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Health and medicine
Course: Health and medicine > Unit 3
Lesson 14: Shock- What is shock?
- Shock - hemodynamics
- Shock - oxygen delivery and metabolism
- Shock - diagnosis and treatment
- Cardiogenic shock
- Sepsis: Systemic inflammatory response syndrome (SIRS) to multiple organ dysfunction syndrome (MODS)
- Septic shock - pathophysiology and symptoms
- Septic shock: Diagnosis and treatment
- Hypovolemic shock
- Neurogenic shock
- Obstructive shock
- Anaphylactic shock
- Dissociative shock
- Differentiating shock
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Shock - oxygen delivery and metabolism
Created by Ian Mannarino.
Want to join the conversation?
- so is shock essentially severe ischemia?(1 vote)
- Nope. Ischemia implies that the blood supply is restricted because of vessels not being able to deliver the blood from occlusion. Shock is from oxygenated blood not being delivered for a variety of reasons. Cardiogenic shock is caused indirectly from ischemia, because coronary artery ischemia prevents the heart from delivering oxygenated blood effectively to the body.(12 votes)
- is there a calculation for anaerobic metabolism. I have a question the first part was how much ATP is produced from 4 moles of glucose. So have that covered the next part of the question is Would the same number of ATP be produced if the four molecules of glucose were metabolized by muscle tissue?(1 vote)
- Yes, anaerobic metabolism extracts two molecules of ATP for every molecule of glucose. While aerobic respiration can produce up to thirty-eight molecules of ATP for every molecule of glucose. So, if four molecules of glucose were being broken down in muscle tissue with poor perfusion we would expect an gain of eight molecules of ATP to keep the cells alive. Muscle tissue with proper perfusion could expect to gain up to one-hundred and fifty-two molecules of ATP from the same four molecules of glucose.(2 votes)
- How does dioxygen leave the hémoglobbin to go to the cell?(0 votes)
- By following its concentration gradient, which is low in active tissues compared with in the blood. It drops off hemoglobin, then into the plasma, then into the tissues.(2 votes)
Video transcript
- [Voiceover] To understand
the pathophysiology of shock, we first need
to remind ourselves what shock is. Shock at its basic level means cells are not getting oxygen they need. Essentially the O2 delivery,
the amount of oxygen that the body can deliver to its cells becomes less than the amount of oxygen that is required by the body. Shock is essentially a
failure to deliver oxygen to the different tissues and
organs and cells of the body. Why do cells need oxygen? Basically cells, in this
little box here I' going to designate as a cell,
and cells need oxygen to be able to create energy. This is titled "aerobic metabilism." Creating energy metabolism
with the assistance of oxygen, aerobic. And this is really the reason we breathe. We go through respiration because we need the oxygen to help create energy. However, the cells of the body can also create energy through
anaerobic metabolism. The cells of the body can
survive without oxygen just for a little while. However, there's a
problem with going through anaerobic metabolism
versus aerobic metabolism. With oxygen, you're able
to create a lot more energy to be able to satisfy the
needs of each cell in the body. Yet if the body is forced to undergo anaerobic metabolism, not enough energy can be created to meet the
requirement to sustain life. So that's one problem with undergoing anaerobic metabolism
and why we need oxygen. But another issue with
anaerobic metabolism is a by-product of trying
to create this energy is this substance called "lactic acid." I'll come back to this
point a little bit later to show what the issue is
with creating lactic acid, but for now it's important to remember that anaerobic metabolism
creates this by-product. lactic acid. Okay, so we know now
that aerobic metabolism is necessary to create
the amount of energy we need to sustain cellular
function to sustain life. We know that the body
has to deliver oxygen. And to understand how the body
fails to do this in shock, let's go ahead and take
a look at a blood vessel. I'm gonna go ahead and draw
a blood vessel right here. Note that this blood vessel is going to be delivering oxygen through the blood to distribute oxygen to the tissues. So let's make oxygen this
little light blue color. This is oxygen. As you know, oxygen is
carried in red blood cells in hemoglobin, so this is how oxygen is delivered to the
tissues, through hemoglobin, through red blood cells. Let's go ahead and draw
some different cells. These little boxes, of course, are representing our cells. Just a smaller version
than this big one up here. Now remember, in shock the
issue is tissue perfusion. Tissues and cells are not
getting enough oxygen, they're not getting enough
blood that they need for oxygenation, and without this oxygen they can't create the energy
necessary to sustain life. In shock, these cells
are desperate for oxygen. There are two scenarios
that we can see in shock. In the first scenario, there is increased extraction of oxygen. This is because there's
an increased demand for the cells to have oxygen. There might be an increased requirement. These cells have so little oxygen in them. They're oxygen-starved. It's not really an active process, but because there's so
