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Preventing Acute Mountain Sickness

What is acute mountain sickness?

Acute mountain sickness (AMS) can be broadly defined as symptoms experienced when your body is not acclimatised to its current altitude.

When you travel to altitude, as you ascend, the air becomes thinner. There is the same proportion of oxygen (21%) in the air. However, due to a lower pressure of the air, there is less oxygen available per breath.

This lack of oxygen triggers changes in your body to help it adapt to its new environment. These normal changes are acclimatisation and they include breathing faster than usual, getting more short of breath with exertion and passing urine more frequently.

What are the symptoms of acute mountain sickness?

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 (o)edema (HACE) not covered in this leaflet.

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

  • Poor appetite and/or nausea/vomiting.
  • Fatigue/weakness.
  • Dizziness/lightheadedness.
  • Difficulty sleeping.

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

How do I calculate my own score?

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

Symptom Severity Score
Headache No headache
Mild headache
Moderate headache
Severe headache
0
1
2
3
Gastrointestinal (gut) symptoms None
Poor appetite or nausea
Moderate nausea and/or vomiting
Severe nausea and/or vomiting
0
1
2
3
Fatigue and/or weakness Not tired or weak
Mild fatigue/weakness
Moderate fatigue/weakness
Severe fatigue/weakness
0
1
2
3
Dizziness/lightheadedness Not dizzy
Mild dizziness
Moderate dizziness
Severe dizziness
0
1
2
3
Difficulty sleeping Slept 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.

How can I prevent developing acute mountain sickness?

Remember to keep well hydrated and well nourished. Try to drink at least three litres of water a day (more if there is strenuous exercise/increased sweating). A useful thing to remember is ‘if you think you’re drinking too much – drink more!’ The most important method for prevention is to ascend safely at an appropriate rate (see below).

There are also drugs that can be taken to prevent AMS, the most widely known being acetazolamide (Diamox®). However, this is only really advised for those needing to ascend quickly – for example, for mountain rescue. The better strategy for prevention is to ascend slowly.

How can I ascend safely?

When ascending, initially try to spend at least one night just under 3,000 m. When above 3,000 m try to sleep no more than 300-500 m above the last altitude slept at. For every 1,000 m gained, try to spend the second night at the same elevation. Aim to climb high and sleep low. If you experience any symptoms of AMS, do not ascend.

What if I have to ascend quickly/I have a tight schedule?

If for any reason you have to ascend quickly, it is important to remember to put your own health and safety first. If you are experiencing any symptoms of AMS remember to share this with your team members/leader. Remember that AMS can be fatal if you continue to ascend; however, the mountain will always be there next year. Therefore, don’t put yourself at risk. You can consider using acetazolamide if you know you will be ascending quickly.

What should I do if I get acute mountain sickness?

If you are suffering with symptoms of mild AMS, firstly inform someone else (ideally the team leader/guide). It is important initially to rest at the same altitude. Usually symptoms resolve with rest and painkillers (paracetamol/ibuprofen) within 24 hours. If symptoms do not resolve, consider acetazolamide. If symptoms get worse, then descend.

If you experience symptoms of severe AMS then descend and consider acetazolamide. Sometimes, if you have descended and rested at a lower altitude, it may still be possible to re-ascend if you have recovered and your schedule allows for this.

Tell me more about acetazolamide (Diamox®)

Acetazolamide can used for the prevention and treatment of AMS. Acetazolamide speeds up your rate of acclimatisation, but it does not mask the symptoms of AMS. Acetazolamide does not protect against worsening AMS with continued ascent. You cannot buy acetazolamide from a pharmacy (chemist); you will require a prescription from your GP. The dose of acetazolamide for prevention is 125 mg twice a day. The treatment dose (if you have symptoms) is 250 mg twice a day. Remember that if you are needing the treatment dose of acetazolamide, you should not be ascending.

Things to remember

  • If you feel unwell at altitude, it is altitude illness until proven otherwise.
  • Never ascend with symptoms of AMS.
  • If you have severe AMS or mild AMS that is not improving or is worsening, then descend.

A list of things to consider taking when travelling to altitude.

  • Painkillers – paracetamol and ibuprofen.
  • Antidiarrhoeal and oral rehydration sachets (to prevent dehydration).
  • First aid kit – for minor injuries.
  • Acetazolamide (Diamox®).
  • Antisickness medication.
  • Water purification tablets/liquid (to purify water).

EMIS wishes to thank Dr Laura Hand for writing this article.

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