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Climbing Kilimanjaro

High altitude trekking comes with obvious risks. In particular, Acute Mountain Sickness (AMS) and its severe variants, High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE), are your biggest concerns on Mount Kilimanjaro. In this page we provide an overview on how the body is affected by changes in altitude and how it acclimatizes to these changes. We then provide a detailed overview on AMS, HACE and HAPE, before closing with some guidelines, tips and medications you can use to properly acclimatize. We have gathered this information from various sources but we particularly indebted to Rick Curtis’ Outdoor Action Guide to High Altitude, written for Princeton University, and recent insight from the Everest Base Camp Medical Centre.

Please note: The information in this page is provide as an information resource only, and is not to be used or relied on for any diagnostic or treatment purposes. The information is not intended to be patient education, does not create any patient-physician relationship, and should not be used as a substitute for professional diagnosis and treatment. Research in this area is always progressing which may mean some of this information is out of date. It is your responsibility to seek the latest information should you be going to high altitude.


At sea level the atmospheric oxygen level is at about 21% saturation (i.e. % of oxygen in the air) and the barometric pressure is around 760 mmHg (millilitres of mercury). As one climbs in altitude the oxygen saturation level remains about the same (up to approximately 21,000 meters or 69,000 feet), however, the percentage of oxygen per breath reduces considerably with lower air density. For example, at about 3,600 meters (12,000 feet), barometric pressure is around 480 mmHg, and hence there are approximately 40% fewer oxygen molecules available in each breath.

The body deals with this decrease in available oxygen by breathing faster and deeper (even at rest) so as to increase the oxygen content in the blood. Acclimatization is the process by which the body becomes accustomed to lower availability of oxygen in the air and can only be achieved by spending time at various levels of altitude before progressing higher. To illustrate this point it is worth thinking about a term that climbers call the acclimatization line

The term is used to describe a point at which someone’s altitude sickness symptoms occur. For example, let’s say a person’s acclimatization line is 3,000 metres on day one. After trekking to this height and spending a night or two there, the body would acclimatize to that altitude and that person’s line might move to 3,800 metres. If they then climb to 3,700 metres they will remain asymptomatic, but if they climbed to 4,000 metres they would begin to experience altitude sickness symptoms.

Very near to one’s acclimatisation line the body can continue to adjust and a day or two’s rest at that height will usually result in resolution of symptoms. However if one continues to ascend beyond ones acclimatization line it is almost guaranteed that symptoms will worsen and further acclimatization will not occur. It is critical that one gets below the point where symptoms began in order to see improvement.

This last point illustrates why it is so dangerous to ascend with any symptoms of altitude sickness. There are four main physiological changes that result as your body acclimatizes to changes in altitude. The firstwehave already mentioned; breathing becomes faster and a lot deeper. The second is an increase in red blood cell count which allows more oxygen to be carried in the blood. Thirdly, pressure in pulmonary capillaries increases which forces blood into areas of the lungs that are not used when breathing at sea level. And finally, more of a particular enzyme is produced which causes oxygen to be released from haemoglobin to the blood tissue

As highlighted in Chapter 4 there are three altitude zones on Kilimanjaro – high altitude (2,500 – 3,500 metres), very high altitude (3,500 – 5,500 metres) and extreme altitude (above 5,500 metres). Most people can ascend to 2,400 meters without experiencing the negative effects of altitude. However, as one enters the high altitude zone changes in air density and available oxygen begin to impact one’s physiology. One’s susceptibility to these changes is very difficult to predict, though, as there is no correlation to factors of gender, age, fitness etc.

We do however know that going too high, too fast is the key cause of AMS. Other contributing factors are dehydration and over exertion at altitude. A proper acclimatization strategy involves not going too high, too fast whilst also ensuring you don’t overexert yourself and remain well hydrated.

Acute Mountain Sickness

Acute Mountain Sickness (AMS) is caused when the body has not had enough time to adapt to reduced levels of oxygen at higher altitudes. Over 75% of people start experiencing mild AMS symptoms at about 10,000 feet (3,000 m). Some people can experience symptoms as low as 8,000 feet (just over 2,400 m). Typically symptoms begin 12-24 hours after arriving at altitude. If your symptoms are mild and you remain at the altitude at which your first symptoms began, they should completely disappear after 48 hours. Once they have disappeared you have acclimatized.

