Acute Mountain Sickness - Everything you need to know before going on a trek in Nepal

1. What is AMS (Acute Mountain Sickness)?

It is an acute condition of illness that develops gradually along with the elevation or ascent of altitude higher than 2400 meters/8000 feet above sea level, in the lack of acclimatization or adaptation of the body to the changing atmosphere. Some might develop it below 2400 meters also. It occurs most commonly among mountaineers and other travelers hiking uphill. It develops when the rate of ascent exceeds the body’s ability to adjust according to the change. The symptoms are usually mild and can be easily cured by following simple treatment methods.

2. What is the cause of AMS?

As the altitude increases, the air pressure decreases and there is less availability of oxygen. When the body fails to adapt to the atmosphere having low oxygen, the signs and symptoms of AMS begin to appear resulting in the slowing down of mental and physical performance. The symptoms get worse as the altitude increases. Faster ascent without proper acclimatization is the main reason people get AMS. People living in lower altitudes or having no prior experience of trekking in high-altitude areas are also more prone to getting sick. Other risk factors include people with heart and respiratory problems and dehydration.

3. What are the signs and symptoms of Acute Mountain Sickness (AMS)?

Symptoms of AMS usually begin to develop between 6 to 24 hours after reaching altitudes above 2400 meters. The common symptoms of AMS are:

• Headache
• Fatigue 
• Dizziness
• Nausea
• Loss of appetite
• Vomiting
• Difficulty in sleeping
• Light-headedness
• Shortness of breath

4. What happens when AMS is neglected?

AMS can progress to more serious conditions like High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE) which can be fatal if immediate treatment is neglected.

High Altitude Pulmonary Edema (HAPE)

HAPE is when fluids accumulate in the lungs in a response to lack of oxygen or hypoxia. The symptoms are shortness of breath at rest, noisy breathing, extreme fatigue, blueness of lips/tips of fingers/tongue, cough – dry in the beginning, and later producing frothy or blood-tinged sputum.

High Altitude Cerebral Edema (HACE)

HACE is a condition when the fluids accumulate in between the brain cells and get swollen caused by a lack of oxygen or hypoxia. Symptoms include mental confusion, disorientation, irritability, and difficulty with balance and coordination.

5. How is AMS treated?

If the symptoms are mild, one can rest at the same altitude for some time to see if the symptoms go away entirely or not. If not, there is no better treatment except going down at least 300 meters or 1 camp down with another person to take care of.

For serious conditions like HAPE and HACE, immediate descent is needed as soon as possible, or even an evacuation by helicopter. Secondary treatment like Gamow or PAC (Portable Altitude Chamber) Bag and supplementary oxygen can be given to improve the person’s condition until the helicopter arrives or the person can descend. Nowadays, most trekking agencies provide Gamow or PAC Bag on high-altitude treks.

However, these are not replacements for the descent. Remember, the descent is the only treatment for all types of altitude sickness.

6. How can AMS be prevented?

• One of the most effective ways is to adjust your body to the increasing altitudes through the process of acclimatization. Most of the high-altitude trek itineraries have 1 or 2 days allocated as a rest day for acclimatizing. On the rest day, hike up to the surrounding areas ascending between 300 meters-1000 meters, and later return to the rest point for the night stay. This is also called the ‘Climb High Sleep Low’ method.
• Certain medications like Diamox (Acetazolamide) are useful for preventing and even reducing symptoms of AMS. Take 125mg twice a day for at least 24 hours before ascending and continue until reaching the highest altitude. No need to use it for the descent.
•  Keep up to date with the body conditions every day. Recognizing the symptoms of AMS earliest as soon as possible is important. Devices like pulse oximeters can be handy.
•  Drink plenty of fluids and eat plenty (4000-5000 calories per day). If possible, avoid alcoholic beverages.
•  Make slow and gradual ascent.