Acute Mountain Sickness: Causes, Symptoms and Treatments

Everest Trek
No matter where you are, if you go in high altitude without acclimatization then you may face headache, nausea and shortness of breath which is called AMS – Acute Mountain Sickness. Also known as Altitude sickness, Acute Mountain Sickness not only stops people from enjoying high altitude treks, but also make people suffer from HAPE (High Altitude Pulmonary Edema ) and HACE (High Altitude Cerebral Edema)  both of which are life threatening. HAPE is a condition which causes fluid to enter the lungs and affect the lungs function whereas HACE is a state in which the brain accumulates extra fluid, swells and stops working properly.

Acute Mountain Sickness has the potential to affect all trekkers from 2500m and higher. At higher altitudes, the pressure of the air decreases which leads to less oxygen in surrounding air. At higher altitudes the air pressure is approximately half that of sea level. AMS is caused by going up high too fast and can be fatal if all the warning signals are ignored. Note that it is not the actual altitude, but the speed at which you reach higher altitudes which causes the problems.

Altitude sickness is preventable. Go up slowly, giving your body enough time to adjust. The ‘safe’ rates for the majority of trekkers is to spend 2-3 nights between 2000m and 3000m before going higher. From 3000m sleep an average of 300m higher each night with a rest day every 900-1000m. It is up to you to recognize the symptoms, and only ascend if you are relatively symptom-free. But if you catch the symptoms in the higher altitude, descend down as soon as possible before the symptoms get worse.

  1. Normal Symptoms
    Don’t expect to feel perfect at altitudes of more than 3000m. There are some normal altitude symptoms that you should expect but not to worry about. Every trekker will experience some or all of these, no matter how slowly they ascend. Some of the symptoms of Acute Mountain Sickness are:
  • Periods of sleeplessness.
  • Need for more sleep than normal, often 10 hours or more.
  • Occasional loss of appetite.
  • Vivid, wild dreams at around 2500-3800m in altitude.
  • Unexpected momentary shortness of breath, day and night.
  • Periodic breathing that wakes you occasionally – consider taking Diamox.
  • The need to rest/catch your breath frequently while trekking, especially above 4000m.
  • Your nose turning into a full-time snot factory.
  • Increased urination – many trekkers have to go once during the night. (a good sign that your body is acclimatizing)
  1. Mild Symptoms
    You only need to get one of the symptoms to be getting altitude sickness, not all of them. Some of the mild symptoms of Acute Mountain Sickness that occurs in high altitude are:
  • Headache

Headache is the symptom of pain in the face, head, or neck which can occur as a migraine, tension-type headache, or cluster headache.  Often a headache comes during the evenings and nearly always worsens during the nights. If you experience headache during high altitude treks then always consider raising your head and shoulders while trying to sleep which sometimes offers partial relief. Never take sleeping tablets.

  • Nausea (feeling sick)

Nausea can occur without other symptoms, but often nausea will develop with a bad headache. If you are better in the morning take a rest day, or if you still feel bad then its better to descend.

  • Dizziness (mild)

If dizziness occurs while walking, stop out of the sun and have a rest and drink. Stay at the closest teahouse.

  • Lack of appetite

One of the major symptoms of altitude sickness is lack of appetite. If you experience loss in appetite which includes not wanting to eat and the idea of food makes you nauseated even if you haven’t eaten for a long time then it might be the symptom of altitude sickness.

In other words, anything other than diarrhea or a sore throat could be altitude sickness. If you have a headache from dehydration, ascending further is not dangerous, but if it’s due to AMS, the consequences could be very serious. You cannot tell the difference, so caution is the safest course. Do not try to deceive yourself and accept that you body needs more time to adapt.

If you find mild symptoms developing while walking, stop and relax with your head out of the sun and drink some fluids. If the symptoms do not go away completely then it’s better to stay in same altitude. Or if symptoms get worse, descend down as soon as possible. A small loss of elevation can make a big difference to how you feel and how you sleep. If symptoms develop at night then, unless they rapidly get worse, wait them out and see how you feel in the morning. If the symptoms have not gone after breakfast then have a rest day or descend. If they have gone, consider having a rest day or an easy day walk.
Altitude sickness should be reacted to, when symptoms are mild – going higher will definitely make it worse. You trek to enjoy, not to feel sick.

Also note that there is a time lag between arriving at altitude and the onset of symptoms. In fact it is common to suffer mild symptoms on the second night at a set altitude rather than the first night.

3. Serious Symptoms

  • Persistent severe headache
  • Persistent vomiting
  • Ataxia – loss of co-ordination, cannot walk in a straight line, looks drunk
  • Losing consciousness – cannot stay awake or understand things very well
  • Liquid sounds in the lungs
  • Very persistent cough
  • Real difficulty breathing
  • Rapid breathing or feeling breathless at rest
  • Coughing blood or pink goo or lots of clear fluid
  • Marked blueness of face and lips
  • High resting heart beat – over 120 beats per minute
  • Severe lethargy and drowsiness

Mild symptoms rapidly getting worse
Ataxia is the single most important sign for recognizing the progression from mild to severe. This is easily tested by trying to walking a straight line, heel to toe. Compare with somebody who has no symptoms. 24 hours after the onset of ataxia a coma is possible, followed by death, unless you descend.

