Preventing Acute Mountain Sickness

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The popularity of adventure travel is increasing. As a result greater numbers of people are travelling to altitudes of 2500 metres (8,000 feet) or above each year. However, there are risks associated with climbing to altitude. Acute mountain sickness (AMS) can be unpleasant and may reduce enjoyment of activities. In addition, if it is not managed appropriately it can result in more serious illness which can lead to death. An understanding of the prevention and recognition of AMS is important to anyone travelling to high altitude.

As you climb or travel (ascend) to altitude the air becomes thinner. Due to the lower pressure of the air, there is less oxygen available per breath.

This lack of oxygen triggers changes in your body to help it adjust to its new environment. These normal changes are 'acclimatisation'. This means that your body is changing to help manage the new conditions. Changes include breathing faster than usual, getting more short of breath with increased activity (exertion) and passing urine more frequently.

AMS may be experienced when your body is not acclimatised to the altitude.

The main symptom is headache, which is as a result of mild swelling of the brain, caused by the reduced oxygen levels. This can vary in severity. Rarely, people can experience more severe swelling leading to a condition called high altitude cerebral oedema (HACE). See separate leaflet called Altitude/Mountain Sickness for more details.

For a diagnosis of AMS to be made you need a headache plus one other symptom from:

  • Poor appetite.
  • Feeling sick (nausea).
  • Being sick (vomiting).
  • Feeling tired (fatigue) or weak.
  • Dizziness/light-headedness.
  • Difficulty sleeping.

If you experience any of these symptoms at altitude and wonder whether you have AMS, you can score yourself to find out.

The Lake Louise score is a scoring system used to make a diagnosis of acute mountain sickness (AMS). This is something you can do yourself to decide how severe your symptoms are and what they mean. The scoring is as follows:

SymptomSeverityScore
HeadacheNo headache
Mild headache
Moderate headache
Severe headache
0
1
2
3
Gut (gastrointestinal) symptomsNone
Poor appetite or nausea
Moderate nausea and/or vomiting
Severe nausea and/or vomiting
0
1
2
3
Fatigue and/or weaknessNot tired or weak
Mild fatigue/weakness
Moderate fatigue/weakness
Severe fatigue/weakness
0
1
2
3
Dizziness/light-headednessNot dizzy
Mild dizziness
Moderate dizziness
Severe dizziness
0
1
2
3
Difficulty sleepingSlept as well as usual
Did not sleep as well as usual
Woke many times, poor sleep
Could not sleep at all
0
1
2
3

A total score of 3 to 5 = mild AMS and 6 or more = severe AMS. Remember that any symptoms at altitude are altitude illness until proven otherwise.

The best way to try to prevent altitude sickness is to climb up (ascend) to higher altitudes slowly. This gives time for your body to adjust to conditions (acclimatise). Different people will acclimatise at different rates. Remember to drink enough fluids (keep well hydrated) and eat enough food (stay well nourished). Avoid alcohol, especially in the first two days at high altitude.

There are also medicines that can be taken to prevent AMS. The most widely used one is acetazolamide (Diamox®). These are most suitable for people who have been known to have problems in the past or who unavoidably have to ascend more quickly than recommended. The routine use of acetazolamide before ascent is not recommended. The better strategy for prevention is to ascend slowly and to be aware of any developing symptoms.

  • There are recommended rates of ascent to altitude to help with adjusting to conditions (acclimatisation):
    • If possible, spend at least one night at an 'intermediate' elevation below 3000 metres.
    • Above 3000 metres, increase your sleeping altitude by only 300-500 metres per day.
    • Above 3000 metres, take a rest day for every 1000 metres of elevation gained (ie spend a second night at the same altitude).
    • If possible, don't fly or drive directly to high altitude.
  • If you do go directly to high altitude by car or plane, do not over-exert yourself or move higher for the first 24 hours.
  • Always try to sleep at a lower altitude. Climbers commonly use the phrase, "climb high, sleep low".
  • Take special care if you have previously had acute mountain sickness (AMS).
  • When planning an ascent as a group, plan for members acclimatising at different rates. How will you support those remaining behind to recover from AMS?
  • If symptoms of AMS develop, delay further ascent.
  • If symptoms become worse, move down (descend) as soon as possible.

If you are experiencing symptoms of mild AMS, the first step is to rest at the same altitude. Usually symptoms resolve with rest and painkillers (paracetamol or ibuprofen) within 24 hours. If symptoms do not resolve or if symptoms become worse, move down (descend). It is common that even a short descent and rest will improve symptoms significantly. It may still be possible to climb up again (re-ascend) if you have recovered and your schedule allows for this.

Acetazolamide (Diamox®) can be used for the prevention and treatment of AMS. There is good evidence for its effectiveness. Acetazolamide speeds up your rate of adjusting to conditions (acclimatisation) but it does not mask the symptoms of AMS. Acetazolamide does not protect against worsening AMS with continued climbing upwards (ascent). You cannot buy acetazolamide from a chemist; you will require a prescription from your GP. The usual dose of acetazolamide for prevention is 125 mg twice a day. A common side-effect with acetazolamide is pins and needles.

There is also evidence that a steroid tablet called dexamethasone can be used to prevent AMS. However, this is not recommended for routine use in travellers to high altitudes. Other options are being studied - for example, ibuprofen. However, there is not yet any evidence that it is as effective as acetazolamide. Until further studies are done, it is best not to take this to prevent AMS.

There is no reliable evidence for any other medications (including gingko biloba) at present. In some parts of South America travellers to high altitude may be offered coca leaves. These can be used to make tea or the leaves can be chewed. These are known to act as a mild stimulant but there is no evidence they help prevent AMS. 

Further help & information

Original Author:
Dr Tim Kenny
Current Version:
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
13573 (v3)
Last Checked:
07/03/2016
Next Review:
07/03/2019
The Information Standard - certified member
Now read about High-altitude Illness

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