Altitude sickness

For most people, it causes mild symptoms that improve with rest and with time spent getting used to altitude. However, in some people, it can lead to serious symptoms which can become life-threatening. This is particularly the case if the signs are not recognised and the person does not descend to a lower altitude.

As soon as the first symptoms of altitude sickness develop, the most important treatment is stop the ascent and rest. If the symptoms are severe, do not improve, or are getting worse, then descent to a lower altitude is essential. There are various preventative measures, the most important being slow ascent so that the body can adjust to conditions at the right pace (this is known as "acclimatising").

What is a high altitude?

• 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).

What are the normal responses of the body to altitude?

As altitudes increase, air pressure reduces. Air contains the same proportion of oxygen (21%) at high altitude as at low altitude. However, because there is a 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 taken contains fewer oxygen molecules. This means that people have to breathe faster and deeper to get enough oxygen. After a few days, the body starts to acclimatise to the higher altitude and the breathing rate starts to slow down again to normal. More red blood cells are also manufactured by the body to help with oxygen transport around the body.

Because of these bodily changes, there are some symptoms which are "normal" at higher altitudes whilst acclimatising and adjusting to the reduced availability of oxygen. They include:

• Faster, deeper breathing. An increased breathing rate or a feeling of breathing more deeply.

• Shortness of breath on exertion. A feeling of shortness of breath on doing exercise.

• Night breathing pattern. It is common to have a change in breathing pattern at night which is usually periods of hyperventilation (breathing more rapidly) interspersed with periods of hypopnoea (breathing more slowly and shallowly.

• Sleep problems. Disturbed sleep is very common at high altitude.

• Frequent urination. It is common for people to pass more urine than usual when at high altitude.

What is altitude sickness?

Altitude sickness is something that can affect people who travel to an altitude of more than 2500 metres, particularly if they ascend too quickly. It is rare at altitudes of less than 2500 metres (8,000 feet) - the height of a typical ski resort - and is more common at altitudes of 3500 metres (11,500 feet) or more.

Altitude sickness is due to the fact that the body has not acclimatised to a higher altitude. For most people, it produces mild symptoms that improve with rest and time spent at altitude. However, in some people, it leads 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 descend to a lower altitude.

There are three main elements of altitude sickness.

• Acute mountain sickness (AMS).

• High-altitude cerebral oedema (HACO or HACE). Oedema is spelt edema in some countries, so this condition is shortened to either HACE or HACO.

• High-altitude pulmonary oedema (HAPO or HAPE).

Each of these is explained in more detail later in the leaflet.

How common is altitude sickness?

This varies with the location and with the way people tend to ascend. It is more 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.

HACE and HAPE are much less common than AMS.

If proper preventative measures are taken (such as not ascending too fast), the risks of developing AMS can be reduced

Who is at risk of altitude sickness?

It is difficult to predict who will be affected by altitude sickness. However, the following increase the risks:

• Very quick ascent. Travelling to high altitude too quickly significantly increases the risks of altitude sickness. This may particularly be a risk if starting the trip by flying to an altitude of more than 2750 metres, or 9,000 feet.

• Place of origin. People who have come from, and are used to living in, a very low altitude are at higher risk of altitude sickness.

• History of altitude sickness. People who have had altitude sickness before are more likely to develop it again. However, people who have travelled to high altitudes previously without altitude sickness still have the possibility of developing it in the future.

• Genetics. There may be a genetic susceptibility to developing altitude sickness.

• Exertion. People who are more active at altitude are more likely to develop altitude sickness.

Note: The level of physical fitness does not seem to play a part in the chance of developing altitude sickness. Being more or less fit does not affect the risk of developing altitude sickness. However, people who are more fit may be tempted to try to ascend too quickly.

Can altitude sickness be prevented?

There are a number of things 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 the body to adjust to the conditions (acclimatise). It allows the body to cope with lower oxygen levels. Different people will acclimatise at different rates.

• There are recommended rates of ascent to altitude to help with acclimatisation:

  • If possible, spend at least one night at an 'intermediate' elevation below 3000 metres.

  • Above 3000 metres, increase the sleeping altitude by only 300-500 metres per day.

  • Above 3000 metres, take a rest day for every 1000 metres of elevation gained (ie spend a second night at the same altitude).

  • If possible, don't fly or drive directly to high altitude.

• People going directly to high altitude by car or plane should not over-exert themselves or move higher for the first 24 hours.

• It is best to try to sleep at a lower altitude. Climbers commonly use the phrase, "climb high, sleep low".

• It is advisable to take special care if having previously had acute mountain sickness (AMS).

• When planning an ascent as a group, it is important to plan for members acclimatising at different rates.

• If symptoms of AMS develop, further ascent needs to be delayed.

• If symptoms become worse, descent as soon as possible is essential.

Acute mountain sickness

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.

Acute mountain sickness symptoms

For most people, AMS gives 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 feeling sick (nausea). Other possible symptoms are being sick (vomiting), feeling light-headed or dizzy and having difficulty sleeping.

These symptoms tend to come on 6 to 12 hours after arrival at a particular altitude. Which altitude causes this depends on the individual person and situation. Symptoms usually get better after 1 to 3 days, provided that there is no further ascent to a higher altitude. Symptoms can vary from mild to severe. Mild symptoms can be quite vague. If at altitude and feeling unwell, it is best to assume that the cause is AMS unless there is another obvious cause.

