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HACE - High Altitude Cerebral Edema
AMS is a spectrum of illness, from mild to life-threatening. At the
"severely ill" end of this spectrum is High Altitude Cerebral Edema;
this is when the brain swells and ceases to function properly. HACE can
progress rapidly, and can be fatal in a matter of a few hours to one or
two days. Persons with this illness are often confused, and may not
recognize that they are ill.
The hallmark of HACE is a change in mentation, or the ability to think.
There may be confusion, changes in behavior, or lethargy. There is also
a characteristic loss of coordination that is called ataxia. This is a
staggering walk that is similar to the way a person walks when very
intoxicated on alcohol. This loss of coordination may be subtle, and
must be specifically tested for. Have the sick person do a straight line
walk (the "tandem gait test"). Draw a straight line on the ground, and
have them walk along the line, placing one foot immediately in front of
the other, so that the heel of the forward foot is right in front of the
toes behind. Try this yourself. You should be able to do it without
difficulty. If they struggle to stay on the line (the high-wire
balancing act), can't stay on it, fall down, or can't even stand up
without assistance, they fail the test and should be presumed to have
HACE. (The formal diagnostic definition is here)
Descend immediately
Immediate descent is the best treatment for HACE. This is of the utmost
urgency, and cannot wait until morning (unfortunately, HACE often
strikes at night). Delay may be fatal. The moment HACE is recognized is
the moment to start organizing flashlights, helpers, porters, whatever
is necessary to get this person down. Descent should be to the last
elevation at which they woke up feeling well. Bearing in mind that the
vast majority of cases of HACE occur in persons who ascend with symptoms
of AMS, this is likely to be the elevation at which the person slept two
nights previously. If you are uncertain, a 500-1000 meter descent is a
good starting point. Other treatments include oxygen, hyperbaric bag,
and dexamethasone. These are usually used as temporizing measures until
descent can be effected (see physician section for more details).
People with HACE usually survive if they descend soon enough and far
enough, and usually recover completely. The staggering gait may persist
for days after descent. Once recovery has been complete, and there are
no symptoms, cautious re-ascent is acceptable.
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