If you are not doing well at altitude it is safe to assume it is AMS until proven otherwise. The symptoms of AMS almost always have a gradual onset, and get worse slowly over several hours if ascent continues. AMS symptoms also tend to be worse at night when respiratory drive decreases. You cannot develop AMS while descending if you were asymptomatic at height. In almost all cases of severe AMS, symptoms began at a lower height which were ignored or attributed to something else and then got worse as ascent continued. Denial is common on mountains. The first step to staying out of trouble is to admit that you have altitude sickness.

There are three levels of AMS symptoms – mild, moderate and severe.

Mild AMS

Symptoms include:

  • Fatigue
  • Headaches
  • Nausea & Dizziness
  • Shortness of breath
  • Disturbed sleep
  • Loss of appetite

Mild AMS is common on Mount Kilimanjaro. Many trekkers will experience one or more of the symptoms above, which will decrease in severity as you spend more days on the mountain.

As soon as you start experiencing any of the above symptoms it is important to note your altitude (remember the acclimatization line illustration above) and notify your trekking partners’ of your condition so that they can help monitor the symptoms with you. The natural progression for mild AMS is to get better and often simply resting at the altitude at which you became ill is adequate treatment. Ascent, at a moderate rate, can continue as long as symptoms are mild.

Moderate AMS

Symptoms include:

  • Very bad headache that is not relieved with medication
  • Feeling very nauseous which often results in vomiting
  • Very fatigued and weak
  • Decreased coordination (known as ataxia)
  • Shortness of breath

A clear sign that you are experiencing moderate AMS symptoms is when one or all of the mild symptoms start getting worse to a degree that becomes debilitating. Typically people experiencing moderate symptoms have very bad headaches and usually vomit. A feeling of decreased coordination is common (i.e. ataxia). People can often walk on their own when experiencing moderate AMS; however ascent under such symptoms will almost certainly result in worsening of the symptoms to a degree where one cannot walk anymore. This would necessitate a stretcher evacuation (see figure 31) which should be avoided at all costs.

If you experience moderate AMS the only cure is descent. Ascending under moderate symptoms can lead to death. It is important you descend to the altitude at which you first started experiencing symptoms, and remain at a lower altitude until the symptoms subside. Once the symptoms have disappeared you have acclimatized and you can ascend again.

Severe AMS

Symptoms include:

  • Inability to walk
  • Shortness of breath whilst resting
  • Loss of mental capacities and hallucination
  • Fluid build-up in the lungs

Ascent under severe AMS symptoms is extremely dangerous and should never be attempted. People experiencing severe AMS are usually unable to walk, struggle to breathe and lack their mental capacities to think straight. There are two conditions associated with severe AMS, each of which occurs when fluid leaks through the capillary walls either into the lungs (this is called High Altitude Pulmonary Edema – HAPE) or into the brain (this is call High Altitude Cerebral Edema – HACE). Both conditions are rare but almost always occur because of ascending too high, too fast, or because one has stayed too long at very high altitude.

High Altitude Pulmonary Edema (HAPE)

HAPE occurs when fluid enters the lungs through the capillary walls. The build of fluid in the lungs prevents the effective exchange of oxygen in the lungs and thus a decrease of oxygen into the bloodstream. As the condition worsens, cyanosis or impaired cerebral function sets in and ultimately results in death.

Clear symptoms that one is suffering from HAPE include:

  • Very short of breath, even while resting
  • Very tight chest
  • The feeling of suffocation, particularly while sleeping
  • Coughing that brings up white, frothy fluid
  • Extreme fatigue and weakness
  • Confusion, hallucination and irrational behaviour

If the last symptom occurs (i.e. confusion, hallucination and irrational behaviour) one can assume that the pulmonary edema has started to affect the brain due to a lack of oxygen in the bloodstream. There is no medication that one can take to prevent the onset and worsening of HAPE symptoms. Immediate descent is paramount. Trekkers should take care to ensure that the person descending with HAPE doesn’t exert themselves as this can result in worsening of the condition. A stretcher evacuation is the preferred method of descent. Once the person has reached the lower limits of the mountain, medical support should be sought immediately.

