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Expedition Health and Saftey Series

What You Really Need to Know about Altitude Sickness

By Sara Tiffany

At sea level the percentage of oxygen in the air is about 21%. So what is the percentage of oxygen in the atmosphere at the summit of Kilimanjaro? The answer is still 21%. Why does the body react to altitude if the percentage of oxygen doesn’t change? Well, the air is “thinner” or less dense. As altitude increases, air pressure decreases meaning that at 10,000 feet, you inhale fewer molecules of oxygen per breath than you do at sea level. In fact, at 12,000 feet, you intake 40% fewer molecules of oxygen per breath than you do at sea level. You adapt to these lower levels of oxygen by a process called acclimatization.

It doesn't take long for your body to react to the lower level of oxygen; it quickly begins to make small adjustments to help you adapt. Many of the changes the body makes are quite complex, but here is a simplified list:

  • Your breathing rate increases, but not enough to fully compensate for the lesser amount of oxygen meaning that more adaptations become necessary.
  • Your lungs will expand more fully allowing for an increased lung capacity.
  • Your heart rate will increase to move oxygenated blood more quickly through the blood stream.
  • Over time, your body will start making more red blood cells to carry the oxygenated blood and it will also build more capillaries to receive oxygen.
Top: The Himalayan Rescue Association (HRA) is an organization that sends doctors to the Everest region of Nepal each climbing and trekking season to assist with medical emergencies. They give an Altitude Trek for trekkers each afternoon at their clinic in Pheriche; Middle: Dr. Kami Sherpa operates one of the medical clinics in the Everest Region; Bottom: Attending a lecture about altitude at the Himalayan Rescue Association

Top: The Himalayan Rescue Association (HRA) is an organization that sends doctors to the Everest region of Nepal each climbing and trekking season to assist with medical emergencies. They give an Altitude Trek for trekkers each afternoon at their clinic in Pheriche; Middle: Dr. Kami Sherpa operates one of the medical clinics in the Everest Region; Bottom: Attending a lecture about altitude at the Himalayan Rescue Association

If you’re traveling above 8000ft / 2440m you will likely experience a High Altitude Headache or mild symptoms of AMS (Acute Mountain Sickness) during your trip. True AMS is seen in less than a quarter of the people who trek to Everest Base Camp (17,500ft / 5333m) at the pace that Berg Adventures travels¹ and usually the AMS symptoms go away when you spend an extra day at the same altitude. Make sure you travel with someone who is experienced at altitude (and never alone!) and be honest with your guides and companions about your symptoms. Your experienced Berg Adventures guides will help you make good decisions.

AMS symptoms include:

  • Headaches: The most common symptom of altitude is by far the “high altitude headache”. While high altitude headaches are caused by a number of factors, dehydration is one of the most common. Dehydration is very common at altitude because you expel more water vapour with each exhale due to the lack of humidity. Also, the acclimatization enhancing medication Diamox is a diuretic and this can contribute to dehydration. If your headache goes away after you take Tylenol, Ibuprofen or Aspirin, it is not a concern.
  • Fatigue and weakness: Your body is working hard to acclimatize and that can zap your energy. Additionally, your heart rate and breathing rates have increased so your general energy requirement will be higher than it is at home. Remember to eat regularly and don’t shy away from sports drinks or sweetened beverages between snacks, especially if you are being active.
  • Shortness of breath: Your cardiovascular efficiency is decreased, so naturally you will become winded faster when you exercise. Take your time and move with intention. Be the tortoise, not the hare when you’re climbing and trekking at altitude.
  • Lack of appetite: Your digestive system will slow down to reserve energy for your heart, brain and lungs. This will mean that you will not digest food as quickly as normal. If you are acclimatizing well, this symptom won’t last long. Even if you are not hungry, eat a little something to keep yourself fuelled.
  • Difficulty sleeping: Like the high altitude headache, there are many factors at play which can hinder sleep. Irregular breathing patterns are the most common sleep disturbance.
  • Vomiting: If a person is vomiting, it is likely because their digestive system has slowed dramatically. If vomiting persists and is accompanied by a severe headache, this could indicate a more serious condition and should be treated as such (see HACE below).
  • Pins and needles in your extremities: This is usually due to the medication Diamox, however it can also be a result of your increased breathing rate.
Top: In general, helicopters cannot fly for rescues on Everest because the air is too thin for them to safely fly. In serious situations, they will fly to Everest Base Camp to take patients to hospitals in Kathmandu; Bottom right: A list of acclimatization adaptations from the HRA Bottom left: Everest climbers usually wear oxygen on summit day because there is so little oxygen in the atmosphere at 29,000ft / 8840m;

