Wilderness: Altitude Sickness

Altitude Sickness Overview

Acute mountain sickness (AMS), or altitude sickness, occurs in up to 67% of people who rapidly ascend above 8,000-10,000 feet (moderate altitude) over a period of 1-2 days. Symptoms (primarily headache) can appear within hours.

High-altitude pulmonary edema (HAPE) occurs when the air spaces of the lungs fill with fluid from leaking pulmonary blood vessels. This makes breathing and oxygenation difficult. While rare, high-altitude pulmonary edema is the most frequent cause of death in people with altitude illness. Symptomatic high-altitude pulmonary edema occurs in 2-4% of people who ascend to altitudes above 14,000 feet.

High-altitude cerebral edema (HACE) occurs when the brain swells due to fluid retention and low oxygen levels. This causes confusion and disorientation. High-altitude cerebral edema is the least common, but most severe, form of altitude illness. While less common than high-altitude pulmonary edema, high-altitude cerebral edema frequently occurs in people who already have high-altitude pulmonary edema.

Both high-altitude pulmonary edema and high-altitude cerebral edema are more common in people who ascend too rapidly and who continue to sleep at higher altitudes despite having symptoms of acute mountain sickness at lower elevations. Both conditions are gradually progressive and tend to occur over a period of days.

Women in the premenstrual water-retaining phase are more likely to develop symptoms.

Altitude Sickness Symptoms

Symptoms for each of the forms of altitude sickness are as follows:

• Altitude mountain sickness (AMS) – Headache (chief symptom), poor appetite, nausea, fatigue, dizziness, difficulty sleeping
  
  
• High-altitude pulmonary edema (HAPE) – Shortness of breath at rest (chief symptom), cough, weakness, headache, elevated respiratory rate and heart rate
  
  
• High-altitude cerebral edema (HACE) – Difficulty walking due to imbalance (ataxia, chief symptom), severe headache, vomiting, confusion, seizures, coma

Altitude Sickness Treatment

To prevent acute mountain sickness, a climber's initial sleep altitude should be lower than 8,000 feet. At altitudes above 10,000 feet, the sleeping elevation should increase no more than 1,000 feet per day.

A simple, fundamental rule will help to prevent severe altitude illness in almost every case: If a person experiences any symptoms of altitude sickness, the person should not ascend or increase the sleeping elevation until all symptoms have resolved. Failure to follow this rule can allow simple altitude mountain sickness to progress to potentially fatal high-altitude pulmonary edema or high-altitude cerebral edema.

Treatments for the forms of altitude sickness are as follows:

• Altitude mountain sickness (AMS): Stop the ascent and rest. Symptoms typically go away by themselves; however, the person with AMS may need supplemental oxygen. Acetazolamide (a diuretic), if prescribed, will minimize fluid retention, and acetaminophen (Tylenol) or aspirin will relieve headaches.
  
  
• High-altitude pulmonary edema (HAPE): The climber with HAPE must rest, get supplemental oxygen, and descend immediately. In severe cases, nifedipine (Procardia), if prescribed, may be used as a "rescue agent," but it does not replace the need for descent.
  
  
• High-altitude cerebral edema (HACE): A person with HACE must receive supplemental oxygen and descend immediately. Use dexamethasone (Dexone) to decrease brain swelling. The person may require a Gamow bag (a bag that increases the air pressure around the climber which simulates descent) or other hyperbaric chamber treatment. However, this does not replace the need for descent.