Acute mountain sickness (AMS)

What is AMS?

Altitude sickness also known as acute mountain sickness (AMS) is the effect of altitude on humans. Altitude sickness is caused by reduced air pressure and lower oxygen levels at high altitudes. To put it in layman’s term as we climb higher, the air pressure decreases, which becomes harder for the atmospheric pressure to push in so much air (oxygen) into your lungs. Oxygen is, after all, very essential to our physical well-being and when it is not pumped into blood stream, vital organ such as brain malfunctions due to lack of oxygen.

Our body is by nature adaptable machinery. Unconsciously you will start to breathe deeper and heart will beat faster almost as soon as your body realizes that there is less oxygen available. In order to counter low oxygen level at high altitude, our body produces more red blood cells, which would take a few days. If you keep walking or ascending not giving enough time for your body mechanism to effect all these changes, the result is the AMS.

Levels of AMS

There are three categories of AMS – mild altitude sickness, moderate altitude sickness and severe altitude sickness.

Having symptoms of mild AMS is not necessarily a sign that the sufferer should give up trekking and descend immediately. Indeed, most or all of the symptoms of mild AMS will disappear if the person rests and ascends no further. The trekker can continue trekking once recovery is complete.

The same goes for moderate AMS too. However the symptoms of a patient should be monitored far more closely to ensure that they are not getting any worse and developing into severe AMS, which is lot more serious. Trekkers with severe AMS should always descend immediately, even if it means going down by torchlight in the middle of the night or harsh environment.

Symptoms of AMS

Symptoms of mild AMS

The symptoms of mild AMS are similar to the symptoms of a vicious hangover, namely a thumping headache, nausea and a general feeling of lousiness. An AMS headache is a dreadful headache you can get with a blinding pain that thuds continuously at ever decreasing intervals. The usual headache remedies should prove effective against a mild AMS headache.

Mild AMS sufferers often have trouble sleeping and, when they do, that sleep can be light and intermittent. They can also suffer from a lack of appetite.

Symptoms of moderate AMS

As moderate AMS is more serious, it requires careful monitoring of the sufferer to ensure that it does not progress to severe AMS. With moderate AMS, the sufferer’s nausea will lead to vomiting and the headache will not subside even after pain-relief remedies. In addition, the sufferer will appear to be permanently out of breath, even when doing nothing.

Symptoms of severe AMS

The severe forms of AMS are HACE and HAPE, which are life threatening. With severe AMS, there should be no debate about whether or not to continue. If any trekker is showing symptoms of severe altitude sickness, it is imperative that they descend immediately.

1. HACE (High Altitude Cerebral Edema)

AMS and HACE are two extremes of the same condition. If appropriate action is not taken at the stage of moderate AMS, it could lead to HACE. However HACE may come on so quickly (in an hour or two) that the AMS stage is not noticed. Typically, symptoms and signs of AMS become worse and HACE develops. The important dividing line between AMS and HACE is that with HACE there is also declining brain function with loss of physical coordination and balance, a symptom known as ataxia and altered level of consciousness.

Tests for HACE: A quick and easy way to check for ataxia is to draw a 10m line on the flat ground and ask the victim to walk along placing the heel of one foot in front of the toes of the other foot as they go. The victim should not be helped but be prepared to catch them if they fall over. If they clearly struggle to complete this simple test, suspect ataxia and descend. Even if the victim refuses to cooperate, assume they are suffering from HACE.

The other symptoms of HACE: The victim has a severe headache (not relieved by headache remedies such as ibuprofen) and impaired brain function such as loss of physical coordination (ataxia, clumsiness). The victim has difficult with simple tasks such as tying their shoelaces or packing their bag, or is staggering or falling over. Their level of consciousness is declining and the victim may have personality changes: disorientation, confusion, irritability, uncooperativeness, poor decision making. As HACE progresses they become drowsy, semiconscious and unconscious.

2. HAPE (High Altitude Pulmonary Edema)

HAPE is the accumulation of excess fluids in the lungs. The important sign is breathlessness. HAPE is more likely to occur in people with chest infections or when the weather is very cold. It is easily mistaken for bronchitis, pneumonia or asthma. HAPE may appear on its own without any preceding symptoms of AMS or it may develop at the same time as AMS or HACE. Severe cases of HAPE may result in the development of HACE in the later stages. HAPE may also develop very rapidly (in 1 to 2 hours) or very gradually over days. It often develops during or after the second night at a new altitude or while descending from a higher altitude.

Symptoms of HAPE: The earliest sign of HAPE is a loss of physical performance with increased tiredness or fatigue, with or without a dry cough. The victim will experience increased breathlessness with exertion, and eventually increased breathlessness even at rest or while lying flat that they need to sit up or be propped up. As HAPE gets worse, persistent dry cough may start to bring out a clear liquid, pinky phlegm or possibly even blood. There may also be a gurgling, liquid sound in the lung when the victim breathes in deeply (it is heard when your ear is placed on the bare skin of the victim’s back below the shoulder blades). As HAPE gets worse, lips, tongue or nails may become blue due to lack of oxygen in the blood. There may be a mild fever, a sense of inner cold, or pains in the chest or even upper belly. Other symptoms of severe HAPE include mental confusion, slurred or incoherent speech, and an inability to stay awake.

