Meghnac78,
You describe two different concentrations of alcohol in your question,
but these do not represent the same thing. If you have 95% ethanol, it
means that you have a solution containing 95 grams of ethanol per 100
grams of solution. The other five grams is something else: most
probably water.
The 0.5% alcohol level that you mention may cause death refers to the
concentration not of the alcohol in the drink, but in the blood after
absorption. Someone may drink a solution containing 95% alcohol and
thereby achieve a 0.5% blood alcohol level, resulting in death.
Likewise they may drink a solution containing 5% alcohol and achieve
the same blood level, once again resulting in death. It is the percent
sign that is misleading.
Your 0.5% blood alcohol level probably refers to 0.5g/100ml, or 0.5
grams of ethanol per 100 milliliters of blood. This is often written
as 0.5 grams percent or just 0.5%, but it is not exactly the same as
someone having blood composed of one-half of one percent ethanol.
Blood and water do not have the same density. If they did, then you
could say that someone with 0.5g of ethanol per 100ml of blood had a
circulating level of alcohol of 0.5%. If blood had a density of 1g/ml,
like water, then you would have .5g of ethanol for every 100g of
blood. In fact we use this as a shorthand, but it is inaccurate. The
density of blood varies depending upon its content, but it is
generally always greater than that of water.
An approximate figure for the density of blood would be 1.05g/ml. This
means that if you have 0.5g of ethanol per 100ml of blood, the percent
of ethanol in the blood by weight is about 0.48%
In fact, the test is usually reported as "serum ethanol". "Serum" is
the fluid that is left after the blood cells are removed, and it has a
density closer to that of water. It is more correct to say that a
serum ethanol level of 0.5% represents an amount, by weight, of 0.5
grams of ethanol per 100 grams of serum, but that is still not exactly
correct.
Also, you are correct about the blood alcohol concentration that
causes death, but it is an oversimplification. A recent study showed
that, "The 5th and 95th percentiles for blood-ethanol concentration in
acute poisoning deaths were 0.22 and 0.50 g/100 mL, respectively."
Here's the link: http://aafs.micronexx.com/PDF/JOFS/JFS2002420_484/JFS2002420_484.pdf
This means that, for people who died of acute alcohol poisoning, five
percent of them had a blood alcohol concentration less than or equal
to than 0.22g/100ml, and five percent of them had a blood alcohol
concentration of greater than or equal to 0.5 g/100ml. As with any
toxic substance, there is a large variation in how much it takes to
kill someone. That is why we often talk about toxicity in terms of a
measure called an LD-50, the (L)ethal (D)osage in (50) percent of
subjects, or the amount of a thing that normally kills half of a
sample population.
In this study, the LD-50 would fall at the 50th percentile, somewhere
between 0.22 and 0.5 g/100ml.
So, anyway, back to your question.
If you injected a person with a solution containing 95% ethanol, they
would not achieve a blood level of 95% until you had injected quite a
lot of it. The average human has about 6 liters of circulating blood,
so you would have to inject about 6 liters of 95% ethanol to achieve a
blood level of just under 50% (assuming the blood vessels of the human
body could hold that much, which they can't). As our study shows, our
subject would be long dead by then. As you started to inject, blood
ethanol levels would gradually rise, and once they went much over 0.5
g/100ml, the subject would expire for exactly the same reason the
subjects in the study did: alcohol poisoning.
Here's the overall mechanism: When you drink ethanol (no matter what
the concentration) it gets absorbed by the membranes of your
gastrointestinal tract, and a lot of it goes through the liver. The
liver recognizes it as a poison, and works to eliminate much of it
before it enters the bloodstream. This is called "first-pass
metabolism". Some gets past the liver and goes into the blood. As the
blood circulates around the body, it comes back through the liver,
which tries to eliminate the alcohol again, but again, some gets
through. The more you drink, either by drinking more volume or a
higher concentration, the more gets past the liver, and the higher
your blood alcohol becomes.
The mechanism by which alcohol affects nerve cells (and other cells)
at blood levels up to 0.5g/100ml is uncertain, but it is probably by
affecting a protein involved in the transmission of nerve impulses. As
blood ethanol levels rise, the effect increases, resulting in
increased depression of neural activity and ultimately leading to
unconsciousness, depression of autonomic functions (like respiration
and heart rate) and death.
When alcohol is injected (no matter what the concentration) exactly
the same thing happens, with one important difference: it doesn't go
through the liver first. This means that the "first-pass metabolism"
doesn't occur, and blood levels rise much faster than they would if
you drank the same amount (at the same concentration).
Death, however, probably occurs by the same mechanism.
At really high concentrations, however, the behaviour of alcohol
changes. It becomes a protein denaturant and, ultimately, a
preservative. To "denature" a protein means to change its shape,
normally in a way that stops it from functioning. For alcohol to have
this function, it must be present in very high concentrations, say
around 70%. That is exactly what we are doing when we apply alcohol to
a wound: denaturing the proteins in the bacteria (thereby hopefully
killing them) and sterilizing the wound. That is also why it hurts so
much!
There is no way that you could get alcohol levels INSIDE the body up
that high without killing a person, no matter whether you drank the
alcohol or injected it.
Finally, when alcohol levels reach about 90% or so, alcohol begins to
act more as a preservative than a denaturant. That is why we don't use
90% or greater alcohol to sterilize wounds: it would preserve rather
than just kill the bacteria.
If you could, somehow, get blood alcohol levels up to 95% very quickly
the mechanism of death would be very different from normal alcohol
poisoning. Metabolism would stop abruptly due to alcohol's effect upon
proteins, and a great deal of preservation of tissues would likely
occur. This is analogous to the process of embalming, though the
fluids used in embalming are more likely to be a mixture of alcohol
with something like formaldehyde. Embalming, I need not say, is rarely
practiced upon the living.
One last note: I have used "ethanol" and "alcohol" interchangeably
here because ethanol is the only alcohol we routinely consume.
Actually, there are many different alcohols, of which ethanol is one
specific example. The mechanisms of toxicity may be drastically
different for other types of alcohol, so this discussion may not
apply.
Best Regards,
Alan Kali |
