ALTITUDE TREKKING & CLIMBING
The pleasures of trekking in the world's highest
mountain ranges cannot be overstated. Neither can the dangers. Altitude
sickness can occur in some people as low as 8,000 feet, but serious
symptoms do not usually occur until over 12,000 feet. Even then
it is not the height that is important, rather the speed in which
you ascended to that altitude.
sickness (AMS) is actually more common in fit young men because
they are more likely to attempt a rapid ascent by racing up the
mountain like some indestructible super hero! As a general rule,
it is far safer (and more enjoyable) to avoid altitude sickness
by planning a sensible itinerary that allows for gradual acclimatisation
to altitude as you ascend, (you can race back down as fast as you
is High Altitude?
to 4,000 metres
8,000 to 13,000 feet
to 5,500 metres
to 18,000 feet
over 5,500 metres
over 18,000 feet
It is difficult
to determine who may be affected by altitude sickness since there
are no specific factors such as age, sex, or physical condition
that correlate with susceptibility. Some people get it and some
people don't because some people are more susceptible than others.
can ascend to 2,500 metres (8,000 feet) with little or no effect.
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 acclimatised. If you haven't been to high altitude
before, you should exercise caution when doing so.
Causes of Altitude Sickness
of oxygen in the atmosphere at sea level is about 21% and the barometric
pressure is around 760 mmHg (1 bar). As altitude increases, the
percentage remains the same but the number of oxygen molecules per
breath is reduced. At 3,600 metres (12,000 feet) the barometric
pressure is only about 480 mmHg (0.63 bar), so there are roughly
40% fewer oxygen molecules per breath so the body must adjust to
having less oxygen.
In addition, high
altitude and lower air pressure causes fluid to leak from the capillaries
in both the lungs and the brain which can lead to fluid build-up.
Continuing on to higher altitude without proper acclimatisation
can lead to the potentially serious, even life-threatening altitude
The main cause
of altitude sickness is going too high too quickly. Given enough
time, your body will adapt to the decrease in oxygen at a specific
altitude. This process is known as acclimatisation and generally
takes one to three days at any given altitude, e.g. if you climb
to 3,000 metres and spend several days at that altitude, your body
will acclimatise to 3,000 metres. If you then climb to 5,000 metres
your body has to acclimatise once again.
take place in the body which enable it to cope with decreased oxygen:
- The depth of
- The body produces
more red blood cells to carry oxygen.
- Pressure in
pulmonary capillaries is increased, "forcing" blood into parts
of the lung which are not normally used when breathing at sea
- The body produces
more of a particular enzyme that causes the release of oxygen
from haemoglobin to the body tissues.
Note: There is NO substitute for proper acclimatisation!!
further information on drugs used in mountain sickness
go to the Mountain Medicines page.
3,000 metres (10,000 feet) 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 even ceasing 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.
This type of breathing is not considered abnormal at high altitudes.
Acetazolamide is helpful in relieving
this periodic breathing.
Mountain Sickness (AMS)
AMS is very common
at high altitude. At over 3,000 metres (10,000 feet) 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 acclimatisation
process. The symptoms usually start 12 to 24 hours after arrival
at altitude and begin to decrease in severity around the third day.
symptoms of Mild AMS include:
- Nausea &
- Loss of appetite
- Shortness of
- Disturbed sleep
- General feeling
to be worse at night and when respiratory drive is decreased. Mild
AMS does not interfere with normal activity and symptoms generally
subside within two to four days as the body acclimatises. 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.
The signs and symptoms of Moderate AMS include:-
headache that is not relieved by medication
and vomiting, increasing weakness and fatigue
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 only 300 metres (1,000 feet)
will result in some improvement, and twenty four hours at the lower
altitude will result in a significant improvement. The person should
remain at lower altitude until all the symptoms have subsided (up
to 3 days). At this point, the person has become acclimatised 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 would be
unable to walk a straight line. This is a clear indication that
an 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 stretcher evacuation).
Severe AMS results
in an increase in the severity of the aforementioned symptoms including:
Ÿ Shortness of breath at rest, Ÿ Inability to walk, Ÿ Decreasing
mental status, Ÿ Fluid build-up in the lungs, Severe AMS requires
immediate descent of around 600 metres (2,000 feet) to a lower altitude.
There are two
serious conditions associated with severe altitude sickness; High
Altitude Cerebral Oedema (HACO) and High Altitude Pulmonary Oedema
(HAPO). Both of these happen less frequently, especially to those
who are properly acclimatised. But, when they do occur, it is usually
in people going too high too fast or going very high and staying
there. In both cases the lack of oxygen results in leakage of fluid
through the capillary walls into either the lungs or the brain.
Altitude Pulmonary Oedema (HAPO)
HAPO results from
fluid build up in the lungs. This fluid prevents effective oxygen
exchange. As the condition becomes more severe, the level of oxygen
in the bloodstream decreases, which leads to cyanosis, impaired
cerebral function, and death.
of HAPO include:-
- Shortness of
breath at rest
- Tightness in
the chest, and a persistent cough bringing up white, watery, or
- Marked fatigue
- A feeling of
impending suffocation at night
and irrational behaviour
and irrational behaviour are signs that insufficient oxygen is reaching
the brain. One of the methods for testing yourself for HAPO is to
check your recovery time after exertion.
In cases of HAPO, immediate descent of around 600 metres (2,000
feet) is a necessary life-saving measure. Anyone suffering from
HAPO must also be evacuated to a medical facility for proper follow-up
you, or someone you know, ever suffered from HAPO or HAPE (high
altitude pulmonary oedema/edema)? Then join the "International
HAPE Database" a registry of previous HAPE sufferers worldwide
who might consider participating in future research studies.
