Definition and Pathophysiology of Shock, by Dr. Anthony Olivero.
Hello, my name is Tony Olivero.
I'm a pediatric critical care attending here at Boston Children's Hospital.
I'll be talking today about shock, and specifically, the definition and pathophysiology of it.
Introduction.
So what is shock?
It's a tough question and a difficult concept to define, but overall can be categorized
as an acute complex state of circulatory dysfunction that results in failure to meet the metabolic
demands of the tissue.
There are generally considered to be about five types of shock, but at any point a patient
may exhibit more than one type of shock.
Those general categories are: hypovolemic shock, cardiogenic shock, obstructive shock,
distributive shock, and septic shock.
We'll go through each category and talk about the etiologies and pathophysiologies.
Hypovolemic shock.
- Hypovolemic shock, which is defined by a decrease in the intravascular blood volume
which results in inadequate substrate delivery to meet the metabolic demand of the tissue.
This is the most common type of shock in pediatrics.
And as far as etiologies go, gastroenteritis is probably the number one cause in pediatrics
for hypovolemic shock.
Results in fluid and electrolyte losses and is typically fluid responsive, and in another
lecture series we'll talk about the evaluation and treatment of shock.
Other causes of hypovolemic shock can be endocrinopathies including diabetes insipidus and DKA, whole
blood loss including hemorrhage, and some crossover type things like burns and capillary
leak syndromes.
As far as the pathophysiology for hypovolemic shock, you generally have a decreased intravascular
blood volume, which leads to decreased preload, decreased stroke volume, therefore decreased
cardiac output and decreased oxygen delivery.
Initially this leads to an activation of peripheral and central baroreceptors and a release of
catechols to help maintain the blood pressure and perfusion pressure to vital organs.
Cardiogenic shock.
The next type of shock that we'll talk about his cardiogenic shock.
And as you can imagine, it results from acute cardiac dysfunction.
Again, which meets-- makes the heart unable to meet the metabolic demands of the tissue.
As far as etiologies for cardiogenic shock, common ones include infections and myocarditis,
heart rate abnormalities-- so frequently SVT or a ventricular arrhythmia can result in
cardiogenic shock-- and sometimes bradycardias as can as well.
Other things, hypoxic-ischemic events, metabolic disorders, connective tissue disorders including
lupus, JRA, neuromuscular disorders including Duchenne's and spinal muscular atrophy, and
toxin ingestions.
One of the more common ones that we also see here at Children's is congenital cardiac diseases.
As far as the pathophysiology, they can be broadly categorized into systolic or diastolic
dysfunction.
As far as systolic dysfunction, it's an inability of the heart to squeeze and properly eject
an adequate blood volume, again, to meet the metabolic demands of the tissue.
So toxins accumulate, there's myocardial edema, impaired calcium flux and cycling, decreased
coronary blood flow, poor cardiac contractility, a decreased cardiac output, and ultimately,
decreased oxygen delivery.
As far as diastolic dysfunction, it's slightly different and a bit more difficult to manage
because there aren't many drugs available to treat it.
But there's impaired relaxation of the heart-- so an inability to accept blood volume-- increase
left-sided or left ventricular end-diastolic pressures which result in increased pulmonary
venous pressures and the respiratory and hemodynamic effects afterwards.
Obstructive shock.
The next type of shock that we'll talk about is obstructive shock, and that's the inability
to produce adequate cardiac output despite normal intravascular volume and myocardial
function.
I think the key things that differentiate this from other types of shock are that there's
a normal intravascular volume and that the heart is functioning properly.
And again, the end of that statement is that the cardiac output is unable to meet the metabolic
demands of the tissue.
Point of clarification.
Etiologies for obstructive shock include: acute pericardial tamponade, tension pneumothorax,
pulmonary or systemic hypertension, cardiac congenital or acquired outflow tract obstructions,
and pulmonary embolism.
Pericardial tamponade, there's an accumulation of pericardial fluid which the heart can tolerate
up to a certain point.
Generally a pretty large or sizable amount of fluid collecting which impairs the cardiac
filling, ultimately decreasing cardiac output and oxygen delivery.
Some things that you might see on exam or vital sign changes are pulsus paradoxus, a
narrowed pulse pressure, pericardial rub, [SOUND OF PERICARDIAL RUB] and JVD, or Jugular
Venous Distention.
Distributive shock.
The next type of shock that we'll talk about is distributive shock, which is a maldistribution
of blood flow which, again, results in an inadequate substrate delivery to meet the
metabolic demands of the tissue.
Etiologies for this-- anaphylaxis, spinal cord trauma, or surgeries are common examples,
and vasodilatory medications and sometimes overdoses of drugs.
As far as the pathophysiology, it's very similar to hypovolemic shock, where there's some form
of vascular dilation and an inadequate amount of blood volume to adequately perfuse the
organ bed.
Decreased preload, decreased stroke volume, decreased cardiac output, and ultimately,
decreased oxygen delivery.
Septic shock.
Last but not least is septic shock, which includes many of the problems seen in other
versions of shock-- relative and absolute hypovolemia, maldistribution of blood flow,
myocardial depression, and a variety of electrolyte and endocrinopathies.
As far as septic shock etiologies, the majority of them are infectious, so we won't go into
that.
The pathophysiology, like I described, is hypovolemia, cardiac dysfunction, vascular
tone dysfunction, distributive shock, and at a cellular level, impaired utilization
of substrates.
Phases of shock.
Shock typically has three phases.
And the goal of the evaluation and management of shock is to recognize shock early and try
and intervene to prevent the progression of shock.
So the first phase is compensated, where organ function is maintained.
The second is uncompensated, where you start to see organ dysfunction.
You may see abnormal vital signs at that point.
You may see abnormal lab values.
And finally, irreversible, which clearly we're looking to prevent.
Shock is a dynamic process, so there's changes throughout.
And you just want to be very aware that patients need multiple and serial exams throughout
their course to properly evaluate them.
So this concludes the discussion on the definition and pathophysiology of shock.
And thank you for your attention.
Please continue with the next video, Evaluation and Treatment of Septic Shock.
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