High Altitude Illnesses Explained

I attended a free seminar at the premises of Wild Medix in Montague Gardens, Cape Town on Monday 26 June 2017. This was part of a series of free seminars hosted by Wild Medix on the last Monday evening of each month.

The seminar entitled “Physiology of Altitude – Human Physiology, Performance, Acclimatization and Adaption to High Altitude” was presented by Dr Ross Hofmeyr.



Dr Hofmeyr is the Medical Director at Wild Medix and an expeditionary doctor for the company. Dr Hofmeyr is also an anaesthetist at the University of Cape Town. Dr Hofmeyr describes himself as:

“… a doctor trained and practising in South Africa, with primary interests and experience in the fields of anaesthesia, trauma, emergency, critical care, wilderness, pre-hospital and aeromedicine.  I’ve spiced things up with some Antarctic expeditions, and have too many outdoor hobbies…but everyone has to have vices.  I have a beautiful talented wife, an awesome baby daughter, a loyal labrador, and live in the best city in the world (Cape Town!).”




The seminar was pitched at doctors and other registered medical professionals. This was way above my level of understanding, but it was an interesting subject nonetheless. Belinda and I are toying with the idea of climbing Mount Kilimanjaro at some stage and thought it would be a good idea to attend this seminar to see what we were letting ourselves in for.

I believe that this is an extremely interesting topic even if you are not interested in climbing to the top of a mountain peak covered in snow. I have decided to put together a very brief overview about what Dr Hofmeyr had to say in a way that those of us without any medical training would be able to understand it.

The purpose of the free seminar series hosted by Wild Medix is to sow the seeds of wilderness medicine in the greater community and I can’t think of a better way to do this than to write a short blog post about the subject of high altitude illnesses.


What is High Altitude?

Dr Hofmeyr started off by asking us what we thought was a high altitude. The answers ranged from 2500 m – 5800 m above sea level. Dr Hofmeyr responded, quite surprisingly, by saying that high altitude was considered to start from as little as 1500 m above sea level.


Lowland Sea level – 1500 m
High       [Intermediate] 1500 m – 3500 m   1500m – 2500 m]
Very High 3500 m – 5500 m
Extreme Above 5500 m
Death Zone Above 7000 m


At high altitude the barometric pressure decreases. It is a common misconception that the higher you go the less oxygen is present in the air and that is what causes you to experience breathing difficulties. This is not what is happening to your body. It is important to know that your brain works around the atmospheric pressure and not the proportion of Oxygen in the air.


“In fact, 21 percent of Earth’s atmosphere consists of life-giving oxygen (78 percent is composed of nitrogen and the remaining 1 percent a number of other gases).  And the proportion of that 21 percent is virtually the same at sea level as well as at high-mountain altitudes.

The big difference is not the amount of oxygen present, but rather density and pressure. ” 

For more detail go to this website.


The simple steps climbers can take to prevent high altitude illnesses is to ascend slowly and allow their body to properly acclimatize to the changes in the atmosphere pressure.

Acclimatization was described by Dr Hofmeyr as the “process by which an individual organism adjusts to a gradual change in its environment, allowing it to maintain performance across a range of environmental conditions.”

The process of acclimatization results in an increased rate and depth of breathing, an increased production of red blood cells and an increased renal excretion of bicarbonate in response to respiratory alkalosis.


What is Respiratory Alkalosis?


“Respiratory alkalosis occurs when the levels of carbon dioxide and oxygen in the blood are not balanced.

Your body needs oxygen to function properly. When you inhale, you introduce oxygen into the lungs. When you exhale, you release carbon dioxide, which is a waste product. Normally, the respiratory system keeps these two gases in balance.

Respiratory alkalosis occurs when you breathe too fast or too deep and carbon dioxide levels drop too low. This causes the pH of the blood to rise and become too alkaline.”

The above explanation can be found on this  website.


Dr Hofmeyer then spoke about the highest major cities in the world and what altitude their citizens live at. The citizens of these cities would obviously be acclimatized to these high altitudes.


Mexico City 2 250 m
Johannesburg 1 750 m
Nairobi 1 660 m
Denver City 1 610 m
Guatemala City 1 530 m


What is interesting to note is that if any of the inhabitants of these cities had to go to the coast on holiday for an extended period of time, they would need to acclimatize to the altitude after returning home.

The table below describes the relationship between the increase in altitude and the increased rate of a high altitude illnesses (HAI) occurring:


ALTITUDE PREVALENCE OF HAI       Oxygen Saturation (SPO2)
Below 1500 Little to no acclimatization needed.      90 – 100 %
1500 m – 3500 m HAI occurs with rapid ascent      Minor decrease below 90 %
3500 m – 5500 m Most common range for HAI. Requires acclimatization for efforts to be tolerated      75 – 85 %
5500 m – 8850 m Abrupt ascent always causes severe HAI. Always requires acclimatization to avoid HAI.      55 – 75 %





The Different Types Of High Altitude Illnesses


High Altitude Headache (HAH)

This occurs within 48 hours of an ascent above 2500 m where the headache cannot be attributed to another cause like: Dehydration, Heat stroke, Hypoglycaemia or muscle spasm.


