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Hiking Hazards - High Altitude


  • Introduction
  • Acclimatization
  • Acute Mountain Sickness
  • High Altitude Pulmonary Edema (HAPE)
  • High Altitude Cerebral Edema (HACE)
  • Helpful drugs (diamox and dexamethasone)
  • Food, alcohol, and drugs
  • At-risk groups
  • Suggested reading and references



The first hours after arrival at a certain altitude the resting heart rate (RHR) decreases, then increases. At 2000 meters this increase is 10% and at 4500 meters it is 50% (compared to RHR at sea level). After some days (depending on the altitude), the RHR goes back to "normal," and in many cases even goes below normal. When the RHR reaches normal, that's a clear sign of good acclimatization. [Janssen] Aerobic capacity drops about 4 percent per 1000 feet above the 4000 foot level in a sedentary person, but only half that in an aerobically fit person. [Prevention91]



The rate and depth of breathing increase to improve oxygen delivery to the blood. The heart beats more quickly and strongly, increasing the flow of blood and transport of oxygen. [Wilderness]

The bone marrow produces more red cells to carry oxygen; an increase in the number of capillaries improves oxygen supply to muscles and other tissues. [Wilderness]


Acute Mountain Sickness

Symptoms develop within 6 to 48 hours after ascent to altitudes above 8000 feet. Usually improves in 36 to 72 hours if there is no further ascent. [Wilderness]

Cold and wind, fear, fatigue, dehydration, strenuous exercise soon after ascent, and upper respiratory infections all predispose to AMS. [Wilderness]

Symptoms [Wilderness]:

  • a generalized headache that often develops during the night and is present on waking; by day, the victim may feel light-headed
  • unusual tiredness out of proportion to the activity
  • appetite loss and nausea
  • restless sleep with irregular breathing
  • shortness of breath with exertion
  • the face is swollen, with bags under the eyes; rings on fingers feel tight

What to do [Wilderness]:

  • Stop ascending or go down
  • Drink fluids
  • Rest
  • Take aspirin or ibuprofen
  • Take Diamox


High Altitude Pulmonary Edema


High Altitude Cerebral Edema


Helpful drugs (diamox and dexamethasone)

Diamox (acetazolamide) has been effectively used to prevent AMS for more than thirty years. It seems to prevent HAPE and HACe as well, although it is almost impossible to prove this because these two conditions are not very common. [Houston] It works by inhibiting the breakdown in the blood of bicarbonate anhydrase. This creates an over-supply of carbon dioxide in the blood to which the body reacts by 1) increasing breathing rate, to get oxygen into the blood stream, and 2) increasing renal activity (peeing), to equalize the acidity in the bloodstream.

Diamox is a diuretic, which means you should take in more fluids if you take Diamox. Diamox may have side effects, such as dizziness, weakness, or a skin reaction. So you should try it at "home" to see how you react before you head up to the mountains.

Experience now suggests that a half tablet (125 mg) on the morning and evening of the ascent, and twice a day for two more days, is enough, without causing the unpleasant tingling and spoiling the taste of carbonated beverages that higher doses cause.

Dexamethasone has also been used, but has added risk. Talk to your doctor.


Food, alcohol, and drugs

Alcohol, sedatives, and sleeping pills depress respiratory ventilation at night and increase the likelihood of disturbed sleep. [Wilderness]

Eat a high-calorie, high-carbohydrate diet. [Wilderness]


At-risk Groups

Those who have suffered AMS before are more likely to suffer again, and at a similar altitude. [Wilderness]

Fitness and training do not guarantee protection, and both sexes succumb equally. The young appear more prone to sickness. [Wilderness]


Suggested reading and references

  • [Bezruchka] Altitude Illness - Prevention & Treatment. Stephen Bezruchka, 1998.
  • [Hackett] Mountain Sickness - Prevention, Recognition and Treatment. Peter H. Hackett, 1980.
  • [Houston] High Altitude: Illness and Wellness. Charles Houston, 1993.
  • [Wilderness] Wilderness First Aid: Emergency Care for Remote Locations. 1998.

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