Acute Mountain Sickness (AMS), often referred to as altitude sickness, is a fairly common and serious risk when trekking at high altitude in Nepal. AMS can develop at altitudes above 2000 meters (6500 ft), and the risk increases significantly as you ascend to higher altitudes.
The early symptoms of AMS are headache, extreme fatigue, and loss of appetite/nausea. Some people also experience shortness of breath while resting. AMS is a result of the excessive accumulation of fluid in certain parts of the body, specifically the brain and lungs. When mild symptoms occur you must stop immediately at the current altitude until the symptoms have gone away. If symptoms persist after you have rested for a day or two, you must descend to a lower altitude (300 – 500m/1000-1700 ft lower)
Worsening symptoms of AMS including increasing tiredness, severe headache, vomiting, and loss of coordination. These are the symptoms of the more severe case of AMS call High Altitude Cerebral Edema (HACE). HACE can lead to unconsciousness and death within 12 hours if the symptoms are ignored. Increasing shortness of breath, coughing, and tiredness are signs of High Altitude Pulmonary Edema (HAPE), which can also be rapidly fatal if ignored.
A person suffering from AMS may not be thinking clearly and may have to be forced to descend. A person with AMS should not be allowed to descend alone. They should descend to an altitude where they feel their symptoms improve (usually after 300 – 500 meters of descent). Always follow your trek guide’s advice about how to deal with AMS symptoms.
If you experience any AMS symptoms but are unsure whether it is AMS, always err on the side of caution and stop ascending and consider descending to lower altitude.
Medications are not a good substitute for proper acclimatization in reducing the risk of AMS. Acclimatization requires a planned, slow ascent of not more than 300 – 500m (1000-1700 ft) per day. If you are acclimatizing properly you can also consider taking Diamox to prevent or alleviate AMS symptoms.
You should not plan to trek to high altitude (over 3000 meters) if you have heart disease, difficulty breathing at sea level, or are pregnant. Children may be more susceptible to AMS, and because they may not be able to describe their symptoms should be watched very closely.
Good physical conditioning does not prevent AMS, and persons who have not experienced AMS at high altitudes in the past may still develop symptoms on subsequent treks.
Sleeping pills, sedatives and alcohol should not be used at high altitudes as they tend to decrease breathing and can lead to AMS. Drinking 3-4 liters of water or other fluids per day to avoid dehydration will help in the acclimatization process. It is also possible to use a Gamow bag to treat the effects of AMS. A Gamow bag, available at the Himalayan Rescue Association’s outposts in Periche (Everest) and Manang (Annapurna), simulates the air pressure of low altitude.
While it is possible to employ helicopter rescue in case of serious AMS symptoms you should not rely on this, or wait for a helicopter if you experience AMS. Your first recourse should be to descend to lower altitude. However, because it may become necessary to call in a helicopter for evacuation, you should have an insurance policy in effect that covers this (very expensive) service. The helicopter service company requires a financial guarantee to implement a rescue so having this is essential if you are planning to trek at high altitudes, especially at or above 5000m/16,000 ft.
Key facts about AMS:
- Anyone is susceptible to AMS, regardless of physical fitness or previous high altitude experience.
- AMS can be deadly so act immediately at the first sign of any symptoms.
- AMS can start to occur at altitudes as low as 2500 meters (8000 ft)
You can also read more about AMS at this professional site dedicated to the subject: