mountain sickness is an entirely different condition,
recognized by Carlos Monge Medrano in high altitude
long-term residents of South America during the
Twenties. Such maladaptation is seldom found in the
Sherpas or Tibetans, possibly due to thousands of
years of exposure to high altitude living. (south
Americans populations are relative newcomers to high
altitude.) The present discussion will be confined to
acute exposure to altitude in short-term sojourners.
Acute Mountain Sickness
participant on an Everest trek suffers from a mild
headache and nausea at Namche Bazaar (12,300ft), he
might take an aspirin and wait for these symptoms to
go away; however if the symptoms progress to
vomiting and a splitting headache, he must assume
that he is suffering from AMS and make plans to
descend. It is amazing how many people in this
situation ignore the dangers and continue to ascend
with their friends, trying to blame their symptoms
on poor fitness or flu. For some people, it's the
high investment of time, effort and money, for
others perhaps it's peer pressure or reluctance to
accept defeat. A further is that many in the
burgeoning adventure travel industry are clueless
about mountain sickness.
set in within hours to days of arrival at high
altitude: the onset of symptoms is usually gradual,
which is why it is so vital to watch out for early
warnings: does a person feel excessively tired; is
she the last one to drag herself in to camp?
caused by a lack of oxygen. Although the proportion
of oxygen in the atmosphere always remains the same
(21%), as we go higher the "driving pressure"
decreases. The driving pressure depends directly on
the barometric pressure, and forces oxygen from the
atmosphere into the capillaries of the lungs.
Reduced driving pressure results in decreased
saturation of oxygen in the blood and throughout the
what causes some people to suffer from AMS but not
others is largely unknown, but there are clear-cut
and important preventive factors that are now well-
established (see below). The exact mechanism (pathophysiology)
of AMS has similarities to that of HACE.
Altitude Cerebral Edema (HACE)
trekker in the above example would probably go on to
suffer form HACE if he continue to ascend despite
the headache and vomiting; the symptoms of HACE are
an extension of those to AMS.
fatigue, there is progression to lethargy and then
to coma. Or there may be confusion and
disorientation, A useful test is to see if the
person can walk a straight line. If he walks like a
drunk or is unsteady, it has to be assumed that he
has life-threatening HACE and needs to descend
promptly with assistance. This situation is serious
enough to justify immediate helicopter evacuation.
probably caused by shifts of fluid into the tissues
of the brain. Reduced oxygen levels cause swelling
within the confines of the bony skull. The resulting
rise in pressure may lead to lethargy and eventually
High Altitude Pulmonary Edema (HAPE)
disease may follow AMS, but often it may appear
independently. The typical scenario would be a
trekker who has no headache or nausea, but finds he
has a harder time walking uphill, that he is out of
breath on slight exertion compared with the initial
days of the trek. There may be a nagging cough and
he too may have ascribed these symptoms to a cold.
He may be suffering from sub-clinical or early HAPE,
a well-recognized entity. With further ascent this
may progress to shortness of breath even at rest -
descend is now obligatory, or the outcome may be
oxygen causes the pulmonary artery to narrow and
this results in exudation of blood near the smaller
branches of the lungs (the alveoli). If the
exudation continues, blood may escape into the
alveoli leading to a cough with watery, blood-tinged
phlegm. Such exudation, or "water logging" of the
lung tissue interferes further with oxygenation. A
popular, compact device called a pulse oximeter can
measure the oxygen level in the blood simply and
rapidly, using a sensor attached to the index
finger. It can be very helpful in confirming if HAPE
What is acclimatization?
Acclimatization is a state of physiological "truce"
between the body of a visitor and the hostile
low-oxygen environment of high altitude. This truce
permits the trekker of ascend gradually. (This is
distinct from "adaptation" - permanent change to the
organism, perhaps over thousands of years, perhaps
even at a genetic or evolutionary level, to
facilitate survival at altitude. Scientists are
trying to decipher if the Sherpas or Tibetans have
made such an adaptation.)
acclimatization to take place the single most
important step is hyperventilation- the trekker
unconsciously breathes faster and more deeply than
normal, even at rest, to make up for the lack of
oxygen. However, hyperventilation also leads to loss
of carbon dioxide from the blood, making the blood
more alkaline, and it turn depressing ventilation.
