DIP Episode 233 - Shock

Okay, welcome. My name is Divine, I'm a resident. This is episode 233 of the Divine Intervention Podcast. And in this podcast I'm going to be talking about a topic that I'm going to call shock. I'm going to try to make this a short and sweet podcast. But I don't know, people just keep getting shock, shock, shock questions wrong. So let's just kind of fix that right away. So there are many kinds of shock, right? There are many kinds of shock. And you know, shock is bad, right? Like I mean, there's like hyperbolemic shock, there is distributive shock and all that badness. And we're going to talk about those. But basically I'm just going to focus on what's likely going to be tested on the USML exams, right? So let's start with like very common kind of shock, septic shock, right? So septic shock is something that will happen to a person that has some kind of infection, right? There's some kind of infection, some kind of inflammatory state. And because they have that infection or that inflammatory state, essentially the thing that happens is that they release all these inflammatory mediators like histamine and heparin and bradyclinins and leukotriids and first agglendants. And those things cause a very powerful visual dilation, right? Because of powerful visual dilation. And when you get that visual dilation, right? Well, it happens to your systemic vascular resistance. It goes down. And if your SVR goes down, well, what's happening to your after-loop?

Your after-loop will go down, right? And if your after-loop goes down, that means it's easier for blood to be ejected from the heart, right? It's easier for blood to be ejected from the heart. And if blood is easier to eject from the heart, the thing that will ultimately happen is that the presence cardiac output will go up, right? So cardiac output goes up in septic shock, right? And if your cardiac output is going up, think about it. Or happen to like the left-here pressures and the right-here pressures. They will both go down because blood is moving forward through the heart, right? Blood is moving forward through the heart, right? So the presence pulmonary capillary wedge pressure, which is a surrogate for left-here pressure, or the central venous pressure, which is a surrogate for right-here pressure, will go down. Again, very important to know that. And then what happens to the presence mixed venous oxygen saturation? Mixed venous oxygen saturation. So the mixed venous oxygen saturation, the MVO to essentially represents for the most part, for the most part, the oxygen saturation of the blood that is in the right-here, basically the blood that has returned from all the veins in the body. That's why it's called the mixed venous O2-sat because all the venous blood has mixed. And then you measure an O2 saturation from that, right? If you see that the mixed venous O2-sat would actually be high in a presence that has septic shock, right? So why is that?

Because this is something that may put on understand. Well, I think that nice we don't understand it, is to look at fixed principle. So fixed principle, you probably remember it from step one, that the cardiac output is equal to the oxygen delivery divided by the difference between the oxygen content of the arteries minus the oxygen content of the veins, right? So the thing is we just proved literally right now that in septic shock the cardiac output goes up, right? The cardiac output goes up. If the cardiac output goes up, that denominator, right? Which is the difference between the arterial oxygen content minus the venous oxygen content, right? That whole quantity should go down, right? And for that quantity to go down, and we know that that quantity is the basically the spread between the arterial oxygen and venous oxygen content for that whole quantity to go down. That means that the the thing that has a minus in front of it has to be going up, right? So that means the CVO2, which is the oxygen content of the veins has to go up, right? It has to go up, right? So that if you are taking, let's say like, oh, like normally let's say like the oxygen content of the arteries is 100 and the oxygen content of veins is like, I don't know, like 75. So the difference is 25, where if that difference is going up to like, I mean, sorry, if that difference is going down, right? Because again, remember I said cardiac output goes up, right? cardiac output goes up in septic shock.

So that difference, right? The spread between arterial oxygen content and venous oxygen is going down. So let's say that difference before was 25. If you want it to become like 10, well, the protein thing that should happen is maybe that the non-soxygen content goes up from 75 to 90, right? That's how you obey that equation, right? So your oxygen content of the veins goes up, right? So your MVO2 goes up in a pressing that has septic shock. Because I'm pretty sure I've seen like one of these, I think, is like a public flashcard deck, you know, that many people used to study for, I don't know, like maybe like step one or step two or something like that. And the erroneously defined that quantity. So that's something you don't want to get into trouble with. The MVO2 goes up in septic shock, right? And the thing is, how do you kind of go about septic shock, right? So I mean, in this day, at age, most hospitals or you know, most like big-time hospitals, they use QSOFA, but on MDM is, and in many hospitals in the country, they still use like these serves whatever criteria, right? So you want to make sure you know your source criteria. So serves, right? Basically, you need their four criteria. If you meet at least two or more of these things, right? The person is set to have septic shock, right? So I mean, sorry, serves positive, right? So there's a temperature criteria, right? So if your temperature is less than 36 or greater than 38, there's a heart rate criteria.

