High Altitude

Climbing at high altitude

Climbing at high altitudes presents mountaineers with unique challenges to overcome. The ‘thin air’, reduced atmospheric pressure and cold can conspire to make life very difficult indeed. Add in steep, difficult terrain and new strategies and skills are needed for successful, safe climbing. Diagnosing and treating altitude illness and acclimatising correctly are two of the most important subjects to learn before climbing at altitude.

There are no specific factors such as age, sex, or physical condition that correlate with susceptibility to altitude sickness.Altitude graphic


The higher the altitude the lower the concentration of oxygen available for you to breathe. Hence your body must adjust to having less oxygen than normally. The lower air pressures at altitude cause fluid to leak from capillaries which can cause general swelling and in some cases dangerous fluid build up in the lungs and brain.

It is likely that a climber ascending to high altitude will experience some of these physiological changes


Shortness of breath (especially during exercise)

Lethargy, tiredness

Loss of appetite


Racing pulse

Increased urination

Changed breathing patterns at night (periodic breathing)

Poor sleep

Weird dreams are common

Peripheral swelling and facial swelling

Retinal haemorrhages (capillary bleeding in the eye)

These are normal responses of the body.

Acute Mountain Sickness (AMS)

AMS, also known as Acute Altitude Sickness, is common at high altitude. 75% of people experience mild forms of AMS at elevations over 3000m.

AMS symptoms





Loss of appetite


Sleep disturbance

AMS Prevention

The best prevention is to acclimatise adequately – see below for acclimatisation advice.

Stay well hydrated.

Avoid alcohol, tobacco and other depressant drugs (eg sleeping pills). These things decrease respiration.

Avoid additional salt.

Eat frequent small meals high in carbohydrates and low in fat for the first several days.

AMS Treatment

If you begin to show symptoms of AMS don’t go higher until symptoms decrease. Rest.

If symptoms increase, decrease altitude.

If symptoms continue:

Diamox (Acetazolamide) is a medication which helps oxygen to be more efficiently used and helps increase breathing rates.

The recommended dose is 125mg twice a day until AMS symptoms resolve (typically 3-5 days). It may also be used if periodic breathing is a continuous problem. In this case take 125mg at bedtime until at an altitude where symptoms are not troubling.

People allergic to Sulfa should not take Diamox. Dexamethasone is an alternative treatment.

There is some evidence that the herb Ginko Biloba might be helpful at the dose of 120mg twice a day starting 5 days before ascent and continuing while at high altitude.

Mild analgesics such as Ibuprofen and Paracetamol can be used for headache pain relief.

For those with moderate AMS only advanced medications and descent can reverse the symptoms. Putting people with moderate AMS on oxygen at 4 litres/ minute and getting them to a hospital at lower elevation for treatment is recommended.


High altitude cerebral oedema (HACE) is the severe end of the AMS spectrum. It is a rare (about 1-2% of those ascending to 4500m) but life threatening form of altitude illness.

HACE usually occurs after a week or more at high altitude and presents as an increase in the severity of AMS symptoms as mentioned above:

Shortness of breath at rest

Inability to walk

Loss of coordination



Behaviour change

Decreased level of consciousness


Anyone suffering from HACE should immediately descend or death is likely.

Dexamethasone, 8mg initially followed by 4mg every 6 hours and oxygen if available should be administered. If a portable hyperbaric chamber is available its use may improve the patients condition temporarily and allow descent.


High altitude pulmonary oedema results from a build up of fluid in the lungs. It usually occurs in the first 2 to 4 days after ascent to above 2500m. Incidence is more than 2% of people ascending above 4000m. AMS precedes most cases of HAPE.

Symptoms of HAPE:

Shortness of breath at rest

Tightness in the chest

Feeling of suffocation at night

Persistent cough bringing up white, watery, or frothy fluid

Confusion and irrational behaviour

Immediate descent is the treatment of choice or death is a likely outcome.

The patient should be kept warm and upright.

Oxygen can lead to dramatic improvement allowing descent, preferably to below the last altitude the patient was symptom free at.

Nifedipine 10mg sublingually (a capsule broken and held under the tongue) followed by 20mg slow release preparation by mouth 4 times a day can relieve symptoms.


Standard advice for successful acclimatisation is to ascend no more than 300m per day and having every third day as a rest day when above 3000m. Reduce this to 150m per day above 4000m. These are the altitude differences between sleeping locations. You can go higher during the day as long as you sleep lower down. These recommendations  vary between individuals. Many people can climb above 5000m after 5 to 7 days at about 3500m to 4000m. After weeks at around 4000m many people will be able to climb to well over 6000m very rapidly. A climber recently arrived at altitude would get very ill attempting to ascend so quickly.

If arriving at altitudes greater than 3000m rapidly, particularly if flying, don’t over exert yourself or move higher for at least the first 24 hrs.

Exercise only lightly for the first couple of days. This is better than sleeping during the day because respiration decreases during sleep, exacerbating symptoms.

Eat mainly carbohydrates and very little fat.  A high carb diet can reduce the onset and severity of AMS. Fats are metabolised slowly at altitude. A diet of 2/3 carbohydrate and 1/3 protein is about right.

Keep hydrated. At altitude the cold dry air can cause high water loss.

At altitude water boils at a lower temperature. If you need to boil water because you suspect it may be contaminated then you will need to boil it for a bit longer than you would at sea level.

Key Points

Acclimatise properly

Climb high, Sleep low

Take it easy early on

Don’t go up further if you have AMS symptoms

Descend if symptoms get worse



Duff J, Gormly P. (2000) First Aid And Survival In Mountain And Remote Areas. Dr Jim Duff, Kathmandu.

Pollard J, Murdoch D. (1997) The High Altitude Medicine Handbook. Radcliffe Medical Press.


Bezruchka s. (2005) Altitude Ilness: Prevention and Treatment. The Mountaineers Books, Seattle.