Anaphylactic shock | Circulatory System and Disease | NCLEX-RN | Khan Academy

Anaphylactic shock | Circulatory System and Disease | NCLEX-RN | Khan Academy

August 20, 2019 43 By William Morgan


– [Voiceover] 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 immunologic
and those that are non-immunologic.
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 a food allergy that
somehow gets in to 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 B cells like the
insect, the bee 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.
IgE stands for immunoglobulin E.
Globulin means protein and
immuno just means immune.
So really it’s immune protein
and the classification is E.
Now the reason I want to emphasis this,
is because IgE specifically
docks on to other immune cells
which are known as Mast Cells,
and these mast cells are
mediators of the immune system.
So what ends up happening
is, once IgE is created,
it will dock on to 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 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, 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 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-immunologic.
Now non-immunologic 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?
Well 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.
Histamine not only causes vessel dilation,
one of it’s 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 breath.
What makes it worse also is that swelling
can be occuring in the throat as well,
which can close off the airway,
making it even more difficult to breath.
So a patient comes in
whose 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 ABC’s,
airway, breathing and circulation.
So number one, you want
to establish the airway.
If a patient is not breathing,
you want to give them 100% 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.
And there’s one medication
that’s especially effective
at maintaining blood pressure in patient’s
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 effects the lungs
and causes bronchodilation,
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 antihistamines
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.