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Acute Mountain Sickness (AMS)

Also referred to as hypobaropathy, "the altitude bends", or soroche.

Symptoms | Causes | Prevention | Treatment | Sources

Acute Mountain Sickness (AMS) (TD) occurs commonly at altitudes above 3,000 m./10,000 ft and usually causes a severe headache, exhaustion and feeling generally unwell. Rarely (but even at these altitudes) the condition progresses to cause more serious problems which are potentially fatal - Pulmonary and Cerebral Edema.

It will start at High Altitudes, 8,000 - 12,000 feet (a few people can get symptoms as low as 5,000 ft); It occurs in 17 to 24% of those who travel from sea level to 8,000 ft.; 7% will have severe headache. At 10,000 ft. 75% of people will have mild symptoms. The incidence of symptoms increases at Very High Altitudes (12,000 - 18,000 feet [3,658 - 5,487 meters]) with 67% becoming ill at 14,000 feet. There is little data for non-mountaineers at Extremely High Altitudes, greater than 18,000 ft.

In the Death Zone, above 8,000 m (26,000') your body can not metabolize food and starts eating itself.

Note: Most airplanes are pressurized to the equivalent of 7,000 - 8,000 ft. Newer planes may pressurize down to 5,000 ft equivalent.


Symptoms usually start 12-24 hours after arrival at altitude and begin to decrease in severity about the third day. The symptoms of Mild AMS are:
  • headache
  • dizziness
  • nausea or vomiting
  • fatigue
  • shortness of breath during exertion
  • loss of appetite
  • disturbed sleep
  • decreased coordination (ataxia)
  • a general feeling of malaise
  • Hyperventilation (breathing fast)
  • Increased urination (altitude diuresis)
  • Changed breathing pattern at night
  • Awakening frequently at night
  • Weird dreams
Initial adaptive responses to altitude include: Symptoms tend to be worse at night and when respiratory drive is decreased. Mild AMS does not interfere with normal activity and symptoms generally subside within 2-4 days as the body acclimatizes. As long as symptoms are mild, and only a nuisance, ascent can continue at a moderate rate. When hiking, it is essential that you communicate any symptoms of illness immediately to others on your trip.


The atmospheric pressure at sea level about 14.7 pounds per square inch (760 mm of mercury). Pressure at 12,000 feet (3,658 meters) is 40% less than that at sea level resulting in fewer oxygen molecules per breath (at 18,000' pressure is about 50% of that at sea level. at 29,000' it is 33% of sea level). Pulse rate and blood pressure go up sharply. Your breathing rate cannot increase enough to raise the oxygen content in the blood to sea level concentrations. The body must adjust to having less oxygen. In addition, for reasons not entirely understood, high altitude and lower air pressure causes fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain.

Preventing Altitude Illness During Active Vacations There are two other severe forms of altitude illness, High Altitude Cerebral Edema (HACE) (severe headache, confusion, double vision, loss of coordination and delirious thinking) and High Altitude Pulmonary Edema (HAPE) (a cough, rapid pulse and breathing, shortness of breath, and ultimately turning blue and producing frothy, bloody foam from the lungs). Both of these happen less frequently (< 1%), especially to those who are properly acclimatized. When they do occur, it is usually with people going too high too fast or going very high and staying there.



  • If possible, don't fly or drive to high altitude. Start below 10,000 feet (3,048 meters) and walk up.
  • If you do fly or drive, do not over-exert yourself or move higher for the first 24 hours.
  • If you go above 10,000 feet (3,048 meters), only increase your altitude by 1,000 feet (305 meters) per day and for every 3,000 feet (915 meters) of elevation gained, take a rest day.
  • move SLOWLY,; don't over-exert yourself when you first get up to altitude. The body does not recover from overexertion until you get back to lower altitude. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.
  • Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least 3-4 quarts per day). Urine output should be copious and clear.
  • "Climb High and sleep low." This is the maxim used by climbers. You can climb more than 1,000 feet (305 meters) in a day as long as you come back down and sleep at a lower altitude.
  • If you begin to show symptoms of moderate altitude illness, don't go higher until symptoms decrease ("Don't go up until symptoms go down").
  • If symptoms increase, go down, down, down!
  • Keep in mind that different people will acclimatize at different rates. Make sure all of your party is properly acclimatized before going higher.
  • Avoid tobacco and alcohol and other depressant drugs including, barbiturates, tranquilizers, and sleeping pills. These depressants further decrease the respiratory drive during sleep resulting in a worsening of the symptoms.
  • Eat a high carbohydrate diet (more than 70% of your calories from carbohydrates) while at altitude.
  • The acclimatization process is inhibited by dehydration, over-exertion, and alcohol and other depressant drugs.
Preventing Altitude Illness During Active Vacations


The mainstay of treatment of AMS is rest, fluids, and mild analgesics: acetaminophen (paracetamol), aspirin, or ibuprofen. Source Base Camp MD

Acetazolamide (Diamox ®)
Brand Name: Diamox®
Generic name: Acetazolamide

Acetazolamide forces the kidneys to excrete bicarbonate, the base form of carbon dioxide; this re-acidifies the blood, balancing the effects of the hyperventilation that occurs at altitude in an attempt to get oxygen.

