expert advice / mountaineering


1. What is altitude sickness?

High altitude sickness is a condition that is triggered by ascending to high altitudes without allowing your body the time to adjust, or acclimatise, as it’s known.

High altitude sickness, or Acute Mountain Sickness (AMS) as it’s also known, should always be taken seriously. If you are planning on undertaking a mountain adventure that’s going to take you to higher elevations, including in the Alps, it’s important you’re aware of the symptoms and methods for treating it.

2. Why do you get it?

There’s a risk of altitude sickness from around 2,200 - 2,500 metres above sea level and beyond. Acclimatisation is necessary because the higher you go, the less oxygen concentration there is in the atmosphere. This is because the air pressure is lower, so the air you breathe has fewer oxygen molecules. This is what’s meant when people say that the air is ‘thin’.

3. Who does it affect?

High altitude sickness can happen to anyone, regardless of age, level of fitness or ability. Those who are not used to being at altitude will usually struggle more to adjust, but altitude sickness can strike even the youngest, fittest mountaineers.

4. What are high altitude sickness symptoms?

Many describe the symptoms of altitude sickness as being like a bad hangover. The first signs to look out for when moving at higher altitudes are:

  • headache
  • nausea/ vomiting
  • fatigue
  • dizziness
  • loss of appetite
  • insomnia

If you experience any of these, however mildly, or feel unwell in any way, it’s important you immediately tell your climbing partner, someone in your party or your guide.

5. How does AMS progress?

Mild AMS has symptoms such as slight headache and fatigue, that might still allow you to carry on with your normal activities. These should improve after one or two days, once your body adjusts to the decrease in oxygen.

Moderate AMS is when these symptoms worsen, with more severe headaches, nausea and difficulty performing regular actions.

Severe AMS comes with a further decline in symptoms, such as shortness of breath, even when resting, tightening of the chest, confusion, hallucinations etc. This is an emergency. If this is the case, you must descend to lower altitudes immediately and seek medical attention.

6. What is HAPE and what are its symptoms?

With severe AMS, there’s the possibility that fluid has built up in the lungs. This is known as HAPE or High Altitude Pulmonary Edema. Fluid in the lungs further reduces the amount of oxygen moving around your body. Left untreated, HAPE can quickly turn deadly.

HAPE symptoms include:

  • Shortness of breath, even when resting
  • Persistent cough that develops into a wet, gurgly cough
  • White or pink frothy fluid coughed up
  • Extreme fatigue
  • Confusion
  • Feelings of suffocation at night
  • Cyanosis (skin, nails or whites of eyes start to turn blue)

7. What is HACE and what are its symptoms?

Another possible outcome of severe AMS is the build-up of fluid in the brain. This is called HACE or High Altitude Cerebral Edema. Here, the brain tissue starts to swell from leaking fluid.

HACE symptoms include:

  • Disorientation, memory loss, hallucinations
  • Cannot balance on one foot
  • Loss of coordination
  • Weakness
  • Psychotic behaviour
  • Difficulty walking heel to toe in a straight line

8. How do you treat altitude sickness (AMS)?

The golden rule if any of these symptoms are present, is to assume it is AMS. Do not ascend any further.

Simply hoping it will go away and carrying on with an ascent regardless is a dangerous approach to take. With milder altitude sickness, rest and acclimatisation will usually alleviate symptoms within a day or two.

Treatment might include a dose of ibuprofen, aspirin or paracetamol to relieve the pain of a headache. For all other types of high altitude sickness, the most important treatment is getting the person to lower altitudes.

If a person becomes disorientated and struggles to breathe even at rest, or feels a tightening of the chest, it’s important to get them down to a lower altitude immediately (roughly 500-1000 metres lower – or the last elevation where the person had no symptoms). With the increase in oxygen concentration in the air at these lower levels, and rest, the symptoms should improve in two to three days.

Where conditions deteriorate into severe altitude sickness, HAPE or HACE, returning to a lower altitude immediate and medical attention are needed.

9. How do you treat HAPE?

HAPE (High Altitude Pulmonary Edema) or fluid build-up in the lungs, can turn deadly within hours. The most important treatment for HAPE is descent.

Bottled oxygen can help if available, as can using a Gamow bag, a kind of portable lightweight inflatable bag, which raises the air pressure around the person and redresses the lack of oxygen to some extent. But these measures are no substitute for a rapid retreat down the mountain. Medical attention is necessary and, if possible, a chest X-ray. Some drugs might alleviate high-altitude sickness symptoms too but should only be administered by medical professionals.

10. How do you treat HACE?

HACE (High Altitude Cerebral Edema), or fluid on the brain, is also life-threatening and requires immediate treatment. As with HAPE, the most important action is a quick descent. Administer oxygen if available and a steroid called dexamethasone can also be given. Medical attention is essential.

11. How to prevent altitude sickness?

11.1. Ascend slowly

Since altitude sickness is caused by ascending too rapidly to elevations where the air is thinner, the most effective way to prevent this from happening is to ascend slowly and allow the body to acclimatise to changes in oxygen saturation in the air.

When it comes to acclimatising, everyone is different. So it’s important to listen to your body as you ascend. Our bodies are amazing at adapting to altitude if given enough time.

  • Limiting the vertical metres we climb every day above 2,500 m to no more than 300-500 metres is a good benchmark.
  • It’s fine to ascend higher than 500 metres, say, but then descend to within that limit to sleep. The height you sleep at is what counts here.
  • Factoring in a rest day every 3-4 days is also good for effective acclimatisation.

11.2. What other precautions can you take?

1. Drink plenty

The higher up we are, the colder the air becomes and the less moisture it holds. This makes it even more important than usual to drink lots and stay hydrated. Your body is losing more moisture than you realise through a combination of this drier air, the increased frequency of breathing and increased urination which naturally occurs at altitude. The more hydrated you are, the better your body works, and the better it can transport oxygen. Staying hydrated helps acclimatisation and will help prevent high altitude sickness.

2. Eat plenty

Even though being at altitude tends to cause a drop in appetite, it’s important to eat plenty so that your body can carry out the extra work it needs to do to stay healthy despite the lack of oxygen. Light meals, with a high calorie content and plenty of carbohydrates are the way to go.

3. Acetazolamide and dexamethasone

These drugs can be used as a means of preventing high altitude sickness, but they have side effects and should not be used without professional medical advice beforehand.

4. Avoid alcohol and caffeine

Alcohol dilates the blood vessels and caffeine narrows them. Alcohol can also dehydrate you. So it’s best to avoid them both before and during an ascent to higher altitudes.

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