What is altitude sickness

Altitude sickness also called acute mountain sickness, can occur when you travel to a high altitude too quickly. Altitude sickness (acute mountain sickness) is caused by your body’s reaction to the reduced oxygen level in the air at altitudes above about 2,500 meters (8202 ft) and resultant tissue hypoxia ¹. Altitude sickness occurs when your body has not had time to adjust to less oxygen.

The incidence of altitude sickness increases with increasing altitude. Up to half of people who ascend to heights above 2500 meters (8202 ft) may develop acute mountain sickness, pulmonary edema (high altitude pulmonary edema) or cerebral edema (high altitude cerebral edema), with the risk being greater at higher altitudes, and with faster rates of ascent ². While altitude sickness (acute mountain sickness) is very uncommon under 2500 meters (8202 ft), the percentage of non-acclimated travelers affected at 3000 meter approaches 75%. Any travelers with prior episodes of altitude sickness are at greater risk than those who have tolerated similar trips in the past ¹.

Altitude sickness can affect anybody – being young or physically fit does not decrease your risk of getting altitude sickness. And just because you haven’t had it before doesn’t mean you won’t develop it on another trip.

If you have a medical problem that affects your lungs, heart or circulation, you are at increased risk of getting altitude sickness. The most common conditions in this category include anemia, with a reduced oxygen-carrying capacity of the blood, and chronic obstructive pulmonary disease (COPD), due to the reduced degree of oxygenation occurring in the lungs.

Whether or not you get altitude sickness could depend on:

• your height above sea level
• the time you took to make the ascent
• whether or not you have any problems affecting you heart and lungs

If you have signs of altitude sickness affecting your lungs or your brain, this is a medical emergency. You need help to descend as soon as possible. Breathing oxygen from a tank can help. Altitude sickness can be fatal if not treated.

Where does altitude sickness happen?

Most people remain well at altitudes of up to 2,500m (8202 ft), the equivalent barometric pressure to which aeroplane cabins are pressurised. However, even at around 1500m above sea level you may notice more breathlessness than normal on exercise and night vision may be impaired. Above 2,500m (8202 ft), the symptoms of altitude sickness become more noticeable.

Can I take drugs to prevent altitude sickness?

As with everything, many ‘quack’ treatments and untested herbal remedies are claimed to prevent mountain sickness. These treatments can make altitude sickness worse or have other dangerous side effects – many herbs are poisonous. Only one drug is currently known to prevent altitude sickness and to be safe for this purpose: acetazolamide (Diamox). It causes some minor side effects, such as tingling fingers and a funny taste in the mouth.

Who gets altitude sickness?

Anyone who travels to altitudes of over 2500m (8202 ft) is at risk of acute mountain sickness. Normally it doesn’t become noticeable until you have been at that altitude for a few hours. Part of the mystery of acute mountain sickness is that it is difficult to predict who will be affected. There are many stories of fit and healthy people being badly limited by symptoms of acute mountain sickness, while their older companions have felt fine.

There are a number of factors that are linked to a higher risk of developing altitude sickness. The higher the altitude you reach and the faster your rate of ascent, the more likely you are to get acute mountain sickness. On the Apex high altitude research expeditions, flying from sea level to the Bolivian capital, La Paz (3600m), caused over half of the expedition members to have acute mountain sickness on the day after they arrived. If you have a previous history of suffering from acute mountain sickness, then you are probably more likely to get it again. Older people tend to get less acute mountain sickness – but this could be because they have more common sense and ascend less quickly.

Figure 1. Gamow bag for treating altitude sickness

Altitude sickness causes

Two things are certain to make altitude sickness very likely – ascending faster than 500m (1640 ft) per day, and exercising vigourously. Physically fit individuals are not protected – even Olympic athletes get altitude sickness. Altitude sickness happens because there is less oxygen in the air that you breathe at high altitudes, but how this shortage of oxygen actually leads to altitude sickness is still not fully understood.

Some scientists believe that altitude sickness is due to swelling of the brain but the evidence for this hypothesis is not conclusive. The theory is that in susceptible individuals, brain swelling could cause a small increase in the pressure inside the skull and lead to symptoms of acute mountain sickness. The swelling may be due to increased blood flow to the brain or leakiness of blood vessels in the brain.

Altitude sickness signs and symptoms

The hallmark of altitude sickness (acute mountain sickness) is a headache, with other symptoms including nausea, vomiting, loss of appetite, fatigue/malaise (particularly at rest), sleep disturbance, and dizziness/lightheadedness ¹. Altitude sickness can feel like a bad hangover. Altitude sickness (acute mountain sickness) symptoms can begin after only a few hours and typically present the first day at a given altitude, resolving after one to three days, even without treatment, as the body adjusts physiologically (acclimates) to the lower oxygen levels.

