Anyone can, at some point, be affected by acute mountain sickness (most commonly abbreviated to AMS). Little known to the general public — and sometimes even to hikers — it's essential to understand its symptoms and risks in order to guard against it effectively. This article isn't the place for in-depth medical explanations or a theoretical lecture; rather, it aims to outline the key points, the risks involved, and to raise your awareness of the essential warning signs and basic principles to follow in order to avoid the dangers and consequences of AMS.
What is AMS?
At altitude, pressure decreases and, as a result, at equal volume, there are fewer oxygen molecules available in the air. Faced with this reduction in oxygen, the human body tries to compensate by breathing more rapidly, increasing heart rate and producing more red blood cells — this is the acclimatisation phase.
Acute mountain sickness is therefore a sign of incomplete or partial acclimatisation of the human body to altitude.
The key determining factors are:
- The rate of ascent
- The altitude reached
- The length of your stay
- Individual susceptibility (age, specific weaknesses, medical history)
The early warning signs and progressive symptoms include mild headaches that intensify over time, digestive disorders, drowsiness, disorientation, dizziness, stress, irritability, breathing difficulties and/or neurological disturbances.
It is essential to understand that these symptoms are not at all progressive and/or chronological, and do not follow a step-by-step logic — which is, in fact, one of the greatest dangers of this condition!
Possible complications
HAPE (High Altitude Pulmonary Oedema) typically occurs in the early hours of the morning, usually 3 or 4 days after arriving at altitude. It starts with a dry cough (which is, of course, attributed to something else: a cold, rhinitis, etc.), after which the airways become congested. When you start coughing up pinkish foam, you need to act fast — you are essentially drowning from the inside (blood begins to pass through the pulmonary alveoli). You must call for emergency services or descend to a lower altitude as quickly as possible. Rescuers will administer oxygen, a hyperbaric chamber or a Dexamethasone injection.
HACE (High Altitude Cerebral Oedema) affects the brain and has an immediate impact on behaviour (dizziness, vomiting, headaches, "unusual" behaviour).
At altitude, you must stay alert and react quickly to any behaviour that seems out of the ordinary or unusual — as it can often lead to accidents through falls or inappropriate actions. Treatment is usually the same as for HAPE.
Localised oedemas can also occasionally appear (ankles, hands, face), but these are less common.
How do you prevent acute mountain sickness?
The essential rule to remember is: don't go too high too fast. Ideally, above 3,000 m, you should not gain more than 400 metres of elevation between two consecutive nights (although between those two nights you can climb a pass that is more than 400 m higher).
Individual factors must also be taken into account: it is well established that stress, cold and fatigue are aggravating factors.
Good hydration is also essential during the acclimatisation phase.
If you are not yet acclimatised, avoid alcohol, muscle relaxants and sleeping pills, as these have a depressant effect on ventilation and will therefore increase the effects of AMS.
Individual behaviour is, of course, a significant factor. With the current obsession with speed and always pushing further, virtually nobody takes the time to acclimatise properly — on Mont White, for example! Some people are even tempted to imitate the feats of high-profile athletes. On top of that, the duration of holidays, weather windows and the cost of an expedition can all create pressure to ascend faster than is wise.
Some general advice
In a high-altitude hiking group, the first priority is to make sure everyone can recognise the symptoms of AMS. The common mistake is to attribute the signs of AMS to something else: headache = too much sun, dizziness = earwax blockage, nausea = something you ate, strange behaviour = "dodgy bloke"… which can sometimes be the case, but not always!
- Look out for your fellow trekkers
- Stay well hydrated
- Stay humble and listen to your body
- Don't hide your symptoms hoping they'll "just pass"
- Acclimatisation is a matter of time
- Know when to turn back or adapt your plans
- Equip yourself with suitable hiking gear
Of course, this article is simply intended to raise awareness of a subject that can sometimes be dangerous and lead to critical situations. Don't hesitate to consult medical professionals, mountain specialists and guides to ask questions or get advice tailored to your health, fitness level and your intended destination or ascent.