High Altitude Cerebral Edema (HACE)

Like HAPE, HACE is also caused when one ascends too high, too quickly, and the increase in pressure results in fluid breaching the capillary walls and entering the brain. The fluid build-up in the cranium results in swelling of the brain tissue which can result in death if not treated immediately.

HACE can be identified if someone is suffering from the following symptoms:

  • Severe headaches which cannot be relieved by medication
  • Hallucination
  • Loss of consciousness
  • Disorientation
  • Loss of coordination (i.e. ataxia)
  • Memory loss
  • Coma

Immediate descent is the only way to treat HACE. Unfortunately HACE often strikes at night. Trekkers shouldn’t wait until morning to evacuate someone with HACE symptoms as delay at altitude can be fatal. Other treatments, in addition to decent, include using oxygen, being placed in a hyperbaric bag and dexamethasone (a steroid that is sometimes used following a brain injury, to help reduce swelling on the brain).

Guidelines, Tips and Medications

There are a few guidelines and tips to remember when trekking at altitude. Belowwehave distilled them into short sound bites.wehave also included information on key medications that can be used to prevent and treat the symptoms of AMS in addition to descent.


There are 6 main things to remember to do on Mount Kilimanjaro

  1. Drink lots of fluids (at least 3-4 litres a day). You will be sweating out a lot of fluids during your trek. It is critical that you replace these fluids and remain well hydrated. Include an isotonic energy supplement in your water to improve the taste and encourage water abortion. Obviously do not overhydrate as this can also be potentially dangerous.
  1. Go slowly, always. From the outset you will hear your porters and guides reminding you to go ‘Pole, Pole’ (‘slow, slow’ in Swahili). Listen to them.

Trekking Kilimanjaro is not a race. Enjoy the scenery, stop regularly to drink water and take pictures.

  1. Climb high and sleep low at least once on your ascent. Try to choose a route (see Chapter 4) that gives you an opportunity to climb high, sleep low. For example, the six day Machame, Lemosho and Shira Route have a climb high acclimatization day to Lava Tower (4,600 meters), which then descends to Barranco Camp (3,900 meters) where trekkers spend the night at a very similar altitude to the night before. The Northern Circuit gives the most opportunities to climb high, sleep low
  1. Focus on exhaling slowly and fully, forcing all air out your lungs before the next breath. This is not a natural way for us to breathe but is effective in encouraging oxygen exchange in the blood. It is also a nice way to take your mind off things during the long, dark and slow summit night trek.
  1. Eat frequently. Most trekkers experience a loss of appetite at altitude.

However, if you don’t eat you will not have the energy reserves to get to the summit. It is important that you try to eat as much food as you can. Focus on foods that are high in carbohydrates and low in fats and protein.

  1. Monitor yourself and others for symptoms and listen to your guides and trekking partners. Do not ignore or deny symptoms.


Here are the five don’ts to remember.

  1. Avoid alcohol and tobacco and minimize caffeine which result in slowing respiration during sleep and therefore worsen the symptoms of AMS
  1. Avoid high salt intake which causes your body to retain fluid and can hence increase the severity of AMS
  1. Avoid an empty stomach. A biscuit or small snack can go a long way in providing that additional bit of energy you need to get to the summit
  1. Avoid sleeping tablets, antihistamines and tranquilisers. Like alcohol, tobacco and caffeine, these depressants also inhibit respiratory drive during sleep
  1. Don’t succumb to peer-pressure. It is easy when trekking in a group to feel pressured to continue when you know that your body is giving you all the signs that you should descend. Listen to your body.

Altitude Medication – Diamox

Acetazolamide, or what is commonly sold under the trade name Diamox, is a drug that is used for various medical treatments – including glaucoma, sleep apnea, epilepsy and hypertension. It is also used to help mitigate the effects of altitude sickness. Using Diamox on Kilimanjaro is a question you are going to face when you start your preparations to reach the Roof of Africa.

What is Diamox?

