Trekking in some of the world’s highest mountains is becoming much more common as travellers go off to destinations such as Mount Kilimanjaro in Tanzania and the Inca Trail in Peru on treks for charity or pleasure. Trekkers to these popular destinations are at risk of Altitude Sickness, though not all trekkers will experience it.
Mount Kilamanjaro, Tanzania - a popular trekking destination
What is Altitude Sickness?
Altitude sickness or Acute Mountain Sickness (AMS) is a potentially life threatening condition caused by a decrease in atmospheric pressure, which makes breathing difficult. AMS is caused when you are exposed to high altitude without acclimatising first and can occur at altitudes usually higher than 2,500 metres. At high altitudes the percentage of oxygen in the air remains the same, however partial pressure drops. This pressure drives oxygen into the blood stream and the decrease results in lower oxygen levels in the blood. The way our bodies cope with this lack of oxygen is to increase our breathing rate, which then increases carbon dioxide levels in the blood and symptoms of AMS occur. AMS symptoms usually occur 6 – 12 hours after arrival at altitude, but can begin more than 24 hours after ascent. Common symptoms include: headache, nausea, sleep disturbance, dizziness and exhaustion. If you start to experience these symptoms they will usually resolve within a couple of days if further ascent does not occur.
Am I at Risk?
It is difficult to predict who will get AMS, and being physically fit does not necessarily put you at lower risk. If a traveller has previously experienced no symptoms at altitude, they are less likely to get AMS, however even this may be unreliable. Rapid ascent is the highest risk factor. 50% of trekkers in Nepal developed AMS at altitudes of between 4,500 and 5000 metres. Another study showed that 84% of trekkers experienced AMS when they flew directly to 3,860 metres [1].
Prevention
The most important factor in the prevention of AMS is adequate acclimatisation and regular rest days. A short period of acclimatisation (1-3 days) at 3,000m should be followed by further ascent which should be gradual, with no more than a 300-500m increase in sleeping altitude per day. You should have a rest day every 3 days. If you start to experience mild AMS symptoms, no further ascent should be taken until symptoms have resolved. If you experience severe symptoms of AMS rapid descent should be immediate.
Diamox (Acetazolamide)
Diamox is used as prevention for AMS, although it is unlicensed in the UK. Diamox should not be considered as an alternative to adequate acclimatisation and gradual ascent, Diamox will hasten acclimatisation, and may help to relieve the symptoms of AMS but will not relieve symptoms immediately when taken for treatment. Symptoms usually resolve within 12-24 hours when used in treatment.
If travellers use Diamox, a trial dose of 250mg once daily for two days should be taken prior to travel.
If no adverse events are experienced, it should then be commenced one to two days prior to ascent to 3,500m and then continued for at least two more days after reaching the highest altitude.
Diamox can cause nausea, increase in urine output, and oral and finger tingling. More unusual side effects include rashes, flushing and thirst.
It is contraindicated in those with hypersensitivity to sulphonamides and anyone who has experienced an anaphylactic reaction in the past.
How Does It Work?
Put simply Diamox works by forcing the kidneys to excrete bicarbonate the base form of carbon dioxide.
It speeds up the acclimatisation process
It also stimulates breathing during the night
Lessens the symptoms of AMS
Severe Mountain Sickness
Acute mountain sickness progresses in less than 10% of cases to the more severe form where travellers experience lethargy, confusion and lack of coordination or muscle movements.
Initial symptoms include shortness of breath with exertion, and a dry cough, progressing to shortness of breath at rest. The cough may become productive with blood stained sputum.
Anyone with symptoms of severe mountain sickness should descend immediately. This can progress rapidly and death is the likely consequence if a descent is not made as soon as the symptoms are recognised.
Diamox is used as prevention for AMS, although it is unlicensed in the UK. Diamox should not be considered as an alternative to adequate acclimatisation and gradual ascent, Diamox will hasten acclimatisation, and may help to relieve the symptoms of AMS but will not relieve symptoms immediately when taken for treatment. Symptoms usually resolve within 12-24 hours when used in treatment.
If travellers use Diamox, a trial dose of 250mg once daily for two days should be taken prior to travel.
If no adverse events are experienced, it should then be commenced one to two days prior to ascent to 3,500m and then continued for at least two more days after reaching the highest altitude.
Diamox can cause nausea, increase in urine output, and oral and finger tingling. More unusual side effects include rashes, flushing and thirst.
It is contraindicated in those with hypersensitivity to sulphonamides and anyone who has experienced an anaphylactic reaction in the past.
How Does It Work?
Put simply Diamox works by forcing the kidneys to excrete bicarbonate the base form of carbon dioxide.
It speeds up the acclimatisation process
It also stimulates breathing during the night
Lessens the symptoms of AMS
Severe Mountain Sickness
Acute mountain sickness progresses in less than 10% of cases to the more severe form where travellers experience lethargy, confusion and lack of coordination or muscle movements.
Initial symptoms include shortness of breath with exertion, and a dry cough, progressing to shortness of breath at rest. The cough may become productive with blood stained sputum.
Anyone with symptoms of severe mountain sickness should descend immediately. This can progress rapidly and death is the likely consequence if a descent is not made as soon as the symptoms are recognised.
References
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