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Altitude sickness

This factsheet is for people who plan to visit a high altitude area, or take part in treks or mountaineering and wish to learn more about altitude sickness.

Altitude sickness (also known as acute mountain sickness - AMS) can occur in healthy adults at heights of around 2,500 metres above sea level - a common height for ski resorts. Altitude sickness is more common, and also more severe, at higher altitudes of 2,500 metres and above. It happens in four to five in 10 people going to heights of 4,200 metres.

What counts as high altitude?

High altitude is altitudes of 2,500 to 3,500 metres but altitude sickness can occur at lower altitudes between 1,500 - 2,500 metres.

Examples of commonly visited areas of high altitude include:

• Cusco, Peru (3,000 metres)
• La Paz, Bolivia (3,444 metres)
• Lhasa, Tibet (3,749 metres)

What is altitude sickness?

The symptoms of altitude sickness are due to lower air pressure at high altitudes, which results in lower oxygen levels as you breathe the air in. The air is under less pressure and this makes it harder for your body to get the oxygen out of the air and into the circulation. It's this extra strain on the body that causes altitude sickness, which can be dangerous.

Altitude sickness is not related to physical fitness. It happens more often if you ascend heights quickly. If you fly into a region that is around 2,500 metres or above for example, you are more likely to get altitude sickness than if you ascend slowly via road travel.

Altitude sickness is a common condition and is treatable but, in rare cases, it can lead to two serious medical conditions that are potentially fatal:

• High altitude pulmonary oedema (HAPE) in which fluid accumulates in the lungs.
• High altitude cerebral oedema (HACE) in which excessive fluid collects in the brain causing it to swell.

Symptoms

You may notice symptoms of altitude sickness about six to 36 hours after you have arrived at an area of high altitude, although this can vary among different people.

If you have altitude sickness you may have some or all of the following symptoms:

• headache
• tiredness
• feel sick or vomit
• loss of appetite
• shortness of breath
• racing heartbeat
• dizziness
• difficulty sleeping
• irregular breathing when sleeping

Symptoms usually start to ease within about two days as your body gets used to the high altitude (acclimatises), particularly if you do not go any higher. If your symptoms get worse, you should descend to a lower altitude as soon as possible.

Complications

Altitude sickness progresses in less than 10 percent of cases to the more severe HACE where you will also:

• feel lethargic
• feel confused
• your behaviour may alter and you may be irrational
• you may get hallucinations
• you may feel disorientated and have double vision
• lose your co-ordination and be unsteady on your feet
• in severe cases, you may fall into a coma

HAPE can occur by itself or in conjunction with HACE. Initial symptoms are:

• shortness of breath, even when resting
• excessive tiredness
• dry cough (sometimes with blood)

If you have these symptoms, you should descend to a lower altitude as soon as possible and get urgent medical advice.

High altitude may also cause peripheral oedema. This is swelling of the face, arms or legs. This usually lasts a few days and disappears.

Retinal haemorrhages can occur at altitudes of over 5,000 metres. These are tiny blood blisters that form at the back of the eyes, but people usually don't notice these and they only occasionally interfere with vision

Cause

The cause of altitude sickness isn't fully understood at present but is probably due to the way your body responds to the reduction in oxygen supply. The reduction in oxygen to your muscles and brain causes your heart and lungs to work harder, for example. This increases your breathing and pulse rates.

There are certain factors that may make you more likely to develop altitude sickness including:

• having had altitude sickness before
• physical exertion
• if you rapidly ascend to high altitude
• if you are younger than 50
• if you normally live at an altitude less than 900 metres
• if you are obese

Diagnosis

The diagnosis for altitude sickness is based on your symptoms and whether you have ascended to an altitude of 2,500 metres or more and are otherwise well. The key criteria are if you have a headache combined with one or more of the other symptoms described above.

Treatment

If you have mild altitude sickness, you should not ascend any higher. You should:

• rest
• drink plenty of fluids
• take painkillers for your headache
• take anti-sickness medicines, such as cinnarizine (eg Stugeron) or promethazine (eg Avomine), which can be used to ease the feelings of nausea and dizziness - these can be bought from a chemist without a doctor's prescription

Symptoms usually resolve within one to two days.

If your symptoms become more severe, then descent is the best treatment. You should descend at least 500 to 1,000 metres.

Drug treatments

There are a number of drug treatments for severe altitude sickness. These include the medications dexamethasone, acetazolamide, nifedipine and oxygen. These medications should only be administered by appropriately qualified people.

Acetazolamide has been used increasingly as a preventive medication to decrease the symptoms of altitude sickness. This medicine should only be taken after consulting a doctor and is not a substitute for common sense and immediate descent, should your symptoms of altitude sickness worsen.

For more advice about drug treatments, ask your doctor or travel adviser.

Preventing altitude sickness

There are a number of steps you can take to avoid getting altitude sickness. Wherever possible, you should:

• acclimatise yourself to the high altitudes by slowly ascending the height over several days if possible - don't sleep at altitudes greater than 300 metres of the previous night
• keep warm
• drink lots of liquids
• avoid alcohol and tobacco
• eat a high carbohydrate diet such as pasta
• not do any strenuous exercise or activity for the first few days after arrival at high altitude and have rest days planned if you are ascending further

Further information

• National Travel Health Network and Centre
  www.nathnac.org
• Foreign and Commonwealth Office: know before you go
  0845 850 2829
  www.fco.gov.uk

References

• Altitude illness. UK Department of Health National Travel Health Network and Centre.
  www.nathnac.org
  accessed 22 September 2005
• Mountain sickness, oedemas, and travel to high altitudes - UIAA Mountain Medicine Centre Information Sheet 1. British Mountaineering Council.
  www.thebmc.co.uk
  accessed 22 September 2005
• British National Formulary 49, March 2005.

Published by BUPA's health information team, healthinfo@bupa.com February 2006.

Reviewed by Dr Paul Stoddart, MBChB DipObs DOccMed, senior regional physician, London BUPA Wellness.

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