The risk of getting altitude sickness

Many people think that altitude sickness only occurs at a very high altitude in distant countries. That is a mistake. Even in the Alps, the disease is already regularly seen at relatively low altitudes. It should be noted here that altitude sickness does not occur with 'round trips', that is, when it descends to the starting level again within an hour or eight after reaching the highest point. Slight symptoms such as some headache or some light in the head may occur, but the time to develop serious symptoms is simply too short. There must therefore always be a stay at a height of at least an hour or eight (usually an overnight stay).

A widely used rough classification of the risk of altitude sickness in relation to altitude is the following:

• 2500 to 3500 meters: High. Chance of usually mild form of altitude sickness on average 25%;
• 3500 to 5500 meters: Very high. Chance of also serious and sometimes fatal forms of altitude sickness on average 65%;
• 5500 to 8850 meters (you can't climb higher if there are no mountain tops): Extremely high. The risk of mild to very severe forms of altitude sickness is almost 100%.

Three factors are crucial to the risk of altitude sickness:

• the speed of rise;
• the sleeping height;
• instance.

The chance of getting altitude sickness has little to do with the physical condition. There are indications that people in good condition are inclined to overestimate themselves and climb too fast, which increases the risk. Of course a good condition is needed to be able to perform.

Age and gender are also little related to the risk of altitude sickness. It is possible that the sensitivity above the age of 60 itself will decrease somewhat.

People (including the mentally disabled and small children) who are unable to express their possible complaints themselves should not be exposed for more than a few hours at altitudes above 2500 meters. Some people are more susceptible to altitude sickness than others. That is a matter of 'construction'. The best predictor for getting altitude sickness is the fact that they also got it on a previous climb. People who have had altitude sickness once run the same risk of getting altitude sickness again in comparison with others. For them, taking precautionary measures is even more important than for those who know from experience that they are not 'susceptible' to this disease.

The following factors increase the risk of altitude sickness:

Rapidly rise (for example in one day) from sea level to heights above about 2500 meters, or rise above that height faster than 300 meters per day (sleeping height) without inserting rest days.

• Being (much) too fat.
• Instruction. It is not yet known exactly what this predisposition entails, but whoever once got altitude sickness while he / she has adhered to all the advice neatly runs a higher risk the next time altitude sick to become.
• Make heavy physical exertion, due to the extra large oxygen requirement. We often see this in fit people who, due to their condition, climb up too quickly and therefore get into trouble.
• Diseases that people already had before climbing. In particular some heart and lung diseases, but also other diseases are important here. It is better not to use some medicines.

Factors that, although not directly promoting altitude sickness, can make climbing very difficult and aggravate symptoms are the following:

• Smoking, because then the oxygen delivery from the hemoglobin to the tissues is reduced.
• Use of alcohol during rest breaks of the trip, since alcohol increases urine output and thereby disrupts your fluid balance. In addition, alcohol has many other harmful side effects, including on your nervous system and motor skills. The use of alcohol can also make you more optimistic about your condition than it is, causing you to deny or not recognize symptoms and to increase further while your condition actually does not allow it.
• High ambient temperature, due to the sometimes extreme loss of moisture, in combination with too little drinking.
• Very low ambient temperature, due to cooling, and due to moisture loss through breathing because the air is very dry at height. The air temperature drops by an average of 6.5 degrees Celsius per 1000 meters rise.

From this list you can already conclude that altitude sickness in general can be prevented by taking the aforementioned factors into account. You can also derive the right treatment from it. This also applies to people who have been susceptible to this disease. The above percentages of people who fall ill are much higher than might be expected if people adhered to a number of guidelines. Because of ignorance, time pressure or stubbornness, many people do not do that.

By the way: If you have recovered without complaints, or have become complaint-free in the meantime, and you get complaints (again) during the descent, then that will never be altitude sickness. You cannot get altitude sickness during the descent!

Sometimes people wonder why you can't get altitude sickness on an airplane. After all, the artificially maintained air pressure in most aircraft that cross at a height of 10,000 meters is comparable to a height of 1000 to nearly 3000 meters. The American legal limit is a maximum of 2400 meters for commercial flights. However, such flights usually take too short to have a lot of effect on the body and, in addition, the end point is often at sea level again. Only for people with relatively serious respiratory diseases and certain heart diseases can the slightly lower oxygen concentration in the aircraft be an objection, but then there is usually also objection to an altitude requirement. If the pressure in the cabin on the way suddenly disappeared, you would die fairly quickly due to acute oxygen shortage, not due to altitude sickness, but luckily there are solutions for this on the plane. So feel free to fly.

Author: Han Willems - More info about altitude sickness