Altitude sickness (AMS) is a serious medical condition brought on by travelling too quickly to altitude, and/or performing physical exercise at altitude when unacclimatised.

Tolerance to altitude varies greatly amongst individuals, but a fit person who does not go too fast will not strain their cardiovascular system as much as an unfit person for the same amount of exercise and will therefore be at a lower risk of developing AMS. Even a very fit person however is still very likely to develop AMS if they trek to altitudes above 3500m without some days spent acclimatising or they walk too quickly.

Altitude sickness can occur in some people as low as 8,000 feet (2,400 metres), but serious symptoms do not usually occur until over 12,000 feet (3,700m). AMS is brought on by changes in the body caused by the reduction in air pressure at altitude. At 5000m the air pressure is reduced to 55% of that at sea level and at 6000m it is down to 49%.

This drop in pressure has three major effects.

Drop in oxygen saturation

With less actual air in each breath the amount of oxygen in the blood reduces. Mild reductions in oxygen saturation will cause you to feel breathless and tired. Bigger falls can impair mental functions and have serious adverse effects. Below is a graph which shows the normal reduction in oxygen saturation levels that occur at altitude.

If your oxygen saturation drops below 80% we consider this is serious and if it drops below 75% you will be asked to descend.

Cerebral Oedema

As a result of the reduction in air pressure, fluid from the brain leaks into the air cavities between the skull and the brain. This starts off by causing mild headaches but if continues leads to pressure on the brain, complete disorientation and eventually coma and death. The onset of cerebral oedema can be very quick.

Pulmonary oedema

Again the effect on the lungs is caused by the reduced air pressure inside the lungs which allows fluid from the blood to pass through into the lung itself. This produces symptoms like pneumonia. This is particularly a concern when sleeping.

Recognising AMS

It is a mistake to think that AMS is the result of a gradual worsening of mild altitude symptoms such as breathlessness and headache. AMS is in fact a sudden and dramatic onset of symptoms and leaves the person hardly able to walk or look after themselves.

Symptoms of Altitude Mountain Sickness (AMS)

Headaches are a primary symptom used to diagnose altitude sickness, although a headache is often a symptom of dehydration and can be confused with symptoms of AMS. You must drink a minimum of 3 litres of water during the day to prevent dehydration (see further information below).

A headache occurring at an altitude above 2,400 metres (8,000 feet) with any one or more of the following symptoms, can indicate some degree of altitude sickness and should always be reported to your guide. General symptoms of AMS can include:

Specific symptoms of High Altitude Cerebral Oedema (HACE)

Specific symptoms of High Altitude Pulmonary Oedema (HAPE)

You should be aware that HAPE can occur without any of the other signs of AMS. Characteristic symptoms are:

Whatever type of AMS you might suffer from the treatment is the same:immediate descent by over 1000m or until symptoms abate.

Our client descent protocol

If our guides have any doubts about your health and believes that continuing to ascend would be dangerous then they will insist that you descend to ensure your safety. Before making this decision your guide will follow the following protocol:

How to avoid AMS