At high altitude

Many hiking routes in Chile are made at high altitudes

When hiking at an altitude higher than 3500m you must plan and prepare your excursion at the very best

Altitude tactics

An active acclimatization to altitude is, in any case, preferable to a passive one. However, and due to the distances involved, long sections must be traveled by vehicle, especially in the Atacama region, north of Chile. For this reason, great heights are reached too quickly. The trek to base camp in central Chile is done in general with mules, which are rented by the day. For costs reasons, there is a tendency to climb faster than what is advisable health-wise. Besides, without carrying any equipment it is obvious that it is easier to climb faster.

Independently of how you approach the goal in the mountain, be it by foot or by means of a vehicle, the same practical rule applies:

Up until 3000 m, very seldom there are problems related to altitude. Beginning from there, the places to spend the night should not be over 500 m from the highest altitude reached during the day. After ascending 1000 m more, two nights in a row must be spent at the same place. During the day, you can ascend without problems to higher altitudes to get a better acclimatization, but then you have to come back to the camp. According to this practical rule, you should count at least eight days to climb a 5000 m mountain.

The 10 golden rules for ascending a high mountain (Thomas Lämmle)

  • Do not climb too fast!
  • Watch the altitude at which you’ll spend the night!
  • Control your heart beat and take your time!
  • Watch your teammates!
  • In case of altitude sickness: descend immediately!
  • Take care of your health!
  • Drink a lot!
  • Do not stay too long at extreme altitudes!
  • Sleep well!
  • Plan your stay at high altitudes!

Air composition and atmospheric pressure

Normally, it is supposed that oxygen concentration in air decreases with altitude. However, air is composed of 78% nitrogen, 21% oxygen and 1% carbon dioxide in constant measures at any altitude. As altitude increases, the only thing that decreases is atmospheric pressure, and consequently, the oxygen pressure diminishes (partial oxygen pressure pO2), which act so as to make the vital gas enter the lungs. At 5000 m the oxygen pressure has already reduced to half (see diagram).

Acclimatization capability

Unlike Tibetans and Nepalese, who through the centuries have adapted to great altitudes, our permanence in those places can only be temporary. Even aboriginal people from South America settled in the Altiplano high plains, as the Quechua and Aymara, haven’t yet adapted entirely. A chronic variant of altitude sickness make some of them move to lower areas. Beginning at 5300 m performance diminishes continuously that sooner or later leads to death by exhaustion.

Beware of altimeters

Altimeters that show altitude by measuring atmospheric pressure must be constantly adjusted. Practical tests done with different altimeter clocks demonstrated that, for each 1000 m of ascent, they show between 50 and 80 m less. Due to this, you could be lead to believe you are camping at 4700 m, but in reality you are situated over 5000 m. This difference can mean drastic consequences at that altitude. Because air is compressible, atmospheric pressure adopts a curved form as altitude increases. However, altimeters function in a lineal way, so even the best models show differences in altitude.

Adaptation mechanisms

If there was no adaptation mechanism of the body we could only climb as far as 5 000 m. The most important altitude adaptation mechanisms are, first of all, the increase in the frequency and depth of breathing (hyperventilation), which has a relative importance of 60%; the raise in red cells production improves adaptation in 20%; and a higher efficiency of the cells in the use of oxygen make up the last 20%. The breathing frequency, in normal conditions, is controlled by the carbon dioxide pressure in blood, but as altitude increases, it doesn’t raise in the same measure. So the body regulates breathing by saturating with oxygen the blood in the arteries. Hyperventilation leads to the exhalation of carbon dioxide and so it increases the oxygen content in pulmonary alveoli.

Cheyne-Stoke breathing

At night it would seem that we sometimes partially forget breathing. Suddenly, we realise this and we start breathing fast and deep, as a diver surfacing. When we sleep, such pauses in breathing are generally perceptible only to our tent mates. In most cases, these respiratory difficulties persist at the same altitude only for the firsts few nights.

Dangers at high altitude

Starting at 3000 m, climbing too fast leads to acute mountain sickness, and as a second consequence, it can cause altitude brain oedema or lung oedema. Not only oedemas represent a mortal threat. Lack of oxygen (hypoxia) can also cause a loss of performance of the body, which brings the possibility of accidents with, unfortunately quite frequently, fatal results.

Acute Mountain Sickness (AMS)

Most problems at high altitude are caused by climbing too fast after 3 000 m, which prevents an adequate adaptation to the lower partial oxygen pressures, a feature of these places. Physical condition and sex seem, after all, not to have a great incidence in the problems that could arise in altitude. The problems in altitude should affect in less degree older people because of their slower walking rhythm and their experience. Personal experience and the numerous expeditions that we have organized have shown us that every case of serious acute mountain sickness was somehow announced. Only the participants’ obsession with reaching the summit and not reckoning in the AMS symptoms have lead to jeopardize not only their own lives, but also their expedition mates’.