However, 48 to 72 hours after exposure to high
altitude, the kidney comes to the rescue and begins
to excrete alkali from the blood to restore a more
balanced environment in which hyperventilation can
Preventing altitude illness
little doubt that altitude illness is one hundred
percent a preventable illness. No one should die
from it. For the past quarter of a century, one of
the most important objectives of the Himalayan
Rescue Association in Nepal has been to preach the
gospel of prevention, from its aid posts in Pheriche
(at around 14000ft in the Everest region) and Manang
(at around 12000ft in the Annapurna region). There
are four golden rules, plus some important general
principles that should always be followed:
Understand and recognize the symptoms of AMS.
Recent growth in adventure travel
has made trekking at high altitude simpler and more
accessible, with the result
that more and more people who go trekking are
ignorant of the basic facts Of
Never ascend with obvious symptoms. Incredibly,
I have known people who have
hired a horse or a yak to go up higher when they
were too sick to walk. This is
Descend if symptoms increase. It is amazing how
striking and dramatic the relief may be
with even a couple of hundred feet of descent.
People with signs of
HACE have to descend.
Group members need to look out for one another
like the buddy
in SCUBA diving).
This rule gets broken with unfailing regularity
season in the Himalayas, because people are just too
anxious to complete
trek, even if one of their party members is ill. A
trekker with AMS, HAPE
will want nothing more than to be left alone,
unbothered, at the same
Altitude- potentially a fatal option. There is no
alternative but to bring the person
a lower altitude accompanied by a friend who speaks
the same language.
Following a conservative rate of ascent
too high, too quickly, is the single most important
cause of susceptibility to AMS. Beyond about 9000ft,
the sleeping altitude should be no higher than about
1500ft from the previous night's altitude. The
sleeping altitude, not the altitude achieved during
the daytime, is what is important. Altitude sickness
often manifests at night because during sleep the
oxygen level in the blood may dip further. Many
mountain climbers will have been to 14000ft or high
in the Alps or in North America but few will have
slept at the altitude. In the Himalayas, you don't
have to be an experienced climber, or use crampons,
to be able to "hang out" at 15000ft or higher for
days: easy accessibility to these altitudes makes
exposure to AMS also mush easier.
ascending, every second or third day should be rest
day for acclimatization. "Climb high and sleep low"
is the dictum, but it is important not to exert
oneself excessively in trying to fulfil this.
trekker should not be in a hurry in the mountains.
The itinerary should be planned so that there are
enough "leeway days" in case more time is needed to
acclimatize. Trying to do a high-altitude two-week
trek in one week is always fraught with problems.
of excessive exertion in the initial days
Excessive physical exertion at high altitude makes
one more susceptible to AMS. It is important to take
it easy at high altitude, especially in the initial
days. People who are very fit for example marathon
runners or those who carry very heavy backpacks seem
more vulnerable to AMS than others, probably because
they push themselves harder. I once looked after a
trekker who felt he could not break his morning
jogging sessions despite a strenuous trek day ahead,
even at 4000m! The feeling of" man against nature"
may be stronger in this fitter group.
rock star, decided to "whoop it up" with four
bottles of beer, on arrival at 3500meters in the
Everest region. He felt ill with severe AMS and
needed to be helicoptered out two days later. He had
been warned not to drink alcohol on the trek,
especially while ascending. Alcohol may dehydrate
the trekker but more importantly it depresses
breathing or ventilation. Sleeping pills may have a
Maintaining adequate hydration
amounts of fluid (about 3 liters a day) are
necessary in the mountains:- dehydration mimics
altitude sickness and may even predispose to it. On
the other hand excessive water drinking should also
be avoided as this may lead to electrolyte
Maintaining a high carbohydrate diet
carbohydrate diet aids ventilation and efficient use
of oxygen. The good news is that - in many high
altitude places - there is not much alternative:
rice, potatoes and other strach-laden foodstuffs
tend to be the staple, with not much else to choose
may be necessary for people going on rescue missions
at high altitude or flying in to high altitude
cities like La Paz or Lhasa. People with sulpha
allergy should not take diamox, the primary drug for
prevention, and further details are given below. A
second drug, dexamethasone (see below) should also
be carried, particularly if the destination is
remote: this can be life saving if HACE supervenes.