The presence of facial or extremity edema can be present with or without altitude sickness symptoms and is felt to be a marker for not yet being acclimated to the altitude. Rarely, retinal hemorrhages can occur and affect visual fields.

Altitude sickness symptoms are similar to those of a bad hangover. They include:

• headache
• nausea and vomiting
• dizziness
• tiredness
• loss of appetite
• shortness of breath

The symptoms are usually worse at night.

Altitude sickness can affect your lungs, in which case it is sometimes known as high altitude pulmonary edema or HAPE. People with HAPE (high altitude pulmonary edema) can feel short of breath and have a cough and a racing heart. In extreme cases, their lips turn blue.

Altitude sickness can also cause your brain to swell with fluid, which is sometimes known as high altitude cerebral edema or HACE. People with HACE (high altitude cerebral edema) can feel confused and irritable and behave in an erratic way.

Altitude sickness can be worse at night and can last for days, even if you stay at the same altitude.

3 forms of altitude sickness

Mild altitude sickness is called acute mountain sickness and is quite similar to a hangover – it causes headache, nausea, and fatigue. This is very common: some people are only slightly affected, others feel awful. However, if you have acute mountain sickness, you should take this as a warning sign that you are at risk of the serious forms of altitude sickness: HAPE (high altitude pulmonary edema) and HACE (high altitude cerebral edema). Both HAPE and HACE can be fatal within hours.

High altitude pulmonary edema (HAPE)

HAPE (high altitude pulmonary edema) is excess fluid on the lungs, and causes breathlessness. It is never normal to feel breathless when you are resting – even on the summit of Everest. This should be taken as a sign that you have HAPE (high altitude pulmonary edema) and may die soon. HAPE can also cause a fever (a high temperature) and coughing up frothy spit. HAPE and HACE often occur together.

High altitude cerebral edema (HACE)

HACE (high altitude cerebral edema) is fluid on the brain. It causes confusion, clumsiness, and stumbling. The first signs may be uncharacteristic behaviour such as laziness, excessive emotion or violence. Drowsiness and loss of consciousness occur shortly before death.

Altitude sickness complications

If the symptoms of altitude sickness are ignored, they can lead to life-threatening conditions affecting the brain or lungs.

High altitude cerebral edema (HACE)

High altitude cerebral edema (HACE) is a build-up of fluid in the brain caused by a lack of oxygen. HACE is life-threatening and requires urgent action. It can be fatal if it’s not treated immediately.

HACE can develop quickly over a few hours and can kill in only a few hours.

Symptoms of HACE:

• headache
• weakness
• nausea and vomiting
• loss of co-ordination
• feeling confused
• hallucinations
• coma

A person with HACE often doesn’t realize they’re ill, and may insist they’re all right and want to be left alone.

A person with HACE will find it difficult to walk heel-to-toe in a straight line – this is a useful test to perform in someone with severe symptoms of acute mountain sickness. HACE should also be suspected if a companion starts to behave irrationally or bizarrely.

Who gets HACE?

About 1% of people of ascend to above 3000m get HACE. The lowest altitude at which a case of HACE has been reported was 2100m. HACE can also occur in people with HAPE and vice versa. Factors that increase the risk of HACE are similar to those for acute mountain sickness and HAPE. The faster the rate of ascent and the higher the altitude, the more likely it is that HACE will develop. HACE is thought to occur mainly in trekkers or climbers who have ignored symptoms of acute mountain sickness and climbed higher rather than staying at the same altitude or descending.

What causes HACE?

The cause of HACE remains unknown. Several factors may play a role including increased blood flow to the brain. An increase in blood flow is a normal response to low oxygen levels as the body needs to maintain a constant supply of oxygen to the brain. However, if the blood vessels in the brain are damaged, fluid may leak out and result in HACE. Although we know that reactive chemicals are released when oxygen levels are low and that these chemicals can damage blood vessel walls, it still hasn’t been proven that the blood vessels in the brain are actually more leaky.

How is HACE treated?

Treating HACE:

• Move down to a lower altitude immediately
• Take dexamethasone
• Give bottled oxygen, if available

Descent is the most effective treatment of HACE and should not be delayed if HACE is suspected. A Gamow bag, or portable altitude chamber, can be used as a temporary measure and, if available, oxygen and a drug called dexamethasone should be given.

Dexamethasone is a steroid medication that reduces swelling of the brain.

