Altitude sickness or mountain sickness happens when the body is not able to adapt to the lack of oxygen (hypoxia) at higher altitude. People often think that the amount of oxygen in the air decreases with altitude but this is not exact. In reality, the oxygen concentration in the air is always the same (around 21%) at all altitudes. What changes with the altitude is the atmospheric pressure. The atmospheric pressure decreases when the altitude increases and therefore the quantity oxygen in a given volume reduces with the altitude. The consequence of this is that the quantity of oxygen in each breath is less at higher altitude (since we inspire a same volume of air containing less oxygen).
Travelers, trekkers and mountaineers are getting more and more aware of the risks due to altitude sickness when travelling to high mountains and they are better prepared and informed about the right things to do to prevent altitude sickness. The trekking and climbing routes are adapted so as to allow a good acclimatization. Unfortunately, accidents still occur each year. According to studies, the main cause of fatal accidents in high mountains is not injuries but pathologies which are derived from altitude sickness, especially cerebral and pulmonary edema. For example, a survey conducted in 2018 showed that 35% of the tourists flying directly to the city of Leh in Ladakh at an altitude of 3,500m to do a trek in the Himalayas experienced from altitude sickness. Among them, 20% developed a more severe form of altitude sickness which forced them to modify their travel plan.
The incidence of altitude sickness varies greatly among individuals and nobody can know predict how well he or she will be able to adapt to the high altitude during a climb. Some people can withstand rapid ascension better than others. The first symptoms of altitude sickness usually appear after 6 to 10 hours. Altitude sickness is more frequent in children under fifty years of age and in subjects who usually reside at less than 1,000 meters altitude. A good physical condition does not prevent from the risk of altitude sickness as it can affect even the most experienced athletes.
Symptoms of altitude sickness
The first symptoms of mountain sickness can occur from 2,500 to 3,000 meters above sea level. It should be noted that many ski resorts are within this altitude range and that a few persons who are more sensitive can start feeling some symptoms even at lower altitudes. The most common symptom of altitude sickness is headache. Other usual symptoms are sleeping difficulty, dizziness, fatigue, loss of appetite, nausea or vomiting and tachycardia.
In case of severe altitude sickness, symptoms can be: the bluish coloration of the skin (cyanosis), pectoral stiffness, confusion, cough, decreased consciousness, paleness, inability to walk and respiratory distress. When this symptoms occur, immediate actions must be taken to avoid complications.
What to do in case of altitude sickness
The first thing to do in case of symptom of altitude sickness is to do descend as quickly as possible to a lower elevation. The second efficient measure is to administer oxygen through a mask. If the condition of the patient does not improve, the patient must be urgently evacuated to a medical facility with equipment to treat altitude sickness in order to avoid a risk of cerebral and pulmonary edema which is potentially fatal if not treated on time.
Tips to avoid altitude sickness
The best recommendation to avoid altitude sickness is to make a gradual ascent. It is very important to climb very slowly, and to have adequate acclimatization periods of 2 to 3 days at a certain height (starting from 2,000 meters above sea level). The following ascent rates usually ensure that the body can acclimatize: one can ascend an average of 340-400 meters per day up to 5,000 meters altitude; between 5,000 m and 6,000 m, ascend maximum 250 meters per day; and above 6,000 m, ascend a maximum of 150-200 m per day.
Rest and hydration
In case of problem of altitude sickness, it is essential to go down to a lower elevation than the one acclimatized and rest for 24 to 48 hours until the symptoms disappear before resuming the ascent. If the symptoms are severe, start the descent immediately, always accompanied by someone in good shape who can assist you if needed. In these situations, you have to drink a lot of liquid (at least 3 or 4 liters a day), avoid drinking alcohol and follow a hyperglycemic diet, rich in sugars and carbohydrates.
Profiles with risk
People with heart and lung diseases have a higher risk of suffering from a severe form of altitude sickness, even if they have been treated successfully. Pregnant women, children, people with high blood pressure or with sleep apnea problems and those who have had altitude sickness before have a higher risk of suffering of mountain sickness and they should be more careful.