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Published by Bupa's health information team, June 2008.
This factsheet is for people who plan to visit a high-altitude area, or who would like information about altitude sickness.
Altitude sickness (also known as acute mountain sickness - AMS) can occur in healthy adults at heights of around 2,500m above sea level - a common height for ski resorts. Altitude sickness is more common, and also more severe, at higher altitudes of 2,500m and above. About one in two people going to heights of over 4,000m develop altitude sickness.
About altitude sickness
Altitude sickness isn't related to physical fitness. It happens more often if you ascend heights quickly. If you fly into a region that's around 2,500m or above, for example, you are more likely to get altitude sickness than if you ascend slowly via road travel.
What counts as high altitude?
High altitude is altitudes of 2,500 to 3,500m but altitude sickness can occur at lower altitudes between 1,500 and 2,500m.
Examples of commonly visited areas of high altitude include:
Cusco, Peru (about 3,300m)
La Paz, Bolivia (about 3,600m)
You may notice symptoms of altitude sickness about six to 24 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 a headache
feel sick or vomit
lose your appetite
have an increased heart rate
have difficulty sleeping
have 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 don't go any higher. If your symptoms get worse, you should descend to a lower altitude as soon as possible.
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.
These complications are more likely if you ascend rapidly (more than 300m per day) to an altitude over 4,000m.
HAPE can occur by itself or in conjunction with HACE, normally within two to five days after you arrive at high altitude. HAPE is rarely seen below 2,500m or after one week of acclimatisation. Initial symptoms are:
shortness of breath, even when resting
dry cough (sometimes with blood)
difficult or painful breathing when lying down
Pink, frothy spit when you cough is a sign of severe HAPE.
Fewer than two percent of people with altitude sickness develop HACE and it's rarely seen below 4,000m. If you have HACE you may:
have blurred or double vision
act differently, for example you may be unhelpful or irritable
fall into a coma, although this is only in severe cases
If you have these symptoms, you should descend to a lower altitude as soon as possible and seek urgent medical advice.
High altitude may also cause swelling of the face, arms or legs (peripheral oedema). This usually lasts a few days and then disappears.
Tiny blood blisters at the back of the eye (retinal haemorrhages) can form at altitudes of over 5,000m. However, people usually don't notice these and they only occasionally interfere with vision.
At high altitudes, air is at a lower pressure, which means that there is less oxygen available for you to breathe in. The low air pressure makes it harder for your body to get the oxygen out of the air and into your bloodstream.
This lack of oxygen causes the symptoms of altitude sickness - the reduction in oxygen to your muscles and brain requires your heart and lungs to work harder. This increases your breathing and heart rate.
There are certain factors that may make you more likely to develop altitude sickness including if you:
have had altitude sickness before
do strenuous activity or exercise at high altitude
rapidly ascend to high altitude
are younger than 50
have a lung infection
If you have heart or lung disease, you should consult your GP before travelling above 4,000m.
The diagnosis for altitude sickness is based on your symptoms and whether you have ascended to an altitude of 2,500m or more and are otherwise well. If you have a headache, you should look out for other symptoms. If possible ask a travelling companion to watch you as well.
If you have mild altitude sickness, you shouldn't ascend any higher. You should:
drink plenty of water
take painkillers for your headache
take antisickness medicines, such as cinnarizine (eg Stugeron) or promethazine (eg Avomine), which can be used to ease the feelings of nausea and dizziness - you can buy these from a chemist without a doctor's prescription
Symptoms usually go away within one to two days.
If your symptoms become more severe, oxygen is the best treatment. You can easily get more oxygen by descending 500 to 1,000m. You can also get extra oxygen from oxygen tanks or hyperbaric treatment.
There are a number of medicines for severe altitude sickness. These include the medicines dexamethasone and nifedipine. Only people who are very experienced in treating altitude sickness should give these medicines.
For more advice about these medicines, ask your GP or a travel advice centre.
There are a number of steps you can take to prevent altitude sickness. Wherever possible:
acclimatise yourself to the high altitudes by slowly ascending the height over several days if possible - don't sleep at altitudes greater than 300m of the previous night
drink lots of water
eat a high-carbohydrate diet such as pasta
don't 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
Acetazolamide (Diamox) has been used increasingly as a preventive medicine to decrease the symptoms of altitude sickness. You should only take this medicine after consulting a doctor. It's not a substitute for common sense and you should descend immediately if your symptoms of altitude sickness get worse.
Alternatively, you may be able to take dexamethasone. This medicine is effective for both prevention and treatment of altitude sickness and can prevent HAPE if you have suffered from severe altitude sickness before.
If you have had HAPE before, you may be able to take preventive drugs. Both nifedipine and tadalafil can help to prevent HAPE but aren't suitable for preventing altitude sickness.
Altitude sickness Q&As
See our answers to common questions about altitude sickness, including:
- Altitude Illness Information Sheet, Health Professionals. National Travel Health Network and Centre. www.nathnac.org, accessed 2 January 2008
- Clarke C. Acute mountain sickness: medical problems associated with acute and subacute exposure to hypobaric hypoxia. Postgrad Med J 2006; 82:748-753. http://pmj.bmj.com
- Hill skills: Altitude. The British Mountaineering Council. www.thebmc.co.uk, accessed 3 January 2008
- Travel at High Altitude. Medex. www.medex.org.uk, accessed 3 January 2008
- Mountain sickness, oedemas, and travel to high altitudes - UIAA Mountain Medicine Centre Information Sheet 1. The British Mountaineering Council. www.thebmc.co.uk
- Bartsch P, Gibbs JSR. Effect of altitude on the heart and the lungs. Circulation 2007; 116:2191-2202. http://circ.ahajournals.org
- Maggiorini M. High altitude-induced pulmonary oedema. Cardiovasc Res 2006; 72:41-50. http://cardiovascres.oxfordjournals.org
- HACE (high altitude cerebral oedema). Altitude.org. www.altitude.org, accessed 3 January 2008
- Altitude or travel sickness. The Travel Doctor. www.traveldoctor.co.uk, accessed 3 January 2008
- British National Formulary (BNF). BMJ Publishing Group, 2007. 54: 217
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Dr W H Simpson, MBBS, General Practitioner, and by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
Publication date: June 2008.