Nepal Gov. Reg. No: 78007/067/068  |  Tourism Liscence No: 1293

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High Altitude Sickness

High Altitude Sickness

Altitude sickness often known as Acute Mountain Sickness (A.M.S.) is the most common unhealthy response to altitude: it's a collection of signs that your body is becoming ill and has not adapted successfully to a higher altitude.  In general A.M.S may occur when people ascend too quickly normally in altitudes of over 3000 m. We ensure minimal risk by building in rest days into our trekking itineraries. Most people will feel some affect of altitude, shortness of breath and possibly a light headed, which is fairly common. Acute mountain sickness is very different and normally involves a severe headache, sickness and loss of awareness. In almost every potential case there are enough warning signs to take appropriate action. If ignored and not treated when symptoms appear it can lead you to death



The further you move away from sea level up into higher altitudes, the lower the air pressure is. The body has two main problems with high altitude and the corresponding lower air pressure:

* Air at lower pressure has less oxygen per lungful. Your body adjusts to this by making more red blood cells to carry oxygen more efficiently. Most of the cell-building happens while you sleep; however, the process can take days and in the meanwhile, you may be ill.

* At lower air pressure, water evaporates faster. This can lead to dehydration. These are the two major factors that cause altitude sickness.

How high is high?

A minority of people, about 20%, have some symptoms of altitude sickness if they ascend to about 2500 m (8000 ft) above sea level and sleep there. However, most people will acclimatize to 3000 m (10,000 ft) with relative ease, perhaps having symptoms after the first night. Acclimatizing to heights of 3000 – 5000 m (10,000 – 16,000 ft) is much more difficult, and it is absolutely necessary to ascend slowly and return to a lower altitude to sleep if you have been travelling around at a higher altitude during the day. Over 50% of people will become ill if they ascend rapidly from sea level to 3500 m (11,000 ft) without acclimatization, and everyone will if they ascend rapidly to 5000 m (16,000 ft). It is thought to be impossible to permanently acclimatize to heights above 5500 m (18,000 ft). It is possible to spend several weeks sleeping as high as 6000 m (20,000 ft) once acclimatized, but gradual deterioration of physical well-being will still occur. Regions above 7500 m (25,000 ft) are referred to as the death zone: you will deteriorate noticeably while you remain at such high altitudes, some of your body's major systems will shut down and climbers will only remain there for two or three days. Death rates from altitude sickness above 7000 m (23,000 ft) are estimated at 4% of all people who venture that high.

Risk Factors

Altitude sickness tends to affect men more than women, especially men between the ages of 16 and 25, for unknown reasons. It is important to remember that just because you are young and healthy, and haven't experienced altitude sickness in the past doesn't mean you are immune to it on future climbs. Physical fitness is not necessarily a good indicator, and neither are strength or good health. You may react badly to altitude despite being fit, young and healthy. In fact, the fit, young and healthy have a hidden risk: their general physical capacity leads them to believe that they should handle altitude just fine, which is not always true. Bad health, on the other hand, is a risk factor: particularly cardiac or respiratory problems. Healthy hearts and lungs have a hard enough time getting oxygen to your tissues at high altitudes. Naturally, if you have physical problems that make exertion difficult for you, you have reason to think carefully about exertion at high altitude, where it is much harder!


Rates of Acclimatization

Individual rates of acclimatization vary enormously but ascending very rapidly and staying there will ALWAYS result in problems. Even Sherpas who live in Kathmandu upon returning to the Khumbu occasionally get AMS. Studies have shown that people who live at moderate altitudes (1000-2000 m/ 3281-6562 ft are acclimatized to those altitudes. They are much less susceptible to AMS when ascending to around 3000m /9842 ft (i.e. going to Namche). However the benefits decrease once higher and they should follow the same acclimatization program as others. This has implications for people who have spent a week or two in Kathmandu (at an altitude of 1400m/4593ft): they are becoming acclimatized to that altitude. For trekkers that fly from sea level to Kathmandu then almost immediately walk to Namche, they have no advantage and are more likely to suffer AMS.


