Altitude sickness

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Altitude sickness is a reaction to the lower amounts of oxygen available at high altitudes (due to the lower air pressure). Your body will respond in various ways to this: some are normal, some are illnesses. The illnesses are a serious health hazard and if left unchecked can kill you.

Table of contents
	altitude sickness Travel Guide : 1 Understand 1.1 How high is high? 1.2 Risk factors 2 Effects of altitude 2.1 Hyperventilation 2.2 Altitude diuresis 2.3 Periodic breathing 3 Illnesses at altitude 3.1 Dehydration 3.2 AMS 3.3 HACE 3.4 HAPE 4 Prevention 4.1 Keep hydrated 4.2 Acclimatize to altitude gradually 4.3 Avoid rapid ascents 5 Treatment 5.1 Acetazolamide 6 External links

Understand

The body has two main problems with high altitude:

• Thinner air has less oxygen. Your body adjusts to this by making more red blood cells to carry oxygen more efficently. Most of this happens while you sleep. However, the process can take days and in the meanwhile, you may be ill.
• At lower air pressure, water evaporates faster. This can lead to dehydration.

The changes to your body at altitude are complex and can be quite dramatic. Some changes are normal, some are signs of illness. The difficulty your body has maintaining a good oxygen supply and keeping related problems under control is directly related to how high up you are, and also to recent changes in your altitude. These are the two major factors that cause altitude sickness.

Hence this article talks a lot about ascent and descent. Ascending further away from sea level is the risky activity and the time you must be alert. Conversely, descending towards sea level is the single major factor that helps with moderate to severe altitude sickness.

Altitude sickness is very dangerous for four reasons: its rapid progression; its deadliness; the fact sufferers are usually some distance from medical help and are difficult to evacuate swiftly; and the fact that in many cases sufferers are reliant on their health because they're doing a lot of physical activity in dangerous environments.

How high is high?

A minority of people, something like 20%, have some symptoms of altitude sickness if they ascend to at about 2500 meters (8000 feet) above sea level and sleep there. Many ski resorts and even major cities are located at or above this altitude: it's very rare but it's not entirely unheard to die of altitude sickness at US ski resorts. However, most people will acclimatise to 3000 meters (10000 feet) with relative ease, perhaps having symptoms after the first night.

Acclimatising to heights of 3000 - 5000 meters (10000 - 16000 feet) is much more difficult, and it is here that it is absolutely necessary to ascend slowly and return to a lower camp to sleep. Over 50% of people will develop AMS (below) if they ascend rapidly to 3500 meters (11500 feet) without acclimatisation, and everyone will if they ascend rapidly to 5000 meters.

It is meant to be impossible to permanently acclimatise to heights above 5500 meters (18000 feet). It's possible to spend several weeks sleeping as high as 6000 meters (19500 feet) once acclimatised.

Altitudes above 7500 meters (25000 feet) are referred to as the death zone: you will deteriorate noticeably while you remain at such high altitudes, some of your body's major systems will shut down and climbers will only remain there for two or three days. Death rates from altitude sickness above 7000 meters are estimated at 4% of all people who venture that high.

Risk factors

The only reasonably reliable test of whether or not you will struggle with altitude or cope with it comparatively easily is previous experience of high altitudes. If you've ascended without sickness before you're reasonably likely to do it again; if you've had altitude sickness before, you're likely to have it again, although slowing your ascent rate may help.

Physical fitness is not necessarily a good indicator, and neither are strength or good health. You may react badly to altitude despite being fit, young and healthy. In fact, the fit, young and healthy have a hidden risk: their general physical capacity leads them to believe that they should handle altitude just fine, which is not always true. Unless you have previous experience at high altitudes, you should regard yourself as as likely to become ill from it as anyone else.

Bad health, on the other hand, is a risk factor: particularly cardiac or respiratory problems. Healthy hearts and lungs have a hard enough time getting oxygen to your tissues at high altitudes. Naturally, if you have physical problems that make exertion difficult for you, you have reason to think carefully about exertion at high altitude, where it is much harder!

Effects of altitude

Hyperventilation

You will naturally breathe faster at higher altitudes to compensate for the lower air pressure. It's possible you won't notice this: a similar effect happens during air travel.

Altitude diuresis

Your body will try and concentrate your blood to compensate for the lack of oxygen. This will make you urinate a lot at altitude. If you aren't urinating much more than you usually would, then you might actually be dehydrated.

Periodic breathing

Because of the disruption to oxygen and carbon dioxide levels in your blood due to the body chemistry changes and hyperventilation that occurs at altitude, your body's "when to breathe" chemical signals become confused. While you're awake you will remember to breathe, but when you sleep it is common to have interrupted breathing: holding your breath for up to fifteen seconds and then breathing very rapidly when you start breathing again.

This can be very alarming when you wake up knowing that you weren't breathing or were short of breath; or when you notice someone else has stopped breathing. But it is a normal response to altitude, and happens to almost everyone. Acclimatisation only improves it a little.

Illnesses at altitude

Dehydration

You need to drink a lot of water at high altitudes. If you don't, you will dehydrate. Unfortunately, it is easy to mistake dehydration headaches for AMS (below) headaches and vice versa. If a headache does not improve after you drink water and take a paracetamol painkiller, it is more likely to be AMS than dehydration.

AMS

Acute mountain sickness (AMS) is the most common unhealthy response to altitude: it's a collection of signs that your body is becoming ill and has not adapted successfully to a higher altitude.

For your own safety, assume any illness at altitude is AMS. The most common reasons that people fail to descend as soon as they should are bad assumptions:

• having AMS is a sign of weakness
• your level of fitness means you can't have AMS
• this feels like flu; it isn't AMS
• etc.