Wherever, possible this has to be attempted. There
is really no magic altitude to descend, but the sick
patient may suddenly feel something lift and feel
hungry. This is the altitude to which the body is
adjusted. Patients with HAPE need to descend slowly
and with assistance: excessive exertion even during
descent may increase the blood flow to the lungs and
exacerbate the problem.
oxygen at altitude is the chief reason why people
suffer from altitude sickness, so breathing
supplemental oxygen is obviously going to make a
difference. But oxygen is a hard commodity to come
by in the mountain - cylinders of oxygen are not
easily portable. When oxygen available in AMS
settings, it should be used.
This is the most tried and tested drug for altitude
sickness prevention and treatment. Unlike
dexamethasone 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 acclimatization.
prevention, 125 mg twice daily starting the evening
before and continuing for three days once the
highest altitude is reached, is effective. A recent
article in the British Medical Journal suggested
taking a higher dosage -- 750mg daily. Our
experience in the Indian subcontinent has
consistently been that 250 mg per day has been
rewarding, while excessive dosage may just increase
the side effects.
effects of diamox are: an uncomfortable tingling of
the fingers, toes and face (called "jhum jhum" in
Nepali); carbonated drinks tasting flat; excessive
urination; and rarely, blurring of vision. In most
of the treks in Nepal, gradual ascent is possible
and prophylaxis tends to be discouraged. Certainly
if trekkers develop headache and nausea or the other
symptoms of AMS, then treatment with diamox is fine.
The treatment dosage is 250 mg twice a day for about
This steroid drug can be life saving in people with
HACE, and works by decreasing swelling and reducing
the pressure in the bony skull. The dosage is 4 mg
three times per day, and obvious improvement usually
occurs within about six hours. Like the hyperbaric
bag (See below), 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.
Dexamethasone 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 HACE 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, however, 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 HACE 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.
This drug is generally used to treat high blood
pressure, but 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 HAPE, though
unfortunately its effectiveness is not anywhere as
dramatic that of dexamethasone in HACE. The dosage
is 20 mg of long acting nifedipine, six hourly.
cause 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 HAPE in people with a
past history of this disease.
a simple, effective device, made of airtight nylon;
it is about 7 feet long ad looks like a long duffel
bag. With the patient inside, the bag is inflated
with a foot pump until it becomes like a large
sausage-shaped balloon. There is a one-way valve to
avoid carbon dioxide build up inside, and it has
transparent panels to assist communication with its
pressure insde the bag is 2 p.s.i,. so the effect is
about the same as bringing the patient down a couple
of thousand feet. For both HACE and HAPE (but
especially, in our experience, for HACE) the changes
are usually dramatic within an hour. However there
may be a "rebound" tow or three hours after therapy
and the patient may need to get in the bag again.
Just like the dexamethasone, this bag only helps to
"buy tome". Descent is still mandatory as soon as
Other problems at altitude:-
abnormal breathing pattern whilst asleep is a common
occurrence at high altitude: short spells of an
increased breathing rate alternate with brief
periods when breathing slows down seems to stop the
medical term for this is "Cheyne Stokes"
respiration. It is only a problem if it makes the
suffers wake up repeatedly, breathless, anxious and
unable to sleep. An effective remedy is Diamox 125
mg before dinner, which counteracts the low oxygen
dips during sleep that trigger the problem. Sleeping
pills should be avoided.
