Altitude sickness, also called Acute Mountain Sickness (AMS) affects the body in low air pressure conditions in high altitudes where atmospheric pressure conditions are lower than at sea level.

A change in weather or temperature affects barometric pressure and the level of oxygen molecules available in the air you breathe. The surrounding environment has a role to play. Cold, heat, wind or wetness affect trekkers or climbers exposed to altitude. Dehydration, fatigue, strenuous exercise and even anxiousness can also increase the development of AMS.

How to explain AMS?
There is no definite cause. But, we know that the low level of oxygen molecules in high altitude generates hyperventilation. Even if altitude is an important factor, the speed in which you ascend has a significant influence in the development of AMS symptoms. Remember not to get too high too fast!

As you gain altitude, the barometric pressure decreases. Even though the air still contains 21% oxygen, the molecules expand and every breath you take contains fewer molecules of oxygen to feed the body with the necessary fuel. As a consequence, you breathe deeper and also faster to get the same level of oxygen molecules as you need at sea level pressure. This phenomenon is named Hypoxia with lungs getting less efficient to absorb oxygen.

AMS can appear from approx. altitude 2500 m and the body has to adjust itself in a slow process of acclimatization. Extra days in your trip itinerary always help the body to get used to low pressure and lack of oxygen. As it is difficult to determine who may be affected by altitude sickness, it is highly recommended to improve your stamina and lungs capacity by training regularly (running, biking, swimming ...), getting a gradual acclimatization and sufficient rest to avoid altitude sickness. Surprisingly, AMS is often more likely to strike young, healthy and sportive climbers! Why? They usually prefer to attempt a rapid ascent by climbing up rapidly, challenging themselves. Both genders are affected equally and the age has no influence on AMS. Doing a test of effort is often the only way to know if you are sensitive to altitude sickness.

The main symptoms are:
- Headache or dizziness
- Increasing of breathing rate
- Nausea and vomiting
- Swelling of the face, hands, feet
- Loss of appetite
- Insomnia
- Persistent drowsiness during the day, weakness, fatigue
- Shortness of breath or irregular breathing
- Loss of coordination

At 3,600 meters (12,500 feet) there is approx. 45% fewer oxygen molecules per breath than at sea level and  if AMS is not treated these above mentioned symptoms can rapidly turn into Pulmonary edema (HAPE) - with fluid in the lungs - or cerebral edema (HACE) - with swelling of the brain.

To improve oxygen delivery to the blood, the heart beats more quickly and strongly, the breath gets deeper and quicker and the marrow produce more red blood cells to transport the oxygen to the main organs and to provide oxygen to the whole body. As a consequence, the blood gets much thicker and it increases the risks of AMS. To prevent AMS, climbers should not gain too much altitude in one day to reach the upper camp for the night - not more than 700 meters altitude / about 1000 feet -. Getting some rest is mandatory. Alcohol, sleeping pills, cigarettes are respiratory depressant and increase the disturbance in breathing and sleeping.

How to detect the early signs of AMS?
The inability to control arms motions, the lack of coordination, strong headache that cannot be cured with aspirin, sometimes retinal hemorrhages, general confusion or when stumbling while walking must urge you to get back to lower altitude as soon as possible. If this simple rule is not respected, AMS can progress in severity and rapidly turn into edema. Some medicines can improve AMS symptoms as Diamox. This medicine has to be taken at least 3/5 days before ascent but side effects can be noticed as tingling in hands and feet that can hide frostbite problems, nausea and the increase of urination frequency as Diamox is a diuretic. Viagra is also sometimes used and appears to be effective in preventing AMS. When mild Altitude Sickness gets severe, dexamethasone can be provided and a quick descent is strongly recommended. With Pulmonary edema, lungs slowly fill with water hindering the oxygen transfer to the red blood cells and climbers drown in their own fluid. With Cerebral edema, the brain swells with heavy shivering, poor decision making, stiff muscles or painful cramps and strong feeling of cold.

What to do to prevent AMS?
- drink at least 4/5 liters of liquid per day
- get in a Gamow bag : portable compression bag
- give oxygen
- administer suitable medicament as Diamox or similar (with doctor prescription and beforehand instructions)
- get warm (drink and eat hot, change wet clothes, build a shelter ...)

Important advice before getting on altitude trek or climbing trip
- Have a dental check-up.
- Write down your blood group on your insurance papers and travel bags in case of emergency.