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The weather was wonderful and of course the views were amazing. We never met any other ’walkers’ which was a real bonus.
Keir and Ruth Woodward (UK) | Luxury Kathmandu Valley

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Altitude & Acclimatisation

Our itineraries are carefully planned to ensure there is a gradual ascent in height over a number of days to allow for the necessary time for your body to acclimatise to high altitude. Most people can ascend to 2,500m without a problem however it is impossible to determine who might be more susceptible to altitude sickness at higher elevations. 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 must adjust to having less oxygen.


The human body can adapt to the decrease of oxygen at altitude however this process takes time; this is known as acclimatisation. The cause of altitude sickness is a result of 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 starting at mild acute mountain sickness (AMS). 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 your ascent can continue at a moderate rate. It is essential that you communicate any symptoms of illness to the Leader of 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 do this then an immediate descent is required. Often only a small decrease in altitude of 300m will relieve the symptoms.

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 one being high altitude cerebral oedema and the other high altitude pulmonary oedema. These should not occur if a sensible acclimatisation schedule has been adhered to and usually happens 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 is also medication that may be used for treatment.

Guidelines for the prevention of AMS

The guidelines state that 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 immediately!
  • 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

Additional website resources

Base Camp MD

Medex Travel at High Altitude booklet (recommended)

High Altitude Medicine

British Mountaineering Council