With travel opening up again, maybe you are considering a trip at altitude?
Altitude illness is common among unacclimatised people travelling to altitudes over 2500 m but you can prepare yourself.
With increasing numbers of tourists travelling to high altitude environments globally, many are being exposed to potentially significant risks. There are tour operators in Australia that offer treks to Nepal, South America and Mt Kilimanjaro, where hiking to extreme altitudes (defined as >5500 m) can be achieved without any technical climbing experience, making these expeditions readily available to the general population. In addition, some international ski resorts expose travellers to altitudes of almost 4000 m (e.g. Breckenridge, Zermatt, Chamonix, Aspen Snowmass), which can be underestimated.
What happens to your body at altitude?
At high altitudes, lower atmospheric pressure means less oxygen is available for your body to use (so called “thin air”).
When you are exposed to high altitude, your body undergoes short term physiological changes that eventually lead to acclimatisation-
- increased respiratory (breathing) rate.
- extra urination (to remove additional blood bicarbonate produces from breathing more).
- increase heart rate and blood pressure.
The extent of these short term changes varies between individuals, and is mainly dependent on the rate of ascent and maximum altitude reached, rather than your level of fitness or your age. Longer term adaptive changes start to take place over the space of weeks.
The term ‘altitude illness’ refers to a number of different diagnoses.
- High altitude headache and acute mountain sickness (AMS).
- High altitude cerebral oedema (HACE).
- High altitude pulmonary oedema (HAPE).
Acute mountain Sickness (AMS)
AMS is common and presents as non-specific symptoms that range in severity from mild through to severe-
- headache plus one or more of the following-
- gastrointestinal upset (loss of appetite, nausea or vomiting)
- sleep disturbance
HIGh altitude cerebral oedema (HACE)
Brain blood flow is very sensitive to low oxygen levels, and this leads to dilation of blood vessels which in turn causes cerebral oedema or swelling of the brain (HACE). Patients in whom AMS becomes more severe and progresses to HACE display evidence of increasing neurological disturbance such as
- loss of balance
- coma (and eventually death).
Descent is the single most effective strategy for managing AMS and HACE. The amount of descent required varies and can be as little as 300m to 1000m. If symptoms are mild then it may be more appropriate to rest and allow symptoms to settle, but this is often dependant on the itinerary of the trek/expedition. Medications such as dexamethosone or acetazolamide might help, as will oxygen if it is available.
High altitude pulmonary oedema (HAPE)
Altitude illness can also affect the lungs. This results from persisting blood vessel constriction in the lungs, causing high pressures and leakage of fluid into lung tissue which is usually filled with air (pulmonary oedema).
HAPE is far less common than AMS or HACE, but untreated can be life-threatening and is thought to be the leading cause of death at high altitude.
Signs of HAPE include-
- increasing breathlessness with exertion
- breathlessness at rest
- dry cough
- pink frothy sputum.
Immediate descent is the best treatment for HAPE and should be continued until symptoms resolve. If descent has to be delayed due to weather or nightfall then oxygen can be used. This is usually supervised by medical teams looking after extreme altitude expeditions. Other equipment such as portable hyperbaric chambers can even be used in these settings.
The best strategy for the prevention of all forms of altitude illness is gradual ascent – slowly does it!
Let your body adjust. If you are high risk (such as very high altitude, fast ascent or past episode of AMS / HACE) then some medications can be used to prevent symptoms.
Acetazolamide (Diamox) is the most common medication used and works by forcing the kidneys to pass bicarbonate, which keeps the breathing rate higher for longer. It is most effective if started the day before ascent to altitude and continued until descent is started (people with sulfur allergy should be careful). Temporary tingling of hands, feet or lips are a common side effect, occurring in up to 45% of people.
Ibuprofen (Nurofen) can be used to relieve headache associated with altitude.
Make sure you are well prepared for your next adventure!
Written by Dr James Lawrence