Prevention of AMS


The time-period, in which the body accustoms itself to the new altitude, is called adaptation. When the body has successfully adapted itself to the new altitude, it is acclimatization. One can avoid altitude sickness by making a slow ascent allowing for gradual acclimatization to altitude. Almost anyone can suffer from altitude sickness if they go too high, too quickly. Biologically, human beings are much better equipped to live in lower regions. If you walk into higher regions, your organism has to be adapted to the new environment. This process of adaptation already begins at an altitude of 1500 meters.

Follow the Itinerary

All our itineraries are sensibly planned with proper night halts and rest days to allow you to slowly acclimatize to altitude. With a view to save money, you must not bulldoze your company to do the trek as quickly as possible. It might turn out to be false economy because you will have to turn back because of altitude sickness and all your efforts and money will be wasted. One must not attempt to do it without designated acclimatization halts for you think you can do it because you are fit. Altitude sickness can hit anyone at anytime. There are evidences that people who supposedly have climbed K2 had to be rescued by helicopter in Bhutan. None did a comparative research so far as why some experienced climbers suffer from altitude in Bhutan. It could be because of difference in air pressure and mountain terrain.

Walk as slowly as possible

The goal of a trek is not to walk ahead of rest of the group or reach the pass first, but to enjoy the walk and scenery. You can keep a sensible pace by following the pace of your guide. Do not be tempted to hare off ahead of him, but stick with him. Statistically, young ones are more likely to suffer from AMS than elders. The reason is obvious. The competitive streak in most youth causes them to walk faster than the group with a mistaken belief that greater fitness and strength will protect them against AMS. Physical fitness offers no protection from altitude illness. Everyone, regardless of fitness, is susceptible to AMS if not acclimatized. Indeed, the slower you walk, the greater chance you have of acclimatizing properly.

Physical fitness

Medically it has been proven that people who have had prior trekking experience has less chance of suffering from altitude sickness. If you have time and money, take a pre-acclimatization climb to a minimum height of 3000 meters before you come for trek in Bhutan. If you do have time, you can train yourself before coming for a trek in Bhutan. Walk up and down hills or inclines as much as possible with a backpack weighing 5-6kg to increase the strength. Take walks over weekends, try riding a bicycle, jogging or training intensively with exercise machine.

Other ways for avoiding altitude sickness

The other things that may reduce the chance of getting AMS is to eat well and also a high-calorie diet while at altitude. Fatigue is said to be a major contributor to AMS, so try to keep energy levels up by eating as much as you can on trek.

Dehydration can also exacerbate AMS, so keep well hydrated by drinking plenty of fluids. 60% of the human body is water. This water can be lost in several ways: urine, bowels, sweat and breathing. Drink sufficient quantity of liquid using drinks with mineral salts. Rule of thumb is, for one hour of physical effort, you must drink 1 additional liters of liquid.

Avoid use of alcohol or medication such as tranquilizers and sleeping pills while you are on mountains. They could make any symptoms of altitude sickness worse since they both suppress breathing and result in lower blood oxygen.

In higher altitudes several factors come together, which may lead to frostbites: coldness, wetness, wind, lack of exercise, insufficient warmth-protection (clothes), lack of liquid (thickening of blood). Due to insufficient supply of blood, parts of the body such as toes, fingers, nose, ears, and cheeks are especially endangered. To prevent these, you must wear appropriate and warm clothes.

The risk of sunburn and sunstroke is increased at altitude, so take full precautions to prevent them from happening. Make sure you have appropriate eye protection (sunglasses, snow goggles or equivalent) and use them to prevent snow blindness. Sunstrokes appear, when the sun intensively effects the uncovered head or neck region. Wear appropriate hats to cover you.

Treatment of AMS

For mild AMS

Rest at the same (or lower) altitude until the symptoms disappear. This will take a few hours to few days. Consider giving painkillers and anti-vomiting medication as required. If symptoms do not subside even after the treatment, the victim must be brought to a lower altitude, at least to 500-1000 meters.

For moderate to severe AMS

Descent: Descend the victim to at least 500 to 1000m. Oxygen: Consider giving oxygen from the can at 2 L/min or more. Hyperbaric bag: Until symptoms clear and then for an additional 30 minutes. Acetazolamide (Diamox): 250 mg 12-hourly for the rest of the time at altitude. Other treatment: Consider giving painkillers and anti-vomiting medication as required.

If HACE is present

Descent: Descend immediately as low as possible, at least 1000m or more. Oxygen: Start with higher flow and reduce as condition improves. Hyperbaric bag: Typically for 4 hours or more. Acetazolamide (Diamox): 250 mg 12-hourly for the rest of the time at altitude. Other treatment: Consider giving painkillers and anti-vomiting medication as required.

If HAPE is present

Descent: Descend immediately as low as possible, at least 1000m or more. Oxygen: Start with higher flow and reduce as condition improves. Hyperbaric bag: Typically for 6-8 hours or more. Acetazolamide (Diamox): 250 mg 12-hourly for the rest of the time at altitude.