Anyone can, at some point, be affected by acute mountain sickness (most commonly abbreviated to AMS). Not well known by the general public — and sometimes even by hikers — it is essential to understand its symptoms and risks in order to protect yourself effectively. This is not the place for in-depth medical explanations or a theoretical lecture, but rather to outline the key points and risks, and to trigger in you the essential "alerts" and basic principles to put in place to avoid these problems and their consequences.
What is AMS?
At altitude, pressure decreases and therefore, in air at equal volume, fewer oxygen molecules are available. Faced with this reduction in oxygen, the human body tries to compensate by breathing faster, increasing heart rate and producing more red blood cells — this is the acclimatisation phase. Acute mountain sickness is then the 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 duration of the stay
- Individual susceptibility (age, particular vulnerabilities, medical history)
Possible complications
HAPE (High Altitude Pulmonary Oedema) often occurs in the early hours of the morning, generally 3 or 4 days after arriving at altitude. It starts with a dry cough (which of course gets attributed to something else: a cold, bronchitis, etc.), then the airways become congested. When you start coughing up a pinkish foam, you need to act fast as you are essentially drowning from the inside (blood begins to cross the pulmonary alveoli). You must call for rescue services or lose altitude as quickly as possible. Rescue teams will use 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, "strange" behaviour). At altitude, you must be vigilant and reactive to any behaviour that is out of the ordinary or seems strange (which can often lead to accidents through falls or inappropriate actions). The treatment is often the same as for HAPE. Localised oedemas can also sometimes appear (ankles, hands, face) but are less common.How to avoid acute mountain sickness?
The essential rule to remember is not to ascend too high too fast. Ideally, above 3,000m, you should not exceed 400 metres of elevation gain between 2 consecutive nights (though between those 2 nights you can climb a pass more than 400m higher in elevation gain). Individual factors must also be taken into account: stress, cold, and fatigue are recognised as aggravating factors. Good hydration is also essential during the acclimatisation phase. If you are not yet acclimatised, avoid alcohol, muscle relaxants, and sleeping pills, which will have a depressant effect on ventilation and will therefore increase the effects of AMS. Individual behaviour is, of course, a key factor. With the trend for speed and always pushing further, almost nobody takes the time to acclimatise to Mont Blanc for example! And some are even tempted to imitate the feats of high-profile athletes. Furthermore, the length of holidays, the weather window, and the cost of an expedition can also push people to ascend faster than is sensible.A few general tips
In a group of hiking at altitude, it's essential to make sure everyone knows how to recognise the symptoms of AMS. The mistake is often to attribute the signs of AMS to something else: headache = too much sun, dizziness = earwax blockage, nausea = food, strange behaviour = "dodgy bloke"… which can sometimes be the case, but not always!- Keep an eye on your fellow travellers
- Drink plenty of water
- Stay humble and listen to your body
- Don't hide your symptoms hoping they'll "just pass"
- Acclimatisation is a matter of time
- Knowing when to turn back or adapt your plan
- Equipping yourself with the right hiking gear
