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Altitude sickness

AMS - Acute Mountain Sickness (Altitude sickness)
Although trekking and climbing programmes are designed to maximize individuals acclimatization to the high altitudes experienced on most treks to the Nepal Himalaya, anyone, including your porters, can be affected by altitude sickness or Acute Mountain Sickness (AMS) to use it's medical title. This page is intended to provide an overview of AMS, its symptoms and treatments including medication.

What is AMS?
Acute Mountain Sickness (AMS) is a constellation of symptoms that represents your body not being acclimatized to it's current altitude. As you ascend, your body acclimatizes to the decreasing oxygen (hypoxia). At any moment, there is an "ideal" altitude where your body is in balance; most likely this is the last elevation at which you slept. Extending above this is an indefinite grey zone where your body can tolerate the lower oxygen levels, but to which you are not quite acclimatized. If you get above the upper limit of this zone, there is not enough oxygen for your body to function properly, and symptoms of hypoxic distress occur - this is AMS.

Go too high above what you are prepared for, and you get sick. This "zone of tolerance" moves up with you as you acclimatize. Each day, as you ascend, you are acclimatizing to a higher elevation, and thus your zone of tolerance extends that much higher up the mountain. The trick is to limit your daily upward travel to stay within that tolerance zone. The exact mechanisms of AMS are not completely understood, but the symptoms are thought to be due to mild swelling of brain tissue in response to the hypoxic stress. If this swelling progresses far enough, significant brain dysfunction occurs. This brain tissue distress causes a number of symptoms; universally present is a headache, along with a variety of other symptoms.

The diagnosis of AMS is made when a headache, with any one or more of the following symptoms is present after a recent ascent above 2500 meters (8000 feet)

  • Loss of appetite, nausea, or vomiting
  • Fatigue or weakness
  • Dizziness or light-headedness
  • Difficulty sleeping
All of these symptoms may vary from mild to severe. A scoring system has been developed based on the Lake Louise criteria; look at the AMS questionnaire for a simple method to evaluate an individual's AMS severity.

Mr. Pasang Sherpa briefing about PAC bag

AMS has been likened to a bad hangover, or worse. However, because the symptoms of mild AMS can be somewhat vague, a useful rule-of-thumb is: if you feel unwell at altitude, it is altitude sickness unless there is another obvious explanation (such as diarrhoea). Anyone who goes to altitude can get AMS. It is primarily related to individual physiology (genetics) and the rate of ascent; there is no significant effect of age, gender, physical fitness, or previous altitude experience. Some people acclimatize quickly, and can ascend rapidly; others acclimatize slowly and have trouble staying well even on a slow ascent. There are factors that we don't understand; the same person may get AMS on one trip and not another despite an identical ascent itinerary. Unfortunately, no way has been found to predict who is likely to get sick at altitude.

It is remarkable how many people mistakenly believe that a headache at altitude is "normal"; it is not. Denial is also common - be willing to admit that you have altitude illness, that's the first step to staying out of trouble. Always inform your guide if you have any symptoms.

It is OK to get altitude illness, it can happen to anyone. It is not OK to die from it. With the information in this tutorial, you should be able to avoid the severe, life-threatening forms of altitude illness.

Preventing AMS
The key to avoiding AMS is a gradual ascent that gives your body time to acclimatize. People acclimatize at different rates, so no absolute statements are possible, but in general, the following recommendations will keep most people from getting AMS:

  • If possible, you should spend at least one night at an intermediate elevation below 3000 meters.
  • At altitudes above 3000 meters (10,000 feet), your sleeping elevation should not increase more than 300-500 meters (1000-1500 feet) per night.
  • Every 1000 meters (3000 feet) you should spend a second night at the same elevation.

Remember, it's how high you sleep each night that really counts; climbers have understood this for years, and have a maxim "climb high, sleep low".

The day hikes to higher elevations that you take on your "rest days" (when you spend a second night at the same altitude) help your acclimatization by exposing you to higher elevations, then you return to a lower (safer) elevation to sleep. This second night also ensures that you are fully acclimatized and ready for further ascent. It's also important to avoid dehydration, so drink a lot of water during the day, particular if the temperature is hot. Urine color is a good indication of your hydration state, it should be pale to clear. If it's not you must drink more, and avoid tea and coffee which have a diuretic effect.

