- Septic shock is a very serious condition.
About half the patients who have septic shock
will die within the first month of their diagnosis.
But what is septic shock?
Let's break down the two words.
Septic comes from the old Latin term meaning "rotten",
and the word shock, of course, means
decreased tissue oxygenation and low blood pressure.
So combined, it's decreased tissue oxygenation
caused by something that is rotten.
Now, this rotten thing is an infection,
infective material, that causes
some sort of inflammation.
So it's infective material that causes
decreased oxygenation of tissues.
So how does infective material do that?
Let's take a look at a blood vessel
and of course the blood is used
to deliver oxygen to tissue.
So here's some red blood cells, and
I'll put some tissues right here.
These little boxes represent cells.
So these red blood cells are supposed to
transfer oxygen, this little purple substance
right here, to these cells.
Delivery of oxygen to the tissues.
Now let's say there's some sort of
infective material in the bloodstream.
White blood cells will encounter this infective material
whether it's bacteria, virus, or a fungal infection,
that's in the bloodstream.
So now your blood vessels are like pipes,
septic pipes, containing this sewage,
this unclean material.
It's no longer sterile.
So this white blood cells, their job is
to find this and clean it up.
Of course when white blood cells encounter
this infective material, they activate.
When they activate, there are several things
these white blood cells do.
First, they're going to call on other
white blood cells to come and check this out,
because the idea is you want to recruit
as many white blood cells to wherever this
infective material is so you can eradicate it.
So first, white blood cells
recruit their buddies.
Now here comes a major point.
This infective material is normally
not in the bloodstream, in fact,
it's usually out here in the interstitial tissue.
So usually white blood cells have to get
into the interstitial tissue and eliminate the threat.
White blood cells do that by releasing molecules,
such as nitrous oxide.
The molecules that are released
interact with the blood vessels, and cause
the blood vessels to do a couple things.
First of all, blood vessels will dilate.
Or in other words, the diameter of the blood vessel
will increase in size.
So let me go ahead and erase some of this
so we can show the dilation of the blood vessel.
So let's make this dotted,
showing that it was this size,
and now, blood vessel diameter increases.
We've increased from this size
to a little bit larger.
This causes a localized decrease in vascular resistance,
systemic vascular resistance.
The blood, all of the blood contents, have more space
to move around, and there's less resistance that
they're bumping up against, because of this
widened diameter of the blood vessel.
So there's increased diameter
of the vascular space.
Of course, this makes sense if this is happening
locally, blood slows down in an area
where there is an infection.
Because remember, the immune system usually
encounters infective material in the peripheral tissues.
To be able to get into the peripheral tissues,
white blood cells need to make the blood vessels leaky.
So that's the second thing that's happening here.
Increase diameter and increase permeability,
or leakiness, of the blood vessels.
Here is actually the cause of shock.
You have this infective material
in the blood vessels all throughout the body,
so this happens everywhere,
systemic vascular dilation, or vasodilation.
This decrease in vascular resistance causes
a drop in blood pressure, because remember,
vascular resistance and cardiac output
equals blood pressure.
A large drop in this causes a large
decrease in pressure.
But also they have low tissue perfusion,
because the equation for tissue perfusion
is really the same, cardiac output and systemic
vascular resistance contribute to tissue perfusion.
But let me show you something else
that's causing low oxygenation of the tissues,
low tissue perfusion.
You've got these cells that are
receiving oxygen from red blood cells.
With the increased leakiness,
fluid will get into the tissues.
So you have all this fluid buildup
in the tissues, and this makes it really
difficult for oxygen to get to the cells it needs to.
It has to diffuse through all this fluid.
These cells become starved of oxygen.
This is primarily what causes shock.
There's a third thing that happens when these
white blood cells encounter this infective material.
They want to destroy it, right?
If you've got bacteria, or a virus, or fungus,
that's the job of the white blood cells,
to destroy this infective material.
These white blood cells release lytic enzymes
and reactive oxygen species that cause
damage to destroy this pathogen, but again,
this is happening everywhere.
So not only do you damage the pathogens,
but you'll end up damaging the blood vessels as well.
So that's number three.
You have damage of blood vessels.
Remember, this is happening everywhere,
and because of that, serious complications can occur.
First of all, when blood vessels get damaged,
there are things called coagulation factors in the blood.
I'm gonna make them this little lavender color.
They're a protein that helps cause clotting,
so when blood vessels get ruptured,
you want to create a clot to patch this up,
so that blood doesn't spill into the extravascular space
outside of the blood vessel.
Again, this is happening to blood vessels
everywhere in the body, I cannot
emphasize that enough.
So what ends up happening is these coagulation
factors end up getting used up.
They're trying to patch up all these blood vessels,
so clots are forming everywhere.
Some of these clots actually break off
into the bloodstream, so an interesting thing happens.
There's coagulation that's happening
in the vascular system, but the coagulation
can't keep up with the breakage of blood vessels.
So sooner or later, blood is spilling
out of the blood vessels.
This weird state of coagulation in the blood vessels
with simultaneous bleeding is called
disseminated intravascular coagulation.
Coagulation in the intravascular space,
inside the blood vessels, and it's everywhere.
It's disseminated everywhere.
This is a very serious complication
that can be seen in septic shock.
Another complication that can be seen
in septic shock is ARDS,
acute respiratory distress syndrome.
As you know, the lungs are highly vascularized,
they have a lot of blood vessels,
because they need to be able to take oxygen
from the atmosphere to saturate blood vessels.
Let's, again, return to our pathology of septic shock.
This is happening everywhere,
and the damaging enzymes and cytokines
and different immune molecules end up
damaging blood vessels in the lungs as well.
If you damage all of these blood vessels in the lungs,
then oxygen won't be absorbed properly
into the bloodstream.
So patients with severe septic shock end up
in respiratory distress,
because they can no longer pull in oxygen
from the environment into their bloodstream.
So that's acute respiratory distress syndrome.
A final point that I want to touch on
is the cardiac output.
Cardiac output will initially increase
to try to compensate for this decreased
vascular resistance, right?
It makes sense that if you increase cardiac output,
it will even out the blood pressure.
However, as septic shock goes on, the heart, too,
can become paralyzed and damaged by all these molecules,
these immune molecules.
If left untreated long enough, cardiac output
will start to be depressed.
Cardiac output will decrease.
Of course, if you decrease cardiac output instead,
then blood pressure will also decrease.
For symptoms, think about a very severe infection.
With a severe infection, you'll see things
such as fever, chills, and sweating.
But a major symptom of septic shock is warm skin.
As these blood vessels dilate in size,
as they increase in size, this happens in all organs,
and the largest organ in your body is technically the skin.
So the skin takes out a lot of the blood
from the rest of the body.
So initially, patients will have very warm skin.
However, as a patient is in shock long enough,
and their sympathetic nervous system tries
to increase blood pressure, it's going to
clamp these vessels back down to try to improve
the resistance, the systemic vascular resistance,
and maintain blood pressure.
With progression of septic shock,
patients will eventually have cooler skin,
and this is a bad sign, because, obviously,
it means septic shock has been occurring
for a long period of time.
And the clamping down of these blood vessels
doesn't necessarily mean that fluid can't escape
anymore, the blood vessels are still going to be leaky
from all these vasoactive molecules that are
increasing the leakiness and permeability
of the blood vessel.
So you'll still have this decreased tissue perfusion
from all of this fluid that's accumulating
in the tissues.
Also, you'll see other symptoms such as
respiratory distress, altered mental status,
and decreased urination.
As organs get starved from oxygen, they start
to lose the functions they normally carry out.