If your heart rate is more than 90, there's a respiratory criteria, right? So if your respiratory rate is more than 20 bits per minute, or your P little ACO2, so the partial pressure of carbon dioxide in your arteries, if it's less than 32, right? And then there's a white blood cell count criteria, right? So if it's more than 12,000 or if it's less than 4,000, basically if you meet two or more out of those criteria, you're serves positive. Well, if you're finding like pulmonary infield trade, or dirty urine, or dirty CSF, or whatever, like if you see a source of infection, and the person has made those search criteria, then that person is set to be septic, right? That person is set to be septic. And then, if for example, you begin to notice that, hmm, this person is hypotensive, or this person is organs are not working, like you can see, like elevated, like increase the lefties, or increase creatinine, or increase proponents, like telling you that this person's organs are not functioning very well, right? Then that person is set to be severe sepsis, okay? Well, if you notice that the person has a lactic acid dosage, let's say the bicarb is low, because they won't tell you all lactic acid is 4, no, they'll give you a low bicarb or low pH. If you see that, that's severe sepsis, right? And then, if you typically for person has sepsis, you know, you give those people antibiotics, you give them fluids. Usually, antibiotics, you want to give something, brospectrum, right?

Like something that covers pseudomonas, and something that covers merse, right? So you want to give them like septazidium and vancomycin, right? Or you want to just straight up give them like a carbapenem, opiprasilin, plaza, taisobacter, right? So you want to give them those drugs, right? Then you want to give them fluids. Typically, if you give people fluids, they respond, they have blood pressure per sub, they are mapp, they are miniaturial pressure, right? I remember that's like two-thirds, that's 12 plus 1-thirds systolic, because the heart spence of its time in dastily, right? That is supposed to go up, that is supposed to go up, okay? That is supposed to go up, right? But if they are not responding to that fluid repression, and you're like, okay, let's go ahead and start pressures, which in this case would be neuropinephrine, right? And that septic shock, septic shock is a person that has sepsis, where you're giving them fluids and they are not responding. So you need to initiate pressures on those people. And remember, the pressure of choice in septic shock is neuropinephrine. So again, as a quick recap, in septic shock, the systemic vascular resistance is low. The cardiac output is high, okay? The mixed vinox auto saturation is high. The CVP, which is the central vinox pressure, achy in reditro pressure, or the PCWP, pulmonary capillary wedge pressure, which is essentially the leftitro pressure is low, okay? CVP and PCWP are both low in septic shock.

So hopefully you understand that again, very high you to know this for example, and give them fluids, give them antibiotics, you do source control, let's say they have an indwelling catheter or whatever you remove it, and then you give them pressures if they're not doing very well with that. And one key principle I think, maybe let me use this to make life easy for you, right? In general, your cardiac output and your systemic vascular resistance go in opposing directions in shock. Your cardiac output and your systemic vascular resistance go in opposing directions in shock. That's just a nice handy dandy road to remember, but there is one exception to that road. In fact, let me go ahead and talk about that exception. That's if a person has neurogenic shock. When a person has neurogenic shock, right? Typically, on mbim exams, you'll arise, when a person has like some kind of high spinal injury from like anesthesia, like they're getting an epidural and they become profoundly hypotensive, or they tell you that the person was having like spinal cord surgery or something, or the person's an IV drug user and they have like a spinal epidural abscess, those things can essentially like impact like your spinal cord at like thoracic levels. If you have that, that can essentially take out your sympathetic nervous system. If you take out your sympathetic nervous system, you will lose vascular tone. So your systemic vascular resistance will go down, right?

