What is altitude sickness ? And how to prevent it

Written by

What is altitude sickness ?

Altitude sickness or mountain sickness is a situation that can affect mountain climbers, hikers or travelers at high altitudes above 8,000 feet (2,400 meters).
It is likely that most of them will experience at least some form of mild altitude sickness during these altitudes, but serious symptoms do not usually occur until over 12,000 feet.

NOTE: When hiking it is essential that you communicate any symptoms of illness immediately to others on your trip.

There are three main types of altitude sickness,

1). Acute (mild) altitude or mountain sickness (AMS)
AMS is very common at high altitude. At over 3,000 meters (10,000 feet) 75% of people will have mild symptoms. The occurrence of AMS is dependent upon the elevation, the rate of ascent, and individual susceptibility. Many people will experience mild AMS during the acclimatization process.

2). High-altitude pulmonary edema (HAPE)
HAPE results from fluid build up in the lungs. This fluid prevents effective oxygen exchange. As the condition becomes more severe, the level of oxygen in the bloodstream decreases, which leads to cyanosis, impaired cerebral function, and death.

3). High-altitude cerebral edema (HACE)
HACE is the result of the swelling of brain tissue from fluid leakage.It generally occurs after a week or more at high altitude. Severe instances can lead to death if not treated quickly.

How does altitude sickness occurs ?



It is caused by the failure of the body to adapt quickly enough to the reduced level of oxygen in the air at an increased altitude. There are many different symptoms but the most common are,

    • Headaches,
    • Light-headedness,
    • Nausea,
    • Loss of appetite,
    • Tingling in the toes and fingers, and a mild swell of ankles and fingers.

These mild forms are not serious and will normally disappear within 48 hours.

You are at higher risk for acute mountain sickness if:

    • You live at or near sea level and travel to a high altitude
    • You have had the illness before

Six factors that affect the incidence and severity of altitude illness:
1). Rate of ascent
2). Altitude attained
3). Length of exposure
4). Level of exertion
5). Hydration and diet
6). Inherent physiological susceptibility

How can you prevent altitude sickness?

  • If possible, don’t fly or drive to high altitude. Start below 3,000 meters (10,000 feet) and walk up.
  • If you do fly or drive, do not overexert yourself or move higher for the first 24 hours.
  • If you go above 3,000 meters (10,000 feet), only increase your altitude by 300 meters (1,000 feet) per day, and for every 900 meters (3,000 feet) of elevation gained, take a rest day to acclimatize.
  • Climb high and sleep low! You can climb more than 300 meters (1,000 feet) 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 sickness, don’t go higher until symptoms decrease.
  • If symptoms increase, go down, down, down!
  • Keep in mind that different people will acclimatize at different rates. Make sure everyone in your party is properly acclimatized before going any higher.
  • Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least four to six litres per day). Urine output should be copious and clear to pale yellow.
  • Take it easy and don’t overexert yourself when you first get up to altitude. But, light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.
  • Avoid tobacco, alcohol and other depressant drugs including, barbiturates, tranquillisers, sleeping pills and opiates such as dihydrocodeine. These further decrease the respiratory drive during sleep resulting in a worsening of symptoms.
  • Eat a high calorie diet while at altitude.Remember: Acclimatization is inhibited by overexertion, dehydration, and alcohol.

Read and follow this BMC Travel at high altitude guide for more information.


Preventative Medications

Acetazolamide (Diamox): This is the most tried and tested drug for altitude sickness prevention and treatment. Unlike dexamethasone (below) this drug does not mask the symptoms but actually treats the problem. It seems to works by increasing the amount of alkali (bicarbonate) excreted in the urine, making the blood more acidic. Acidifying the blood drives the ventilation, which is the cornerstone of acclimatization.

For prevention, 125 to 250mg twice daily starting one or two days before and continuing for three days once the highest altitude is reached, is effective. Blood concentrations of acetazolamide peak between one to four hours after administration of the tablets.

Studies have shown that prophylactic administration of acetazolamide at a dose of 250mg every eight to twelve hours before and during rapid ascent to altitude results in fewer and/or less severe symptoms (such as headache, nausea, shortness of breath, dizziness, drowsiness, and fatigue) of acute mountain sickness (AMS). Pulmonary function is greater both in subjects with mild AMS and asymptomatic subjects. The treated climbers also had less difficulty in sleeping.

Side effects of acetazolamide include: an uncomfortable tingling of the fingers, toes and face carbonated drinks tasting flat; excessive urination; and rarely, blurring of vision.

The original post is here for more detailed information on AMS and preventative medications.

Article Categories:
Health · Nepal · Safety

Leave a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Hot Line
+94 77 234 7157