AMS - Acute Mountain Sickness
Acute Mountain Sickness (AMS) is a constellation of symptoms that
represents your body not being acclimatized to it's current altitude. As
you ascend, your body acclimatizes to the decreasing oxygen (hypoxia).
At any moment, there is an "ideal" altitude where your body is in
balance; most likely this is the last elevation at which you slept.
Extending above this is an indefinite gray zone where your body can
tolerate the lower oxygen levels, but to which you are not quite
acclimatized. If you get above the upper limit of this zone, there is
not enough oxygen for your body to function properly, and symptoms of
hypoxic distress occur - this is AMS.
Zone of Tolerance
Go too high above what you are prepared for, and you get sick.
This "zone of tolerance" moves up with you as you acclimatize. Each day,
as you ascend, you are acclimatizing to a higher elevation, and thus
your zone of tolerance extends that much higher up the mountain. The
trick is to limit your daily upward travel to stay within that tolerance
The exact mechanisms of AMS are not completely understood, but the
symptoms are thought to be due to mild swelling of brain tissue in
response to the hypoxic stress. If this swelling progresses far enough,
significant brain dysfunction occurs (See next section, on HACE). This
brain tissue distress causes a number of symptoms; universally present
is a headache, along with a variety of other symptoms.
The diagnosis of AMS is made when a headache, with any one or more of
the following symptoms is present after a recent ascent above 2500
meters (8000 fee
- Loss of appetite, nausea, or vomiting
- Fatigue or weakness
- Dizziness or light-headedness
- Difficulty sleeping
All of these symptoms may vary from mild to severe. A scoring system has
been developed based on the Lake Louise criteria; look at the AMS
questionnaire for a simple method to evaluate an individual's AMS
AMS has been likened to a bad hangover, or worse. However, because the
symptoms of mild AMS can be somewhat vague, a useful rule-of-thumb is:
if you feel unwell at altitude, it is altitude sickness unless there is
another obvious explanation (such as diarrhea).
Anyone who goes to altitude can get AMS. It is primarily related to
individual physiology (genetics) and the rate of ascent; there is no
significant effect of age, gender, physical fitness, or previous
altitude experience. Some people acclimatize quickly, and can ascend
rapidly; others acclimatize slowly and have trouble staying well even on
a slow ascent. There are factors that we don't understand; the same
person may get AMS on one trip and not another despite an identical
ascent itinerary. Unfortunately, no way has been found to predict who is
likely to get sick at altitude.
It is remarkable how many people mistakenly believe that a headache at
altitude is "normal"; it is not. Denial is also common - be willing to
admit that you have altitude illness, that's the first step to staying
out of trouble.
It is OK to get altitude illness, it can happen to anyone. It is not OK
to die from it. With the information in this tutorial, you should be
able to avoid the severe, life-threatening forms of altitude illness.