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Traveling 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. Princeton University and
the author assume no liability for any individual's use of or reliance
upon any material contained or referenced herein. This paper is prepared
to provide basic information about altitude illnesses for the lay
person. Medical research on high altitude illnesses is always expanding
our knowledge of the causes and treatment. When going to altitude it is
your responsibility to learn the latest information. The material
contained in this article may not be the most current. Copyright
© 1995 Rick Curtis, Outdoor Action Program, Princeton University.
High altitude-we all enjoy that tremendous view from a high summit,
but there are risks in going to high altitude, and it's important to
understand these risks. Here is a classic scenario for developing a high
altitude illness. You fly from New York City to a Denver at 5,000 feet
(1,525 meters). That afternoon you rent a car and drive up to the
trailhead at 8,000 feet (2,438 meters). You hike up to your first camp
at 9,000 feet (2,745 meters). The next day you hike up to 10,500 feet
(3,048 meters). You begin to have a severe headache and feel nauseous
and weak. If your condition worsens, you may begin to have difficulty
hiking. Scenarios like this are not uncommon, so it's essential that you
understand the physiological effects of 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 acclimatized.
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.
Prevention of altitude illnesses falls into two categories, proper
acclimatization and preventive medications. Below are a few basic
guidelines for proper acclimatization.
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).
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.
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, "tightness in the chest,"
marked fatigue, a feeling of impending suffocation at night, weakness,
and a persistent productive cough bringing up white, watery, or frothy
fluid. Confusion, and irrational behavior are signs that insufficient
oxygen is reaching the brain. One of the methods for testing yourself
for HAPE is to check your recovery time after exertion. If your heart
and breathing rates normally slow down in X seconds after exercise, but
at altitude your recovery time is much greater, it may mean fluid is
building up in the lungs. In cases of HAPE, immediate
descent is a necessary life-saving measure (2,000 - 4,000 feet
[610-1,220 meters]). Anyone suffering from HAPE must be
evacuated to a medical facility for proper follow-up treatment.
HACE is the result of swelling of brain tissue from fluid leakage.
Symptoms can include headache, loss of coordination (ataxia), weakness,
and decreasing levels of consciousness including, disorientation, loss
of memory, hallucinations, psychotic behavior, and coma. It generally
occurs after a week or more at high altitude. Severe instances can lead
to death if not treated quickly. Immediate descent is a
necessary life-saving measure (2,000 - 4,000 feet [610-1,220 meters]).
There are some medications that may be prescribed for treatment in the
field, but these require that you have proper training in their use.
Anyone suffering from HACE must be evacuated to a medical
facility for proper follow-up treatment.
This clever invention has revolutionized field treatment of high
altitude illnesses. The bag is basically a sealed chamber with a pump.
The person is placed inside the bag and it is inflated. Pumping the bag
full of air effectively increases the concentration of oxygen molecules
and therefore simulates a descent to lower altitude. In as little as 10
minutes the bag can create an "atmosphere" that corresponds to that at
3,000 - 5,000 feet (915 - 1,525 meters) lower. After a 1-2 hours in the
bag, the person's body chemistry will have "reset" to the lower
altitude. This lasts for up to 12 hours outside of the bag which should
be enough time to walk them down to a lower altitude and allow for
further acclimatization. The bag and pump weigh about 14 pounds (6.3
kilos) and are now carried on most major high altitude expeditions. Bags
can be rented for short term trips such as treks or expeditions.
Above 10,000 feet (3,000 meters) most people experience a periodic
breathing during sleep known as Cheyne-Stokes Respirations. The pattern
begins with a few shallow breaths and increases to deep sighing
respirations then falls off rapidly. Respirations may cease entirely for
a few seconds and then the shallow breaths begin again. During the
period when breathing stops the person often becomes restless and may
wake with a sudden feeling of suffocation. This can disturb sleeping
patterns, exhausting the climber. Acetazolamide is helpful in relieving
the periodic breathing. This type of breathing is not considered
abnormal at high altitudes. However, if it occurs first during an
illness (other than altitude illnesses) or after an injury (particularly
a head injury) it may be a sign of a serious disorder.
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