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Of course, altitude and air pressure tolerance varies widely from person to person. People who are more fit tend to have less trouble with AMS. However, even very fit people are vulnerable to AMS if they trek too high in too short a time, or without acclimatising properly.
AMS hits some people at altitudes as low as 2,400 metres (8,000 feet), but serious symptoms are quite rare below 3,700 metres (12,000 feet). It is the lack of oxygen, coupled with physical exertion that most often triggers AMS. It is not always a gradual worsening of the kinds of mild altitude related symptoms most people experience, including headache and shortness of breath. It can have a rapid, severe onset and can completely disable a trekker in minutes.
AMS has three primary components
Drop in oxygen saturation
Each breath you take at high altitude will deliver less oxygen to your blood, while increased physical activity will only increase oxygen demand. Slight reductions in the oxygen saturation in your blood will lead to feelings of fatigue and breathlessness. Larger drops in blood oxygen levels can cause impaired mental function and have other dangerous effects.
Any drop below 80% is considered very serious. If your blood oxygen saturation ever drops below 75% you will have to begin your descent immediately.
Cerebral Oedema (HACE)
Reduced air pressure can also cause body fluids to seep into your skull, or even into the fluid that protects your brain. At low levels, this results in mild headache. If it advances, it can put excessive pressure on the brain itself. If this occurs it can result in severe disorientation, coma or death. The onset (and development of the most serious symptoms) can be extremely fast.
Pulmonary Oedema (HAPE)
In the same way, the lack of pressure in the air can cause fluid to seep into your lungs. This can lead to pneumonia-like symptoms, and can be very dangerous if it occurs during sleep.
High Altitude Pulmonary Oedema can occur without any other symptoms of AMS, and can be serious on its own.
Protecting yourself from AMS
Our guides monitor all of our trekkers closely. They are highly experienced in working at altitude, and know how to look after our trekkers. It is vitally important that you share information about your health and any symptoms you may be experiencing fully and openly. Failing to do so puts not only yourself at risk, but your fellow trekkers as well.
Recognising the Symptoms of AMS
- Vomiting, nausea or loss of appetite
- Weakness or fatigue
- Feeling light-headed or dizzy
- Difficulty sleeping
- Numbness, pins and needles
- Shortness of breath
- Rapid pulse (especially if persistent)
- Sleepiness or drowsiness
- Overall malaise
- Swelling or oedema of face or extremities
Symptoms Common to High Altitude Cerebral Oedema (HACE)
- Disorientation or confusion
- Unusual behaviour
- Fatigue
- Difficulty speaking or walking
- Nausea or vomiting
- Hallucination or vision problems
Symptoms Common to High Altitude Pulmonary Oedema (HAPE)
- Extreme fatigue and trouble walking
- Tight or congested feeling in the chest
- Productive cough, with or without blood
- Gurgling or crackling sound whilst breathing
- Shortness of breath, especially during rest
- High pulse at rest (90 to 100 bpm)
- Excessive sweating or fever
- Blue or grey lips and/or fingernails
No matter what symptoms of AMS you experience, the treatment is the same: descending at least 1000m immediately, until symptoms abate.
Kandoo’s Emergency Descent Protocol
If your guides have concerns about your health, or believe that continuing the trek would be dangerous for you, they will insist that you begin your descent immediately. This decision will be made to make sure that you remain safe, while maximising your chances of a successful trek. Please notify your guide immediately if your condition worsens, even slightly.
Avoiding AMS Altogether
‘Walk High, Sleep Low’
Our routes crosses several passes before reaching the summit to give you the opportunity to ascend to a higher altitude, rest there for approximately 30 minutes, then descend again to sleep that night. This encourages the body to acclimatise to the altitude, giving you a greater chance of summit success in the following days.
Go slowly!
You need to maintain a breathing rate low enough that you could easily maintain a conversation. If you find you are breathing hard, slow down. Overworking your heart and lungs puts you at much higher risk of AMS. There is no pressure to run up the mountain, take your time and allow your body to get used to the altitude.
Drink plenty
Proper hydration not only makes AMS less likely, it makes you less vulnerable to a host of other problems as well. To protect yourself, you need to drink at least 3 litres of water each day, especially if you don’t feel thirsty. If your urine is yellow (or worse, orange) you are not drinking nearly enough. Dehydration can be mistaken for HACE, and cause you to be taken back down the mountain, so drink up!
Our altitude information and emergency descent protocols are periodically reviewed by a medical professional specialising in high altitude. This was most recently completed in October 2024.