Effects of Altitude on Atmospheric Pressure

Atmospheric pressure halves for every 5 500m of elevation. Above 4 000m, almost half of the atmosphere is below you and the upper half is relatively dry and particularly clear in autumn and winter. From high ground peaks can be seen at great distances. Stars and early evening satellite tracking is exceptional.

AMS:

Acute Mountain Sickness As trails rise, air thins and the volume of oxygen/breath decreases. From 3 000m upwards, thin air will start to take affect (from Namche Bazaar upwards – and especially so above 3 700m; from Tengboche on the EBC trail or Phortse Thenga on the Gokyo trail). From 3 700m, altitude increases should be limited to 300m – and not exceed 450m/day.

Rest days should be built in. From 4 300m, 3-4 litres of liquid should be drunk/day. The first stage of AMS is the early mountain sickness: headache, nausea, loss of appetite, sleeplessness, fluid retention and/or swelling of the body. Either stay put until it disappears or descend to a lower elevation. Mild symptoms usually clear within 24–48 hours.

The second stage is pulmonary oedema, characterized by breathlessness, even while resting, and by a persistent cough accompanied by congestion of the chest. Descend at once. The third stage is cerebral oedema which is less common. Symptoms are extreme tiredness, vomiting, severe headache, difficulty in walking (as if drunken or with uneven steps), abnormal speech and behaviour, drowsiness and even unconsciousness. Descend and abandon trek. There is no substitute for descent: a patient needs to have firm decisions taken for her/him and to be accompanied until down.

The HRA (Himalayan Rescue Association) does not recommend any medicine to counter AMS, although Diamox is frequently prescribed by doctors, with probable positive effect.

A Gamow Bag:

An inflatable ‘sleeping bag’ can be used to simulate lower altitudes and its use is designed to assist patients in chronic distress – which must then be followed by an immediate return to a lower altitude.

Trekking Routes You might caught by Altitude Sickeness

Everest Base Camp Trek

Three High Passes Trek

Annapurna Circuit Trek

Kanchejunga Base Camp Trek

Gokyo Valley Trek

Manaslu Circuit Trek