And if you also lose sympathetic tone, your cardiac output will go down as well. So if you notice a person is in shock and you're like, hmm, this person's heart rate is like 50. And this person's systemic vascular resistance is decreased. That is neurogenic shock. That is at least for purposes of the mbim is at least as far as I know. The only kind of shock where the cardiac output will be low and the systemic vascular resistance will be low at the same time. Hopefully that is something that makes sense to you. But now let's go into cardiac shock. If a person has cardiac shock, let's say like they're a post-MIP patient or the patient has cardiac tamponat or you know like something bad going on with the heart, like heart failure, right? Those people's cardiac output will be decreased because literally the heart cannot pump fluid forward, right? That's very important to know, right? So the cardiac output will go down and if the cardiac output goes down, those people like again if you're just going with that simple that I told you that oh cardiac output and SBR going opposing directions with the exception of neurogenic shock, if the cardiac output is down, the SBR will be up, right? And again, that should make sense. If your cardiac output is low, your hypotensive, your body is like, out, I need to find a way to prep up my blood pressures. So your systemic accelerators distance will go up, right?

And again, because the cardiac output is low, the heart is not able to pump fluid forward. So fluid, aka blood will back up in the heart. So those people's central venous pressures and central venous pressures and pulmonary capillary wedge pressures will both be high, right? And then the misvenous auto saturation will actually be low because the cardiac output is low, right? So the tissues will get very efficient at extracting oxygen because they're like, I don't know, I don't know when next this blood is going to come around. So let me grab as much oxygen as possible. So the auto-sact of the blood that is getting back to the right at room will be low on NV Me exams. That's something that is super, super important to understand, right? I mean, if you're like divine, this doesn't make sense. Let me give you two examples. If you think about that fixed principle, if the cardiac output is going down, then that means that spread between your atrial oxygen content and your venous oxygen content has to go up. And for that spread to go up, then that means your CVO to the oxygen content of your venous has to go down, right? Another way you can also think about it, right? Just think about this coronavirus business that's going on, right? So for example, today, I went to I went to a Walmart to buy stuff, right? My initial intention was to buy just two quick things that I needed to cook, right?

But when I go to the Walmart, I was like, man, these people have water, they had like tons of water, like almost like no limits on how much you could get. They had water, they had paper towels, they had everything. What did they do? I was like, uh, divine, I don't know if this rodeo will shop anymore. So what I did was I ended up like, oh, I was supposed to buy two things and they don't buy like what, like 10 or 15 different things, right? So that's the same thing. When a person's cardiac output is low, the tissues in the body are like, I don't know when this blood is going to come around anymore. Let me extract as much oxygen as possible, right? So that's why the mixed venous auto saturation goes down, right? In cardiogenic shock. And obviously the way you treat cardiogenic shock is you give those people like a positive I know trop, you can give them like the jox in or you can give them the built-in, remember the built-in means a better one agonest or you can give them merino, right? You can give merino, it's a phosphodistory inhibitor that will increase cardiac contractility. So it's a positive I know trop, but it will actually decrease a systemic vascular resistance because remember if you inhibit phosphodistory is your cyclic ampere will go up. When cyclic ampere is high in cardiac muscle, it causes you to contract better. When cyclic ampere is high in smoke muscle, which is what you find in the blood vessels, it causes those blood, uh, smoke muscle to relax.

So you have a decrease in SVR, right? So I will encourage you to maybe try to work out why the pulse pressure goes up when a patient gets merino, right? I've talked about this, I've not seen many podcasts, your cardiac output is going up, so your SVP goes up, your SVR is going down, so your DVP goes down and your pulse pressure, which is the spread between the systolic and the dastrolybular pressure will get wider, right? So that's something higher to know. So that's the thing for cardiogenic shock. And then for hypervolumic shock, which is the last one I'll talk about, especially in hypervolumic shock, right? Your person is like bleeding out or something weird, right? So their blood volume goes down. Well if your blood volume goes down, well, what happens to your preload? Your preload will go down. If your preload goes down, well, guess what, surprise, surprise, your cardiac output is going to go down. If your cardiac output goes down, well, if you're following that rule, I just gave you, your SVR should go up, right? And one common mistake that is made by people on NBM exams, they're like, okay, so this person's cardiac output is down. So that means the PCWP and the SVP must be high. No, right? That is why you need to understand the mechanism behind the person's decrease in cardiac output. If your cardiac output is decreased because there's an intrinsic problem with the heart, for example, heart failure or cardiac tamponant, right? Or post-MI person, right?

