Acute Mountain Sickness
any medical condition, the prevention of mountain sicknes
is always better than the cure.
Acute mountain sickness is caused by a lack of
oxygen in the body of individuals exposed to higher elevations.
This usually occurs when they travel to an altitude over 10,000
feet (3,000 metres) without proper acclimatisation before
engaging in physical activities. Mountain climbers, trekkers,
skiers, and travellers to the Andes or Himalayas etc. are
at greatest risk.
While individual tolerance varies, symptoms usually appear
within several hours of ascending, with those in poor physical
condition being most susceptible. Headache, fatigue, shortness
of breath, nausea, and poor appetite occur initially. Inability
to sleep is also frequently reported. In more severe cases
thinking and judgement may become impaired.
uncommon but potentially fatal complication called high altitude
pulmonary or cerebreal oedema (HAPO & HACO), caused by
fluid build-up in the lungs and brain, can also occur.
The symptoms of acute mountain sickness can be prevented or
minimized by gradually ascending (less than 500 meters/day)
over several days to give your body a chance to acclimatize
to the higher altitude.
Once the symptoms begin to occur, they usually subside over
several days without treatment provided there has been adequate
time for acclimatisation. However, if they worsen, they can
be relieved with the administration of oxygen or descent to
a lower altitude.
Acetazolamide (Diamox): This is the most
tried and tested drug for altitude sickness prevention and
treatment. Unlike dexamethasone (below) this drug does not
mask the symptoms but actually treats the problem. It works
by increasing the amount of alkali (bicarbonate) excreted
in the urine, making the blood more acidic. Acidifying the
blood drives the ventilation process, which is the cornerstone
prevention, one 250mg tablet should be taken daily starting
one or two days before and continuing for three days once
the highest altitude is reached. Blood concentrations of acetazolamide
peak between one to four hours after administration of the
tablets. It may therefore, be better to take 125mg (half a
tablet) twice daily. Gradual ascent is always desirable to
try to avoid acute mountain sickness even when acetazolamide
is being taken.
Studies have shown that prophylactic administration of acetazolamide
at a dose of 250mg every eight to twelve hours before and
during rapid ascent to altitude results in fewer and/or less
severe symptoms (such as headache, nausea, shortness of breath,
dizziness, drowsiness, and fatigue) of acute mountain sickness
(AMS). Pulmonary function is greater both in subjects with
mild AMS and asymptomatic subjects. The treated climbers also
had less difficulty in sleeping.
gradual ascent is always desirable to try to avoid acute mountain
sickness but if rapid ascent is undertaken and actazolamide
is used, it should be noted that such use does not obviate
the need for a prompt descent if severe forms of high altitude
sickness occur, i.e. pulmonary or cerebral oedema.
Side effects of acetazolamide include: an uncomfortable tingling
of the fingers, toes and face carbonated drinks tasting flat;
excessive urination; and very rarely, blurring of vision.
On most treks, gradual ascent is possible and prophylaxis
tends to be discouraged. Certainly if trekkers do develop
headache and nausea or the other symptoms of AMS, then treatment
with acetazolamide is fine. The treatment dosage is 250 mg
twice a day for about three days.
Acetazolamide may be obtained on prescription in the UK from
This powerful steroid type drug can be life saving in people
with HAPO & HACO, and works by decreasing brain swelling
and reducing the pressure in the skull. The dosage is 4 mg
three times per day, and obvious improvement usually occurs
within about six hours. It's use is highly specialised and
can be very dangerous if used incorrectly or by inexperienced
It can be a good "emergency drug" since it "buys
time" especially at night when it may be problematic to descend.
Descent should be carried out as soon as possible the next
day. It is unwise to ascend while taking dexamethasone: unlike
diamox this drug only masks the symptoms.
can be highly effective: many people who are lethargic or
even in coma will improve significantly after tablets or an
injection, and may even be able to descend with assistance.
Many pilgrims at the annual festival at Gosainkunda lake in
Nepal suffer from HACO following a rapid rate of ascent, and
respond remarkably well to dexamethasone. Mountain climbers
also sometimes carry this drug to prevent or treat AMS. However,
it needs to be used cautiously. It has been known to cause
stomach irritation, euphoria or depression.
It may be a good idea to pack this drug for a high altitude
trek for emergency usage in the event of HACO. In people allergic
to and therefore unable to take acteazolamide, dexamethasone
can also be used for prevention: 4 mg twice a day for about
three days should be sufficient but only under experienced
This drug is normally used to treat high blood pressure and
angina, but also seems able to decrease the narrowing in the
pulmonary artery (pulmonary vasodilation) resolving the pulmonary
hypertension responsible for the high pressure leak in the
lungs caused by low oxygen levels, thereby improving oxygen
transfer. It can therefore be used in the treatment of HAPO,
though unfortunately its effectiveness is not anywhere as
dramatic that of dexamethasone in HACE. Oxygen saturations
gusually improve slightly after administration of nifedipine.
The dosage is 20 mg of long acting nifedipine, six hourly.
Nifedipine can cause postural hypotension; a sudden lowering
of blood pressure so the patient has to be warned to get up
slowly from a sitting or reclining position. It has also been
used in the same dosage to prevent HAPO in people with a past
history of this disease.
Frusemide may clear the lungs of water in HAPO and
reverse the suppression of urine brought on by altitude. However,
Frusemide can also lead to collapse from low volume shock
if the victim is already dehydrated. Treatment dosage is 120mg
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