Slight symptoms

AMS symptoms start with slight dizziness, accompanied with an unsure step, fast breathing, loss of appetite, a slight headache, urinary retention and respiratory difficulties (dysnea) at nights. If these symptoms persist more than two days, some measures have to be taken.


Do not continue ascending until feeling better. Medication, in most cases, only hides the symptoms and lead to dangerous side effects. Thus, it is not advised to take any medicine, especially analgesics, sleeping pills or Diamox. The affected person must rest with the trunk straight, which helps breathing. Liquids should be taken often and in small quantities, even without thirst.

Serious symptoms

If the affected person continues to climb, the seriousness of the symptoms increases, too. The lack of appetite worsens, becomes nausea and triggers vomiting. Headaches get partially unbearable and Aspirin can barely help it. In addition, oedemas can appear in the hypodermis (the deepest skin layer). These are easy to recognise since they show through the swelling of eyelids, cheeks and fingers. Besides, the body is quite weakened and the affected person looks apathetic. In these cases, it is necessary to take immediate action. The person must descend until feeling better.


In most cases, a 300 m to 500 m descent usually leads to a fast and clear improvement. Additionally, all points mentioned in the slight symptoms section are important to look into. The person who craves for oxygen, in the mountains of Chile, is not in conditions to climb and should descend immediately.


If serious symptoms are ignored and the affected person does not descend, as a consequence the person could develop a high altitude cerebral oedema (HACE) and/or a high altitude pulmonary oedema (HAPO). If this happens, in most cases the descent will not be possible without external help, and the person is in danger of dying.

High Altitude Pulmonary Oedema (HAPE)

Starting at 3500 m, the blood pressure in the lungs increases. This facilitates the passage of blood plasma into the alveoli if there is a damaged membrane. Typical additional symptoms of HAPE are noisy breathing, coughing, bluish lips (cyanosis) and exhaustion. The noisy breathing symptom is due to the accumulation of fluids in the alveoli. After climbing too fast, the body doesn’t develop an oedema immediately, but there is a latency period of up to a day. According to our experience, oedemas often appear during the night and even while sleeping.


If at all possible, the descent must be undertaken immediately or at least to transport the affected person until he or she gets better. The descent can be backed by oxygen administration (4-6 lt/min) or medication (20 mg sublingual Nifedipin, each 6 hours). If for climatic reasons the person cannot be transported, there exists the possibility of using a hyperbaric chamber. If there is not one available, the only alternative is the continuous administering of oxygen (5 lt/min).

High Altitude Cerebral Oedema (HACE)

Not only HACE is rarer than HAPE, but in most cases, it appears higher than 5 000 m. HACE begins with the symptoms of acute mountain sickness (AMS) extending for several days. Because of the increased brain pressure, the oedema causes a strong headache, strange behavior, somnolence, speech trouble and confusion. The effects of cortisone preparations come from the diminution of brain pressure. As with HAPE, HACE often appears by night, even during sleep. Unlike HAPO, the affected person can no longer react or control the body movements. The person can no longer descend by himself, which elevates the mortality rate over 40%.


Administer cortisone as soon as possible (if you don’t know how to, the best way is by inhalation) followed by tablets of 4 mg, each 6 hours. Then transport the affected person with oxygen administration (4-6 lt/min). The person should get better within a few days.

Retina hemorrhage

Relatively frequently small clots form in the retina. Often, they are noticed only by other persons. They don’t need treatment and disappear by themselves.

Hyperbaric chamber (PAC, Certec or Gamov-bag) and oxygen

It consist of a polyamide bag which is adjusted with a manual pump to an overpressure of 220 mb (equivalent to 2 500 to 3 000 m of altitude). In order to use it, the person must not present breathing problems nor pressure compensation. Eventually, nasal drops must be given in order to diminish the inflammation in the nose mucose. The trunk must be kept slightly raised to an approximately 30º angle. Close the bag hermetically according to the instructions and inflate to the indicated pressure. Fresh air must be introduced into the pump every 5 minutes approx. Used air is automatically expelled through an overpressure valve. Pressure can be monitored through the included manometer or the altimeter situated in the chamber.

The chamber doesn’t replace the descent. After 1-2 hours of staying in the chamber, the patient is in conditions to descend or be transported without any danger. In addition, the person can take oxygen (4-6 lt/min) or medication.

Altitude cough

As altitude increases, absolute air humidity decreases. Dry air puts a strain in the mucose of the respiratory tract and causes dry coughing without expectorations. As a consequence, the irritated mucose form an ideal breeding ground for bacteria. Cough pills and lots of liquids have a preventive effect. Dry nasal mucose provokes nasal hemorrhage and bad sleep. Mentholated creams, easy to find in Chile, irrigate the nasal mucose keeping it humid. As an alternative, drops of an isotonic saline solution mixed with a couple of drops of glycerin can be used.