Then yes, fluid will not be pumped forward, right? So the PCWP, which is a surrogate for left-hillsure pressure and the CVP, which is a surrogate for right-hillsure pressure, would both be high. On the flip side, on the flip side, when a person has, when a person has low cardiac output because they just have no fluid in the body, aka in the case of, in the case of hypzovolimic shock, right? Yes, their cardiac output will be low, but their PCWP and their CV Ps will both be low. I'll say that again, their PCWP and their CVP will both be low. They will both be low. Again, this is very, very, very, very important to keep at the back of your mind, for example, right? And obviously, again, if the cardiac output is low, the SVR will be high. And if the cardiac output is low, the mixed virus will also be decreased, okay? The mixed virus will also be decreased. I've already explained this already, like a few minutes ago, literally, right? So that's something I really hope that you, that you keep at the back of your mind, for example. And some people may be saying, divine, what do you mean by Q-sofa criteria? Basically, it's just three things. If a person has altered mental status, has a respiratory that is 22 or greater, right? So if your respiratory is 22, you meet the criteria. Or your system, the pressure is less than or equal to 100, right? If you meet at like more than one of those criteria, the person is septic, the person is septic, right?

It's actually, like, there's many studies, at least from the literature that I've heard and reviewed. That's essentially show that Q-sofa is better than SARS. Because think about if you work out, you're going to be SARS positive. If you work out, your heart rate is going to go up, right? Your body temperature may go up a little, right? So SARS is not great. Let's just put it that way. It's not great, right? So just something to keep in mind. So you can look up Q-sofa on your own. It's not something that you will see on the NVM Es, at least not now, right? So I'm not going to spend time on that. And again, high-bokework will make sure, obviously, you want to go ahead and give those people fluids, right? Normal sailing is just fine. So as I do at the end of every podcast, again, I do offer one on one tutoring for many exams. Step one, two CK, two CSTEP-3. Preclinical medical exams, 30-ish-off exams. I do longitudinal tutoring. So if you're like a first-second or 30-year-old student, I can tutor you for your block exams and then your upcoming USML exam. Basically, as I'm tutoring you for your block exams, I'll be tutoring you for your upcoming USML exam at the same time, right? And then I also offer these booster courses. It's 20 hours for step one, two CK or step three. And basically, in an integrated format, it's either like 21 hours sessions or two 10 hours, 10 to hour sessions.

I review the most notes across all the disciplines tested and other exams in a very short period of time. For some people, I've actually done it in like less than like in a week. So I can do it in a week week. We just need to meet a lot more often than kind of spreading things out. But again, many people have done that with, they've found out to be extremely helpful. And then one other thing I offer is I offer coaching, or you can see consulting for applications, right? So if you're a medicine-applying to residency, so like an ERAS application or a college student applying to med school, so like an Amcass application, I offer like one-on-one advice in for like rec letters, personal statements, editing applications, mocking reviews for many specialties. Again, I've probably worked with most people applying to most specialties. I've worked with people applying to most specialties, right? And again, if you have a tricky application like low scores, so like low scores, or you have you feel that an exam or you don't have research or you've graduated from a medicine-long time ago, or you're a foreign medical graduate, to get rich out to me, I've worked with many people in tricky situations that have matched, right? And many people have worked with, believe it or not, have matched that in first choices. So if that's something you're interested in, feel free to reach out to me and I'll be happy to point you out to, point you in the right direction.

And then if you're a medicine resident or a pediatric student or a college student and you need to learn for like the medicine boards or the pizza boards or the ingredient exam for those specialties or the MCAT or the primate subjects, I go for children for all those things as well. And my life lesson for today is the importance of being excellent, the importance of being excellent, right? The importance of being excellent. I've got to talk about this before, but I think it's just something that I should buckle like double down on a little, right? Excellence means that you do something so well that they don't find anything better, they don't find anything better than what you've just done, right? They literally find nothing better than what you've just done. The thing is, in medicine because we have so much on our plate, it becomes very easy to fall into the pattern of just getting by, right? But I will challenge you and again it's not always easy to do this, right? Even me, I try to hold myself to the standard, but it's not always easy to do this, but try to hold yourself to a standard of excellence, right? Whatever is worth doing, right? Like even the Bible says that if your hand finds something to do, do it diligently with all your heart, right? So like, whenever you're doing something, try to do the best job possible, like try to do your job to where like, you're like, I can't find anything better than this anyway, right? The reason why that is important is one.