little oxygen up here and more oxygen in the blood, oxygen readily diffuses into the cells. These cells are oxygen-starved. They pull out more oxygen,
therefore that would mean that there's lower oxygen
return to the heart. Less oxygen is getting back to the heart. Two types of shock that are an example of this increased extraction
are cardiogenic shock and hypovolemic shock. If you think about it,
hypovolemic and cardiogenic shock, blood is not getting
pushed forward fast enough. It's not getting delivered properly, so the cells are using up their oxygen quicker than it's being delivered. Lower delivery, despite
the required oxygen remaining pretty much the same. The cardiovascular system is just not able to deliver that oxygen to these cells. Second, let's take another look. Let's look at these cells. These cells are still desperate for oxygen and in shock that's really the definition. They require more than
is able to be delivered. But what if there's something
that actually impedes oxygen from being able to be delivered? If oxygen isn't getting to the cells, this is decreased extraction. This is what happens in the type of shock known as "distributive shock." Oxygen can't be distributed to the cells. For example, in septic shock when there's a lot of inflammation
and swelling in the space in between the cells,
the interstitial space, the oxygen has a tougher time diffusing through this space, so
oxygen can't get through all this thick fluid. This extra fluid creates
a diffusion barrier so that oxygen can't be distributed. So again, we have
increased demand of oxygen due to poor oxygen delivery. Again, I'll go ahead and write these down. This first scenario
occurs with cardiogenic and hypovolemic shock. And the second scenario occurs with distributive types of shock. Septic shock, anaphylactic shock, something that creates a barrier that prevents oxygen from getting to the cells. Now again, if oxygen isn't
delivered to the cells, it's going to stay in the blood, so more oxygen will return to the heart. That makes sense, if
there's less extraction, oxygen just kind of remains in the blood, which shows up as increased
oxygen return to the heart. I go over this point in
detail because if we can figure out how much oxygen is extracted from the tissues, we
can have a better idea of what type of shock it may be: cardiogenic or hypovolemic versus a distributive type of shock. So how do we measure that? That's where something
called mixed venous oxygen, or mixed venous oxygen saturation, which is abbreviated SMVO2, saturation of mixed venous oxygen, comes into play. This term is actually interchangeable with the other term, which is known as central venous oxygen saturation, abbreviated SCVO2, central
venous oxygen saturation. Now what are these two terms, what do they mean? It's very hard for us to measure how much oxygen is getting pulled from the tissues at each individual tissue. So what we do is, we
look at how much oxygen is returning to the heart. We take a look at the heart, and you see that blood returns to the
right side of the heart through the superior
vena cava, so up here, and the inferior vena cava. This is how blood returns from the top of the body, the arms and the head, versus the bottom of the body, the legs, the abdomen, so on and so forth. When blood from both the
superior and the inferior vena cava meet in the right atrium, the oxygen of these two major veins, these central veins, mix. This is important because
the oxygen extraction may differ between the
upper part of the body and the lower part of the body. So when they mix, we get
an average of the total oxygen coming from the upper and the lower parts of the body. Now we see if the mixed
venous oxygen saturation, also known as the central
venous oxygen saturation, is lower, that means
less oxygen is returning to the heart, and so therefore we can say that oxygen is being
extracted more than normal. The same goes for if
more oxygen is returning to the heart, so if there's a higher mixed venous oxygen
saturation than normal, then we can conclude
that there's decreased oxygen extraction from the tissues. So again, we look at
the mixed venous oxygen to try to identify what type of shock the patient may be experiencing. From what we've covered so far, what other tests do you think we could do to understand if the patient
is experiencing shock? Well, remember this lactic acid. In anaerobic metabolism
when there is low oxygen within the cells, energy is
created through this process, and as a by-product
lactic acid was created. Patients who have shock may experience lactic acidosis where they have a largely increased amount of lactic acid. Initially this can be overcome and doesn't cause damage to the body. However, over time
because of this increased lactic acid, I'll say
"LA," the body will have an overall decreased pH, which means more acidic composition and
in the presence of acid, if the body becomes too acidic, different proteins and structures that are normally intact in the cells start to degredate and denature, which leads to a cascade of events
that can eventually mean cellular death. So though initially this
process is reversible, if shock continues long
enough, cells may begin to die, they're starved from oxygen and starved from energy. You can see differentiating
these types of shocks and understanding the basics of shock can help health practitioners prevent the potentially devastating problems that can arise in a patient who has shock.