The Acclimatization Process

In a matter of hours your body quickly realizes that there is less oxygen available and it first reaction is to breathe more - hyperventilate. This means more oxygen (O2) in but also more carbon dioxide (CO2) is breathed out and with the O2 - CO2 balance upset the pH of the blood is altered. Your body determines how deeply to breathe by the pH level (mainly the dissolved CO2 in your blood) - at sea level a high level of exertion means your muscles produce a lot of CO2 so you breathe hard and fast. While resting, your body is using little energy so little CO2 is produced, demonstrating that you only need to breathe shallowly. The problem at altitude is that this balance is upset and your body often believes that it can breathe less than its real requirements. Over several days your body tries to correct this imbalance by disposing of bicarbonate (CO2 in water) in the urine to compensate, hence the need to drink a lot because it is not very soluble. Diamox assists by allowing the kidneys to do this more efficiently therefore enhancing some peoples ability to acclimatize. In addition, after a day or two, the body moves some fluid out of the blood effectively increasing the haemoglobin concentration. After 4-5 days more new red blood cells are released than normal. Individual rates of acclimatization are essentially dependent on how fast your body reacts to compensate the altered pH level of the blood. For slow starters Diamox can provide a kick-start but for people already adapting well the effect often less noticeable. If you stay at altitude for several weeks there are more changes, your muscles' mitochondria (the energy converters in the muscle) multiply, a denser network of capillaries develop and your maximum work rate increases slowly with these changes. Expeditions have often run medical programs with some interesting results. Climbers who experience periodic breathing (the majority) at base camp never shake it off and have great difficulty maintaining their normal body weight. Muscles will strengthen and stamina is increased but not the muscle bulk. Interestingly Sherpas who have always lived at altitude, never experience periodic breathing and can actually put on weight with enough food.


How Long Does Acclimatization Last?

It varies, but if you were at altitude for a month or more your improved work rates can persist for weeks meaning you still feel fit upon returning to altitude. You still should not ascend faster than normal if you return to sea level for a few days, otherwise you are susceptible to HAPE. If you have been to 5000 m /16,404 ft then go down to 3500m/11,483ft for a few days, returning rapidly to 5000m/16,404ft should cause no problems, i.e. having been to Lobuche and Kala Pattar, and then rested for two days in Namche you should be able to ascend to Gokyo quickly without problems.


Sleeping At Altitude

Many people have trouble sleeping in a new environment, especially if it changes every day. Altitude adds to the problems. The decrease of oxygen means that some people experience wild dreams with this often happening at around 3000m.



Some people lose appetite and do not enjoy eating. Your energy consumption, even at rest is significantly higher than normal because your body is generating heat to combat the constant cold, especially while sleeping. Energetic trekkers, no matter how much they eat will often be unable to replace the huge quantities of energy used.




Following are the normal altitude symptoms that you should expect but not be worried about it. Every trekker may experience some or all of these, no matter how slowly they ascend. Periods of sleeplessness (Need more sleep than normal) (often 10 hours or more), Occasional loss of appetite, Vivid, wild dreams especially at around 2500 - 3800 m in altitude, Periodic breathing (They need to rest / catch breath frequently while trekking, especially above 3500 m). Runny nose, Increasing urination while moving to/at higher altitudes (a good sign), Dizziness



Many trekkers in the high valleys of the Himalaya get mild AMS. You need to have only one of the following symptoms to be getting altitude sickness. Mild headache, Nausea, Dizziness, Weakness, Sleeplessness, Dry Raspy cough, Fatigue/Tired, Loss of appetite, Runny nose, Hard to breath


What to do if a mild symptom doesn't go way?

If you find mild symptoms developing while walking, stop and relax (with your head out of sun) and drink some fluids. Drink frequently. Take 125 – 250 mg Diamox. Diamox generally takes one to four hours to begin alleviating symptoms. Drink more water and consider staying close by. If symptoms develop in the evening, take 125 – 250 mg Diamox and drink plenty of fluids again. If symptoms partially go away but are still annoying it is safe to take another 250 mg Diamox 6-8 hours later. If mild symptoms continue getting worse try to descending for a few hours which may be more beneficial than staying at the same altitude. Going higher will definitely make it worse. You're here to enjoy trekking not to feel sick.



Persistent, severe headache, Persistent vomiting, Ataxia (loss of co-ordination, an inability to walk in a straight line, making the sufferer look drunk), Losing consciousness (inability to stay awake or understand instructions), Mental confusion or hallucinations. Liquid sounds in the lungs, Difficulty breathing, Rapid breathing or feeling breathless at rest, coughing clear fluid, pink phlegm or blood (a very bad sign), Severe lethargy / fatigue,  Marked blueness on face and lips, High resting heartbeat (over 130 beats per minute),




This is a build-up of fluid around the brain, your brain swells and stops working properly. HACE symptoms include a number of signs of mental functions failing: confusion, fatigue and weird behaviour. But the most reliable one is gait ataxia, and you can test it by walking heel to toe along a straight line on the ground. Healthy people can pass this test easily. Anyone who has difficulty balancing while they do it is showing signs of HACE.  HACE is extremely serious, and you may only have a few hours to help someone with HACE. The main treatment for this is descent. Person experiencing these symptoms will need significant help. Dexamethasone is one drug that can be used to relieve symptoms, but it is just a temporary bridge to give more time for descent. Use PAC (portable altitude chamber) bag if available. Medical study shows HACE as the leading cause of death.


