Sussex Travel Clinic

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01273 749100

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01903 254774

Ain’t no mountain high enough…to keep me from getting to you…

Sign "Way to Mount Everest Base Camp" - Mount Everest (Sagarmatha) National Park

Sign “Way to Mount Everest Base Camp” – Mount Everest (Sagarmatha) National Park

Are you sure? Well acute mountain sickness just might stop you!

Trekking holidays in places like Nepal, Peru and climbing Kilimanjaro are becoming ever more popular amongst travellers. 30,000 people attempt to climb Kilimanjaro every year, with 6 to 8 people dying on the mountain each year. (1)

What is Altitude?

This is a really good question! Ready for the science bit? Altitude generally refers to the height above sea level. High altitude is generally considered anywhere above 2500m.

At high altitude, atmospheric (air) pressure is lower than that at sea level. Decreased air pressure means there is less oxygen. So for example, there is approximately 66% less oxygen in each breath on the summit of Everest than at sea level.

High Altitude

Very High Altitude

Extreme Altitude

Between 2400-3658m Between 3658-5500m Between 5500-8848m
Cochabamba, Bolivia

La Paz, Bolivia -3658m


Mt Everest summit -8850m
Bogota, Colombia- 2645m


Lhaza, Tibet -3685m



Quito, Ecuador -2879m


Everest Base Camp -5500m
Cuzco, Peru -3225m


Interesting Fact:

Did you know Mount Everest is the highest point on planet earth? It grows by about a quarter of an inch every year so it’s getting higher!

What effect does high altitude have on our bodies?

So what’s so important about oxygen? Simply put, it is needed to keep your body alive. It gives you energy, it’s important for brain function and for all those other things that it does for the body to function normally without you even realising it!

Our bodies are accustomed to working where we live, and when we go higher our bodies need to adapt. Altitude starts to have an effect on our bodies around 1500 – 2000m. So it starts to behave slightly differently as it tries to compensate for the change in oxygen levels. The decrease in pressure means you take in less oxygen and this can make it more difficult to breathe. Our bodies adapt by breathing faster and deeper, increasing the heart rate, and adjusting its blood chemistry such as making more red blood cells to carry oxygen around.

This response or adaption is called acclimatisation. It takes approximately 3-5 days to occur but can vary between individuals and conditions.

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:

  • An increased breathing rate or feeling that you are breathing more deeply.
  • Shortness of breath on exercise or increased activity (exertion).
  • A change in your breathing pattern at night.
  • Disturbed sleep.
  • Passing more urine than usual. (3)

Altitude Sickness

Trekker resting in height mountain India

Trekker resting in height mountain India

The lack of oxygen above 2400 metres (8000 ft) can cause serious illnesses.

There are three forms of altitude sickness, the first two are neurological forms of altitude illness:

Acute Mountain Sickness (AMS)

Symptoms of AMS appear 6 to 12 hours after you climb to or arrive at high altitude, although it can take up to 24 hours to develop. Symptoms include headaches, sleep disturbance, tiredness, shortness of breath, loss of appetite, nausea and vomiting. If you get symptoms of AMS you should take this as a warning sign that you may develop more serious altitude sickness called high altitude cerebral oedema (HACE). 10% of people with AMS will develop HACE. [4]

High Altitude Cerebral Oedema (HACE)

This is as a result of swelling of the brain and is typically characterized by the onset of confusion, altered consciousness and or loss of coordination. AMS commonly precedes HACE.

High Altitude Pulmonary Oedema (HAPE)

This affects the respiratory system where fluid builds up in the lungs and is also very dangerous. HAPE symptoms normally develop 2- 4 days after arrival at high altitudes above 2,500 metres and include: breathlessness, cough, bubbling sounds in the chest and pink spit. HAPE can develop even if you have not had symptoms of AMS.

Both HACE and HAPE are uncommon, but can develop very quickly and can be fatal within hours. If you develop symptoms of HACE or HAPE you need urgent medical attention and should go down to a lower altitude immediately.

Am I at risk of developing altitude sickness?

It is difficult to predict the susceptibility of a traveller to AMS, and physically fit travellers are not necessarily at lower risk. If you have previously had AMS you may get it again.

Rapid ascent without a period of acclimatisation puts a traveller at higher risk. In a study, 84% of trekkers who flew directly to 3,860m were affected by AMS. (5)

What can I do to avoid AMS?