respiratory tract infections and symptoms
people develop a persistent, bothersome cough and
cold-like symptoms in the cold dry air of high
altitude. An antihistamine at night like Benadryl 25
mg may help suppress the cough. Antibiotics are
sometimes useful, but keeping the head and face
covered and breathing through a silk or wool scarf
to humidify the air may also help. many studies have
shown that upper respiratory tract infections can
predispose to AMS.
may be swelling around the eyes, fingers, ankles at
high altitude, but this may not indicate AMS per se
unless accompanied by the symptoms of AMS. These
symptoms without AMS usually require no treatment.
altitude syncope (fainting):
This is well known but harmless problem, in which
fainting occurs suddenly, usually shortly after
arrival. Simple measures like keeping the individual
in a reclining position and raising the legs is
Travelers with pre-existing health problems;
children, and birth control pills
Blood pressure initially increases at high altitude
due to the initial stress of low oxygen triggering
neurohumoral changes. However people who suffer from
high blood pressure can go up to high altitude as
long as this is well controlled and they continue to
take their medication.
with a history of heart attack (moycardial
infarction) and even those with coronary artery
bypass grafts or angioplasty but with no angina, can
trek up to high altitude provided they are fit and
able to walk rigorously at low altitude. The high
altitude does not seem to add any extra burden to
Although seizures may be provoked by altitude there
is no convincing evidence that it is unsafe for
well-controlled epileptics travelling to travel to
high altitude, though such people should always take
their anti seizure medications conscientiously.
Sufferers may possibly have more attacks in the
mountains and this may sometimes be difficult to
distinguish from AMS. In doubt it is best to
noteworthy is the limited observation that bronchial
asthma does not seem to get exacerbated at high
altitude due to the cold and exercise. However it is
prudent for asthmatics to carry inhalers and other
medications. Obviously people with chronic
obstructive lung disease may be more short of breath
and travel at high altitude would be inadvisable.
surgery and radiotherapy:
People with treated cancers like lymphoma or tumors
in the neck who have had extensive surgery or
radiation treatment may be especially prone to AMS
because of damage to the carotid bodies - tiny
organs within the carotid arteries that sense oxygen
and aid ventilation.
Diabetics on insulin should have a reliable
glucometer to check their blood glucose regularly,
but high altitude does not seem to cause additional
people who have had non laser surgery (radial
keratotomy) to correct their short sightedness may
run into problems at high altitude due to swelling
of their cornea caused by the low oxygen. Such
people should carry corrective lenses as well if
travelling to high altitude.
Pregnant women should not sleep higher than 12000ft
as this may endanger the fetus; a further problem is
that high altitude places are generally remote,
making emergencies more difficult to deal with.
Children do not suffer any more from the effect of
altitude than adults. However, it is important that
a child should be able to communicate any symptoms
to responsible adult, so that prompt descent can be
arranged. It may therefore be dangerous to take
children to high altitude that is not yet old enough
to do this.
Oral contraceptive pills may predispose to abnormal
blood clotting (thrombosis) at high altitude.
the hypoxia (low oxygen), the excessive red blood
cells (polycythemia) in the blood, and the
possible dehydration in this environment may already
be other predisposing factors for thrombosis. Hence
it if best to use other forms of contraception at
high altitude destinations are in developing
countries, so it is important to be up to date with
vaccinations against disease like typhoid and
hepatitis, to know about travelers' diarrhoea
and its treatment, and to understand the other
precautions described elsewhere in this book.
Malaria is not a risk at altitude - transmission
does not take place above 2000 meters.
Conditions that mimic altitude sickness
Improving medical facilities in countries such as
Nepal have made it much easier to distinguish
between altitude illness and conditions that can
produce similar symptoms, such as bleeding in the
brain (subarachnoid hemorrhage), strokes,
dehydration and blood viscosity related problems
like venous thrombosis.
in the Himalayas
important to be aware that porter may be just as
vulnerable to the effects of altitude as tourist;
for your own safety, it is also vital to confirm
with the trekking agency that your porter has been
provided with proper clothing, boots and equipment
prior to the start of the trek.
the problems of high altitude are totally
preventable. With careful precautions, your
experience in the mountains should be safe and