Basic rule: Immediate and fast descent

  1. Severe Medical Conditions
  • High Altitude Cerebral Oedema (HACE)

This is a build-up of fluid around the brain. It causes the first 4 symptoms of the mild, and the severe symptom lists.

  • High Altitude Pulmonary Oedema (HAPE)

This is an accumulation of fluid in the lungs, and since you are not a fish, this is serious. It is responsible for all the other mild and serious symptoms.

  • Periodic breathing

The altitude affects the body’s breathing mechanism. While at rest or sleeping your body feels the need to breathe less and less, to the point where suddenly you require some deep breaths to recover. This cycle can be a few breaths long, where after a couple of breaths you miss a breath completely, to being a gradual cycle over a few minutes, appearing as if the breathing rate simply goes up and down regularly. It is experienced by most trekkers at 5000m, although many people are unaware of it while sleeping.

  • Altitude immune suppression

At base camp altitudes, cuts and infections heal very slowly. So, for serious infections descend as soon as possible.

Drugs you can take – Diamox (Acetazolamide)
This is a mild diuretic (makes you pee a lot) that acidifies the blood which stimulates breathing. Previously it was not recommended to take it as a prophylactic (ie to prevent it, before you get it) unless you ascend rapidly, unavoidably, or have experienced undue altitude problems previously.

However, now some doctors are coming around to the idea that many people trekking above 3500m should take it using the logic that it has the potential to reduce the number of serious cases of Acute Mountain Sickness as the benefits may outweigh the risks. This topic still requires in depth research. Diamox is a sulfa drug derivative, and people allergic to this class of drugs should not take Diamox. People with renal (kidney) problems should avoid it too. The side effects are peeing a lot, tingling lips, fingers or toes but these symptoms are not an indication to stop the drug.

The older accepted recommendations are to carry it and consider using it if you experience mild but annoying symptoms, especially periodic breathing that continually wakes you up. The dosage is 125 to 250 mg (half to a whole tablet) every 12 hours. Diamox actually helps the root of the problem; so if you feel better, you are better. It does not simply hide the problem. However this does not mean that you can ascend at a faster rate than normal, or ignore altitude sickness symptoms – it is still possible to develop Acute Mountain Sickness while taking it. Note that it was recommended to start taking the drug before ascending for it to be most effective. This is not necessary, but it does help.

Doctors Notes

HACE – can occur in 12 hours but normally within 1-3 days. At first sign of ataxia, begin descent. If it is developed try 4mg of dexamethazone 6 hourly, Diamox 250mg 12 hourly and 2-4l/min O2 or a Gamow bag (if available).
HAPE – descend, Diamox 250mg 12 hourly, Nifed orally, 10mg 8 hourly and 2-4l/min O2 or a Gamow bag.
Oxygen – supplementary O2 does not immediately reverse all the symptoms although it does help significantly. Descent in conjunction with O2 is more effective.
Gamow bag/PAC bag/CERTEC bag – The latest devices to assist with severe Acute Mountain Sickness. Basically, it is a plastic tube that the patient is zipped into. A pump is used to raise the pressure inside the bag simulating going to a lower altitude. It is very effective.
HAF – High altitude farts – slang for HAFE.
HAFE – High altitude flatulence emission. The cure – let it rip! You’re not a balloon that needs blowing up.

AMS Practicals
Rates of acclimatization
Individual rates of acclimatization vary enormously but ascending very rapidly and staying there always result in problems. Even Sherpas who live in Kathmandu upon returning to Khumbu occasionally get Acute Mountain Sickness. Studies have shown that people who live at moderate altitudes (1000m-2000m) are acclimatized to those altitudes. They are much less susceptible to AMS when ascending to around 3000m (ie 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. Unfortunately, it is usually these people who are in a hurry to go higher. This is perhaps why it appears that group trekkers are initially more susceptible to troublesome AMS than individual trekkers, who often walk from Jiri or spend time in Kathmandu beforehand.

The acclimatization Process
In a matter of hours your body quickly realizes that there is less oxygen available and it’s 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 is at altitude 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 hemoglobin 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 is often less noticeable.
If you stay at altitude for several weeks then 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 5000m/16,404ft then go down to 3500m for a few days, returning rapidly to 5000m should cause no problems, ie having been to Lobuche and Kala Pattar, 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. Compound this with a few people suffering from headaches or nausea, a couple of toilet visits, a few snorers and periodic breathers, and it takes someone who sleeps like the proverbial log (or very tired trekker) to ignore all the goings on at night in a large dormitory. Smaller rooms are a definite improvement, and tents, although not soundproof still manage to be relatively peaceful.

Some people lose appetite and do not enjoy eating. Sometimes equally worrying, although it is a good sign, is a huge appetite. 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 often be unable to replace the huge quantities of energy used.

Day trips and what to do if…
The normal accepted recommendations are to go high during the day and sleep low at night, the sleeping altitude being the most important. This is fine for trekkers experiencing no AMS symptoms whatsoever, and will probably aid the acclimatization process, for example in the Everest region, going up to Chhukhung from Dingboche or Pheriche, or visiting Thame from Namche. However if you are experiencing mild or even very mild AMS then this is not the best advice. Instead your body is already having trouble coping so it doesn’t need the additional stress of more altitude. Instead stay at the same elevation. Mild exercise is considered beneficial, rather than being a total sloth but take it as a rest day.
If you have troublesome mild symptoms then descent for a few hours may be more beneficial.