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Altitude Sickness occurs when the body struggles to adapt to reduced oxygen levels at high elevation. Symptoms include headache, nausea, dizziness, and fatigue, with severe cases potentially leading to life-threatening conditions like High-Altitude Pulmonary or Cerebral Oedema. Gradual acclimatisation, hydration, and descending to lower altitudes are key to prevention and management.
Altitude Sickness, also known as Acute Mountain Sickness (AMS), is a condition that can affect individuals when they rapidly ascend to higher altitudes, typically above 8,000 feet (2,400 metres). It occurs due to the body’s difficulty in adapting to the reduced oxygen levels and lower air pressure at higher elevations.
Symptoms of altitude sickness may include headache, nausea, fatigue, dizziness, shortness of breath, and disturbed sleep. In more severe cases, it can lead to High-Altitude Pulmonary Oedema (HAPO) or High-Altitude Cerebral Oedema (HACO), both of which are potentially life-threatening conditions.
Altitude sickness can affect anyone, regardless of age or fitness level, and its severity can vary among individuals. Gradual acclimatisation, staying hydrated, avoiding alcohol and intense physical exertion, and, in severe cases, descending to lower altitudes are essential measures to prevent and manage altitude sickness.
Consulting healthcare professionals before ascending to high altitudes and being aware of the signs and symptoms of altitude sickness is crucial for safe and enjoyable mountain travel.
Altitude sickness is something that can affect people who climb or travel to an altitude of more than 2500 metres, particularly if they climb or travel up (ascend) too quickly. Symptoms usually develop between 6 and 24 hours after reaching high altitude.
Altitude sickness is rare at altitudes of less than 2500 metres (8,000 feet) and is more common at altitudes of 3500 metres (11,500 feet) or more. To give an idea, you can commonly ski at an altitude of 2500 metres in a ski resort.
Altitude sickness is due to the fact that your body has not got used (acclimatised) to the altitude that you are now at. For most people, it produces mild symptoms that improve with rest and time spent at altitude. However, in some people, it can lead to more serious symptoms which can become life-threatening. This is particularly a risk if the signs are not recognised and the person does not move down (descend) to a lower altitude.
Common symptoms of altitude sickness include: headache, nausea, vomiting, dizziness, tiredness, loss of appetite and shortness of breath. Symptoms are often worse at night.
The most important treatment if you develop symptoms of altitude sickness is to stop your ascent and rest. If your symptoms are severe, do not improve, or they are getting worse, you need to descend to a lower altitude. There are various preventative measures, the most important being slow ascent so that your body can adjust to conditions at the right pace.
There are three main ways that altitude sickness can affect you. You may develop one or more of the following:
High altitude is an altitude between 1500-3500 metres (5,000-11,500 feet).
Very high altitude is an altitude between 3500-5500 metres (11,500-18,000 feet).
Extreme altitude is an altitude above 5500 metres (18,000 feet).
As you ascend to higher altitudes, air pressure reduces. Air still contains the same proportion of oxygen (21%) at high altitude. However, because of the lower air pressure, there is less oxygen available because the air is thinner (it contains less of all of the gases in a given volume). So, at high altitude, each breath that you take will contain fewer oxygen molecules. This means that you have to breathe faster and deeper to get oxygen into your body.
After a few days, your body starts to adjust to the higher level of altitude that you are at. You will notice that your breathing rate will start to slow down. Your body also makes more red blood cells to help with oxygen transport around your body. Because of these changes in your body, there are some ‘normal’ symptoms that you will notice at higher altitudes while your body is acclimatising and adjusting to the reduced availability of oxygen. They include:
This varies with the location and with the way people tend to ascend. It is common in places where visitors try to ascend very quickly – for example, climbing Mt Kilimanjaro. It is also more common in places where it is possible to fly to a high altitude to start with, before climbing further. This is the case, for example, with the Everest Base Camp trek in Nepal, where the trek often begins by flying to Lukla at an altitude of 2860 metres (9,000 feet). Up to half of trekkers may develop altitude sickness in this situation. In Colorado, about a quarter of visitors sleeping higher than 2500 metres (8,000 feet) develop altitude sickness.
HACO and HAPO are much less common than AMS. If proper preventative measures are taken (such as not ascending too fast), AMS can be less common.
Altitude sickness does not only affect mountain climbers. Tourists travelling to cities that are 2500m above sea level or higher, such as La Paz in Bolivia or Bogotá in Colombia, can also get altitude sickness.
It is difficult to predict who will be affected by altitude sickness, however, your risk is higher:
Note that your age, sex, and level of physical fitness does not seem to play a part in your chances of developing altitude sickness. Being more fit does not make you more likely to develop altitude sickness, however, if you are more fit, you may be tempted to try to ascend too quickly.
There are a number of measures that may help to prevent altitude sickness. The best way to try to prevent altitude sickness is to ascend to higher altitudes slowly. This gives time for your body to adjust to conditions. It allows your body to cope with lower oxygen levels. Different people will acclimatise at different rates.
It is recommended that you avoid flying directly to areas of high altitude, wherever possible. It is advisable to take 2-3 days to get used to high altitude before ascending above 2500m.
There are suggested rates of ascent to altitude to help with adjusting to conditions:
Other measures to help prevent altitude sickness include keeping warm and well hydrated, avoiding smoking and alcohol, eating a light but high-calorie diet and avoiding strenuous exercise.
If you do go directly to high altitude by car or plane, do not over-exert yourself or move higher for the first 24 hours.
Always try to sleep at a lower altitude. Climbers commonly use the phrase, “climb high, sleep low”.