If you can’t go down immediately, dexamethasone can help relieve symptoms until it’s safe to do so.

You should go to hospital as soon as possible for follow-up treatment.

High altitude pulmonary edema (HAPE)

High altitude pulmonary edema (HAPE) is a dangerous build-up of fluid in the lungs that prevents the air spaces from opening up and filling with fresh air with each breath. When this happens, the sufferer becomes progressively more short of oxygen, which in turn worsens the build-up of fluid in the lungs. In this way, HAPE can be fatal within hours.

HAPE usually develops after 2 or 3 days at altitudes above 2500 m. Typically the sufferer will be more breathless compared to those around them, especially on exertion. Most will have symptoms of acute mountain sickness. Often, they will have a cough and this may produce white or pink frothy sputum. The breathlessness will progress and soon they will be breathless even at rest. Heart rate may be fast, the lips may turn blue and body temperature may be elevated. It is easy to confuse symptoms of HAPE with a chest infection, but at altitude HAPE must be suspected and the affected individual must be evacuated to a lower altitude.

• If you have had HAPE, please register with the International HAPE Database to help develop new treatments for the condition (http://www.altitude.org/hape.php).

Symptoms of HAPE:

• blue tinge to the skin (cyanosis)
• breathing difficulties, even when resting
• tightness in the chest
• a persistent cough, bringing up pink or white frothy liquid (sputum)
• tiredness and weakness

The symptoms of HAPE can start to appear a few days after arrival at high altitude. It can be fatal if it’s not treated immediately.

Who gets HAPE?

Unfortunately, it is currently impossible to predict who will get HAPE. This is one of the reasons why scientists have established the HAPE database (http://www.altitude.org/hape.php). People who have had HAPE before are much more likely to get it again. Therefore, there must be some factor that puts certain individuals at high risk of the condition. However, just like acute mountain sickness, there are some known risk factors. A fast rate of ascent and the altitude attained will make HAPE more likely. Vigorous exercise is also thought to make HAPE more likely and anecdotal evidence suggests that people with chest infections or symptoms of the common cold before ascent may be at higher risk.

What causes HAPE?

Despite years of careful research the exact causes of HAPE remain poorly understood. Fluid has been shown to fill up the air pockets in the lungs preventing oxygen getting into the blood and causing the vicious circle of events that can kill people with HAPE. As with many biological processes many factors play a role in the disease and there is good evidence to support a number of theories about how this fluid gets there.

Normally, oxygen gets into your blood and is supplied to the body from your lungs. Each time you take a breath in, air rushes into the tiny air pockets at the end of all the airway branches in your lungs. At the same time, blood from your heart is brought close to these thin-walled air pockets, so that oxygen can move into your blood while waste products move out. Oxygen-rich blood then returns to the heart and is supplied to the body. If, by accident, you inhaled a small object into your lungs, it would become stuck in one of the airways branches. Little oxygen would get to the downstream air pockets. To prevent this area of lung supplying blood starved of oxygen back to the heart (and therefore the rest of body), blood vessels in the area closed down or constrict. This is normally a very good thing and is an example of the body protecting itself.

At altitude however, this same process is a cause of the disease HAPE. Because the whole lung is starved of oxygen, the whole lung reacts in the same way – blood vessels constricting all over the place and not just in small areas. The blood in these vessels is squeezed and the pressure goes up forcing fluid out of blood and into air pockets.

Very dangerous and reactive substances are formed in your blood when you are starved of oxygen and these can directly damage the special membrane between air and blood in your lungs causing further fluid leak and worsening HAPE.

How is HAPE treated?

Treating HAPE:

• move down to a lower altitude immediately
• take nifedipine
• give bottled oxygen, if available

The most important treatment for HAPE is descent. Providing extra oxygen and/or raising the air pressure around a victim with a Gamow bag can reverse the underlying process, lack of oxygen, but these measures are really no substitute however for rapid descent down the mountain.

Nifedipine is a drug that helps to open up the blood vessels in the lungs. By doing so, it reduces the high pressure in those vessels that is forcing fluid out into the lungs. Nifedipine helps to reduce chest tightness and ease breathing. Sildenafil (Viagra®), by a different mechanism, also opens up the blood vessels in the lung and may be a useful treatment for HAPE.

Some drugs can be helpful, but should only be used by trained doctors. Following recent research, doctors may also give the steroid, dexamethasone. Drug treatment should only ever be used as a temporary measure; the best treatment is descent.

You should also go to hospital as soon as possible for follow-up treatment.

