Altitude Illness
Travelers whose itineraries will take them above
an altitude of 1,829–2,438 m (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.
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
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.
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.
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.
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. 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 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 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 have been shown to be useful in
the prevention and treatment of 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.
— David
Shlim
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