Take special care if you have previously had Acute Mountain Sickness (AMS).
When planning an ascent as a group, plan for members acclimatising at different rates. How will you support those remaining behind to recover from AMS?
If symptoms of AMS develop, delay further ascent. If symptoms become worse, descend as soon as possible.
The exact cause of AMS is not exactly known. It is thought to be a response of the brain to the lower oxygen levels in the blood at higher altitudes. This produces some swelling of the brain.
AMS Symptoms
For most people, AMS will give mild symptoms. Sometimes these are described as being rather like the symptoms of a hangover. Common symptoms can include headache, loss of appetite, tiredness and nausea. Other possible symptoms are vomiting, feeling light-headed or dizzy, having difficulty sleeping and visual disturbances.
These symptoms tend to come on 6 to 12 hours after arrival at a particular altitude. At which altitude this is will depend on the individual person and situation. Symptoms usually get better after 1 to 3 days, provided that you do not ascend to a higher altitude. Symptoms can vary from mild to severe. Mild symptoms can be quite vague. It is best to assume that, if you are at altitude and you feel unwell, you have AMS unless there is another obvious cause.
If you experience any of these symptoms at altitude and wonder whether you have AMS, you can score yourself to find out.
The Lake Louise Scoring System
The Lake Louise score is a scoring system used to make a diagnosis of AMS. This is something you can do yourself to decide how severe your symptoms are and what they mean. The scoring is as follows:
Symptom
|
Severity & Score |
Headache | No headache – 0 |
Gut (Gastrointestinal) Symptoms | None – 0 |
Fatigue and/or Weakness
| Not tired or weak – 0 Mild fatigue/weakness – 1 Moderate fatigue/weakness – 2 Severe fatigue/weakness – 3 |
Dizziness/Light-Headedness
| Not dizzy – 0 |
Difficulty Sleeping
| Slept as well as usual – 0 |
Remember that any symptoms at altitude are altitude illness until proven otherwise.
AMS Treatment
The most important treatment if you start to develop symptoms of mild AMS is to stop your ascent and to rest at the same altitude. For most people, symptoms will improve within 24-48 hours with no specific treatment. Acclimatisation usually occurs after 1 to 3 days at a given altitude.
Simple painkillers such as Ibuprofen or Paracetamol will help the headache. Anti-sickness medication may also be used. Other medicines are sometimes prescribed. The most common is a medicine called Acetazolamide which can be used to reduce the severity of symptoms. Acetazolamide can also be given to prevent AMS. It is thought that Acetazolamide helps to ‘speed up’ your acclimatisation. The usual dose of Acetazolamide for prevention is 125mg twice a day. A common side-effect with Acetazolamide is pins and needles. A steroid medication called Dexamethasone may be an alternative. Sometimes oxygen treatment may be used.
If your symptoms are severe, they do not improve after 24 hours, or they are getting worse, you need to descend to a lower altitude. You also need to descend urgently if you develop any symptoms or signs of HACO or HAPO (see below).
HACO usually develops in those who already have AMS. The swelling of the brain that has led to AMS gets worse and starts to interfere with the function of the brain. HACO can be considered to be a very severe form of AMS. People with HACO usually have a complete recovery if they descend to a lower altitude soon enough and far enough.
HACO Symptoms
Symptoms of HACO include:
These symptoms can develop quickly, over a few hours and are often not noticed by the person who is developing HACO, or by their companions. As the cerebral oedema gets worse, people become more sleepy and less aware of their surroundings. They may have fits. Coma and death can occur if treatment is not started immediately.
HACO Treatment
It is imperative to descend to lower altitude immediately. If this does not happen, or is delayed, death can occur. It may be necessary to descend at night.
Treatment with Oxygen (if possible) and the steroid medicine Dexamethasone can help to relieve symptoms and can mean that getting someone down to a lower altitude becomes easier. However, these treatments do not remove the need for descent. The descent should be at least to the last altitude at which the person woke up feeling well.
A device called a portable hyperbaric chamber may be used. It is, essentially, an airtight bag big enough for a person to fit in, that is pressurised by a pump. The person with HACO is placed inside it and it can provide the same effect as descent. The person will be breathing air equivalent to that at much lower altitude. This can be lifesaving when descent is not possible, and Oxygen is unavailable.
Pulmonary Oedema is a build-up of fluid within the lungs. The exact reasons why HAPO can develop are unknown. It is thought that the high altitude causes an increase in pressure in some of the small blood vessels of the lungs which leads them to become ‘leaky’. This allows fluid to escape from the vessels into the lungs.
HAPO Symptoms
Symptoms of HAPO usually start to appear a few days after arrival at altitude. Symptoms start with shortness of breath on exertion. This then worsens, so that there is shortness of breath even when resting. People affected can also develop a cough and feel generally weak and tired. They may start to cough up pink/white frothy sputum and complain of chest tightness. They may have swelling of their ankles or legs and their skin, lips or fingernails may be blue or grey. In severe cases, they become extremely short of breath at rest and drowsy. Coma and death can occur if HAPO is not treated quickly.
HAPO can occur in someone who also has AMS or HACO, or they may have no obvious symptoms of these other problems.
HAPO Treatment
Someone with HAPO must descend to a lower altitude immediately. Even a descent of a few hundred metres can make a difference but ideally descent should be to the point where symptoms are better. Treatment with Oxygen and the medicine Nifedipine may also help symptoms but does not replace the need for descent.
A hyperbaric chamber can be used if descent is not possible and/or Oxygen and other treatment are not available.
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