Altitude Sickness & Aclimitization Basics

May 9, 2023

Disclaimer: This article is meant to provide general information about altitude sickness & acclimatization. It is not meant to provide medical, training, or any other form of advice. Altitude sickness is a serious condition, please seek the advice of a medical professional if you are worried about experiencing any of the symptoms of altitude sickness.

What is Altitude Sickness?

Altitude Sickness is a serious concern when climbing high peaks. There is a strong genetic component to altitude sickness, so changes in altitude will affect people differently. Always trust how you are feeling, and use your best judgment.

Altitude sickness, also known as acute mountain sickness (AMS), is a common ailment that can affect people who travel to high elevations. Here are some common signs and symptoms of altitude sickness:

  • Headache
  • Nausea and vomiting
  • Dizziness or lightheadedness
  • Fatigue
  • Loss of appetite
  • Shortness of breath
  • Difficulty sleeping

If you experience any of these symptoms, it's important to take action immediately. Here are some things you can do:

  • Rest: If you start to experience symptoms of altitude sickness, stop and rest. Don't try to push through the symptoms.
  • Hydrate: Drink plenty of fluids, as dehydration can make altitude sickness worse.
  • Descend: If your symptoms are severe or worsening, descend to a lower altitude immediately.
  • Medication: Over-the-counter medications like ibuprofen or aspirin can help relieve symptoms like headache and body ache. Acetazolamide (Diamox) is a prescription medication that can help prevent and treat altitude sickness. Consult your doctor before taking any medication.
  • Oxygen: In severe cases, oxygen therapy may be necessary.

It's important to remember that altitude sickness can be a serious condition, and can even be fatal in rare cases. If you experience severe symptoms like confusion, difficulty breathing, or chest pain, seek medical attention immediately. It's always better to err on the side of caution when it comes to high-altitude trekking.

What is Acclimatization?

Acclimatization is the process by which your body adapts to higher altitudes. When acclimatizing to high altitude, the body undergoes a series of physiological changes to adapt to the lower oxygen levels present at higher elevations. These changes occur over a period of days to weeks and may include the following:

Increased breathing rate: The body responds to lower oxygen levels by increasing the number of breaths taken per minute. This helps to bring in more oxygen with each breath and expel more carbon dioxide.

Increased heart rate: The heart responds to lower oxygen levels by beating faster to circulate blood more quickly throughout the body. This helps to deliver oxygen to the tissues more efficiently.

Increased production of red blood cells: The kidneys respond to lower oxygen levels by releasing a hormone called erythropoietin (EPO), which stimulates the bone marrow to produce more red blood cells. Red blood cells are responsible for carrying oxygen from the lungs to the tissues. 

*Note: You may recognize the term EPO from blood doping scandals. Exogenous use of EPO is banned by WADA (learn more here). The amount of endogenous EPO produced when acclimating to altitude is significantly less than what people use to dope. Many athletes use altitude training for performance benefits for this exact reason, and using altitude as a part of a training plan is a common & clean part of many professional athletes training plans.

Increased production of capillaries: Capillaries are small blood vessels that deliver oxygen and nutrients to the tissues. In response to lower oxygen levels, the body may increase the production of capillaries to improve oxygen delivery.

Increased buffering capacity: At high altitude, the blood can become more acidic due to increased carbon dioxide levels. The body responds by increasing its buffering capacity, which helps to maintain the pH balance of the blood.

These adaptations allow the body to function more efficiently at high altitude and reduce the risk of altitude-related illnesses such as altitude sickness and high altitude pulmonary edema. However, it's important to note that the rate and degree of acclimatization can vary greatly between individuals, and some people may require more time or medical intervention to adapt to high altitude.

