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What is Altitude Sickness?

What is Altitude Sickness?

So you’ve been inspired by our article Where to start: Altitude, but if you’re planning your first trip to a high peak overseas, then altitude sickness or Acute Mountain Sickness (AMS) may be something you’ve never encountered or had to consider. Even if you’ve been to high peaks before and not been affected, altitude sickness can still affect you on your next trip.

What is AMS?

As you ascend to high altitudes your body needs time to acclimatize to the decreasing oxygen. At any moment, there is an “ideal” altitude where your body is in balance; this is usually the last elevation at which you slept. Extending above this is a zone where your body can tolerate the lower oxygen levels, but to which you are not quite acclimatized. If you get above the upper limit of this zone, there is not enough oxygen for your body to function properly, and symptoms of hypoxic distress occur – this is AMS.

Each day, as you ascend, you are acclimatizing to a higher elevation, and your zone of tolerance extends that much higher up the mountain. The trick is to limit your daily upward travel to stay within that tolerance zone, it also helps to sleep at a lower altitude to your highest point reached that day.

Climbing Kilimanjaro High Altitude

Emily Pitts, Womenclimb Founder at the summit of Kilimanjaro.

The Body’s reaction to altitude

Certain normal changes occur in every person who goes to altitude:

  • Hyperventilation (breathing faster, deeper, or both)
  • Shortness of breath during exertion
  • Changed breathing pattern at night
  • Awakening frequently at night
  • Increased urination

As one ascends through the atmosphere, every breath contains less oxygen. You need to work harder to obtain oxygen, by breathing faster and deeper. This is particularly noticeable with exertion, such as walking uphill. Being out of breath with exertion is normal, as long as the sensation of shortness of breath resolves rapidly with rest.

Symptoms of AMS

AMS is when you have a persistent headache which is present with any one or more of the following symptoms:
  • Loss of appetite, nausea, or vomiting
  • Fatigue or weakness
  • Dizziness or light-headedness
  • Difficulty sleeping

A headache at altitude is not “normal”. Denial is also common – be willing to admit that you have altitude illness, that’s the first step to staying out of trouble.

It is OK to get altitude illness, it can happen to anyone. It is not OK to die from it.

Using Acetazolamide (Diamox)

Acetazolamide also referred to as Diamox works by helping to accelerate acclimatisation. It works by encouraging your body to remove bicarbonate (carbon dioxide) which does have a negative impact of meaning you will pee even more!!

By doing so it helps to re-acidify the blood acting as a breathing stimulant; this is particularly helpful at night when periodic breathing can disturb sleeping patterns.

It can however cause tingling in fingers, toes and lips, and can cause nausea and headaches – since both of these are symptoms of AMS it is worth saving this for your final ascent days.

I have found Acetazolamide to be difficult to source in the UK as you need a private prescription with NHS.  GPs are reluctant to give as altitude sickness is not the drug’s primary use. Search it out online from reputable online pharmacies.

Diamox on Kilimanjaro

Emily, Womenclimb Founder, in her tent on Kilimanjaro. She used Diamox on her ascent of Kili in 2014.

Further information

If you want further information here’s a really good website written by high altitude medics: www.basecampmd.com



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