body, either working or exposed to working at high altitude
can be hazardous. The information provided here is designed
for educational use only and is not a substitute for specific
training or experience.
is High Altitude?
Altitude is defined on the following scale High (8,000 - 12,000
feet [2,438 - 3,658 meters]), Very High (12,000 - 18,000 feet
[3,658 - 5,487 meters]), and Extremely High (18,000+ feet
[5,500+ meters]). Since few people have been to such altitudes,
it is hard to know who may be affected. There are no specific
factors such as age, sex, or physical condition that correlate
with susceptibility to altitude sickness. Some people get
it and some people don't, and some people are more susceptible
than others. Most people can go up to 8,000 feet (2,438 meters)
with minimal effect. If you haven't been to high altitude
before, it's important to be cautious. If you have been at
that altitude before with no problem, you can probably return
to that altitude without problems as long as you are properly
The concentration of oxygen at sea level is about
21% and the barometric pressure averages 760 mmHg.
As altitude increases, the concentration remains
the same but the number of oxygen molecules per
breath is reduced. At 12,000 feet (3,658 meters)
the barometric pressure is only 483 mmHg, so there
are roughly 40% fewer oxygen molecules per breath.
In order to properly oxygenate the body, your
breathing rate (even while at rest) has to increase.
This extra ventilation increases the oxygen content
in the blood, but not to sea level concentrations.
Since the amount of oxygen required for activity
is the same, the body must adjust to having less
oxygen. In addition, for reasons not entirely
understood, high altitude and lower air pressure
causes fluid to leak from the capillaries which
can cause fluid build-up in both the lungs and
the brain. Continuing to higher altitudes without
proper acclimatization can lead to potentially
serious, even life-threatening illnesses.
The major cause of altitude illnesses is going too high too
fast. Given time, your body can adapt to the decrease in oxygen
molecules at a specific altitude. This process is known as
acclimatization and generally takes 1-3 days at that altitude.
For example, if you hike to 10,000 feet (3,048 meters), and
spend several days at that altitude, your body acclimatizes
to 10,000 feet (3,048 meters). If you climb to 12,000 feet
(3,658 meters), your body has to acclimatize once again. A
number of changes take place in the body to allow it to operate
with decreased oxygen.
The depth of respiration increases. Pressure in pulmonary
arteries is increased, "forcing" blood into portions
of the lung which are normally not used during sea level breathing.
The body produces more red blood cells to carry oxygen, The
body produces more of a particular enzyme that facilitates
the release of oxygen from hemoglobin to the body tissues.
of Altitude Sickness
Prevention of altitude illnesses falls into two
categories, proper acclimatization and preventive
medications. Below are a few basic guidelines
for proper acclimatization.
don't fly or drive to high altitude. Start below 10,000 feet
(3,048 meters) and walk up.
If you do fly or drive, do not over-exert yourself or move
higher for the first 24 hours.
If you go above 10,000 feet (3,048 meters), only increase
your altitude by 1,000 feet (305 meters) per day and for every
3,000 feet (915 meters) of elevation gained, take a rest day.
"Climb High and sleep low." This is the maxim used
by climbers. You can climb more than 1,000 feet (305 meters)
in a day as long as you come back down and sleep at a lower
If you begin to show symptoms of moderate altitude illness,
don't go higher until symptoms decrease (& Don't go up
until symptoms go down").
If symptoms increase, go down, down, down!
Keep in mind that different people will acclimatize at different
rates. Make sure all of your party is properly acclimatized
before going higher.
Stay properly hydrated. Acclimatization is often accompanied
by fluid loss, so you need to drink lots of fluids to remain
properly hydrated (at least 3-4 quarts per day). Urine output
should be copious and clear.
Take it easy; don't over-exert yourself when you first get
up to altitude. Light activity during the day is better than
sleeping because respiration decreases during sleep, exacerbating
Avoid tobacco and alcohol and other depressant drugs including,
barbiturates, tranquilizers, and sleeping pills. These depressants
further decrease the respiratory drive during sleep resulting
in a worsening of the symptoms.
Eat a high carbohydrate diet (more than 70% of your calories
from carbohydrates) while at altitude.
The acclimatization process is inhibited by dehydration, over-exertion,
and alcohol and other depressant drugs.
Diamox (Acetazolamide) allows you to breathe faster so that
you metabolize more oxygen, thereby minimizing the symptoms
caused by poor oxygenation. This is especially helpful at
night when respiratory drive is decreased. Since it takes
a while for Diamox to have an effect, it is advisable to start
taking it 24 hours before you go to altitude and continue
for at least five days at higher altitude. The recommendation
of the Himalayan Rescue Association Medical Clinic is 125
mg. twice a day (morning and night). (The standard dose was
250 mg., but their research showed no difference for most
people with the lower dose, although some individuals may
need 250 mg.) Possible side effects include tingling of the
lips and finger tips, blurring of vision, and alteration of
taste. These side effects may be reduced with the 125 mg.
dose. Side effects subside when the drug is stopped. Contact
your physician for a prescription. Since Diamox is a sulfonamide
drug, people who are allergic to sulfa drugs should not take
Diamox. Diamox has also been known to cause severe allergic
reactions to people with no previous history of Diamox or
sulfa allergies. Frank Hubbell of SOLO recommends a trial
course of the drug before going to a remote location where
a severe allergic reaction could prove difficult to treat.
