What is Altitude Sickness

Acute Mountain Sickness

AMS can afflict any visitor sleeping higher than 6000 feet. In Colorado, between 15 and 40% of visitors sleeping at 8000 ft or higher get AMS, with the incidence the highest at the highest resorts. Most folks visiting these areas travel in one day from low to high altitude; if an intermediate day is spent in Denver or a similar altitude, the incidence of AMS is much lower. One survey done at a Colorado ski resort at 9800 ft found that 60% of visitors developed a headache, the first sign of AMS, and also called high altitude headache. To meet the definition of AMS, other symptoms need to develop, such as loss of appetite, sometimes vomiting, weakness, dizziness, fatigue, and difficulty sleeping. AMS feels exactly like a bad hangover. Symptoms can occur as early as 2 hours after arrival to altitude, or be delayed for 24 hours or so. Symptoms of AMS do NOT develop after 2 days of feeling well, unless one has moved to a higher altitude. . Therefore, a person who has been doing well at altitude and then gets sick after two or three days needs to be evaluated for other conditions.

What causes AMS?

We have to admit that the exact cause of AMS is still not clear. Of course, AMS is due to low oxygen, but the steps between low oxygen and AMS are fuzzy. Current thinking is that hypoxia (low oxygen) in the air and blood causes the blood vessels of the brain to dilate in an attempt to get more oxygen. Something about this vasodilation causes the headache. And because there is more blood in the brain, the brain is slightly swollen. Although everyone going to high altitude has slight brain swelling, it is worse in those who develop AMS. This swelling causes pressure on the brain as it is squeezed against the skull, and the pressure might be the cause of the symptoms. Some researchers think that AMS is more like a migraine headache, and indeed, AMS and migraine have some similarities, but they are not identical. Rarely, AMS will go on to a more severe form of altitude illness, high altitude cerebral edema (HACE). While very unusual in Colorado ski resorts, being aware of this condition, recognizing symptoms early, and seeking treatment will easily avoid severe illness.

How is AMS diagnosed?

Diagnosis of AMS is based on the classic symptoms in someone who has been at high altitude for less than 2 or 3 days. Headache is the cardinal symptom, but is not always present. Other symptoms include dizziness, feeling chilled, trouble sleeping, loss of appetite or nausea, fatigue, and sometimes irritability. The Lake Louise Score is a scoring system of symptoms developed by experts at a conference in Lake Louise, Canada. A score of 4 or more is considered diagnostic for AMS for research purposes. However, a bad headache by itself may be sufficient for the diagnosis of AMS in mountain clinics.

Have you, a family member, or friend had altitude illness in the past?

If you have had altitude illness in the past you may be at risk to get it again, since there is a significant genetic component to altitude illness. People are generally susceptible or resistant to altitude illness, and this is generally reproducible on multiple trips to high altitude if the ascent rate is similar, but as always, there are exceptions. Having been to altitude once without problems should not encourage too great a sense of optimism that you will never get sick in the future. And even though you have had altitude illness in the past, you can safely return to altitude without getting sick again if you educate yourself on altitude illness and follow recommended guidelines.

How can I prevent altitude illness?

As with any illness, prevention is always the best approach. These are things you can do to improve your chances of not getting altitude illness.

Slow ascent to altitude is the key to prevention. Almost anyone can get altitude illness if they go too high, too quickly. Because of the individual differences, a preventive rate of ascent for one person may be too slow or fast for another.
An overnight stay at an intermediate altitude such as Denver (5280 ft) or preferably a bit higher prior to further ascent into the mountains is very helpful. If traveling to Telluride, overnighting in Ridgway, Ouray, Placerville or Durango would be helpful, especially if the destination is Mountain Village.
Staying hydrated is important as it aids your body in acclimatizing.
Avoid use of alcohol or sleeping agents of the benzodiazepine family, since they both suppress breathing and result in lower blood oxygen. Other sleeping pills like Ambien® or Lunesta® do not affect breathing at high altitude and are safe. Avoid over-exertion for 1-2 days after arrival to altitude.
Acetazolamide (Diamox®) taken 24 hours prior to arrival to altitude and the first 2 days at altitude is 75% effective in preventing AMS. It speeds up the acclimatization process in the body, stimulates breathing, raises blood oxygen and increases urination.
Gingko biloba, according to some studies was effective in preventing AMS when started 5 days prior to ascending to altitude, at a dose of 100 mg twice a day.

What are the risk factors for AMS?

Several factors increase your risk for getting AMS:

Your genetic makeup
A history of previous AMS
Residence at an altitude below 3000 ft
Obesity
Current respiratory infection
Most importantly, fast rate of ascent
Over-exertion the first day or two at altitude
Alcohol the first night at altitude

How do you treat AMS?

AMS usually resolves by itself, within 6 to 48 hours. In one study in Colorado, it lasted an average of 16 hours. However, certain actions can help or hinder its resolution.
Do not proceed to a higher altitude if you have AMS. You must stay at the same altitude and rest at a minimum, or you can descend to a lower altitude; this always works, but is often not necessary. If you are getting very ill, then you must go to a lower elevation, or start on oxygen. Descent to 1000 ft lower is generally adequate. At a ski resort, seeking medical attention is the best option.
The headache of AMS improves with rest, and medications such as ibuprofen (Motrin) or acetaminophen (Tylenol®) are often sufficient.
Oxygen breathing will improve symptoms rapidly, usually within minutes.
Acetazolamide (Diamox®) is a prescription medication that increases breathing, raises the blood oxygen level, speeds up acclimatization and therefore resolves AMS. The usual dosage is 125 mg twice a day for a few days.
Dexamethasone (Decadron®) is a prescription steroid medication that reduces swelling in the brain and improves symptoms, but it is generally reserved for moderate to severe illness. Dosage is 4 mg every 6 hours, usually for 24 hours.
A hyperbaric bag is a portable pressurized bag which simulates going to a lower altitude. It is mainly used in remote areas where oxygen and descent are less available options.

What is Altitude Sickness | What is HACE? | What is HAPE? | Altitude Related Issues | Children and Altitude