Acute Mountain Sickness (AMS)

In order to be diagnosed as suffering from AMS the climber will need to be presenting with the following symptoms:

  • High Altitude Headache (HAH)
  • Nauseau
  • Loss of appetite
  • Fatigue
  • Dizzyness
  • Light Headed
  • Sleep disruption
  • Be above 2500 m

If the climber is presenting with 3 or less of the above symptoms then they could be diagnosed with mild AMS. If there are 4-5 symptoms present, the person could be diagnosed with moderate AMS. Having 6 or less of these symptoms could result in a diagnosis of severe AMS.


High Altitude Cerebral Edema (HACE)

The person would need to be diagnosed with AMS first as well as Ataxia or a deceased level of consciousness. Or alternatively Ataxia and a decreased level of consciousness in the absence of AMS.

Ataxia can be defined as “a lack of muscle coordination which may affect speech, eye movements, the ability to swallow, walking, picking up objects, and other voluntary movements

For more detail visit this website

The symptoms of HACE are:

  • Headache
  • Disorientation
  • Loss of Co-ordination
  • Visual impairment
  • Memory loss
  • Bladder / bowel dysfunction
  • Coma


High Altitude Pulmonary Edema (HAPE)

A clinical diagnosis of HAPE would need to include 2 symptoms (cough, body weakness, chest tightness or congestion) and 2 signs (cracked or wheezing in one lung field, central cyanosis or tachycardia).

Symptoms of HAPE are:

  • Chest tightness
  • Persistent cough
  • Frothy sputum
  • Feeling of impending suffocation during sleep


Preventative Action and Treatment for High Altitude Illnesses

This can only be done after consultation with a registered medical practitioner that has experience with the diagnosis and treatment of HAI.


  • High Altitude Headache (HAH):  The climber may need take analgesics and take a rest day.
  • Acute Mountain Sickness (AMS):  The climber may need to stop ascending and rest. More severe AMS may require supplemental O2 and medication (acetazolamide).
  • High Altitude Cerebral Edema (HACE):  The person will need to stop ascending and preparations need to be made as soon as possible for the climber to descend.
  • High Altitude Pulmonary Edema (HAPE):  The treatment for HAPE is similar to HACE, however the climber with HAPE may need to receive supplemental O2 while they are waiting to descend or be placed in a portable hyperbaric chamber (PHC).


Portable Hyperbaric Chambers (PHC)

These are specifically designed to be used while on a mountain expedition and when a climber is in urgent need of an increased atmospheric pressure to assist perfusion of the tissues in the brain.


Types of Portable Hyperbaric Chambers

  1. Gamos bag (USA) weighs 7 kg
  2. Certec bag (Swiss) weighs 5 kg
  3. PAC (Australia) weighs 8 kg


A portable hyperbaric chamber has the ability to manually increase the internal pressure in the bag above the ambient pressure. It has an automatic release valve to ensure that the bag is not over inflated to the point of rupturing. It also ensures gaseous exchange through the release valve. This means that the CO2 that builds up inside the bag has a means to escape. It has tie down straps to hold it in place during bad weather or when the climber is in a less than ideal location. It also has a foot pedal that is used to manually inflate the bag and keep it inflated.


Practical Tips on the use of a PHC

Dr Hofmeyr pointed out the fact that the climber will need to be inside the portable hyperbaric chamber anywhere from an hour to 6 hours. It is a single facet treatment and should not be attempted if the person cannot breathe on their own. Once the bag is zipped up, you will not be able to treat the person for any other ailment they may have.

To assist the climber when inside the bag, provide him or her with items that can pass the time in comfort and to provide some form of entertainment to keep up their spirits. Dr Hofmeyr suggested putting in a foam mattress to insulate the patient from the ground as well as a small cloth to wipe off the condensation that will accumulate inside the bag. It cannot be pleasant to have water dripping on your head for 6 hours.

Other suggestions include a sleeping bag, a book, warm clothing, a beanie, a pee bottle, a vomit bag, a headlamp, an oxygen source, a pulse oximeter to measure their SATS, an altimeter and a small radio.

The climber should be encouraged to empty his or her bladder and bowels before climbing into the bag. The climber can also take some food and water in the bag in case he or she gets hungry.

The climber should be warned that with the pressure increase inside the chamber, they will experience ear pain and that it will be important for them to equalize regularly to avoid discomfort in their ears. If the climber is not fully conscious, he or she should be placed in the safe airway (recovery) position inside the bag.

Once the chamber has been fully inflated, a person will need to push down on the foot pump every 5 seconds (12 times a minute) to maintain gaseous exchange. The person on the foot pump will need to be substituted regularly to avoid fatigue.

Wild Medix has a bag manufactured by Treksafe called a Portable Altitude Chamber. Dr Hofmeyr demonstrated how the bag worked by putting one of the course goers inside and inflating the bag. The person inside that bag reported the experience as being similar to being inside the cabin of a pressured plane.

You can get more information about the Portable Altitude Chamber on Treksafe’s website.


For some additional reading material on HAI check out this article from West (1993), published in the Journal of Wilderness Medicine.


Dr Ross Hofmeyr can be contacted at:

[email protected]


The feature photo at the start of this post is byMarco Bonomo on unsplash.com







The information, including but not limited to, text, graphics, images and other material contained on this blog post are for informational purposes only. The purpose of this blog post is to provide information on various topics relating to mountain climbing and high altitude illnesses. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment and before undertaking a new health care treatment programme, and never disregard professional medical advice or delay in seeking it because of something you have read on this blog post.

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