How to avoid and prevent altitude sickness

If you’re planning to travel to a high altitude, consider talking to your doctor about drugs that can help with acclimatization, particularly if you have had altitude sickness before.

Following the Altitude Sickness Golden Rules should mean that your body can acclimatize as you ascend and so you will be less likely to develop acute mountain sickness. It usually takes a few days for the body to get used to a change in altitude.

You can reduce the chance of getting altitude sickness by:

• Avoiding a rapid ascent from sea level – don’t go above about 2,500 meters (8202 ft) for the first night’s sleep
• Take 2-3 days to get used to high altitudes before going above 3,000m (9842 ft)
• Once you get above 3,000 meters (9842 ft), ascending by no more than 300-500 meters (984-1640 ft) per day
• Have a rest day every 600-900m (1969-2953 ft) you go up, or every 3-4 days
• Spending the night below the day’s highest altitude
• Avoiding strenuous exercise before your body has had time to adjust to the lower oxygen levels
• Make sure you’re drinking enough water
• Eat a light but high calorie diet
• Avoiding alcohol at high altitude
• Avoid smoking

Go up slowly, take it easy, and give your body time to get used to the altitude. The body has an amazing ability to acclimatize to altitude, but it needs time. For instance, it takes about a week to adapt to an altitude of 5,000m (16,404 ft).

Because of the change in respiratory pattern during sleep, the altitude at which the traveler sleeps is more important for altitude sickness risk than the maximal altitude reached during the day. The optimal rate of ascent (sleep altitude) should be no more than 500 m per day at levels greater than 2500 m. Also, allowing at least one day to acclimate around 2500 m before further ascent, and then again for every additional 1000 m ascent, will reduce risk.

However, if you need to go up more quickly, you could consider taking a drug called acetazolamide (also known as Diamox). There is now good evidence ⁴ that acetazolamide reduces symptoms of acute mountain sickness in trekkers, although it does have some unusual side-effects: it makes your hands and feet tingle, and it makes fizzy drinks taste funny.

You should begin taking acetazolamide 1-2 days before you start to go up in altitude and continue to take it while going up.

If using acetazolamide, you should still go up gradually and follow the general prevention advice.

If you get symptoms of altitude sickness while taking acetazolamide, you should rest or go down until you feel better before going up again.

Altitude sickness treatment

It is better to prevent acute mountain sickness than to try to treat it.

If you have altitude sickness, the best treatment is descent until the symptoms disappear. Rest, fluids and pain killers are likely to improve the symptoms. Do not continue to climb higher.

• Don’t go any higher for at least 24-48 hours
• If you have a headache, take ibuprofen or paracetamol
• If you feel sick, take an anti-sickness medication, like promethazine
• Make sure you’re drinking enough water
• Avoid alcohol
• Don’t smoke
• Avoid exercise
• Tell your travel companions how you feel, even if your symptoms are mild – there’s a danger your judgement can become clouded.

Painkillers may ease the headache, but they don’t treat the condition. Acetazolamide may be helpful, especially if you need to stay at the same altitude, and resting for a day or two might give your body time to recover. Acetazolamide decreases the pH level of your blood, which then causes an increased breathing rate. It is well tolerated in general, but patients should be advised that use can cause tingling of the digits and even lips.

It is best not to drink alcohol or take sedatives or sleeping pills because they interfere with the body’s adaptation to high altitude.

You can continue going up with care once you feel fully recovered.

If you don’t feel any better after 24 hours, you should go down by at least 500m (about 1,640 feet).

Don’t attempt to climb again until your symptoms have completely disappeared.

After 2-3 days, your body should have adjusted to the altitude and your symptoms should disappear.

See a doctor if your symptoms don’t improve or get worse.

It is essential that you should NEVER go up higher if you have acute mountain sickness.

If a traveling companion has symptoms of acute mountain sickness and becomes confused or unsteady, or develops an extremely severe headache or vomiting, they may have a life-threatening condition called high altitude cerebral edema (HACE).

Treatment of HAPE (high altitude pulmonary edema) and HACE (high altitude cerebral edema)

If you have signs of altitude sickness affecting your lungs or your brain, this is a medical emergency. You need help to descend as soon as possible. Breathing oxygen from a tank can help.

• Immediate descent is absolutely essential
• Dexamethasone and acetazolamide should both be given, if available
• Pressure bags and oxygen gas can buy time

Altitude sickness medicine

Consider travelling with these medicines for altitude sickness:

• Acetazolamide to prevent and treat high altitude sickness
• Ibuprofen and paracetamol for headaches
• Anti-sickness medication, like promethazine, for nausea

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