Notes for doctors and trek/expedition leaders (Reviewed by Dr Ross Anderson Feb. 2013)
As you ascend to altitudes above 2000m, your body has to acclimatize to the decreasing amount of oxygen available. The three main acclimatization mechanisms are:
If the ascent is too fast and/or the height gain too much, these mechanisms do not have time to work, and symptoms and signs of altitude illness (also called high altitude illness or altitude sickness) will appear.
Altitude illness becomes common above 2500m and presents in the following ways:
Depending on the altitude gain and speed of ascent, the incidence AMS ranges from 20 to 80%. HAPE is roughly twice as common as HACE and together they occur in approximately 1 to 2% of people going to high altitude. These three forms of altitude illness can vary from mild to severe, and may develop rapidly (over hours) or slowly (over days). HACE and HAPE can occur individually or together.
People often refuse to admit they have altitude illness and blame their symptoms on cold, heat, infection, alcohol, insomnia, exercise, unfitness or migraine, and risk death by continuing to ascend.
Warning: do not ascend with symptoms or signs of altitude illness, as this has led to many deaths from HAPE/HACE.
In any group there will be ‘fast’ and ‘slow’ acclimatizers needing different ascent rates. While a flexible schedule is always preferred, the fact is that many trekkers are on tight schedules (often, but not always, members of commercial groups) leading to a higher incidence of altitude illness. Slow acclimatizers in these tight schedule situations are at extra risk, and prompt diagnosis and treatment becomes even more important. However, even if a trekker has a flexible schedule, they may still feel pressurized to ascend with symptoms (by pride, peer pressure, rivalry, not wanting to appear weak, etc).
Interestingly, fit and impatient young people can be more at risk of altitude illness than unfit and patient older ones!
|Flexible Schedule||Tight Schedule|
|FAST ACCLIMATIZERS||LOW RISK||MEDIUM RISK|
|SLOW ACCLIMATIZERS||MEDIUM RISK||HIGH RISK|
AMS varies from mild to severe and the main symptoms are due to the accumulation of fluid in and around the brain. Typically, symptoms appear within 12 hours of the ascent. If the victim now rests at the same altitude, symptoms usually disappear quickly over several hours (but for ‘slow acclimatizers’ this can take up to 3 days!) and they are now acclimatized to this altitude. AMS may reappear as they ascend higher still, as acclimatization to the new altitude has to take place all over again.
A diagnosis of AMS is made when there has been a height gain in the last few days, AND:
In AMS, the victim’s level of consciousness is normal. The Lake Louise Score can be helpful as a guide to quantify your diagnosis of AMS and assess progression.
Note: AMS and HACE are two extremes of the same condition and it can help to think of AMS as ‘mild HACE’.
Note: the only early signs of altitude illness in a young child (under 7 years old) may be an increased fussiness, crying, loss of interest and/or loss of appetite.
HACE is the accumulation of fluid in and around the brain. The important symptoms and signs are: severe headache, loss of physical coordination and a declining level of consciousness.
Typically, symptoms and signs of AMS become worse and HACE develops (but HACE may come on so quickly that the AMS stage is not noticed). Also, HACE may develop in the later stages of HAPE.
A diagnosis of HACE is made when there has been a height gain in the last few days, AND:
Tests for HACE
Failure or difficulty doing any one of these tests means the victim has HACE. If the victim refuses to cooperate, assume they are suffering from HACE. If in doubt about the victim’s performance of the tests, compare with a healthy person. Be prepared to repeat these tests to monitor progress.
Examples of tests include: “Spell your name backwards”, “Take 3 from 50 and keep taking 3 from the result”, or ask their birth date, about recent news events, etc.
HAPE is the accumulation of fluid in the lungs. The important sign is breathlessness. HAPE may appear on its own without any preceding symptoms of AMS (this happens in about 50% of cases) or it may develop at the same time as AMS or HACE.
Severe cases of HAPE may result in the development of HACE in the later stages. HAPE may develop very rapidly (in 1 to 2 hours) or very gradually over days. It often develops during or after the second night at a new altitude. HAPE can develop while descending from a higher altitude. It is the commonest cause of death due to altitude illness. HAPE is more likely to occur in people with colds or chest infections. It is easily mistaken for a chest infection/pneumonia. If you have the slightest doubt, treat for both.
If the illness comes on after 4 days at a new altitude and/or does not respond to descent, oxygen, dexamethasone and/or nifedipine, reconsider your diagnosis:
Unless absolutely sure, treat as HACE or HAPE (or both) PLUS your alternative diagnosis. Note: the basic treatment of all of these problems is roughly the same: re-warm, re-hydrate, ‘resugar’, re-oxygenate and descend.
If someone is ill at altitude after a recent height gain, carry out a full secondary survey (especially level of consciousness and breathing rate), a ‘Lake Louise Score’ and the tests/examination for HACE and HAPE.
Because the victims of altitude illness often fail to take care of themselves, they are likely to develop hypothermia, dehydration and/or low blood sugar (due to not eating). There comes a point when it is vital that the leader/doctor/companion starts making decisions for the victim (e.g. ordering immediate descent), even if the victim disagrees.
