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

December 3, 2019 0 By Kody Olson

So, here I have outlined
just a general concept of the cardiovascular system. We have the heart over here,
the arteries deliver blood to the organs, and the veins deliver
blood back from the organs to the heart. So, the reason I’m going
to draw this is because the cardiovascular system is
critically affected in neurogenic shock. Now, what is neurogenic shock? Neurogenic shock occurs
when the nervous system is no longer functioning properly. And this can happen
from a number of things. Sometimes, and actually most
frequently, it’s from trauma, so if the patient has something
occur to their spinal cord where it’s severed or an epidural
goes wrong and some nerves are damaged, that can
lead to neurogenic shock, if it’s severe enough. Now, what neurogenic shock
essentially is is loss of vascular tone and pooling
of peripheral blood. So, the nervous system provides
tone to the blood vessels and also to the heart. And this tone is known
as “sympathetic tone”. It’s kind of like muscles. If you think about somebody
who’s flexing versus not flexing, of course
there’s a certain tightness that the muscles undergo when you flex. Now, that’s really happening
to the blood vessels at all times, and it’s
done to really maintain blood pressure. Blood vessels are somewhat
tightened and squeezed down a little bit to allow
blood to flow through. The idea is, as blood flows
through the vascular system, it’s going to be maintained
in a forward direction by the blood vessels because if it
hits up against the wall, the blood vessel bounces it back
and pushes the blood forward. If it didn’t do this, if
there was no vascular tone, blood would run up against
the wall and lose a lot of its energy, it would be really dampened. So, it’s kind of like a trampoline. When you’re bouncing on a
trampoline, if the trampoline is taut enough, you’ll be able
to bounce up and down really easily, right? However, if you think about
loosening the trampoline, if you loosen the material
on the trampoline, you won’t be able to bounce
as high, and so that’s the same thing that happens here. When you loosen the blood vessel,
it won’t be able to bounce blood forward as well. So, like I said, the nervous
system provides this tone, this vascular tone, to both
the arteries and the veins. So, what happens if we shut
down this nervous system? Well, the blood vessels
will lose their tightness, both the arteries and the
veins, so I’m going to go ahead and erase this to show that
the blood vessels kind of become floppy. And I’m going to really
exaggerate this by making them really wide, so both the
arteries and the veins become very floppy. So you can see, if this
happens in the arteries, blood is not really going to
make it to the organs as well. It’s supposed to bounce off
and bounce forward, but that’s not really happening anymore,
so it just kind of slowly makes it to the organs, so you have shock, you have decreased oxygen
delivery, decreased tissue perfusion to the organs. And then, blood of course trying
to flow back to the heart, won’t be able to, it’ll just kind of pool. It’ll just stay in the venous
system and only a minimum amount will return to the heart. So this will actually affect
the cardiac output of the heart. Remember blood pressure and
tissue perfusion are related to cardiac output and vascular resistance, systemic vascular resistance. So up here in the arteries,
we’ve already shown that this system vascular resistance is decreased, so that’s going to lead to
a decrease in blood pressure and tissue perfusion. So, let me actually go
ahead and write that out. Blood pressure and O2 delivery. Tissue perfusion is oxygen delivery. So both of these will go down
because resistance in the arteries are going down. And now also, the veins
aren’t able to deliver blood back to the heart. And if you can recall, cardiac
output is stroke volume times heart rate. So, if we decrease the amount
of blood going back to the heart, that means there’s
going to be less blood that the heart can squeeze
forward, so that means less stroke volume, right? Decreased delivery of blood to
the heart leads to decreased stroke volume, which means
decreased cardiac output. And that further worsens blood
pressure and further worsens oxygen delivery. You’re shutting down the
cardiovascular system by not being able to maintain vascular tone. Something else that you
see in neurogenic shock is, the nervous system, the
sympathetic nervous system, controls the heart rate. Now, if you no longer have the
input of the nervous system, the heart rate is going to drop. And so, we go back to our
equation, heart rate drops, cardiac output drops even
further, and blood pressure will drop, and then oxygen
delivery will also drop. So this is truly shock. Tissue perfusion is just
completely demolished and so is blood pressure. So, the entire cardiovascular
system is just not able to maintain blood flow, and
that leads to a shut down of oxygen delivery. So, let me go ahead and scroll
down so we can think about some of the symptoms. I’m going to keep this somewhat
in view so you can still ponder it and think about it. But the symptoms of neurogenic
shock will be those of decreased oxygen delivery
such as altered mental status, decreased urine output. You think about anything that
needs oxygen, any organ that needs oxygen, and think
about what would happen if it wasn’t getting oxygen; it
would start to shut down. So, organ dysfunction can occur… and a major symptom
that you see specific to neurogenic shock is bradycardia. Now, this is something you
should really be thinking about. This is really the only
shock that has bradycardia. Remember, all of the other
shocks are going to try to increase heart rate, speed it
up, to try to deliver oxygen and deliver blood to the body. But here, we have the heart
rate dropping because it’s no longer getting input from
the nervous system, and so, we have a low heart rate, bradycardia. So, this is a key symptom
of neurogenic shock. And, another main symptom
that I want to touch on is warm skin. Warm skin occurs because
of the dilation of all blood vessels. So these blood vessels
in the skin will dilate, they’ll enlarge like we
were showing up here, so blood can flow through
the skin more easily. And that’s a problem because
it diverts blood away from vital organs such as the brain,
the lungs, and the heart. And so, the treatment of
neurogenic shock will focus on trying to maintain this blood
pressure, so you’ll give medication known as “pressers”. Pressers allow the blood
vessels to clamp back down. If you clamp the vessels
down, it directly is affecting the issue in neurogenic shock. And, you’ll also give a
lot of IV fluids to try to maintain the fluid volume. If you increase the amount
of fluid in the vasculature, it’s more likely that you’ll
be able to push it forward and deliver blood to the system. So, IV fluid and pressers help
maintain the blood pressure. And a final medication that
you’ll see is atropine. Atropine works by blocking
the parasympathetic nervous system. So, it’s like stopping the
“rest and relaxation” part of the nervous system, and it
increases the “fight or flight”. So increasing the fight
or flight response, will increase the heart rate. So giving atropine will
help raise up the heart rate to increase cardiac output
and to improve the pumping of blood throughout the
cardiovascular system.