Acute Mountain Sickness
By Dr Beth Hall-Thompson
A headache at altitude is not normal! It could be one of three things, or a mixture: dehydration, excess sun exposure, or ‘high altitude headache’. When the latter is accompanied by:
- Loss of appetite or nausea,
- Fatigue or weakness,
- Dizziness or light-headedness,
- Difficulty sleeping
and, there has been a recent ascent above 2,500m; then we make the diagnosis of Acute Mountain Sickness (AMS).
Unfortunately it is all too common; only allowing the body to acclimatise steadily will prevent it and at some time all of us will suffer no matter what precautions we take (this height varies individually).
Symptoms
Many people describe the early symptoms as ‘like a bad hangover’; these early symptoms are ok – we can deal with those but denying them is when it can lead to trouble.
For me as a doctor, I look to judge how significant the symptoms are; there is a scoring system to help – the Lake Louise Score.
In most situations I can manage a mild case of AMS at the current altitude with a dose of acetazolamide, hydration, and simple analgesia. If symptoms have not improved by the morning then I may suggest descending to a previously comfortable height, or a rest day in location. Mild AMS is usually self-limiting and is not the end to your journey if managed patiently.
A moderate case is a balance between whether to descend immediately, or, if late at night, is this more dangerous or is to wait more risky; but descent is always the best option. Acetazolamide, hydration and maybe dexamethasone (a steroid) would be useful at this stage if required to hold in situ. Again, once recovered there is no reason why you should not try ascending again more slowly.
A severe case needs to be treated by all the above measures and early descent.
High Altitude Cerebral Oedema
It is this advanced sever AMS process that really blends as a spectrum into the life-threatening condition that is High Altitude Cerebral Oedema (HACE). The swelling (oedema) seen on scanning the brain of affected individuals informs scientists that the cause of symptoms is effectively brain swelling within a non-expandable skull. However the mechanism for the swelling is not yet elucidated – it has been suggested to be due to either or both increased blood flow or fluid leaking out of constricted brain vessels.
HACE is characterised by rapid progression of confusion, lethargy, changes in behaviour and a loss of coordination. This last part is well tested by asking the individual to walk in a straight line heel to toe. The late stage is coma, and ultimately death. About 1% of those who travel above 300m will suffer from HACE, few will die and it is a fully recoverable condition if caught early.
Treatment involves immediate descent, it cannot wait until morning, and unfortunately, most cases occur in the evening as the body tries to acclimatise to a new height.
The most common place for this to occur in trekkers is at Lobuche, en route to the Nepali Everest Base Camp. Having slept the previous night at Pheriche 4,300m, the altitude gain to Lobuche at 4930m is too much for some people, no matter how slowly they take it. However effects are insidious over the afternoon to evening; and by nightfall (about 6pm) many evacuations are forced to start to the Himalayan Rescue Association medical aid post at Pheriche.
Whilst working there for half a season, HACE was our most common late night awakening, and the most frequent cause of evacuation by helicopter in the morning.
We have some holding measures to help alleviate symptoms whilst awaiting evacuation; a pressurised chamber in which we can place the patient and raise the internal pressure to simulate descent; as well as oxygen and dexamethasone, a steroid, to decrease the brain swelling.
High Altitude Pulmonary Oedema
High Altitude Pulmonary Oedema (HAPE) is another manifestation of altitude illness that affects primarily the lungs, but can occur alongside AMS or HACE. It is again life-threatening, but generally progresses over a longer period – up to 72hrs. Again the risk factors are as for AMS – fast ascent & vigorous exercise increase the likelihood.
The symptoms are a greater degree of shortness of breath on exertion than companions, breathlessness at rest, with or without a cough which may sound rattling and may be productive of white or pink frothy sputum. Oftentimes it is noticed because lying flat causes an increase in breathlessness; effectively the fluid in the lungs is drowning them.
Again the cause of this excess fluid is not exactly understood, but we do know that the low oxygen of the air in the lungs causes the pulmonary blood vessels to constrict. This increased pressure, and nasty chemicals reactive to low oxygen, cause the vessels to become leaky; the fluid forced out then builds up in the air pockets. This fluid takes the place of potential oxygen and so less is available to be delivered to the rest of the body, including the brain – therefore HAPE is rarely seen without some measure of AMS.
Luckily the treatment algorithm for High Altitude illness is easy – descent is the main treatment priority; however organising the descent is not so simple. In the case of HAPE, both cold and exertion actively worsen the condition and so should be avoided during the journey; Sherpas regularly carry HAPE victims in piggyback position for long distances.
In the meantime a combination of oxygen, dexamethasone and nifedipine (to dilate the affected blood vessels) will help symptoms and delay progression, only descent will cure.
Again HAPE resolves rapidly at a lower altitude, and once the symptoms are fully resolved with a few days rest, cautious re-ascent is acceptable but may be limited. If HAPE has been suffered once, it is likely to recur, including in the longer term future..