Acute Mountain Sickness

Often shortened to AMS, Acute Mountain Sickness is the body's reaction to a lack of oxygen, caused by ascent at a faster pace than acclimatisation. AMS seems to defy research - we still cannot predict who will or won't get AMS, or which conditions cause the specific types of AMS. Despite is prevalence and public awareness, AMS can be said to still baffle scientists after all this time. As far as we know AMS is thought to be caused by swelling of the brain tissue, which occurs in response to a lack of oxygen(hypoxic stress.)

Because we know so little about this affliction, a common rule of thumb is to treat any illness at altitude as altitude sickness. Many people think it is normal to have a headache at altitude when in fact it is not, it is very rare. For this reason if you plan to spend any time at altitude it would be wise to know the signs of AMS. Some people have described it to be similar to a hangover.

Symptoms include a headache partnered with any of the following:

• Loss of appetite, nausea, or vomiting
• Fatigue or weakness
• Feeling dizzy, light-headed or faint
• Disturbed sleeping patterns
• Confusion and disorientation
• Incapable of motor actions
• Apathy
• Impaired memory
• Mood swings
• A reported 'deep inner chill'

A headache typically occurs around the second or third day at high altitude. The headache can range from mild to severe and is characterised by throbbing in the temples and or the back of the head. It is generally worse during the night and in the morning, and made worse by straining or bending over.

All these symptoms can be graded from mild to severe, and there is a questionnaire available from Lake Louise, which is useful in assessing the stages of AMS.

If only a headache is experienced then a good idea is to test for AMS through process of elimination. As dehydration is the most common cause of headaches, drink a litre of water and if necessary take a low dosage pain killer such as paracetamol. If the pain stops completely and no further symptoms develop then it can be assumed that the headache was not due to AMS, and ascent can be continued.

Also experienced with AMS is the condition 'periodic breathing.' This is where a person's normal sleeping pattern is disturbed. The individual will experience bouts of insomnia, alternated with fitful dreams. Their breathing pattern will also be disturbed, consisting of periods when breathing is rapid and deep, and then periods where breathing is stopped, which can be up to 15 seconds. This may improve slightly with acclimatization, but does not usually resolve until descent.

Periodic breathing can cause anxiety, firstly for the person who either wakes up and realises they have stopped breathing, or wakes up during a hyperventilation stage, and so begins to think they have HAPE. But it can also be a scary experience for someone who wakes up and realises their friend has stopped breathing. The best thing to do in a situation like this is simply to wait until the breathing is self-regulated once more, because these periodic breathing cycles will probably continue until the individual is awake.

As always, the best way to approach AMS is prevention. Ascent should be slow in order to give the body time to acclimatize. Every person is different, but as general guidelines, the following should protect the majority of people from AMS:

• Past 3000 meter altitude should not change dramatically in 24 hours. This means do not climb for more than 300m per day.
• At every 1000 meter above 3000 meter two nights should be spent at the same altitude.

Avoid anything which will slow down breathing, such as:

• Alcohol
• Sleeping pills
• Narcotic pain medication
• Tobacco

However, if AMS does occur then a few simple guidelines can prevent a fatality. It is vital that before ascending all parties are aware of the dangers, as ignorance is often the cause of illness.

• Never leave someone with AMS alone.
• Do not ascend any higher. This can easily be fatal, and the symptoms will only get worse.
• If possible, descend to wherever you last felt ok. Symptoms will disappear much more quickly.
• If not, stay at the same altitude until the symptoms are gone and the body has acclimatised. Only then can ascent re-start.
• Rest.
• Drink plenty to stay well hydrated.

Taking Diamox helps greatly in accelerating acclimatization. Read this article on how Diamox helps acclimatization to know the science behind it.

Additional reading: Read this tutorial on Acute Mountain Sickness to understand AMS fully.