anaphylactic shock
is probably one of the shocks that most
people are familiar with it's also known
as anaphylaxis anaphylactic shock is an
allergic reaction
that's severe enough to cause shock and
of course shock is decreased tissue
perfusion or in other words decreased
oxygenation of tissues there are a
number of different things that can
cause an allergic reaction
for example bee stings can cause an
allergic reaction peanut allergies food
allergies pollen can cause allergic
reactions and so can certain medications
as well
now of course allergies can be either
very mild and seasonal such as hay fever
and sometimes allergies can be so severe
that it can cause shock but how does it
cause shock well first of all to answer
that I want to acknowledge that there
are two types of anaphylaxis those that
are immune illogic and those that are
non immune illogic and I'll go ahead and
start with immunologic anaphylaxis
because that's actually the most common
type in immunologic anaphylaxis there's
some sort of allergic agent whether it's
poison from a bee sting or food allergy
that somehow gets into the system and
whatever this material is it's known as
an allergen because it generates an
allergic response so when this allergen
first gets into the body it will
interact with b-cells and not be cells
like the insect that'd be right up here
but b-cells as in the letter B now these
cells are the antibody creating cells of
the immune system they create antibodies
and antibodies are essentially a little
Y shaped protein that is used like a
signal marker to find something that's
foreign foreign material so in this case
the antibodies will be reacting to the
allergen now antibodies that are created
in response to an allergen are known as
IgE IG e stands for immunoglobulin E
globulin means protein and immuno just
means immune so really its immune
protein and the
classification is e now the reason I
want to emphasize this is because IgE
specifically docks on two other immune
cells which are known as mast cells
these mast cells are mediators of the
immune system so what ends up happening
is once I GE is created it will dock
onto these mast cells so this all occurs
when a person is first exposed to an
allergen and this is called
sensitization the immune system is
sensitized to this allergen so the next
time that this allergen comes along it
will create a rapid allergic response
the allergen will dock on to these
antibodies and when they do the mast
cells activate and when mast cells
activate two main things happen first of
all mast cells release immune molecules
known as cytokines cytokines are
essentially used for cellular
communication so mast cells communicate
with other white blood cells and tell
them to come over so what ends up
happening is these white blood cells
continue to recruit more white blood
cells and it's a cycle that that creates
more and more white blood cells being
recruited and activated in response to
these allergens now that activation of
both the mast cells and the immune cells
causes release of another molecule known
as histamine now histamine is a potent
vasodilator in other words it dilates
blood vessels so here i with the dotted
line i'm showing a blood vessel size
before and after histamine the diameter
of the blood vessel increases now this
is happening in the blood stream in the
entire body and it causes a large drop
in blood pressure so patients lose the
function of their circulatory system and
are no longer able to distribute oxygen
and so that's how an allergy causes
shock and also let me note that
histamine causes the blood vessels to
become leaky so fluid escapes the
vascular space which causes swelling to
occur all
throughout the body so a patient has
massive swelling along with a massive
drop of blood pressure now the second
type of anaphylaxis is called non immuno
logic
now non immuno logic anaphylactic shock
is essentially the same as immunologic
shock it's just the pathology is
slightly different
instead of mast cells being stimulated
by IgE the allergen specifically targets
the receptors on the mast cells and so
you get the same process of histamine
release as well as cytokine release
which of course causes the super
immunological response as more white
blood cells are recruited and then also
causes this drop of blood pressure so
what are the symptoms that we see in
anaphylactic shock the symptoms are
going to be characterized by the actions
of histamine so a patient with
anaphylactic shock has this major drop
in blood pressure due to vessel dilation
so we'll see flushing of the skin as
blood vessels dilate and blood starts to
saturate in the skin and swelling as
fluid is getting outside of the blood
vessels and itchiness which is also
caused by histamine release so these are
all symptoms that you would come to
expect from an immune response you may
see other various symptoms such as
rhinorrhea which is a runny nose and
this is caused by vessel dilation in the
nasal vasculature so you have an
overactive release of fluid but the
symptom that I really want to get to
occurs with the lungs is to me not only
causes vessel dilation one of its most
serious symptoms is bronchospasms
spasms of the bronchi the main air
passages to the right and left lungs
so these bronchospasms make it difficult
for a patient to breathe what makes it
worse also is that swelling can be
occurring in the throat as well which
can close off the airway making it even
more difficult to breathe so a patient
comes in who's non-responsive he's not
breathing
and you check and find that the patient
has a very low blood pressure so what do
you do do you order lab tests no that's
a terrible idea
this patient is having a severe bout of
shock it should already be apparent
based off of the clinical symptoms that
this patient has especially the low
blood pressure severe low blood pressure
should indicate that right away
something needs to be done so you
progress right to treatment and
treatment is based off of the ABCs
airway breathing in circulation so
number one you want to establish the
airway if a patient is not breathing you
want to give them a hundred percent
oxygen so you can fill up their lungs
and ventilating the patient with a bag
mask to push air into the lungs may be
one of the first ways to respond to a
patient who has anaphylactic shock along
with this the blood pressure needs to be
maintained there's one medication that's
especially effective at maintaining
blood pressure in patients with
anaphylactic shock and that's
epinephrine first of all of course
patients have these very dilated blood
vessels
now epinephrine has strong sympathetic
activity so it acts in a way to
constrict blood vessels back down to
maintain blood pressure so this directly
counteracts what histamine does to blood
vessels epinephrine also affects the
lungs and causes Branko dilation so it
opens up the Airways so this is
important to allow airflow back into the
lungs now to also maintain blood
pressure IV fluids will help fill up the
vascular space so these are the main
ways to treat a patient with anaphylaxis
and along with this you can give anti
histamines to really directly counteract
the effects of histamine
in the body but of course let me
emphasize that epinephrine and IV fluids
are the mainstay of treatment because
they act to immediately reverse the low
blood pressure and restore a patient's
circulatory system