Specific treatment of altitude illness
|Mild AMS (Lake Louise Score 5 or Less)||Moderate to severe AMS (lake Louise Score 6 pr more)||If HACE is present||If HAPE is present|
|DECENT?||Rest at the same (or lower) altitude until the symptoms clear (this will take a few hours to a few days)||If you have no oxygen, or symptoms do not disappear rapidly, or if symptoms get worse despite oxygen, descend at least 500 to
|Descend immediately, Descend as low as possible, aim for1000m or more||Descend immediately, Descend as low as possible, aim for1000m or more|
|PAINKILLERS FOR HEADACHE (PARACETAMOL / IBUPROFEN)||If necessary||If necessary||If necessary||If necessary|
|ANTI-VOMITIN MEDICATION||If necessary||If necessary||If necessary||If necessary|
|ACETAZOLAMIDE (DIAMOX™))||Consider 125 to 250 mg 12-hourly for the rest of the time at altitude if an unavoidable ascent is due the following morning, or if symptoms are still present at bedtime, or for ‘slow acclimatizers’ on tight schedules||250 mg 12-hourly for the rest of the time at altitude 250 mg 8-hourly for the rest of the time at altitude||250 mg 8-hourly for the rest of the time at altitude||250mg 8-hourly for the rest of the time at altitude|
|DEXAMETHASONE *1||Consider (8 mg at once then 4 mg 6-hourly) for severe symptoms||8 mg at once - IM or by mouth - then 4 mg 6-hourly||Only if symptoms of HACE are present|
|NEFIDIPINE *2 *3||Consider only if symptoms of HAPE are present||MR or LA tablets (20 to 30 mg 12-hourly, for at least 3 days)|
1) 2L/min or more. OR
2) until symptoms clear and then for an additional 30 minutes
|1) 2L/min or more. OR
2) until symptoms clear and then for an additional 30 minutes
|1) 2L/min or more. OR
2) 4 hours or more
|1) 6 to 8 L/min, OR|
2) 6 to 8 hours or more (if you have a pulseoximeter, aim for a PO2 of 90%)
|OTHER TREATMENT||Use an asthma reliever spray 2 puffs 4-hourly|
*1 Dexamethasone is an effective and rapid treatment (especially if given IM). However, once it is started the victim should descend and stay down for at least 3 days because dexamethasone does mask the symptoms and signs of AMS/HACE (unlike acetazolamide). Only stop the dexamethasone after at least 3 days of treatment and once staying below 2500m. Tail off the dose slowly by giving the last 3 doses 12-hourly
*2 Nifedipine can have the serious side effect of dropping the victim’s blood pressure; this is more likely when they are dehydrated and cold (treat as for shock if this occurs). Re-warming and re-hydrating the victim, and avoiding standing up suddenly, reduces this risk. The modified release (MR) or long acting (LA) preparations of the drug are safer in this respect than the fast-acting preparation.
*3Sildenafil (Viagra™) is presently under investigation as a treatment for HAPE, as an alternative to, or
given in conjunction with, nifedipine.
Hyperbaric bags (PAC™, Certec™, Gamow™) are equivalent to a bottled oxygen flow rate of 2 to 4 L of oxygen/min.
lthough you cannot ‘turn up the flow rate’ like you can with a bottled oxygen, they never ‘run out’.
Going Back Up Again?
Acetazolamide increases the breathing rate at altitude and speeds up the acclimatization process. A dose takes 12 hours to become fully effective.
Acetazolamide does NOT mask the onset of AMS, HACE or HAPE. However, taking acetazolamide does not guarantee that altitude illness will not develop.
There are three situations where acetazolamide is useful:
Prevention of AMS
Acetazolamide reduces the incidence of AMS, however routine preventative use for all trekkers on all treks is NOT recommended. It is recommended for those who have a past history of altitude illness, or for everyone when rapid height gain is unavoidable, such as:
Treatment of altitude illness
If someone with mild AMS has a flexible schedule, the preferred option is to rest at the same altitude until symptoms disappear. This ideal approach is sometimes not possible on treks and the argument for prompt use of acetazolamide is stronger. In this situation, a person with persistent symptoms of mild AMS despite treatment should start acetazolamide (125 to 250 mg 12-hourly) as this offers the best chance to safely continue their trek (given that no-one should ascend with symptoms of altitude illness).
See treatment of more severe AMS, HAPE or HACE above.
Poor sleep, disturbed sleep or periodic breathing at altitude
Poor sleep is common at altitude; First, check warmth of sleeping bag, improve ground insulation, avoid caffeine, check peeing arrangement and offer reassurance to the anxious. A trial of acetazolamide is indicated for sleep disturbance at altitude, particularly if the insomnia is associated with periodic breathing. This is recognized by repeated cycles of normal or fast breathing followed by a long pause, then several gasping breaths. The sufferer often wakes feeling like they are suffocating. This can be
frightening for the sufferer's tent ‘buddy’! In the morning the victim feels tired and unwell.
Acetazolamide is often called 'the high altitude sleeping pill' (125 mg one hour before going to bed. If the problem persists, increase the dose to 250 mg).
The side effects of acetazolamide include allergy. Avoid it if there is a history of a severe allergic reaction to acetazolamide or sulfa containing medications (mainly the sulphonamide-type antibiotics such as co-trimoxazole, Septrin™, Bactrim™). Note that if the sulfa allergy is mild (rash, diarrhoea, etc), test doses of acetazolamide (125 mg 12-hourly for 2 days) may be tried well before departure (but do not attempt this if the sulfa allergy is severe!). Most people with mild sulfa allergy can take
Note: the medication acetozolamide used for Acute Mountain Sickness has to be obtained from a doctor on prescription. As its use for AMS is not officially recognized, some doctors may be reluctant to prescribe it for you. Showing your doctor this handout may help.
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We will take time to discuss your requirements and provide you with bespoke advanced training. This is intended for use overseas where medical help is more than approximately 3 hours away.