Saturday, June 15, 2024
HomesingaporeCNA Explains: What is altitude sickness, and why it can be deadly

CNA Explains: What is altitude sickness, and why it can be deadly

SINGAPORE: Reaching the world’s highest peaks is a challenge that brings many climbers to countries such as Nepal and Tanzania every year.

However, such extreme environments also present increased risks to the human body.

Barometic pressures – or air pressures – fall as the altitude increases. This causes a corresponding drop in the partial oxygen pressure, resulting in hypobaric hypoxia, or a lack of oxygen in the air.

For example, the air at 3,000m contains only about 69 per cent as much oxygen compared with at sea level, and drops even further as you ascend.

At the peak of Mount Everest, the world’s highest, there is only about 33 per cent as much oxygen in the air. The mountain’s “death zone”, located above 8,000m, is also notorious for its difficult terrain.

Aside from altitude sickness, climbers are also susceptible to conditions such as frostbite and eye damage.

Last week, a travel agency said a Singaporean man died from health complications due to altitude sickness while attempting to climb Mount Kilimanjaro in Tanzania.

He died of asphyxia, a condition that occurs when the body is deprived of oxygen, and high altitude pulmonary edema (HAPE), an altitude illness that can turn fatal.

In May, another Singaporean climber went missing after reaching the summit of Mount Everest. According to his wife, he developed high altitude cerebral edema (HACE) and “could not make it down”.


High altitude sickness occurs when people travel to high altitudes without giving their bodies enough time to adjust. This usually affects those who ascend to altitudes at least 2,500m above sea level but can also be seen at lower elevations.

There are three types of altitude sickness: Acute mountain sickness (AMS), HACE and HAPE.

Of these, acute mountain sickness is the most common, and is often benign. However, if left undiagnosed, it can lead to the other two types, which are more serious and potentially life-threatening.

HACE occurs when pressure builds up in the brain, resulting in fluid breach and swelling. HAPE, on the other hand, affects the lungs – the fluid build-up interferes with the effective exchange of oxygen to the blood.

How badly people are affected by the lack of oxygen depends on how high they are, the rate of ascent, and how long they stayed at high altitudes.


AMS begins with mild symptoms such as headache and nausea. 

Other symptoms include dizziness, vomiting, fatigue and loss of energy, shortness of breath, sleeping problems and loss of appetite.

According to outdoor travel website SGTrek, symptoms usually set in within 12 to 24 hours of reaching higher elevation, and then get better within a day or two as the body adjusts to the change in altitude.

If left untreated, however, AMS can progress to HAPE and HACE.

Symptoms of HAPE include tightening of the chest, extreme fatigue, breathlessness even when at rest, coughing that may produce a white or pink frothy fluid and fever. People may also experience cyanosis, a condition where the skin, nails or whites of their eyes start to turn blue.

HACE symptoms include headache, loss of coordination, weakness, disorientation, memory loss and hallucinations. It can also cause changes in normal behaviour and ability to think, as well as coma in advanced cases.

An article on Harvard Health’s website noted that symptoms of HACE may not be noticed immediately as the illness can begin during the night.

“Because this low-oxygen injury affects the brain and thought process, a person with HACE may not understand that symptoms have become more severe until a travelling companion notices unusual behaviour,” the article read.

Dr Peter Yan, a cardiologist in private practice at Gleneagles, said that while HACE has lesser incidence, the development of HAPE is more rapidly fatal.

He also noted that about 14 per cent of HAPE cases will have HACE as well.


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High-altitude sickness can affect anyone, regardless of fitness level, age and gender.

However, it has been observed to more likely occur in people who have a previous history of altitude sickness, those who climb quickly and those have been living at low elevation prior to their climb.

Individuals with medical problems involving the heart, the nervous system or the lungs are also at higher risk. According to Harvard Health, obesity also appears to increase the risk.


AMS is temporary and usually resolves by itself when the body is given enough time to adapt to a higher altitude.

In the case of climbers, they should stop ascending immediately and descend to a lower altitude when they feel symptoms of sickness. Taking proper rest and medicine to relieve symptoms such as headaches can also help.

Most people feel better after going down 500m to 1km, said the National Healthcare Group’s (NHG) Pharmacy website. If needed, inhaled oxygen can reduce the symptoms of sickness. However, it can be used only when one has symptoms or while sleeping.

Those whose conditions progress to HAPE or HACE should seek immediate medical help. In cases of delay, a portable hyperbaric (pressure) chamber may be used if available. This device simulates descent to a lower altitude and can help while arrangements are being made for the actual descent.

Medication, such as acetazolamide and dexamethasone, may also be administered.

Acetazolamide – or Diamox – is a respiratory stimulant and improves oxygenation. It can also speed up acclimatisation. However, the drug is related to sulfonamide medications, and should be avoided by individuals with a history of severe allergy to sulfa.

Dexamethasone is a strong steroid that can reduce or prevent symptoms of AMS, as well as decrease brain swelling in HACE cases. 

According to Dr Yan, long-term consequences depend on the severity of sickness sustained.

“For AMS … usually there are no residual long-term consequences,” he said. “Symptoms disappear after descending to a lower altitude and recovery in a few days.”

However, that may not be the case for people who develop HAPE or HACE.

For HACE, individuals may sometimes have long-term or even brain dysfunction, depending on severity and response to initial treatment, said Dr Yan.

If treated early, symptoms of HAPE should resolve, he added, though he noted that severe cases can take weeks to recover.

“HAPE is non-cardiogenic pulmonary oedema and therefore should make good recovery when treated appropriately, such as early recognition or diagnosis, descend to lower altitude, administration of oxygen and if required, diuretics,” he said.

Other long-term symptoms can include fatigue, shortness of breath and aches or pains.

Left untreated, both HACE and HAPE can cause death.


Altitude acclimisation, or adjusting to decreasing oxygen levels at higher elevations, is important in preventing high altitude sickness.

People should travel slowly to allow the body to get used to the change in altitude and avoid directly going to an altitude above 3,000m. 

Those who live in areas less than 1,500m above sea level should not go up too quickly, said NHG.

“For high-altitude climbers, a typical acclimatisation regimen might be to stay a few days at a base camp,  climb up to a higher camp (slowly), and then return to base camp,” said Dr Yan.

“A subsequent climb to the higher camp then includes an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body adjust to the oxygen level there, a process that involves the production of additional red blood cells.”

SGTrek’s recommendation is to take two to three days of getting used to high altitudes before going above 3,000m.

NHG added that those who plan to climb more than 3,000m above sea level should keep their ascent to less than 500m a day, and plan a day of rest for every 1km. “Climb high and sleep low” is also advised – that is, to hike to a higher altitude during the day and go back to lower elevation to sleep at night.

“The general rule of thumb is to not ascend more than 300m per day to sleep,” said Dr Yan.

“This process cannot safely be rushed, and this is why climbers need to spend days (or even weeks at times) acclimatising before attempting to climb a high peak.”

They should also make sure to drink enough water and avoid alcohol and sleeping pills, especially in the first two days, said NHG. Meals containing more starchy food are recommended when at high altitudes.

It added that people who drink caffeine regularly should not stop drinking it before or during their trip as suddenly stopping can cause symptoms similar to high-altitude sickness. Caffeine is safe at high altitudes, it said.

Meanwhile, those who plan to ski, hike or climb should also not overwork their bodies during the first few days at high altitude.

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