Altitude Cerebral Oedema (HACO)
HACO is the result
of the swelling of brain tissue from fluid leakage.
Symptoms of HACO
- Loss of co-ordination
levels of consciousness
- Loss of memory
& Psychotic behaviour
generally occurs after a week or more at high altitude. Severe instances
can lead to death if not treated quickly. Immediate descent of around
600 metres (2,000 feet) is a necessary lifesaving measure. There
are some medications that may be used for treatment in the field,
but these require proper training in their use.
from HACO must be evacuated to a medical facility for follow-up
of Altitude Sickness
proper acclimatisation and the possible use of medications.
basic guidelines for the prevention of AMS:-
possible, don't fly or drive to high altitude. Start below
3,000 metres (10,000 feet) and walk up.
you do fly or drive, do not overexert yourself or move higher
for the first 24 hours.
you go above 3,000 metres (10,000 feet), only increase your
altitude by 300 metres (1,000 feet) per day, and for every
900 metres (3,000 feet) of elevation gained, take a rest
day to acclimatise.
high and sleep low! You can climb more than 300 metres (1,000
feet) in a day as long as you come back down and sleep at
a lower altitude.
you begin to show symptoms of moderate altitude sickness,
don't go higher until symptoms decrease.
symptoms increase, go down, down, down!
in mind that different people will acclimatise at different
rates. Make sure everyone in your party is properly acclimatised
before going any higher.
properly hydrated. Acclimatisation is often accompanied
by fluid loss, so you need to drink lots of fluids to remain
properly hydrated (at least four to six litres per day).
Urine output should be copious and clear to pale yellow.
it easy and don't overexert yourself when you first get
up to altitude. But, light activity during the day is better
than sleeping because respiration decreases during sleep,
exacerbating the symptoms.
tobacco, alcohol and other depressant drugs including, barbiturates,
tranquillisers, sleeping pills and opiates such as dihydrocodeine.
These further decrease the respiratory drive during sleep
resulting in a worsening of symptoms.
a high calorie diet while at altitude.
Acclimatisation is inhibited by overexertion, dehydration,
(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 seems to works by increasing the amount of alkali (bicarbonate)
excreted in the urine, making the blood more acidic. Acidifying
the blood drives the ventilation, which is the cornerstone of acclimatisation.
For prevention, 125 to 250mg twice daily starting one or two days
before and continuing for three days once the highest altitude is
reached, is effective. Blood concentrations of acetazolamide peak
between one to four hours after administration of the tablets.
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.
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.
of acetazolamide include: an uncomfortable tingling of the fingers,
toes and face carbonated drinks tasting flat; excessive urination;
and rarely, blurring of vision.
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.
A trial course
is recommended before going to a remote location where a severe
allergic reaction could prove difficult to treat if it occurred.
Dexamethasone (a steroid) is a drug that decreases brain
and other swelling reversing the effects of AMS. The dose is typically
4 mg twice a day for a few days starting with the ascent. This prevents
most of the symptoms of altitude illness from developing.
Dexamethasone is a powerful drug and should be used with caution
and only on the advice of a physician and should only be used to
aid acclimatisation by sufficiently qualified persons or those with
the necessary experience of its use.
further information on drugs to treat mountain sickness
go to the Mountain Medicines page.
The only cure
for mountain sickness is either acclimatisation or descent.
of Mild AMS can be treated with pain killers for headache, acetazolamide
and dexamethasone. These help to reduce the severity of the
symptoms, but remember, reducing the symptoms is not curing the
problem and could even exacerbate the problem by masking other symptoms.
allows you to breathe faster so that you metabolise more oxygen,
thereby minimising the symptoms caused by poor oxygenation which
is especially helpful at night when the respiratory drive is decreased.
Acetazolamide may be obtained on prescription in the UK from Doctor
Dexamethasone: This powerful steroid drug can be life saving
in people with HACO, and works by decreasing 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. This
drug "buys time" especially at night when it may be problematic
to descend. Descent should be carried out 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. It needs to be used cautiously, because it can cause stomach
irritation, euphoria or depression.
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 sulpha drugs (and
therefore unable to take diamox) dexamethasone can also be used
for prevention: 4 mg twice a day for about three days may be sufficient.
used for treating Altitude Sickness include:-
which is effective in relieving symptoms & altitude induced
This drug is usually used to treat high blood pressure. It rapidly
decreases pulmonary artery pressure and also seems able to decrease
the narrowing in the pulmonary artery caused by low oxygen levels,
thereby improving oxygen transfer. It can therefore be used to treat
HAPO, though unfortunately its effectiveness is not anywhere as
dramatic that of dexamethasone in HACO. The dosage is 20mg of long
acting nifedipine, six to eight hourly.
Nifedipine can cause 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.
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 daily.
· 100% Oxygen also reduces the effects of altitude sickness.
clever invention has revolutionised field treatment of altitude
sickness. The bag is composed of a sealed chamber with a pump.
The casualty is placed inside the bag and it is inflated by pumping
it full of air effectively increasing the concentration of oxygen
and therefore simulating a descent to lower altitude.
In as little
as 10 minutes the bag can create an "atmosphere" that corresponds
to that at 900 to 1,500 metres (3,000 to 5,000 feet) lower. After
two hours in the bag, the person's body chemistry will have "reset"
to the lower altitude.
This acclimatisation lasts for up to 12 hours outside of the bag
which should be enough time to get them down to a lower altitude
and allow for further acclimatisation.
and pump together weigh about 6.5 kilos (15 pounds) and are now
carried on most major high altitude expeditions. Bags can be rented
for short term treks or expeditions.