The use of medication to facilitate acclimatization

Diamox, Nifedipine and Dexamethasone

Personal ambition and the obsession to get to the summit lead, regrettably, nature-loving mountaineers to use doping with increasing frequency. Preparations like Diamox, for instance, are taken as prophylactics without any consideration for the side effects that could eventually arise (dehydration). Mountain climbing in South America, with summits of almost 7 000 m, doesn’t justify the use of acclimatization drugs, neither from the preventive point of view nor from the therapeutic one, therefore, serious mountaineers should not use them. Their use should be limited solely and exclusively to those cases of serious AMS and combined with a simultaneous descent.

Sleeping-pills or soporifics

Almost all soporific drugs reduce respiratory frequency during sleep, and therefore decrease the saturation of oxygen in the blood. For this reason they should not be taken at high altitudes. With adequate altitude acclimatization they shouldn’t be necessary.


Causes and prevention

Reports from well-known scientists in Antarctica and in arctic regions tell, of course, about glacial colds, but contrary to reports from mountain expeditions, they seldom talk about serious frostbite or even loss of extremities. The reason, as it often happens, is altitude and the loss of fluids that this causes. In addition, dry air in high altitudes irritates and even damages mucous membranes, since mucose is normally moistened by the air we breathe. Concerning oxygen, its low content in the body at high altitudes is compensated, as already mentioned, by hyperventilation. An increase in respiratory frequency because of this, naturally leads to less fluid loss. Besides, the absolute humidity of air is, anyways, very low due to low temperatures. Additionally, the efforts made during the climb also carry fluid loss through sweating. Last, but not least, the body feels less thirst at higher altitudes. All these are hostile factors that lead to an increase in blood viscosity, via the loss of fluids. The ratio of solid particles to fluids (plasma) in blood is called hematocrit and it is represented in percentages. Under normal conditions, this ratio raises to approximately 45%. At high altitudes this ratio goes up to 70% due to the already mentioned liquids or fluids loss. Now then, under these circumstances the smallest capillaries are not supplied with enough oxygen and heat because of the viscosity of the blood. In addition, at low temperatures the body concentrates in supplying oxygen and heat to the vital organs without wasting energy irrigating the other parts. For this reason, the most affected parts are fingers and toes, as well as the nose.

Preventing frostbite

Adequate equipment and drinking a lot of liquids are the most important measures, especially at high altitudes. Avoid using wet socks and shoes.

Degrees of frostbite

Frostbite is classified in three degrees. In the first degree, extremities numb and turn pale. After warming them, blood irrigation quickly resume and an ardor not unlike nettles is felt. After a few days, the discomfort diminishes. In the second degree of frostbite, blisters often form after warming the extremities, and there could even be tissue death, with their consequent blackening (necrosis). The inconveniences continue for several months, but in most cases they disappear entirely. In the third degree of frostbite, after a few days there is a serious loss of tissue, and blood blisters and a black coloration appear in the affected area. In most cases, the loss of the extremities is inevitable.

Treatment for frostbite

In cases of slight frostbite it helps to drink hot beverages, take off wet clothes and keep warm. You can also put your fingers under your armpits. The affected areas should never be rubbed with snow, nor warmed artificially. In case of serious frostbite, the person must be transported immediately (eventually, with the administration of analgesic medication) to be treated by a doctor as soon as possible. Artificial warming of body areas that are seriously frozen provokes extreme pain that can be controlled only with preparations of morphine, and can also generate dangerous swelling. Only in extreme situations and administering the strongest tranquilizers can an affected extremity be warmed in a water bath going form 10º C to 37º C in half an hour. Then, let dry in open air, bandaged it with sterilized material and pad it well with cotton.


In the central Andes, especially in the middle of summer (January / February) near midday, strong storms are formed. In high altitude zones, snowstorms are often formed that last about 2-3 hors, accompanied by lightning and thunder. If a person gets hit by lightning it has the same effect as touching a high voltage line: serious burnsheart attack , and death. The greatest risk is when the person is in open-air and at the highest point, which of course happens simply by walking on a flat surface. Equally risky is to remain in the water, for instance while swimming.

General indications on how to behave in case of lightning probabilities

  • Dense woods are relatively safe, however, avoid being near a lonely tree.
  • Do not walk erected, so you are not the highest point. If there is not a safe refuge nearby, look for a depression in the soil where you can crouch as tightly as possible, putting your knees on the backpack.
  • Strictly avoid small caves. Bigger caves with a distance of about two meters to the rock are, on the contrary, an appropriate shelter.
  • Do not carry metallic objects with you, as they could attract lightning.