Altitude sickness: causes, symptoms and diagnosis


Altitude sickness: causes, symptoms and diagnosis

Altitude sickness is also called acute mountain sickness (AMS), altitude illness, hypobaropathy, Acosta disease, puna and soroche. It is a disorder caused by being at high altitude where air pressure is low without prior acclimatization (the process of gradual exposure).

If altitude sickness does occur, it will do so at altitudes above 8,000 feet (2,500 meters) - 8,000 feet is a common height for many ski resorts.

More severe symptoms generally occur at above 3,600 meters (about 12,000 feet). Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).

People with altitude sickness typically have a bad headache, nausea, dizziness and feel exhausted. In this article, we will look at the causes, symptoms, diagnosis, treatment and prevention of altitude sickness.

Here are some key points about altitude sickness. More detail and supporting information is in the main article.

  • At higher elevations, the number of oxygen molecules per breath decreases
  • Rising to a high level without acclimatizing can cause fluid to build up in the lungs and brain
  • Once above 3,000 meters, about 75% of people will experience mild altitude sickness
  • Symptoms of altitude sickness include weakness, sleepiness and lack of appetite
  • The main causes are climbing to a great height too quickly or staying at that height for too long
  • Some evidence suggests there is a genetic component to altitude sickness
  • Diagnosis of altitude sickness only requires gathering information about the patient's recent history
  • There are a number of treatments for altitude sickness, but, firstly, the individual should slowly descend
  • To prevent altitude sickness, it is vital to acclimatize before ascending.

What is altitude sickness?

The higher one climbs, the less oxygen is taken in per inhalation.

At sea level the atmospheric concentration of oxygen is approximated 21% and the barometric pressure averages 760 mmHg.

At higher altitudes the 21% remains the same; however the number of oxygen molecules per breath is reduced.

At about 5,500 meters (18,000ft) each breath contains approximately half the normal amount of oxygen (compared to sea level).

In order to compensate for the oxygen shortfall the person has to breathe faster and their heart has to beat faster too.

Even though breathing faster raises blood oxygen levels, they do not reach sea level concentrations.

Rising to higher altitudes can also cause fluid to leak from tiny blood vessels (capillaries), resulting in potentially dangerous fluid accumulation in the lungs and/or the brain. If a human continues rising to higher altitudes without adequate acclimatization, there is a serious risk of life-threatening illnesses.

Researchers from the University of Edinburgh found that many mountain climbers tend to underestimate the risk of developing acute mountain sickness.1

According to the British National Health Service (NHS):

  • Mountain sickness is fairly common among skiers, mountaineers and people who spend time at high altitudes
  • At a height of over 3,000 meters (10,000 feet) about three-quarters of people will experience mild symptoms
  • 20% to 25% of Colorado (USA) skiers and 53% of Periche (Nepal) trekkers develop symptoms of altitude sickness
  • About 34% of people in the Swiss Alps who ascend to 3,600 meters (about 12,000 feet) or more experience some degree of altitude sickness.

It is not possible to get altitude sickness in places like the UK that do not have areas of necessarily high elevation. Ben Nevis in Scotland - the UK's highest mountain - is 1,344 meters (4,406 feet) high. No matter how fast you went up that mountain, you would not get altitude sickness.

Chronic mountain sickness vs. acute mountain sickness?

Chronic mountain sickness, also known as Monge's disease, develops after spending an extended time living at high altitude (over 3,000 meters). Acute mountain sickness is experienced shortly after ascending too rapidly to a high altitude.

Symptoms of altitude sickness

Severity of symptoms and when they begin depend on several factors, including:

  • The person - age, weight, blood pressure, general fitness, etc.
  • The speed at which people ascended
  • How long was spent at high altitude.

The primary symptom to diagnose altitude sickness is a headache. However, one of dehydration's symptoms is also headache.

Therefore, for proper diagnosis, experts say the patient needs to be at a height of at least 2,500 meters (8,000 feet), has a headache, as well as at least one of the signs and symptoms listed below:

  • Lack of appetite, nausea, or vomiting
  • Exhaustion or weakness
  • Dizziness (light-headedness)
  • Insomnia
  • Pins and needles
  • Panting (shortness of breath) upon exertion
  • Feeling sleepy (drowsiness)
  • General malaise
  • Swelling of the hands, feet and face (peripheral edema).

The following signs and symptoms may indicate something more serious, perhaps a life-threatening altitude sickness:

  • Fluid in the lungs (high altitude pulmonary edema):

    • Persistent dry cough, often with pinkish sputum
    • Fever
    • Panting (even while resting).
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  • Swelling of the brain (high altitude cerebral edema)

    • Persistent headache. Painkillers do not get rid of the pain
    • Unsteady gait, clumsiness
    • Increased vomiting
    • Gradual loss of consciousness
    • Numbness, and dizziness.
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Causes of altitude sickness

The main cause of altitude sickness is ascending too rapidly. It may also be caused by going too high and staying there for too long.

The human body needs time to adapt to altitude.

The human body needs to adapt to the lower air pressure and decreased levels of oxygen - for that it needs a gradual progression (acclimatization).

The average human body needs from 1-3 days to get acclimatized to a change in altitude.

People who do not spend enough time acclimatizing to a new altitude before going further up have the highest risk of developing altitude sickness.

Altitude sickness - our body's response to a lower oxygen supply to the muscles and brain - can become a serious and fatal condition.

If there is less oxygen in the blood, the heart and lungs have to work harder, raising the pulse and breathing rates. More red blood cells are made to enable the body to carry more oxygen. As our bodies respond to a change in altitude our blood acidity level, lung pressure, electrolyte levels and fluid and salt balance change.

Chronic mountain sickness appears to have a genetic component2 - a team from the University of California-San Diego discovered that two genes - ANP32D and SENP1 - are more common in people who suffer from chronic mountain sickness.

Measuring specific, exercise-related responses helps predict severe high altitude sickness3 - researchers from the Université Paris, France, reported in the American Journal of Respiratory and Critical Care Medicine that they could determine who is more likely to develop severe high altitude sickness by measuring oxygen desaturation at exercise and some other exercise-related body responses.


On the next page, we look at diagnosis, treatment, complications and prevention of altitude sickness.

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What is Altitude Sickness? (Video Medical And Professional 2020).

Section Issues On Medicine: Medical practice