Diamox allows you to breathe deeper and faster so that you metabolize more oxygen, thereby minimizing the symptoms caused by poor oxygenation. This is especially helpful at night when respiratory drive is decreased.

How to take Diamox:

If you decide to use the drug, I suggest Diamox 250mg (one tablet) is taken twice daily as a trial at sea level for two days several weeks before a visit to altitude. Assuming no unpleasant side effects are experienced, take the drug in the same dose for one to three days before staying at 3500m (11,500 ft.) and thereafter for two or three days until you feel acclimatised, for about five days in all.
A few trekkers have had extreme visual blurring after taking only one or two doses of acetazolamide; fortunately they recovered their normal vision in several days once the medicine was discontinued.

Caffeine and alcohol may affect the way Diamox works.

Side Effects:

Like all drugs Diamox may have unwanted effects. Tingling of the fingers, face and feet is the commonest; it is not a reason for stopping the drug unless the symptoms are intolerable. Dizziness, vomiting, drowsiness, confusion and rashes have all been reported but are unusual. It makes many people (including myself) feel a little "off colour". Exceptionally the drug has caused more serious problems with blood formation and/or the kidney. Those who are allergic to the sulphonamide antibiotics may also be allergic to Diamox. Carbonated drinks taste strange when you are taking Diamox.

See Acetazolamide at WebMD.

Dexamethasone (a steroid) is a prescription drug that decreases brain and other swelling reversing the effects of AMS. Dosage is typically 4 mg twice a day for a few days starting with the ascent.

Viagra® Recent studies indicate viagra is effective against altitude sickness. I couldn't find any details on dosage etc.
A 2002 study published in the "Journals of the American Heart Association" showed that viagra blocked the increase in the arterial blood pressure which is one cause of AMS.

Ginko Biloba - Take 60 - 120 mg. twice a day for three weeks prior to arriving at altitude.

In a study of mountain climbers on a Himalayan expedition, Ginkgo was found to prevent acute altitude sickness and cold-related vascular problems. The results were that none of the climbers taking Ginkgo got sick and 41% of those who took a placebo did. More recent studies refute these results.

Which Ginko - There is only one Ginkgo that I know of that today's medical research is based on. Any other Ginkgo is virtually absent of scientific support. And, you can find it in your local vitamin store. Read the label. It should say each of the following: 50:1 extract, 24% flavonglycosides, and a minimum of 6% terpene lactones. The 6% terpene lactones is the most critical measurement, as this is where the Ginkgolide B will be. Check to see if there is a minimum of .8% Ginkgolide B claimed on the label. If so, you are probably all right.
(Note: "TruNature®" Ginko is listed as 24% flavone glycosides and 6% terpene lactones. I asked them about the extract and Ginkgolide B and their reply was "we don not routinely test for ginkogolic acid or bilobalides and therefore cannot give you the exact amounts")

(See article at TradGirl.)


Headache medication:
Aspirin, Tylenol, Motrin or Ibuprofen (Advil).

Diamox: (Acetazolamide)
See above.

Garlic helps thin the blood which will help with altitude sickness.

Nifedipine is a calcium channel blocker that rapidly decreases pulmonary artery pressure and relieves HAPE.
Brand Names: Adalat CC®, Nifedical XL, PROCARDIA®

Breathing oxygen reduces the effects of altitude illnesses.

Descending even a few hundred feet may help and 1-2,000 feet will result in significant improvements. The person should remain at lower altitude until symptoms have subsided (up to 3 days)

Severe AMS presents as an increase in the severity of the aforementioned symptoms, including shortness of breath at rest, inability to walk, decreasing mental status, and fluid buildup in the lungs. Severe AMS requires immediate descent to lower altitudes 2,000 - 4,000 feet.

Sources of Information for the above:

Outdoor Action at
UIAA Mountain Medicine Centre
Altitude and Acclimatization at TradGirl
An Altitude Tutorial from the International Socieity for Mountain Medicine, 9/8/2001,
High Altitude Sickness at Mountaineering Council of Ireland

Acetazolamide - Wikipedia, the free encyclopedia
Base Camp MD - Guide to High Altitude Medicine
Diamox (acetazolamide)
Diamox Oral : Uses, Side Effects, Interactions, Pictures, Warnings & Dosing - WebMD
PROCARDIA® and Viagra are registred trademarks of Pfizer.
Adalat CC® is a aregistered trademark of Bayer.

See Also:
Altitude Sickness: Injuries; Poisoning: Merck Manual Professional
How The Body Uses O2 at Humans at Altitude on NOVA (PBS)
Preventing Altitude Illness During Active Vacations
High Altitude Guide in Recreation
Altitude Acclimatization for Trekking | Everest Base Camp Trek Guide

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last updated 10 Sep 2009