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  • Writer's pictureAlice Proia

What is Acute Mountain Sickness (AMS)?

Acute Mountain Sickness (AMS) is the most common form of high altitude illness. Depending on the total elevation gain and speed of ascent, AMS affects 20-80% of individuals ascending to 2500m (8,200ft) in elevation or above. As altitude increases, the amount of available oxygen decreases and the body must adjust through a process of acclimatization. AMS occurs when a person’s body does not have time to properly acclimatize.

Signs of AMS include headache, loss of appetite, fatigue, difficulty sleeping, dizziness, nausea and vomiting. Symptoms typically begin within hours of ascent. Risk factors for AMS include rapid ascent, dehydration, certain underlying health conditions, consumption of alcoholic beverages and/or certain medications, and a history of altitude illness.

Treatment of mild AMS usually involves temporarily halting ascent and management of symptoms (e.g. headache with medications such as Tylenol or Advil). Descent is always an effective treatment for AMS, but it is not mandatory, or even necessary except in the setting of intractable symptoms or suspicion that illness is progressing.

Descent to an altitude lower than that where symptoms started effectively reverses AMS. Although the person should descend as far as necessary for improvement, descending 500 to 1000m (1600 to 3300ft) is usually sufficient. Treatment of more severe AMS may involve descent to lower elevation and administration of supplemental oxygen and medications such as dexamethasone and acetazolamide.

It is a common misconception that AMS can progress to High Altitude Pulmonary Edema (HAPE), another serious form of high altitude illness, because in approximately half of HAPE cases, symptoms of AMS are also present. AMS can however progress to another serious and potentially life-threatening form of altitude illness called High Altitude Cerebral Edema (HACE). Thus, it is imperative to recognize and address AMS as early as possible.

However, despite the fact that 50% of HAPE cases occur in conjunction with symptoms of AMS, AMS does not lead to HAPE contrary to common belief.

If you or anyone in your group experiences any of the symptoms listed above, notify your guide or medic immediately so that appropriate action may be taken.

Disclaimer: This content 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 provider with any questions you may have regarding a medical condition.

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