The Lake Louise score is a scoring system to assess the chances of having AMS when feeling unwell and to help make the diagnosis.

The scoring is as follows:

A total score of 3 to 5 = mild AMS and 6 or more = severe AMS. Remember that any symptoms at altitude are altitude illness until proven otherwise.

What is the treatment for AMS?

• Stop the ascent. The most important treatment if starting to develop symptoms of mild AMS is to stop the 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.

• Painkillers. Simple painkillers such as ibuprofen or paracetamol will help the headache.

• Anti-sickness medication may also be used.

• Acetazolamide. Medicines are sometimes prescribed to help with AMS. The most common is a medicine called acetazolamide. Acetazolamide can be used for the prevention as well as treatment of AMS. It is thought that acetazolamide helps to 'speed up' the acclimatisation. Acetazolamide should not be provided by NHS GPs but is usually available from private travel clinics. A common side-effect with acetazolamide is pins and needles.

• A steroid medication called dexamethasone may be an alternative as a treatment. Sometimes oxygen treatment may be used.

• Descend to a lower altitude. If symptoms are severe, do not improve after 24 hours, or are getting worse, it is essential to descend to a lower altitude. Urgent descent is also needed if any of the symptoms or signs of HACE or HAPE (see below) develop.

• Dexamethasone. There is also evidence that dexamethasone can be used to prevent AMS. However, this is not recommended for routine use in travellers to high altitudes.

• Ibuprofen. Studies suggest that this does reduce the risk of altitude sickness but is not used as a treatment for altitude sickness. It is less effective than acetazolamide so is not recommended for altitude sickness prevention. There is some suggestion that it merely reduces the Lake Louise score by eliminating the headache.

• Alternative treatments. There is no reliable evidence for any other medications (including gingko biloba) at present. In some parts of South America travellers to high altitude may be offered coca leaves. These can be used to make tea or the leaves can be chewed. These are known to act as a mild stimulant but there is no evidence they help prevent AMS.

High-altitude cerebral oedema (HACE)

HACE usually develops in someone who already has AMS. The swelling of the brain that has led to AMS gets worse and starts to interfere with the function of the brain. HACE is effectively a severe form of AMS.

Symptoms of HACE

Symptoms of HACE include:

• Headache, which may be very severe.

• Feeling sick (nausea).

• Being sick (vomiting).

• Being uncoordinated, unsteady or off-balance.

• Hallucinations (for example, seeing or hearing things that are not actually there).

• Feeling disorientated.

• Feeling confused.

• Having seizures.

Often these symptoms are not noticed by the person who is developing HACE, or by their companions. As the cerebral oedema gets worse, people become more sleepy and less aware of their surroundings. They may have fits (seizures). Coma and death can occur if treatment is not started.

HACE can develop quickly, over a few hours. It is possible to have symptoms of high-altitude pulmonary oedema (HAPE) as well, ie to have both conditions at the same time. See below for information about HAPE.

What is the treatment for HACE?

• Descent. This is a move down (a descent) to a lower altitude immediately. If this does not happen, or is delayed, death can occur. It may be necessary to descend at night, if this is possible, and this could be life-saving.

• 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.

• Portable hyperbaric chamber. 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 HACE is placed inside it and it can provide the same effect as (simulate) descent. The person will be breathing air equivalent to that at much lower altitude. This can be life-saving when descent is not possible and oxygen is unavailable.

What is the prognosis for HACE?

People with HACE usually do well if they descend to a lower altitude soon enough and far enough. The outlook (prognosis) is that they will usually have a complete recovery.

High-altitude pulmonary oedema

'Pulmonary' refers to the lungs and 'oedema' means that there is a build-up of fluid. So, pulmonary oedema is a build-up of fluid within the lungs. The exact reasons why HAPE 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 to smaller blood vessels becoming 'leaky'. This allows fluid to escape from the blood vessels into the lungs.

What are the symptoms of HAPE?

If someone develops HAPE, the symptoms usually start to appear a few days after arrival at altitude.

• Shortness of breath. Symptoms start with shortness of breath on exertion. It then worsens, so that there is shortness of breath even when resting.

• Weakness. People affected feel generally weak and tired.

• Cough. They may develop a cough and start to cough up pink/frothy liquid (sputum) and complain of chest tightness.

• Ankle swelling. They may have swelling of their ankles or legs.

• Blue lips. Their lips or fingernails may be blue or grey.

• Drowsiness. In severe cases they become extremely short of breath at rest and drowsy.

• Coma. Coma and death can occur if HAPE is not treated quickly.

HAPE can happen in someone who also has AMS or HACE, or they may have no obvious symptoms of these other problems.

What is the treatment for HAPE?

• Descent. Again, someone with HAPE needs to 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.

• Oxygen and nifedipine. Treatment with oxygen and the medicine nifedipine may also help symptoms but does not replace the need for descent.

• A hyperbaric chamber (as explained above) can be used if descent is not possible and/or oxygen and other treatment are not available.

What is the prognosis for HAPE?

HAPE tends to get better quickly on descent. Outlook (prognosis) is that there is usually complete recovery.