Altitude & Acclimatisation

Summit day on Mera Peak, Nepal

The Mountain Company itineraries are planned with gradual ascents and rest days to allow for the necessary time to acclimatise to high altitude. The following information should give you some background to the effects of altitude on the body and how best to deal with it.

Most people can ascend to 2,500m without a problem however it is impossible to determine who might be more susceptible to altitude sickness. No single factor such as age, sex or fitness will affect your likelihood of being affected.

The Cause of Altitude Sickness
As the altitude increases the partial pressure of oxygen is reduced, for example at 3,600 there is about 40% less oxygen than at sea level. The body now must adjust to having less oxygen.

Acclimatisation
Ones body can adapt to the decrease of oxygen at altitude although this takes time; the process is known as acclimatisation. The cause of altitude sickness is going too high too fast.

The body adjusts to less oxygen by several mechanisms, the main ones being an increasing rate and depth of breathing followed by the slower process of producing more red blood cells.

Mild Acute Mountain Sickness
There is a spectrum of altitude sickness starting from mild acute mountain sickness (AMS) at one end which usually only lasts a day or two. Many people will experience mild AMS during the acclimatisation process. The symptoms of mild AMS include:

nausea & dizziness
headache
loss of appetite
fatigue
shortness of breath
disturbed sleep

Symptoms tend to be worse at night when your breathing rate decreases. As long as symptoms are mild, and only a nuisance, ascent can continue at a moderate rate. It is essential that you communicate any symptoms of illness to others on your trip.

Moderate AMS
The best test for moderate AMS is get the person to walk in a straight line heel to toe, if they are unable to walk in a straight line (ataxia) then an immediate descent is required. Often only a small decrease in altitude of 300 metres will relieve the symptoms, the person should remain here until all symptoms have subsided at which point then can start their ascent again.

The signs and symptoms of Moderate AMS include:

severe headache that is not relieved by medication
nausea and vomiting, increasing weakness and fatigue
shortness of breath
decreased co-ordination (ataxia).

Severe AMS
Severe AMS has two serious conditions: high altitude cerebral oedema and high altitude pulmonary oedema. These should not ocurr if a sensible acclimatisation schedule has been adhered to, it is usually due to people going too high too fast. In both cases the lack of oxygen results in leakage of fluid through the capillary walls into either the lungs or the brain.

Symptoms of High Altitude Pulmonary Edema (HAPE):

shortness of breath at rest
tightness in the chest, and a persistent cough bringing up white, watery, or frothy fluid
fatigue and weakness
confusion, and irrational behaviour

Symptoms of High Altitude Cerebral Edema (HACE):

headache
disorientation
loss of co-ordination
confusion and irrational behaviour
decreasing levels of consciousness
loss of memory
hallucinations
coma.

Immediate descent is essential for someone with HACE and/or HAPE. There are also medication that may be used for treatment but these require proper training in their use.

Guidelines for the prevention of AMS
When you get above 3,000 metres, you should increase your altitude by approx. 300 metres per day, and for every 900 metres of elevation gained take a rest day.

if you have symptoms of moderate AMS do not go higher until symptoms decrease.
if symptoms increase, descend immediatately!
remember that people acclimatise at different rates.
make sure you are properly hydrated by drinking at least four litres per day. Urine should be copious and clear to pale yellow.
do not over exert yourself at altitude

The above summary should by no means to be taken as a full and comprehensive explanation of Acute Mountain Sickness, but rather a brief discussion on the most common symptoms and what a person needs to be aware of before and after arrival at high altitudes. If you have any questions please get in contact with The Mountain Company.