Acute Mountain Sickness

Altitude sickness called Acute Mountain Sickness (AMS) affects the body in low air pressure conditions at high altitudes where atmospheric pressure conditions are lower than that 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 the wet affects 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. However, we know that the low level of oxygen molecules at 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 ascend 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 you need at sea level pressure. This phenomenon is named Hypoxia with lungs becoming less efficient to absorb oxygen.

AMS can appear at an approximate altitude of 2500m 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 and feet
– Loss of appetite
– Insomnia
– Persistent drowsiness during the day, weakness, fatigue
– Shortness of breath or irregular breathing
– Loss of coordination

At 3600 meters there is approximately 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 oedema (HAPE) – with fluid in the lungs – or cerebral oedema (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 produces 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. Getting some rest is mandatory. Alcohol, sleeping pills and cigarettes are respiratory depressants and increase the disturbance in breathing and sleeping.

How to detect the early signs of AMS?

The inability to control arm motions, the lack of coordination, a strong headache that cannot be cured with aspirin, sometimes retinal hemorrhages, general confusion or when stumbling whilst 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 oedema. Some medicines can improve AMS symptoms such as Diamox. This medicine has to be taken at least 3/5 days before ascent, but side effects can be noticed, as tingling in the hands and feet 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 oedema, lungs slowly fill with water hindering the oxygen transfer to the red blood cells and climbers drown in their own fluid. With cerebral oedema, 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 litres of liquid per day
– Get in a Gamow bag : portable compression bag
– Give oxygen
– Administer suitable medicine such as Diamox or similar (with a Doctor’s prescription and beforehand instructions)
– Get warm (drink and eat hot food, 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.