How much oxygen will there be at Mount Everest?
Contrary to popular belief,
the percentage of oxygen in the air doesn’t change significantly with altitude
up to about 85km from the earth! At sea level, oxygen comprises approximately
23% the air by weight and on the summit of Mount Everest it still comprises 23%
of the air. So what happens? Why do you
feel out of breath when you are up high and why do almost all climbers need
oxygen to climb Mount Everest?
The further away from sea
level you are, the pressure of the entire atmosphere decreases so in effect,
there is less air to breathe. Less air
means less oxygen. So it’s true that
there is less oxygen the higher up you go, but there is also less nitrogen,
argon and other gasses that make up the air we breathe. Nothing changes to the proportions of the
gasses in the air, however one breath will deliver less oxygen to your
bloodstream, hence you will feel out of breath.
At the summit of Mount
Everest at 8850 metres, there will be approximately 33% of the oxygen that is
available at sea level. That’s like
climbing up stairs and only getting 1 out of every 3 breathes! The graph below compares the amount of oxygen
available in a given volume of air at altitude relative to the amount at sea
level for the same volume.
Effects of altitude and lower oxygen levels
On arrival at altitude, there
are a number of physiological changes that occur, which enable the body to
function optimally in the low oxygen environment. The process by which individuals gradually
adjust is known as acclimatisation. The
initial and most important adjustments are an increase in the frequency and
depth of breathing. This begins to occur
at altitudes of just 1500m. The heart
pumps faster and blood pressure rises.
Importantly, red blood cell production increases, resulting in an
increased haemoglobin concentration, which is required to pick up oxygen and
transport it around the body. These
mechanisms enable the body to continue to deliver enough oxygen to each cell,
despite the lower oxygen levels. At sea
level our blood is 98% saturated with oxygen and this decreases to 89% at 3000m
and reaches as low as 40% on the summit of Everest.
Without proper
acclimatisation, there are three different types of illness which can occur; acute
mountain sickness (AMS), high altitude cerebral oedema, and high altitude
pulmonary oedema, with considerable overlap between the syndromes.
Acute mountain sickness is by
far the most prevalent of these and usually precedes the other two
life-threatening illnesses. In most
cases, AMS is relatively mild and is treated with rest and fluids. In fact, in the Mount Everest region,
approximately 50% of trekkers who walk to altitudes above 4000m over five days
develop AMS, while 84% of those who fly directly to 3860m are affected in some
way. At present, it seems that there are
no particular factors that make people are any more or less susceptible to
developing AMS – regardless of age, sex, fitness levels, etc. Its symptoms (in decreasing order of frequency)
include;
Headaches
Fatigue
Nausea
Vomiting
Loss of appetite
Dizziness
Irritability
Disturbed Sleep
These symptoms gradually
appear 12-24 hours after arrival at altitude and begin to decrease in severity
by the third day. The number of symptoms as well as their severity, rapidity of
onset, and duration varies markedly among individuals.
The golden rule in avoiding
AMS is a graded ascent and not to go too high, too fast, thus allowing time for
acclimatisation to occur. Although this
is common knowledge to most mountaineers, many factors such a limited time,
poor weather conditions, and the locations of suitable campsites make the rate
of ascent guidelines very difficult in practise. (Currently it is recommended that above 3000m
each night should average not more than 300m above the last, with a rest day
every two or three days, or every 1000m). Most important though is not to
ascend any further if experiencing symptoms of AMS, but to wait until the body
acclimatises.
In severe instances, AMS
develops into cerebral edema (where the brain swells) or pulmonary edema (fluid
build-up in the lungs). The only cure
for these complications is to move to lower altitudes quickly (or use a Gamow
bag which simulates lower altitudes).
Acclimatisation
Although it does not seem to
be a precise science, the best thinking on altitude acclimatisation is to
expose the body to incrementally higher altitudes, and then either rest and
wait at that level, or return to a lower altitude to allow the body to recover
and produce more red blood cells.
In practice, at Everest, this
means taking rest days on the hike into base camp – particularly after sections
of significant increases in altitude.
Once at base camp, more rest will be taken and then the “acclimatisation
rounds” begin. For most climbers, this
will be something like;
Climb from base camp to camp
1, spend the night there then return to base camp
Rest at base camp
Climb from base camp to camp
1, climb from camp 1 to camp 2, spend the night there, then return to base camp
Rest at base camp
Climb from base camp to camp
1, climb from camp 1 to camp 2, climb from camp 2 to camp 3, spend a night
there, return to base camp, hike down further to Dingboche (a lower altitude to
help the body further with recovery and production of red blood cells)
Return to base camp (sometimes this last round is
repeated)
Once these acclimatisation
rounds are completed, climbers are considered “ready” and wait at base camp for
forecasts of good weather.
Acclimatisation in most adults is possible up to about 5000-5500 metres
but above this elevation there is a fine balance between adjustment to altitude
and deterioration. Above 8000 metres, no
acclimatisation occurs and prolonged exposure leads to a deterioration in
condition. This is why it is referred to
as the death zone.
Will we be using additional oxygen?
Bottled supplemental oxygen
is used by most climbers venturing above 8,000 metres and almost all Everest
climbers will be using it (including us). (The Nepalese Sherpas also use bottled
oxygen.) The extra oxygen reduces the impact of the altitude by around 1000
metres and also helps in making the body warmer. The bottles look similar to the ones scuba
divers use (although smaller) and you use an oxygen mask and a regulator to
control the flow.
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