Follow the Golden Rules


If you feel unwell at altitude it is altitude illness until proven otherwise.


Never ascend with symptoms of AMS.


If you are getting worse (or have HACE or HAPE), go down at once. (7)

Reduce your risk by:

  • Avoiding climbing too quickly.
  • Avoid flying directly to high altitudes.
  • Spend a few days getting used to altitude before you go above 3,000 metres.
  • Make sure you climb gradually and do not sleep more 300 to 500m higher than you did the previous night.
  • Do not get dehydrated.
  • Regular rest days are important– a full day of complete rest every three days is best.
  • If any signs of AMS develop, do not go any higher until you have fully recovered.
  • Make sure you have adequate travel insurance that covers you for your climb and medical evacuation should you need it.

Can AMS be treated?

If you rest and do not climb any higher symptoms of AMS usually improve in a few hours or days. DO NOT climb any higher.

Taking over the counter medication such as paracetamol may help with headaches and anti-sickness drugs like promethazine will help nausea and vomiting. Keep hydrated by drinking plenty of clear fluids and avoid alcohol. If you do develop AMS make sure you do not venture off on your own as you could develop more serious symptoms at any time.

If symptoms get worse or do not improve you MUST rapidly go (or be taken) to a lower altitude (at least 500 to 1,000 metres lower).

You should NEVER leave anyone with AMS on their own – they can become very ill very quickly.

Acetazolamide (Diamox®)


Acetazolamide (Diamox®) can be prescribed to try and prevent AMS. Diamox reduces the headache of AMS and increases blood oxygenation at high altitude by altering the body’s acid-base balance. Diamox should be taken 24 hours before arrival at high altitude and continued for 2 days once the highest altitude is reached. A trial course of 250mgs per day for 2 days is recommended before going to a remote location where a severe allergic reaction could prove difficult to treat if it occurred.

Diamox is not suitable for everyone. Your nurse will make a risk assessment to see if it is suitable for use.

Acetazolamide is not a ‘magic pill’, and cure of AMS is not immediate. It speeds up a process that may normally take 24-48 hours to about 12-24 hours.

How does Acetazolamide (Diamox®) work?

Put simply acetazolamide (Diamox) works by forcing the kidneys to excrete bicarbonate, the base form of carbon dioxide. It speeds up the acclimatisation process, stimulates breathing during the night and lessens the symptoms of AMS.

Are there any side effects that I can expect when taking acetazolamide?

Common side effects include:

  • Numbness, tingling or vibrating sensations in the hands, feet and lips.
  • Taste alterations
  • Ringing in the ears (tinnitus)
  • These symptoms usually go away once the medication is stopped.
  • You will urinate more on this medication

Less common side effects include:

  • Nausea
  • Headache
  • Some people have had extreme visual blurring after taking 1 or 2 doses of acetazolamide, normal vision should recover in several days once the medication is stopped (6)

True or False?

Acetazolamide hides symptoms of AMS FALSE

Acetazolamide speeds up acclimatization. As acclimatization occurs your symptoms resolve, reflecting improving health. Acetazolamide does not cover up anything, if you are still unwell with AMS, you will still have symptoms. If you feel well, you are well.

Acetazolamide will prevent AMS from worsening during ascent – FALSE

Acetazolamide does not protect against worsening AMS with continued ascent.

It does not change GOLDEN RULE 2NEVER ASCEND WITH SYMPTOMS OF AMS. Lots of people who have developed HACE AND HAPE believed this myth.

If Acetazolamide is stopped, my symptoms will worsen – FALSE

There is no rebound effect. If acetazolamide is stopped, acclimatization slows down to your own intrinsic rate. If AMS is still present it will take longer to resolve. If AMS is not present, then you don’t need to accelerate acclimatization if you ARE already acclimatized. You won’t become ill by stopping your acetazolamide. (6)

Sussex Travel Clinic can prescribed Diamox for adults from 18 years old – call 01273 749100 or 01903 254774 to book an appointment or book ONLINE.

For further advice visit:

Fit For Travel

Happy travelling!

Written my Nicki Harrison – RGN Lead Clinic Nurse



  1. dangerous-is-it-really.html


Medex – Travel at High Altitude

International Climbing and Mountaineering Federation


Fit for Travel


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