAPE in a small group
of climbers who had previously shown susceptibility to HAPE. Whether
salmeterol will prove beneficial in a more general population remains
to be seen. The mechanism of action of salmeterol suggests that
it could be of benefit in treating already established HAPE, but
there are no studies yet to confirm this.
For trekking groups and expeditions going into remote
high-altitude areas, where descent to a lower altitude could be
problematic, a pressurization bag (e.g., the Gamow bag), can prove
extremely beneficial. Persons with altitude illness can be zipped
into the bag, and a foot pump can increase the pressure inside
the bag by 2 lbs. per in2, mimicking a descent of 1,500-1,800
m (5,000-6,000 ft), depending on the starting altitude. The total
packed weight of the bag and pump is approximately 6.5 kg.
For most travelers, the best way to avoid altitude
illness is to plan a gradual ascent, with extra rest days at intermediate
altitudes. If this is not possible, acetazolamide may be used
prophylactically, and dexamethasone and nifedipine may be carried
for emergencies.
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