Dexamethasone (a steroid) is a prescription drug that decreases
brain and other swelling reversing the effects of AMS. Dosage
is typically 4 mg twice a day for a few days starting with
the ascent. This prevents most symptoms of altitude illness.
It should be used with caution and only on the advice of a
physician because of possible serious side effects. It may
be combined with Diamox. No other medications have been proven
valuable for preventing AMS.
Acute Mountain Sickness (AMS)
AMS is common at high altitudes. At elevations over 10,000
feet (3,048 meters), 75% of people will have mild symptoms.
The occurrence of AMS is dependent upon the elevation, the
rate of ascent, and individual susceptibility. Many people
will experience mild AMS during the acclimatization process.
Symptoms usually start 12-24 hours after arrival at altitude
and begin to decrease in severity about the third day. The
symptoms of Mild AMS are headache, dizziness, fatigue, shortness
of breath, loss of appetite, nausea, disturbed sleep, and
a general feeling of malaise. Symptoms tend to be worse at
night and when respiratory drive is decreased. Mild AMS does
not interfere with normal activity and symptoms generally
subside within 2-4 days as the body acclimatizes. As long
as symptoms are mild, and only a nuisance, ascent can continue
at a moderate rate. When hiking, it is essential that you
communicate any symptoms of illness immediately to others
on your trip. AMS is considered to be a neurological problem
caused by changes in the central nervous system. It is basically
a mild form of High Altitude Cerebral Edema (see below).
Treatment of AMS
The only cure is either acclimatization or descent. Symptoms
of Mild AMS can be treated with pain medications for headache
and Diamox. Both help to reduce the severity of the symptoms,
but remember, reducing the symptoms is not curing the problem.
Diamox allows you to breathe faster so that you metabolize
more oxygen, thereby minimizing the symptoms caused by poor
oxygenation. This is especially helpful at night when respiratory
drive is decreased. Since it takes a while for Diamox to have
an effect, it is advisable to start taking it 24 hours before
you go to altitude and continue for at least five days at
higher altitude. The recommendation of the Himalayan Rescue
Association Medical Clinic is 125 mg. twice a day (morning
and night). (The standard dose was 250 mg., but their research
showed no difference for most people with the lower dose,
although some individuals may need 250 mg.) Possible side
effects include tingling of the lips and finger tips, blurring
of vision, and alteration of taste. These side effects may
be reduced with the 125 mg. dose. Side effects subside when
the drug is stopped. Contact your physician for a prescription.
Since Diamox is a sulfonamide drug, people who are allergic
to sulfa drugs should not take Diamox. Diamox has also been
known to cause severe allergic reactions to people with no
previous history of Diamox or sulfa allergies. Frank Hubbell
of SOLO in New Hampshire recommends a trial course of the
drug before going to a remote location where a severe allergic
reaction could prove difficult to treat.
Moderate AMS includes severe headache that is not relieved
by medication, nausea and vomiting, increasing weakness and
fatigue, shortness of breath, and decreased coordination (ataxia).
Normal activity is difficult, although the person may still
be able to walk on their own. At this stage, only advanced
medications or descent can reverse the problem. Descending
even a few hundred feet (70-100 meters) may help and definite
improvement will be seen in descents of 1,000-2,000 feet (305-610
meters). Twenty-four hours at the lower altitude will result
in significant improvements. The person should remain at lower
altitude until symptoms have subsided (up to 3 days). At this
point, the person has become acclimatized to that altitude
and can begin ascending again. The best test for moderate
AMS is to have the person "walk a straight line"
heel to toe. Just like a sobriety test, a person with ataxia
will be unable to walk a straight line. This is a clear indication
that immediate descent is required. It is important to get
the person to descend before the ataxia reaches the point
where they cannot walk on their own (which would necessitate
a litter evacuation).
Severe AMS presents as an increase in the severity of the
aforementioned symptoms, including shortness of breath at
rest, inability to walk, decreasing mental status, and fluid
buildup in the lungs. Severe AMS requires immediate descent
to lower altitudes (2,000 - 4,000 feet [610-1,220 meters]).
There are two other severe forms of altitude illness, High
Altitude Cerebral Edema (HACE) and High Altitude Pulmonary
Edema (HAPE). Both of these happen less frequently, especially
to those who are properly acclimatized. When they do occur,
it is usually with people going too high too fast or going
very high and staying there. The lack of oxygen results in
leakage of fluid through the capillary walls into either the
lungs or the brain.
Altitude Pulmonary Edema (HAPE)
HAPE results from fluid buildup in the lungs. The fluid in
the lungs prevents effective oxygen exchange. As the condition
becomes more severe, the level of oxygen in the bloodstream
decreases, and this can lead to cyanosis, impaired cerebral
function, and death. Symptoms include shortness of breath
even at rest.