High Altitude Pulmonary Edema (HAPE) is another severe altitude illness. It sometimes occurs in conjunction with AMS or HACE, but sometimes doesn't. This is an accumulation of fluid in the lungs and is very serious. Signs include extreme fatigue; breathlessness (when not due to interrupted breathing — give yourself 30 seconds to recover upon waking); a cough, especially if it is wet and has blood in it; rattling or gurgling breath; chest congestion; very fast heart rate; very fast breathing; and blue extremities. A fever is sometimes present. It most commonly sets in at night. HAPE is another extremely serious illness, and like HACE should be treated as a critical emergency. Nifedipine is the drug of choice for the treatment of HAPE, but it can only provide temporary relief and rapid descent is very important.



Keep Hydrated

Remember to drink a lot. At 3500 meters (12,000 feet), make sure you drink at least 3 litres of water every day. That means two large bottles of water. Do not leave anything in the bottom; drink it all, even if it feels bad. A headache is the punishment for those who do not heed this advice, and that feels worse.

Acclimatize to Altitude Gradually

Acclimatization is the process of getting your body to adapt to the lower oxygen levels by ascending slowly into higher altitudes, spending some time at each one to adapt. The most important factor is to increase your sleeping elevation (the altitude where you're spending the night) slowly. A typical strategy is to spend a day (or initially part of a day) at a higher altitude and return to a lower altitude to sleep. Here are the recommended maximum increases in your sleeping elevation which will stop most people from proceeding to AMS:

* Go no higher than 2400 m (8000 ft) the first night.
* Increase your sleeping elevation by 300 m (1000 ft) per night after 3000 m (10,000 ft).

* Every 1000 m (3000 ft), you should spend a second night at the same altitude. This will be every fourth night if you have been ascending at the maximum pace recommended above. You can, of course, ascend more gradually than these rates. Many people ascending from sea level choose to spend several nights at 2500 m (8000 ft) to 3000 m (10,000 ft) before beginning acclimatization to higher altitude. During acclimatization, drink a lot of non-alcoholic drinks. Some people find vegetarian food slightly accelerates the acclimatization.

Avoid Rapid Ascents

Rapid ascents are the opposite of acclimatization; avoid ascents more rapid than recommended above, particularly any sudden ascent to 3000 meters (10,000 feet) or higher. Even if you are taking Acetazolamide  a rapid ascent makes it more likely you'll get AMS and makes AMS progress to serious illness faster, so you will have less time to respond and descend.

No Alcohol, Sleeping pills and Smoking

Do not trek/travel alone, take guide/porter.


As soon as the symptoms of AMS appear, your first priority is recovering. You must not ascend any further until the symptoms have disappeared. This may take up to 48 hours, if it takes longer, descend. You could also descend on the onset of symptoms; this will make them disappear much faster, probably within hours. If you are getting sicker or showing signs of HACE or HAPE, you must descend to a lower altitude as quickly as possible. If it is night time, do not wait for morning. You should descend immediately at least as far as you were the last night you had no AMS symptoms. You may need to seek hospital care. People with HACE and HAPE are frequently confused or exhausted, and are likely to need help with the descent. Help them down! There is some equipment available to treat people with HACE or HAPE at high altitudes, including hyperbaric bags in which the sufferer can lie in a higher pressure atmosphere. Likewise, because the main cause of these illnesses is a lack of oxygen, breathing oxygen from a tank will slow their onset and may provide some temporary relief of symptoms. Either treatment buys some time if it is too dangerous to descend, but they are not a substitute for descent.



This drug (sold as Diamox) stimulates your breathing. The drug was originally designed as a treatment for glaucoma, but a side effect of increased breathing rates and depth has proven useful to climbers. It has the effect of increasing acclimatization rates; improving periodic breathing; and helping people recover from AMS more quickly. There are some side effects. The drug acts as a diuretic and can cause easy dehydration, so drinking plenty of water is important. This drug can be useful for people who have had AMS in the past; people on a forced ascent (for example, flying into Tibet); and anyone who has AMS, particularly if they are choosing not to descend. Many climbers also take it as a prophylaxis. Acetazolamide is not an absolute preventative measure, particularly in the case of forced ascents. A prescription is necessary, and a doctor should be consulted about proper dosages.


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