Acclimatisation and Altitude Sickness

altitude sicknessWhat is the Cause of altitude sickness?

Insufficient oxygen getting into the blood stream due to reduced oxygen in the air, respiratory problems like the common cold, reduced haemoglobin in the cells and reduced barometric pressure.

It is impossible to predict who will suffer from altitude sickness as it does not seem to be connected with age or general fitness, or even to a particular altitude. Young, fit people are more likely to be affected, perhaps because they rush up the hill too fast or perhaps because their basic metabolic rate is higher. A steady pace, going slower as you go higher, is important. If you start gasping and your heart is beating fast, just stop and rest and admire the view and you will soon feel better. Carrying heavy loads is almost certainly a contributing factor: let the porters carry most of your kit and don’t try to prove how macho you are.


The OEM method

The best way to acclimatise is to do it naturally. By increasing height slowly, the body has time to adjust to the reduced oxygen level and altitude sickness should be avoided. The height at which one sleeps seems to be more important than the height gained during the day. Flying into Lukla at 2800m, the body will already be at the height when it starts to feel the reduced oxygen. We stay in Namche Bazaar at 3340m for two nights  and then ascend very slowly, with several ‘rest’ days when we climb higher during the day but return to the same altitude to sleep.

The OEM trek takes between 3 and 6 days longer than commercial treks to Everest Base Camp as we want to minimise the discomfort and maximise the enjoyment of being in the high mountains. It's important that everyone takes responsibility for their own wellness as well as  keeping an eye out for each other. We have three levels of keeping each other safe and well:

  • your room / tent partner and other team members
  • your team leader
  • the doctors 

Only a few have to descend to a lower altitude and require medication, but recover sufficiently to rejoin the group and run the race. By the time you have acclimatised on the trek up the Gokyo valley, you should not experience further problems on the trek up to Gorak Shep. The medical at Lobuche on the day before the race will check that you are fit enough to go up to Gorak Shep and do the full marathon. On the chance that you're not fit enough to start, you will probably be able to do a shorter run from Lobuche or Pheriche. 


The symptoms

Many people suffer mild symptoms of altitude sickness - a headache above 3500m, lose their appetite, sleep badly and get puffy eyes and fingers; this is usual but should not be ignored. The best description of early altitude sickness is that it is like a massive hangover. Bill Tilman called it ‘Mountaineer’s Foot’: reluctance to put one foot in front of the other. This lassitude and lack of motivation is typical and may be the only symptoms.

If you start vomiting, feel dizzy and have a rapid heart rate after rest we will make arrangements for you to rest at a lower altitude. At a lower altitude your symptoms should disappear and you can attempt to climb again – SLOWLY. It's really important to talk about any symptoms you have as we want to be able to nip any problems in the bud so that you can get to the start in good condition. Conditions do worsen very rapidly, especially at night and the worst case scenario is becoming very ill during the night and having to be evacuated by porter, yak, stretcher or helicopter.

The problem is that the symptoms are relatively minor and can always be attributed to something else. But you must always assume that it is the altitude causing your headache or nausea. One distressing sign of acclimatisation is Cheyne Stokes respiration, or periodic breathing. While you are asleep your metabolism is adjusting to the lower oxygen level and there may be periods when your breathing becomes very heavy and stertorous; suddenly breathing stops, perhaps for as long as a minute, before noisily recommencing. This is a natural sign that you are acclimatising – but it can be extremely worrying for your tent mate!

Another, often ignored, symptom is personality change. Some people become aggressive, argumentative and irrational; others become uncommunicative and just sink into silence. This is why it is important to get to know your trekking and tent companions as you may be the first to spot that something is wrong. Someone suffering from altitude sickness can get dizzy and lose their sense of balance; they are unable to walk in a straight line. The sickness often seems to deteriorate at night, so that emergency evacuation to a lower altitude is necessary. Don’t be frightened of causing an unnecessary fuss; you could be saving a life if your tent mate has developed pulmonary or cerebral oedema.


It has been shown that Diamox (acetazolomide) may prevent and relieves symptoms of altitude sickness. The dosage is one 250mg tablet a day above 3000m or one 125mg tablet taken twice a day. Medical advice used to be to take Diamox before reaching 3000m but it is now accepted that it is much better to acclimatise naturally and to use Diamox only when the preliminary symptoms of altitude sickness are noticed. Diamox becomes effective within a few hours and may help when trying to descend to a lower altitude.

Diamox is a diuretic and you will pass more urine than normal, often having to get up in the middle of the night. So you must drink more to make up for this. One of the side effects is pins and needles in the hands, feet and face but not everyone is affected this way. We have a policy of not relying on Diamox, which may only mask the symptoms while not improving the underlying condition. If your symptoms persist or get worse, you must descend. ONLY TAKE DIAMOX UNDER THE SUPERVISION OF OUR MEDICAL TEAM. 

Your own doctor may advise you to take Diamox as a prophylactic but we do not recommend this unless you have recurrently suffered from altitude sickness in the past.  Diamox is a banned athletic drug, so it should only be used to treat a medical condition.

Our medical team will also carry other drugs to treat altitude sickness as well as oxygen and a pressure bag. If a patient is enclosed in a pressure bag, it is equivalent to carrying them to a lower altitude.

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