Top: In general, helicopters cannot fly for rescues on Everest because the air is too thin for them to safely fly. In serious situations, they will fly to Everest Base Camp to take patients to hospitals in Kathmandu; Bottom left: A list of acclimatization adaptations from the HRA; Bottom right: Everest climbers usually wear oxygen on summit day because there is so little oxygen in the atmosphere at 29,000ft / 8840m.

The above symptoms should not get worse if you are staying at the same altitude. If they do get worse or persist beyond 24 – 48 hours, they are an indication of something more serious. Two conditions that can arise from AMS include High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE). These conditions are quite rare, especially when you travel slowly and don’t travel above 18,050ft / 5500m (everything above this elevation is considered to be extreme altitude). Only 0.05% of Everest Base Camp trekkers who travel at the pace of Berg Adventures develops HAPE or HACE¹. Both conditions are life threatening if left untreated. Treatment, however, is simple when caught early - descend to a lower altitude. Edema is caused by a leaking of fluid from your cells into your lungs (HAPE) or into your brain (HACE).

Symptoms of HAPE include:

  • Extreme Shortness of Breath: The difference between AMS and HAPE is that someone with HAPE is short of breath when at rest. When the person tries to walk or climb, they will become extremely winded and will need to take breaks very frequently.
  • Cough, possibly with frothy sputnum: When there is fluid in the lungs, the body wants to expel that liquid so it will produce a cough.
  • Tightness in the chest: This is due to an increase in pulmonary arterial and capillary pressures.
  • Crackles or wheezing while breathing: When there is fluid in the lungs it causes noisy breathing.
  • Bluish skin, lips or fingernails: Low levels of oxygen circulating through the body will cause cyanosis (that bluish color) to form in some areas.
  • Rapid shallow breathing: When a person is low on oxygen, they generally want to take deep breaths. A person with HAPE will have a decreased lung capacity and will have great difficulty taking deep breaths.
Top: Inside the Everest ER, a medical tent located at Everest Base Camp; Middle left: Examining an expedition medical kit; Middle right: An HRA doctor demonstrates the use of a Gammov Bag – essentially a portable hyperbaric chamber for serious cases of HAPE and HACE; Bottom: Dr. Luanne Freer of the Everest ER on a sunny day at Base Camp

Top: Inside the Everest ER, a medical tent located at Everest Base Camp; Middle left: Examining an expedition medical kit; Middle right: An HRA doctor demonstrates the use of a Gammov Bag – essentially a portable hyperbaric chamber for serious cases of HAPE and HACE; Bottom: Dr. Luanne Freer of the Everest ER on a sunny day at Base Camp

Symptoms of HACE are quite easy to observe and they all have the same cause - an increase in intracranial pressure (pressure on the brain). The person will likely appear drunk or as though they have a head injury. Specific symptoms of HACE include:

  • Severe headache: The difference between AMS and HACE is that a headache caused by HACE will not respond to pain medication and will not get better over time. It may become so severe that the person cannot sit up or walk.
  • Confusion or loss of memory
  • Trouble speaking clearly (ataxia)
  • Loss of coordination
  • Loss of consciousness
  • Fever
  • Sensitivity to light
  • Vomiting

¹ Hacket, Peter H., and Roach, Robert C. (2013). Wilderness Medicine.Sixth ed. Paul S. Auerbach.

If you are interested in learning more here are some great resources:

Altitude Illness: Prevention & Treatment by Stephen Bezruchka

Field Guide to Wilderness Medicine (4th Edition), Edited by Paul S. Auerbach et al.

Medicine for the Outdoors: The Essential Guide to First Aid and Medical Emergencies (5th Edition), Edited by Paul S. Auerbach

Medicine for Mountaineering: And Other Wilderness Activities by James A. Wilkerson

Mountain Sickness: Prevention, Recognition and Treatment by Peter Hackett

Wilderness Medicine (6th edition), Edited by Paul S. Auerbach