Acute altitude sickness occurs when an individual who is accustomed to low altitudes rapidly climbs to high altitude. Altitude sickness is a potentially lethal complication of climbing to altitudes above 8,000 feet.
Three main syndromes of altitude illness may affect travellers: acute mountain sickness, high altitude cerebral oedema (HACO), and high altitude pulmonary oedema (HAPO)
- risk of dying from altitude related illnesses is low, at least for tourists. For trekkers to Nepal the death rate from all causes was 0.014% and from altitude illness 0.0036%
- soldiers posted to altitude had an altitude related death rate of 0.16%
Clinical features of mild altitude sickness are (1):
- headache
- loss of appetite
- nausea
- fatigue
- dizziness
- insomnia
- extremity oedema
- dyspnoea
- palpitations
There is an increased mortality in patients with acute altitude sickness.
Definitions of altitude and associated physiological changes
Intermediate altitude (1500-2500 metres)
- physiological changes detectable
- arterial oxygen saturation >90%
- altitude illness possible but rare
High altitude (2500-3500 metres)
- altitude illness common with rapid ascent
- very high altitude (3500-5800 metres)
- altitude illness common
- arterial oxygen saturation <90%
- marked hypoxaemia during exercise
Extreme altitude (>5800 metres)
- marked hypoxaemia at rest
- progressive deterioration, despite maximal acclimatisation
- permanent survival cannot be maintained
Treatment of altitude related illness is to stop further ascent and, if symptoms are severe or getting worse, to descend
- oxygen, drugs, and other treatments for altitude illness should be viewed as adjuncts to aid descent
Prevention of acute mountain sickness (AMS) (3)
- acetazolamide can be used for preventing AMS according to the National Travel and Health Network Centre and Fit For Travel recommendations (not licensed for this this indication)
- acetazolamide prevents AMS by mimicking the body naturally adjusting to a change in environment
- a Cochrane review demonstrated acetazolamide reduced the risk of AMS vs placebo by a factor of 0.47 (n=2,301, 16 studies). Acetazolamide was administered one to five days prior to ascent with doses of up to 500mg/day to adults at risk of AMS
- overall, evidence for the use of the medicines listed below to prevent AMS is inconclusive and for some, side effects are a concern:
- aspirin
- dexamethasone
- Using dexamethasone has been suggested by some organisations to help prevent AMS. However, the Cochrane review (n=176) assessing four parallel studies comparing dexamethasone with placebo found dexamethasone does not prevent AMS at any dose and does not aid acclimatisation.
- ibuprofen
- iron supplements
- magnesium citrate
- spironolactone
- sumatriptan
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