Here are some tips to help you acclimatize to altitude:

  • Gradual ascent: Ascend gradually to give your body time to adjust. Avoid rapid ascents or ascending more than 300-500 meters per day above 2,500 meters.
  • Stay hydrated: Drink plenty of fluids, preferably water or electrolyte solutions, to prevent dehydration. Avoid alcohol and caffeine, which can contribute to dehydration.
  • Proper nutrition: Eat a balanced diet that includes complex carbohydrates, lean protein, and plenty of fruits and vegetables.
  • Rest: Take time to rest and recover. Adequate rest can help your body acclimate more quickly.
  • Medications: Diamox is a medication that can help prevent and treat altitude sickness. Talk to your doctor about whether this medication is right for you.
  • Controlled breathing: Controlled breathing exercises, such as deep breathing or yoga, can help increase oxygen intake and improve acclimatization.
  • Consider hiring a guide: Hiring an experienced guide who is familiar with the area can be helpful in ensuring a safe and enjoyable trek.

It's important to listen to your body and pay attention to any symptoms of altitude sickness. If you experience severe symptoms, descend to a lower altitude immediately and seek medical attention if necessary.

What are Acclimatization rounds?

Acclimatization rounds, also known as acclimatization climbs or rotations, are a crucial part of mountaineering at high altitude. These are typically repeated ascents to increasingly higher elevations that allow climbers to gradually acclimatize to the lower oxygen levels and reduced atmospheric pressure at high altitude.

The process typically involves ascending to a higher altitude over a period of several days, then descending to a lower altitude for rest and recovery. This cycle is repeated multiple times, with each ascent reaching a higher elevation than the previous one, until the climber has acclimatized sufficiently to attempt the final push to the summit.

During each acclimatization round, climbers typically spend several days at the higher altitude, allowing their bodies to adjust to the lower oxygen levels. This can involve slow and steady climbing, frequent rest breaks, and careful monitoring of one's physical condition and vital signs.

Acclimatization rounds are a critical part of mountaineering at high altitude, as they help to reduce the risk of altitude sickness, which can have serious health consequences, and increase the chances of a successful summit attempt. However, it's important to note that even with proper acclimatization, mountaineering at high altitude can still be very challenging and carries inherent risks that should be carefully considered and prepared for.

A Note on Diamox

Diamox is the brand name of a medication called acetazolamide, which is a carbonic anhydrase inhibitor. It is commonly used to prevent and treat altitude sickness and glaucoma.

In the case of altitude sickness, Diamox works by increasing the body's excretion of bicarbonate in the kidneys, which leads to a mild metabolic acidosis (a slightly more acidic environment in the blood). This acidosis stimulates the body to breathe more rapidly and deeply, which increases the amount of oxygen taken in and helps to counteract the effects of low oxygen levels at high altitude. This increase in breathing rate and depth can help prevent or alleviate the symptoms of altitude sickness.

In addition to its effects on respiration, Diamox also has diuretic properties, which means that it increases the production of urine and helps to decrease the buildup of excess fluid in the body. This can be particularly useful in preventing altitude-related fluid accumulation in the lungs or brain, which can be dangerous.

* * It's important to note that Diamox is not a substitute for proper acclimatization and should only be used in conjunction with appropriate acclimatization measures, such as gradual ascent, hydration, and rest. It is also not recommended for everyone and should be used only under the guidance of a healthcare professional.

Additional Resources:

High Altitude Doctor is the preeminent clinical resource devoted to high altitude medicine. The purpose of High Altitude Doctor is to provide clinical services, education, and conduct research on the effect of altitude on human wellness & performance. 

Uphill Athlete + Peter Hackett In 2018 Steve House and Scott Johnston joined two of the world's preeminent High Altitude Medicine specialists, Dr. Robert Roach and Dr. Peter Hackett, to present an all day seminar on all aspects of preparing military special operations personnel to go to high altitudes. This video is Dr. Hackett's lecture which is approximately one hour in duration. Keep in mind that Dr. Hackett is presenting to an international group comprised of American and American-allies' military field-paramedics, training (physcial/coaching) personnel, and Special Operations officers.

It doesn’t take a trip up Everest to begin to feel the effects of higher altitudes. A visit to one of your favorite mountain destinations can be enough. However, with proper preparation and understanding of how to acclimate your body appropriately and spend time at altitude, as well as what the signs and symptoms of altitude sickness are, you can maximize your enjoyment at higher elevations.