The Golden Rules for managing AMS

GOLDEN RULE I: If you feel unwell at altitude it is altitude illness until proven otherwise.

GOLDEN RULE II: Never ascend with symptoms of AMS.

GOLDEN RULE III: If you are getting worse (or have HACE or HAPE), go down at once.

If you follow these basic rules, your AMS should not progress to the far more serious and potentially fatal HACE or HAPE. These life threatening conditions should be completely avoidable if you are honest with yourself, your companions and your guide. For further information about HAPE and HACE click here.

Diamox (acetazolamide) is of some value in the PREVENTION of Acute Mountain Sickness (AMS). Dexamethasone (Decadron) has a place in the TREATMENT of established AMS and Cerebral Oedema. Nifedipine (Adalat) is used for Pulmonary Oedema. I have used the names by which these drugs are commonly known.

Diamox (acetazolamide) a drug often used in the treatment of the eye condition glaucoma is useful in the prevention of Acute Mountain Sickness (AMS). AMS occurs commonly during visits to 3000-4500m 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 Oedema.

Diamox reduces the headache of AMS and helps the body acclimatize to the lack of oxygen. It also probably reduces the incidence of the complications of AMS mentioned above.

Whether or not one takes Diamox is obviously a matter of personal choice: travel to high altitudes is quite possible without it. I do not recommend the drug as a routine, though there is variation of opinion about this.

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 three days before staying at 3500m and thereafter for two or three days until you feel acclimatized, for about five days in all.

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 color". 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.

The potent steroid dexamethasone (Decadron) has an important place in the treatment of Acute Mountain Sickness. I usually suggest it when someone has an incapacitating headache.

Dexamethasone is also used in the treatment of the life threatening complication of AMS, cerebral oedema. It is due to fluid collecting within the brain. Patients become irrational, drowsy and confused over a period of hours and their walking becomes unsteady. Double vision may occur.

How to take dexamethasone
Take dexamethasone 8mg as tablets (usually 2mg size) initially followed by 4mg every 6hrs. Treatment would normally only last for one day, i.e. a total of 20mg in one day.

If AMS symptoms (headaches) still persist you should not be going higher and should seek medical advice if available. Descend if you can. You can continue to take dexamethasone for a second day but it is unlikely to help, i.e. it usually works in the first few hours. If cerebral oedema is suspected, descent is essential. Oxygen or a pressure bag should be used if available.

Precautions and unwanted effects
Like all drugs dexamethasone may have unwanted effects. In these very short courses the problems are few. However, the following may occur:

Peptic ulceration
If you have indigestion or are known to have had an ulcer, a medical opinion is usually advisable before taking dexamethasone.

Mood changes Steroid drugs sometimes increase excitability and may make one feel `high', or rarely confused. The risk is small.

Nifedipine (Adalat), a drug used for angina and high blood pressure, has an important role in the treatment of high altitude pulmonary oedema.

If you diagnose pulmonary oedema (breathlessness, crackly breathing) you should anyway be evacuating the patient to low altitude, giving oxygen, and using a Pressure Bag, if available. Give immediately nifedipine 20 mg by mouth, and 20 mg nifedipine every 6 hours, for one day.

If you are in doubt, this treatment is unlikely to cause anyone much harm.

It may be very difficult to diagnose what exactly is wrong when someone is gravely ill at altitude. Both treatments, i.e. dexamethasone and nifedipine can be given simultaneously. In my view these drugs should be carried in a small first aid kit, by climbers, and, in the context of high altitude climbing, can be used without medical supervision.

In Britain, these three drugs are sold only on a doctor's prescription: since they would be used for foreign travel a private prescription would usually be given.

Suggested prescriptions
Some physicians may be uncertain about prescribing these drugs for altitude-related illnesses. If so, the following guidelines may be helpful:

  • Acetazolamide 250mg tablets, one twice daily for five days
  • Dexamethasone (2mg tablets) 8mg at once + 4mg six hourly for 24 hours (12 x 2mg tablets)
  • Nifedipine 20mg tablets, one six hourly for 24 hours (7 x 20mg tablets)

Anyone taking these medications should be aware of potential recorded unwanted effects, written details of which should be supplied with them by the dispensing pharmacist.