Anyone can experience acute mountain sickness (commonly abbreviated to AMS). Often misunderstood by the general public and even hikers, knowing the symptoms and risks is essential for effective prevention. The goal here is not to give exhaustive medical theory, but to outline the key risks, identify vital warning signs, and share fundamental rules to stay safe in the mountains.
What is AMS?
Atmospheric pressure drops with altitude, meaning there are fewer oxygen molecules available per volume of air. To cope with this oxygen depletion, your body compensates by breathing faster, increasing heart rate, and producing more red blood cells: this is the acclimatisation process.
Acute mountain sickness occurs when the body fails to adapt adequately or completely to high altitude.
Key determining factors include:
- Rate of ascent
- Altitude reached
- Length of stay
- Individual susceptibility (age, specific health conditions, medical history)
Warning signs and progressive symptoms include mild headaches that worsen over time, digestive upset, drowsiness, disorientation, dizziness, stress, irritability, shortness of breath, and neurological disorders.
It is essential to understand that these symptoms are neither progressive nor chronological and do not follow a linear pattern: that is precisely one of the greatest dangers of altitude sickness!
Potential complications
HAPE (High Altitude Pulmonary Oedema) often occurs towards the end of the night, usually 3 to 4 days after reaching altitude. It begins with a dry cough (which is often mistaken for a common cold or chest infection), followed by congested airways. Once pink, frothy sputum appears, immediate action is critical as fluid fills the lungs (blood enters the pulmonary alveoli). You must call emergency services or descend rapidly, if possible. Rescue teams will administer oxygen, use a hyperbaric chamber, or inject Dexamethasone.
HACE (High Altitude Cerebral Oedema) affects the brain and causes immediate behavioural changes (dizziness, vomiting, severe headache, confusion, and irrational behaviour).
At high altitude, stay alert and react promptly to any unusual or erratic behaviour (which can frequently lead to falls or poor decision-making). The treatment is largely the same as for HAPE.
Localised swelling (oedema) can also occur around the ankles, hands, or face, though it is less common.
How to prevent acute mountain sickness?
The golden rule is never to climb too high, too fast. Ideally, above 3,000m, do not exceed an elevation gain of 400 metres between two consecutive nights (though you can tackle a higher pass during the day before descending to sleep).
Individual factors also come into play: stress, cold, and fatigue are known aggravating factors.
Proper hydration is also essential during the acclimatisation phase.
If you are not acclimatised, avoid alcohol, muscle relaxants, and sleeping pills, which act as respiratory depressants and impair ventilation, thereby worsening the effects of AMS.
Individual behaviour plays a major role. With the current trend of going faster and pushing further, hardly anyone takes the time to acclimatise properly on Mont White, for instance. Some even attempt to copy the extreme feats of media-hyped athletes. In addition, tight holiday schedules, weather windows, and expedition costs often tempt mountaineers to push up faster than reason dictates.
General advice
In an altitude hiking group, you must first ensure that everyone knows how to spot the symptoms of AMS. A common mistake is attributing AMS signs to other causes: headache = sun, dizziness = earwax, nausea = food, odd behaviour = "strange person"... which might sometimes be true, but certainly not always!
- Watch out for your team members
- Drink plenty of fluids
- Stay humble and listen to your body
- Never hide your symptoms hoping they will "just pass"
- Acclimatisation takes time
- Know when to turn back or adjust your itinerary
- Equip yourself with the right hiking gear
This article serves as a general overview of a potentially severe mountain hazard. Always consult medical professionals, mountain specialists, or certified guides to obtain tailored advice suited to your health, fitness level, and planned ascent.
