Everything You Need to Know About Altitude Sickness

Everything You Need to Know About Altitude Sickness

By Ryan Clairmont, PA-C, MPAS

Every year, 30 million people find themselves in resort towns located high in the mountains. Tens of thousands of climbers, trekkers and skiers worldwide ascend to elevations from 9800ft to 18,000ft, often at a rate that exceeds an individual’s ability to acclimatize. As hunters, we fit somewhere amongst these statistics, and unless we understand the physiology of what is happening to our bodies and how to avoid and treat altitude sickness, we are vulnerable to becoming just that…another statistic.

What is Altitude Sickness?

Altitude Sickness is the pathological effect of high altitude on humans, caused by the acute exposure to low partial pressure of oxygen at high altitude. There are three main Altitude Illnesses:

1) Acute Mountain Sickness (AMS)

2) High Altitude Cerebral Edema (HACE)

3) High Altitude Pulmonary Edema (HAPE)

The latter two are late stages of AMS and can be life threatening if left untreated. Anyone traveling above 8,200ft is at risk for getting AMS, and susceptible individuals can get it as low as 6,500ft.

Ryan Clairmont and brother Kenton, both avid hunters, in high country. 

Oxygen at High Altitude

At altitudes below ~70,000ft, the fraction of oxygen in inspired air remains constant at ~21%. So if the amount of available oxygen doesn’t change with altitude, why is it harder to breath at higher elevations?

The answer is that the fall in atmospheric pressure at higher altitudes decreases the partial pressure of inspired oxygen. The partial pressure of inspired oxygen is the driving force of the diffusion of oxygen and gas exchange in the lungs. At low pressures of inspired oxygen, a cascade effect occurs, leaving all of the body’s tissues, vital organs, right down to the cells’ mitochondria in a state of oxygen deprivation. So you see, it’s not that the “air is getting thinner” like most people are led to believe, it’s that the “pressure is getting lower,” hence the reason people have a more difficult time breathing and working at higher altitudes.

Extreme altitude. 

Risk Factors

  • Past history of Altitude Sickness
  • Rate of ascent
  • Vigorous exertion prior to acclimatization
  • Lack of acclimatization
  • Substances (i.e. Alcohol) that interfere with acclimatization
  • Co-morbidities that interfere with inspiration or circulation (i.e. neuromuscular diseases or pulmonary hypertension)

Signs and Symptoms of Altitude Sickness

There are many conditions that mimic Altitude Sickness including Exhaustion, Hypoglycemia (low blood sugar), Dehydration, Hypothermia and Hyponatremia (low serum sodium). It is important to eliminate these conditions one must consider Altitude Sickness when in high elevation environments. Think of Altitude Sickness as a cascade of symptoms. As the individual feels worse, the priority for treatment becomes much greater. I will break the symptoms down into four categories, all getting more serious with each progression.

  1. Mild AMS
    1. Headache plus 1 or more of the following:
      1. Nausea/Vomiting
      2. Fatigue
      3. Dizziness
      4. Difficulty Sleeping
  2. Moderate to Severe AMS
    1. Headache plus 1 or more symptom of moderate to severe intensity:
      1. Nausea/Vomiting
      2. Fatigue
      3. Dizziness
      4. Difficulty Sleeping
  3. HACE (Swelling of the brain)
    1. Worsening of symptoms seen in #2, plus:
      1. Unsteady Gait
      2. Altered Mental Status
      3. Confusion
  4. HAPE (Fluid in the lungs)
    1. Similar to Bronchitis
    2. Persistent Cough, dry at first then productive
    3. Fever
    4. Shortness of Breath, even at rest


Ever heard the saying, “an ounce of prevention is worth a pound of treatment?” Well nothing could be more true than when dealing with Altitude Sickness. The number one prevention method for avoiding Altitude Sickness is Gradual Ascent. A good rule of thumb is above 9,800ft, your sleeping altitude should not be increased by more than around 1,600ft with a rest day planned every three to four days. This will place the odds in your favor of avoiding Altitude Sickness. If you are planning to ascend to very high elevations (11,500ft to 18,000ft) or extreme altitudes (above 18,000ft), pre-acclimatization and a staged ascent must be part of your plan. Spend six to seven days at a moderate altitude (7,200ft – 9,800ft) before proceeding to higher elevations while practicing the sleeping altitude rule. This is why climbers spend so long at basecamps ascending and descending, preparing their bodies for their summit.


Acetazolamide (Diamox) at a dose of 125mg twice daily has been shown to help in AMS prevention. It must be started 24 hours prior to the start of a trip and can be stopped after two days at the target elevation. Ibuprofen and Ginko Biloba have shown some data that reveal some preventative properties but the debate continues. Indigenous people in the Andes have used coca leaves, coca tea and other coca products for centuries but the natural remedy has never been studied. Forced hydration shows no benefit and can cause more harm by increasing the risk of hyponatremia or low sodium levels in the blood.


Just like gradual ascent and pre-acclimatization are the best prevention methods, the number one treatment for Altitude Sickness is Descent. If symptoms occur descending, 1,000ft to 3,000ft is the gold standard of treatment. Depending on the situation, this may or may not be feasible. Dexamethasone at 8mg starting dose then 4mg every six hours until symptoms resolve or descent is possible is the medication of choice. Acetazolamide can be used at 250mg twice a day for treatment, but it is better used for prevention than treatment.

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