Diamox, as it is used for Acute Mountain Sickness (AMS), is a diuretic (i.e. it promotes the production of urine) and a prophylactic (i.e. is used as a preventative medicine – not a cure). It is also a carbonic anhydrase inhibitor (ahem, what?). Essentially this means that it promotes the excretion, via urine, of bicarbonate – which is why it is useful for altitude sickness

The excretion of bicarbonate increases the acidity of the blood, as bicarbonate is a conjugate base of carbonic acid. Increased acidity in the blood is equated by our bodies as increased CO2. The body responds to the imaginary excess CO2 by breathing deeper and faster to get rid of it. Deeper, faster breathing increases the amount of oxygen received by the blood. This helps with the acclimatization process and helps prevent the onset of AMS symptoms. It is important to note that Diamox does not cure the symptoms of AMS, it merely helps prevent the onset of symptoms. Once AMS symptoms have started, the only way to stop them is descent. Therefore, under no circumstances should Diamox be used to continue an ascent with AMS.

So is it worth using Diamox on Kilimanjaro?

In short, yes. Anything that is going to help you reach the summit safely should be considered a worthy investment. Obviously you should first consult your doctor to check whether Diamox is a suitable drug given your particular medical history. It is not suitable for pregnant women or anyone with kidney or liver disease issues (obviously these people shouldn’t be trekking Kilimanjaro in the first place). Diamox is also a sulfonamide drug and hence people who are allergic to sulfra drugs should not take Diamox.

I recommend taking Diamox for 2-3 days 2 weeks before departure to test whether you experience any symptoms.

Typical symptoms associated with Diamox are

  • Frequent urination – everyone experiences this when taking Diamox. It can result in the development of kidney stones so it is important that you drink loads of fluids
  • Numbness and tingling in the fingers, toes and face – Normally people experience this symptom when taking Diamox. The sensation is a little discomforting but not dangerous
  • Taste alterations (some foods might taste weird)
  • Nausea, vomiting and diarrhoea – this is rare. These symptoms should be identified during your test before departing for Kilimanjaro. Unfortunately these symptoms are common with AMS and therefore can easily be misdiagnosed as AMS
  • Drowsiness and confusion is also possible – again these symptoms can be confused with AMS

Typically Diamox comes in 250mg tablets. Most people take half a tablet in the morning and half in the evening. You should start taking tablets one day before arriving in Kilimanjaro and continue taking the same dosage for all ascent days. You can cease taking Diamox on descent.

Diamox myths

  • It hides symptoms – All Diamox does is accelerates acclimatization. It doesn’t cover up symptoms! If you feel sick you are sick
  • It will prevent AMS from worsening during ascent – it does not prevent symptoms from worsening with continued ascent
  • If it is stopped symptoms will worsen – There is no rebound effect. After stopping Diamox, acclimatisation will slow down to your intrinsic rate. You won’t become ill by just stopping Diamox


Dexamethasone is a strong steroid that prevents swelling on the brain and is therefore very effective in helping people suffering from HACE. However, as we mentioned earlier it should only be used in conjunction with immediate and rapid descent. It should not be used to continue ascent.

Consult a doctor for cautions, side-effects and dosage. It is likely, but not guaranteed, that your guide will be carrying Dexamethasone. You may want to check with the tour operator to see whether guides carry this medication.


Nifedipine is used to treat high blood pressure but also seems to improve oxygen transfer in the pulmonary, and can therefore be used in the treatment of HAPE. It is not nearly as effective of Dexamethasone in HACE patients, but can help buy some time to evacuate a trekker experiencing HAPE symptoms.


Some tour operators take oxygen on a climb. You can request to have oxygen but often there is an additional cost for this. Typically oxygen should only be used in serious cases and should never be used to ascend Kilimanjaro. On oxygen AMS symptoms resolve very rapidly (within minutes) on a moderate flow (2-4 litres per minute)

Hyperbaric therapy

A hyperbaric bag is a simple human size contraption made of airtight nylon. The bag is inflated with a foot pump and a patient can be put inside where the pressure is two p.s.i. – this is equivalent to bringing the person down a couple thousand feet. Once a patient is in the bag improvements are usually dramatic and quick; however the bag only serves to buy time so that the patient can walk down to receive proper medical support. Most tour operators on Kilimanjaro don’t carry a hyperbaric bag.


Never use oxygen therapy or medications to continue an ascent once severe symptoms have occurred. The result can be fatal.

footwear - Acclimatization and Acute Mountain Sickness

More Preparation Information:-

Fitness and NutritionVisas, Vaccinations and MedicationsEquipment and Kit ListAcclimatization and Acute Mountain SicknessKilimanjaro Checklist