So what are the different types of shock?
Not all shock is created equal
and there are a number of different physiological arrangements
that all end in the same final common pathway of clinical shock.
Cardiogenic shock is the first one we're gonna talk about
and in some ways it’s the easiest to understand.
In Cardiogenic shock you have acute impairment of cardiac output
for one reason or another,
now it’s most commonly associated with coronary syndromes.
You have a massive MI and you’ve infarct a large amount of you myocardium.
You can imagine that infarcted myocardium isn't gonna squeeze anymore.
So instead of having a nice rigorous contraction with every beat of the heart,
you now have a very weakened ineffective contraction with every beat of the heart
which of course is gonna impair your stroke volume
and ultimately impair your cardiac output.
There are other conditions that can do this though,
various drugs and toxins,
of course cardiomyopathies will have the same effect,
valvular diseases can potentially render your cardiac contractions ineffective.
And dysrhythmias can also impair filling time
and decrease the effectiveness of cardiac output.
So there’s a lot of conditions that can lead to cardiogenic shock,
but they all have the common end result of pump failure.
Reducing the ability of the heart to contract effectively.
Hypovolemic shock is also pretty easy to understand.
That’s all about preload,
so basically if your blood volume is on the floor
instead of inside of you vasculature that’s obviously gonna reduce your preload.
You’re not gonna have blood in the vessels
to put into the heart during diastole,
so your cardiac output is gonna be impaired.
Now, your body will try to compensate for that by raising the heart rate
and by clamping down on the vasculature,
raising the systemic vascular resistance.
These are normal physiologic compensatory mechanisms
to try to maintain perfusion at the tissue level.
However, the disease process is fundamentally all about preload,
and as you can imagine it’s gonna be treated with agents
that will bring your preload back up, namely fluids or blood.
Distributive shock is a form of shock
where all your blood is inside of the vasculature
where it belong but it’s maldistributed.
Your vasculature is dilated, and boggy and has poor tone
and instead of effectively delivering blood to tissue,
you now have vasodilation in the periphery
which causes blood to just kind of hang around
not getting where it supposed to go.
We see this particularly in sepsis and anaphylaxis
and the physiologic effect primarily is loss of systemic vascular resistance.
You’re vasodilated and you’re not gonna be able to effectively distribute blood to tissues.
However, in distributive shock you do also see reduce cardiac output.
There is some direct myocardial effect as well, and that’s important to remember.
Your body will try to compensate for this by raising the heart rate
but that usually only works to a certain extent.
So you’re not gonna get full physiologic compensation.
The last form of shock is obstructive shock.
So these are the conditions where there some sort of extra cardiac blockage
to blood flow that prevents the heart from filling normally.
So in cardiac tamponade there's a pericardial fluid or blood collection
that mechanically compresses the heart and prevents it from filling.
In tension pneumothorax there’s gonna be a big hight pressure air collection
in the chest that again compresses the mediastinum
prevents normal cardiac filling,
actually prevents normal venous return
back up into the chest by making the intrathoracic pressure positive.
Pulmonary embolism, well, very simply,
if you’ve got obstruction to flow on the right side of the heart,
you’ve got a big clot that’s prevents the blood from circulating out of the right heart,
and through the pulmonary vasculature, you’re gonna have impaired input on the left, right?
You’re not gonna be able to fill the heart adequately and send blood out to the body.
So these are also diseases of preload much like hypovolemic shock,
but they’re all conditions where the problem is obstruction of normal blood flow
and maldistribution of blood rather than blood loss.
Alright, so what is shock look like clinically?
Well, as you can imagine it very commonly is gonna involve tachycardia
because as your cardiac output drops,
your heart is gonna try to compensate for that by increasing rate.
That’s a normal physiologic compensatory response
to impaired profusion when the heart is not putting out enough blood
to meet the physiologic needs, the sympathetic nervous system will tell it,
"beat faster, beat harder."
So you see tachycardia in this settings.
You’ll also very commonly see tachypnea,
so as the tissues become hypoxic,
a normal physiologic compensation for that is to try to breathe more
and get more oxygen into the blood in order to provide oxygen at the tissue level.
So it’s not uncommon to see patients breathing quickly
and in some cases even to see respiratory distress.
You’ll often, but not always see hypotension,
so as you can imagine in many of the shock states that I described
were either your blood volume is missing entirely
or it’s not being circulated appropriately to the body,
because of pump failure or vasodilation,
you might see an overall reduction in blood pressure.
Now, one thing I wanna make sure to remind you about
is that’s not always gonna be absolute hypotension.
Generally in a healthy person, you will see numbers that are reflective of true hypotension.
But if it’s a patient who’s chronically hypertensive
and they’re running around with the systolic of 160 or 170 their entire lives
they might be significantly hypotensive at 120.
So you wanna make sure that you’re always thinking about your patient
relative to their baseline rather than just the absolute numbers
that we learned in medical school.
Altered mental status is a common manifestation of shock,
because the brain is extremely sensitive to tissue level hypoxia,
and if you're not delivering adequate oxygen to the brain, it’s not gonna work properly.
We also see oliguria or anuria
when you’re not adequately profusing and oxygenating the kidneys.
You might see pallor or cyanosis which is reflective of the global hypoperfusion of the patient.
You might see cool or mottled extremities
again, reflecting shunting of blood away from the periphery
and toward the vital organs which is a normal physiologic compensation for shock.
And you might find faint peripheral pulses.
Again because the body is trying to shunt blood centrally
and maintain blood flow to vital organs,
so you’re gonna loose blood flow out in the periphery
where you would normally have it in a nonshock state.
Bottom-line, is presentation of shock is gonna be highly variable
based on what the underlying causes.
What's going on with the patient?
And also how well compensated the patient is.
You can see patients in shock who look remarkably well.
And you can see patients in shock where one step away from cardiac arrest.
And you really got a range anywhere in between.
So you always wanna think about what your patient’s personal baseline,
physiologic status and how different they are from that.
And remember there’s gonna be a lot of variability
in what patients in shock look like clinically.