If you've recently ascended, and you have a headache and any other symptom, you have AMS. The other signs of AMS vary for different people, but include:

• fatigue
• dizziness
• loss of appetite
• nausea or vomiting
• confusion
• difficulty walking (called gait ataxia)
• rattling breath
• feeling generally extremely ill

The last three signs in particular are signs that you are becoming quite ill, but you should not wait for the onset of these symptoms before acknowledging you have AMS: they're fairly reliable indicators of the onset of HACE or HAPE.

You and your party should keep an eye on each other for signs of AMS, and if you have AMS, for signs of it worsening. Very sick people can become confused and not realise how ill they are.

If you have symptoms of AMS, do not ascend further. Consider descending.

If you have signs of HACE or HAPE, descend immediately. Your life may depend on it.

HACE

High altitude cerebral edema (HACE) is the end-stage of AMS (conversely AMS can be thought of as the mild form of HACE). When you have HACE, your brain swells and stops working properly.

HACE symptoms include a number of signs of mental functions failing: confusion, fatigue and weird behaviour. But the most reliable one is gait ataxia, and you can test it by walking heel to toe along a straight line on the ground. Healthy people can pass this test easily, anyone who has difficulty balancing while they do it is showing signs of HACE.

HACE is extremely serious, and you may only have a few hours to help someone with HACE.

HAPE

High altitude pulmonary edema (HAPE) is another severe altitude illness. It sometimes occurs in conjunction with AMS or HACE, but sometimes doesn't -- it's thought to have different causes. When you have HAPE, your lungs fill with fluid. Signs include extreme fatigue; breathlessness (when not due to periodic breathing -- give yourself 30 seconds to recover upon waking); a cough, especially if it is wet and has blood in it; rattling or gurgling breath; chest congestion; and blue extremities. A fever is sometimes present. It most commonly sets in at night.

HAPE is another extremely serious illness, and like HACE should be treated as a critical emergency.

Prevention

Keep hydrated

Remember to drink a lot. At 3500 meters, make sure you drink at least 3 litres of water every day. That means, two large bottles of water. Do not leave anything in the bottom, drink it all, even if it feels bad. If you ascend from there, drink even more. A head-ache is the punishment for those who do not heed this advice, and that feels worse.

Acclimatize to altitude gradually

Acclimatization is the process of getting your body to adapt to the lower oxygen levels by ascending slowly into higher altitudes, spending some time at each one to adapt.

For mountain climbers, a typical strategy is to spend a day (or initially part of a day) at a higher altitude and return to a lower base camp to sleep. Here are some recommended ascent rates that will stop most people from proceeding to AMS:

• 1500 meters (5000 feet) per day to an altitude of 3000 meters (10000 feet)
• Increase your sleeping elevation (the height of your camp) by 300 meters (1000 feet) per night after 3000 meters.
• Every 1000 meters (3000 feet), you should spend a second night at the same altitude. This will be every fourth night if you've been ascending at the maximum pace recommended above.

During acclimatisation, drink a lot of non-alcoholic drinks. Some people find vegetarian food slightly accelerates the acclimatisation. Local recipes like mate de coca in Peru (tea from coca leafs) are fine, but its effect is doubtful.

Avoid rapid ascents

Rapid ascents are the opposite of acclimatization; you make a rapid ascent when you're gaining altitude faster than recommended. This may mean climbing and camping higher than recommended, but you can also make an even more rapid ascent by driving to a high altitude location, and flying from low altitude to high altitude is an even more rapid ascent.

Where possible, avoid ascents more rapid than recommended above, particularly any sudden ascent to 3000 meters or higher. Even if you are taking Acetazolamide (below) a rapid ascent makes it more likely you'll get AMS and makes AMS progress to serious illness faster, so you will have less time to respond and descend.

Consider road or rail travel rather than flying directly to somewhere with a very high altitude. Or fly in stages, stopping somewhere at moderate altitude in between. For example, flying from sea level to Lhasa Tibet (3650 meters) is distinctly unwise. If you must fly, at least spend a few days at some intermediate destination such as Kunming (2700 meters) en route. If flying to a more moderate altitude above 2500 meters, you will still want to spend several nights at that altitude before setting off into higher country. Refrain from smoking and alcohol when you arrive by plane in a high altitude area from lower altitudes.

Be particularly wary with oxygen equipment: some tourists have died at altitude when their equipment failed and they were utterly unacclimatized.

Treatment

As soon as the symptoms of AMS appear, your first priority is recovering. You must not ascend any further until the symptoms have disappeared. This may take up to 48 hours, if it takes longer, descend. You could also descend on the onset of symptoms, this will make them disappear much faster, probably within hours.

If you are getting sicker or showing signs of HACE or HAPE, you must descend to a lower altitude as quickly as possible. If it is nighttime, do not wait for morning if you have a choice at all. You should descend at least as far as you were the last night you had no AMS symptoms. You may need to seek hospital care.

People with HACE and HAPE are frequently confused or exhausted, and are likely to need help with the descent. Help them down!

There is some equipment available to treat people with HACE or HAPE at high altitudes, including hyperbaric bags in which the sufferer can lie in a higher pressure atmosphere. These do buy some time if it is too dangerous to descend, but are not a substitute for descent.

Acetazolamide

This drug (sold as Diamox) stimulates your breathing. It has the effect of increasing acclimatisation rates; improving periodic breathing; and helping people recover from AMS more quickly. There are some side effects but it's useful for people who have had AMS in the past; people on a forced ascent (for example, flying into Tibet); and anyone who has AMS, particularly if they are choosing not to descend. Many climbers also take it preventively.

Acetazolamide is not a absolute preventative measure, particularly in the case of forced ascents.

External links

• 1 (http://www.thebmc.co.uk/world/mm/mm0.htm) British Mountaineering Council - Mountain Medicine Centre

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