High Altitude Syndrome
Travellers who will be visiting mountainous areas should be prepared
to recognize and respond to the symptoms of high altitude syndrome. The
human body can adjust to changes in altitude (known as acclimatization)
but needs time. The time needed by each individual varies and also varies
with each trip. If the ascent is too rapid and your body cannot adjust
adequately, high altitude syndrome will occur. The syndrome covers a broad
spectrum of symptoms, ranging from mild headache to Acute Mountain Sickness
(AMS) and to the more severe High Altitude Cerebral Oedema (HACE) and
High Altitude Pulmonary Oedema (HAPE). If the treatment is not received
when symptoms appear, death could result.
What is high altitude syndrome?
High altitude syndrome typically appears on rapid ascent to altitude
above 2,500 metres (8,000+feet), e.g. flying directly to Lhasa or La Paz
from sea level. It is caused by the lowering of atmospheric oxygen pressure
when ascending to high altitudes. The human body will compensate to the
lowered oxygen pressure by increasing the pulse rate, breathing rate,
blood pressure, while increased urination and mild isolated headache can
occur. If the body cannot cope, symptoms of AMS will then occur gradually
after few hours of ascent. AMS is suspected when the following occur on
acute attitude gain:
Headache (usually throbbing, on both sides, worse during the night
and on awakening, made worse by bending over)
Plus one of the following: nausea; fatigue; dizziness; sleep difficulty.
The headache condition in AMS is often described as similar to a bad
hangover. The sleep difficulty may cause sudden awakening and a feeling
of suffocation. Other symptoms include irritability, loss of appetite
and swelling of the face, hands and feet.
Without proper acclimatization and continue to ascend, the illness may
progress to the serious conditions of High Altitude Cerebral Oedema (HACE)
and High Altitude Pulmonary Oedema (HAPE).
HACE means fluids accumulate in the brain. The condition can appear within
as short as 12 hours to 3 days of onset of mild AMS and usually accompanied
by HAPE. Once present, it can progress rapidly and can be fatal in a matter
of a few hours. Such tragic death is preventable and recognition of symptoms
is thus most important. Early symptoms are:-
Changes in behavior (disinterested, cannot count accurately)
Disabling weakness (e.g. cannot rise up and go to toilet)
- Loss of coordination (stumble gait, cannot walk a straight line toe-to-toe).
In HAPE, fluids accumulate in the lungs and further aggravate the lack
of oxygen. It is the most common cause of death in high altitude. Most
victims are young and fit. Its onset may be abrupt and is characterized
Decreased exercise performance (earliest symptom)
Breathlessness even at rest
Lips or fingernails turned blue
Cough with pinkish sputum (usually in late stage)
Long term stay at high altitude can induce chronic mountain sickness
and deterioration of body functioning. This is rare as travellers seldom
stay high for that long.
Who is more prone to high altitude syndrome?
The occurrence of AMS is related to rate of ascent, sleeping altitude
attained, length of stay at altitude, level of exertion and genetic susceptibility.
The young and fit are not less vulnerable, while elderly seems to be so.
Women appear to be slightly more vulnerable, though less susceptible to
HAPE. The risk will be increased if the traveller has too much determination,
exhausted, nervous, dehydrated, exposed to cold, or suffering from respiratory
How can I prevent high altitude syndrome?
In general, cardiopulmonary diseases will be affected adversely
by the decrease of oxygen pressure. Thus travellers with high blood
pressure, angina, chronic obstructive airway disease, anaemia, and
epileptics should seek medical assessment first for fitness to travel
to high altitudes.
Those with illness which affects oxygen exchange, e.g. influenza
should defer travel until full recovery.
Avoid flying or driving directly to higher altitudes (e.g. Lhasa,
La Paz). If this is impossible, take more rest, minimize exertion
and showers, drink more water, avoid alcohol, large meals and sleeping
pills during the first few days after landing for proper acclimatization.
The simplest way to avoid or reduce the symptoms of AMS is to ascend
slowly to allow enough time for acclimatization. Methods include:-
when ascending, acclimatize for 2 to 3 nights at 2,500 to 3,000
after reaching 3,000 metres, keep your sleeping altitude gain
between 300 to 600 metres per day.
for every 1,000 metres gained, stay at same altitude for 1 extra
climb higher during the day, sleep lower during the night.
Keep warm to prevent cold exposure. Adopt a relaxed attitude helps
to get acclimatized.
Be aware of symptoms of AMS, HACE and HAPE in yourself and among
companions, and take appropriate remedial actions. Never ignore the
early warning symptoms and signs.
Don't force yourself to keep up with the pace of the trekking group
or to attain the target altitude. If necessary, leave the group and
descend immediately, even at night. This is because HAPE can be fatal
within a few hours.
What should I do if I begin to have symptoms?
For mild symptoms, limit your activity level and remain at the same
altitude for a day or two until full recovery before resuming the
Descent is the definitive treatment for all forms of high altitude
syndrome. You must descend if symptoms do not subside after 24 hours
or become worse. A drop in altitude of 500 to 1,000 metres is usually
If you suffer from symptoms of HACE and HAPE, you should descend
immediately and seek treatment.
The drug acetazolamide can lessen AMS symptoms and help with acclimatization.
It is taken one day before ascent and continued for several days at
altitude. Please consult your doctor.
Herbal medication Ginkgo biloba and Rhodiola rosea have been used
for prevention and need to be taken at least 5 days before ascent.
However, their effects have not been proven clearly by large scale
randomized control trial. Please consult your doctor for further information.
How to treat high altitude syndrome?
For mild isolated headache, one must rest more and should not rely purely on pain killer to relief pain..
If symptoms of AMS persist for more than 24 hours, one must descend
immediately, which is the best effective treatment.
For AMS, the drug acetazolamide can also be used for treatment. It
is given at onset of symptoms and continued for one day after symptoms
have cleared. For HACE and HAPE, there are specific drugs available,
but their effectiveness cannot match that of immediate descent. Please
consult your doctor for further information.
Breathing oxygen at altitude lessen symptoms but is not advisable
if one stay at altitude for long.
Where are the high risk areas?
Typical examples of cities or areas above 2,500 metres are:
||Jiu Huang airport
Average 3,300 m
Average 3,700 m
Yulong Xueshan cable car
Lhasa , Gonggar airport
Ngari diqu, Naqu diqu
Qomolangma base camp
Average 4,500 m
Sagarmatha base camp