If you're doing an excellent job, one, you have a good reputation. Two, if like demand for your, for that service you provide disappears, let's say there's like very little demand, it's you that they will still keep coming after, right? Because they know that, you know, like, like I kind of think of it this way, right? Like in an economic crisis, right? What are the companies that stand strong? The companies that stand strong are companies that have have like a tradition of excellence over many many years, right? Like many clothing companies, like I mean, like clothing companies and all that stuff, they've kind of gone belly up, right? Or some of these called companies they've gone belly up, right? With this economic crisis, right? But the companies that are standing strong are those that have a tradition of excellence, right? So if you have a tradition of excellence, even if it's just like, oh, the economy is bad for everyone, it may not necessarily be bad for you because you have a competitive advantage that many other people do not have, right? And again, if you do an excellent job, right? Like when they are looking for someone to reward, when they are looking for someone to give an award to, when they're giving looking for someone to honor, right? They're gonna give, they're gonna give that award to the person that has this tradition of excellence, the person that they know will do a good job, right?

Again, I know, you may say like, oh, these are such high standards, but again, it's just one of those things if if you're just a little more disciplined and you're proactive in life, you can be an excellent person. So thank you for listening to this podcast again. This is, this is one of those podcasts, you know, you're gonna see the stuff on any of the USML exams you're taking. So pay attention to this, take good notes, go right over and over again, and try to not memorize this. I see people memorizing all these hours. Did you see me give you anything you have to memorize here? No, I just explained everything easily, right? So just understand these things and then you will never have problems with them anymore. So thank you for listening to this podcast. God bless you. I'll see in the next podcast and have a great weekend. Thank you.

Cardiac Output ($\text{CO}$) = Oxygen Delivery ($\text{DO}_2$) / (Arterial $\text{O}_2$ Content - Venous $\text{O}_2$ Content).

SVR is low due to vasodilation; CO is high.

Neurogenic Shock (due to loss of sympathetic tone).

Both CVP and PCWP are high due to blood backup/congestion.

Hypovolemic shock has low $\text{MVO}_2$; Septic shock has high $\text{MVO}_2$.

Norepinephrine.

Increased cardiac output forces the denominator $(\text{CaO}_2 - \text{CvO}_2)$ in the Fick principle to decrease, requiring $\text{CvO}_2$ (and thus $\text{MVO}_2$) to rise.

Temperature ($\text{T} < 36^\circ \text{C}$ or $> 38^\circ \text{C}$), Heart Rate ($\text{HR} > 90$), Respiratory Rate ($\text{RR} > 20$), and $\text{PaCO}_2 < 32$.

Both CVP and PCWP are low because of decreased preload/blood volume.

Loss of sympathetic nervous system input leads to profound vasodilation (low SVR).

Positive inotropes (e.g., dobutamine, milrinone) or phosphodiesterase inhibitors (Milrinone).

Low bicarbonate/low pH coupled with elevated lactate levels.

Increased cardiac output forces the denominator $(\text{CaO}_2 - \text{CvO}_2)$ in the Fick principle to decrease, requiring $\text{CvO}_2$ (and thus $\text{MVO}_2$) to rise.

Temperature ($\text{T} < 36^\circ \text{C}$ or $> 38^\circ \text{C}$), Heart Rate ($\text{HR} > 90$), Respiratory Rate ($\text{RR} > 20$), and $\text{PaCO}_2 < 32$.

Both CVP and PCWP are low because of decreased preload/blood volume.

Loss of sympathetic nervous system input leads to profound vasodilation (low SVR).

Positive inotropes (e.g., dobutamine, milrinone) or phosphodiesterase inhibitors (Milrinone).

Low bicarbonate/low pH coupled with elevated lactate levels.