welcome back to another incredibly high-yield video brought to you by dirty medicine in today's video I'm going to be teaching you about the different types of shock now I hope that you're calm I hope that you're not having a panic attack the things that you need to focus on when you're learning the different types of shock are two main high-yield points and I'm gonna pay special attention to these two points as I move throughout the video today the first is the pathophysiology so we've got five different types of shock okay and in these five different types of shock you need to understand what is going on with the pathophysiology that takes you from the underlying insult or the underlying problem and ultimately leads to shock okay the second thing that you need to know is what's happening to all of our different cardiogenic parameters and I'll explain what I mean by that in just a second but what's happening to all of our different cardiogenic parameters in each of these different types of shock now when I say cardiogenic parameters I'm talking about things like what's happening to cardiac output what's happening to heart rate what's happening to the systemic vascular resistance what's happening to the oxygen saturation what's happening to the pulmonary capillary wedge pressure so all of these different things that I've just mentioned can be measured and they're different in each of these five different types of shock so on USMLE in on comlex the test writers have an awesome question that they can ask you they can describe a type of shock either by telling you the name of the shock directly or telling you about the insult or the underlying pathophysiology and forcing you to recognize which type of shock it is and then they can ask you a really challenging question such as which of the following sets of up/down arrows might you expect to find and what they'll do is they'll have this tiny little chart with all of those things I just mentioned cardiac output heart rate etc and they'll have up and down arrows and you'll have to pick the right answer so because there's so much information that you need know about the different types of shock the underlying pathophysiology what's happening and how all of those cardiogenic parameters change this is a topic that medical students hate so my goal in this video is to first go through all of the shock types one at a time and before we even get into that I'll start with a little flow chart that will help you conceptualize the different types of shock we'll talk about each type of shock individually paying special attention to the causes and the underlying pathophysiology and as I move through this video we'll create a chart with all of those up down arrows that you need to know so this video is shocked now the first way that you should think about shock is how do you conceptualize this into its different types so the first question that we should ask ourselves is what's the main problem that's going on in order to determine which type of shock we're dealing with and really what I'm talking about are three different things option one the heart doesn't work option two there's a change in fluid status or option three which is sort of a more specific version of option two there's low levels of fluid if the heart doesn't work we're talking about cardiogenic shock if there's a change in fluid status we're talking about distributive shock and don't get overwhelmed by the term distributive think about it if there's a change in fluid status there is a change in the distribution or distributive there's a change in the distribution of fluid in the body and if there's simply low levels of fluid we're talking about hypovolemic shock so should be rather easy to conceptualize this so far if the heart doesn't work it's cardiogenic kind of makes sense because cardio is in the name if there's a change in the distribution of fluid or a change in fluid status its distributive shock and if there's low fluid it's hypovolemic shock and after all hypovolemic means low volume now let's touch on one more question that we need to ask ourselves if you look at distributive shock this is technically an umbrella term that describe three different types of shock so distributive shock itself is really three different types so the next question that you need to ask if you've determined that the problem is a change in the fluid status but we're not talking about hypovolemic shock the next thing is you say well what's the underlying problem and this can be three different underlying problems which will help us better classify which type of distributive shock were actually talking about so this is a specifier because distributive distributive shock is an umbrella term that really describes three different types of subtypes of shock now what's the underlying problem if we've already determined that this is distributive well you can have an abnormal response to an infection you can have a loss of sympathetic tone or you can have an anaphylactic reaction now if it's an abnormal response to the to an infection we're dealing with septic shock if we've lost sympathetic tone and I'll get into how exactly that happens but if we've lost sympathetic tone then we're dealing with neurogenic shock and if it is an anaphylactic reaction then of course as the name implies we're dealing with anaphylactic shock so this is how I conceptualize the different types of shock and as you can see by reading this flowchart I try to keep it rather stupid and simple right heart doesn't lurk change in fluids low fluids abnormal infection loss of sympathetics or anaphylaxis so these are our five different types of shock we've got cardiogenic septic neurogenic anaphylactic and hypovolemic again all of distributive shock really refers to three different subtypes and that's septic neurogenic and anaphylactic so now that I've shown you how to conceptualize this in your brain I think it would be a good idea if I went through each of these types of shock the five different types one at a time talked about the underlying causes and the underlying pathophysiology and then we'll wrap up each type of shock with that that nice chart with the up/down arrows and I'll even throw in some mnemonics at the end so let's start with cardiogenic shock and again this is because the heart won't work hence the name cardio so you've got some type of underlying event that damages the heart and when the heart gets damaged this causes a decrease in cardiac output a decrease in blood pressure and of course as a result a decrease in tissue perfusion now this is going to cause three things to happen the first is that you're going to get an increased release of catecholamines and catecholamines of course cause vasoconstriction the next thing that you're going to get is activation of the RAS system now this will also cause vasoconstriction and it will also cause the retention of sodium and free fluid to attempt to correct the decrease in cardiac output and the last thing that you'll get is the shunting of blood to the brain and the vital organs because after all if the heart is having some type of issue and can only supply a little amount of blood then the body preferentially wants that blood to reach the brain and the vital organs and it's willing to sacrifice what's considered non vital organs so these changes these compensatory mechanisms lead to one thing and that's an increase in the myocardial work and oxygen demand because think about it with more vasoconstriction and more retention of sodium and free fluid and shunting of blood to other areas that otherwise would not normally have blood Shunta to them there the demand on the heart is going to increase but as you can quickly see that is problematic because the underlying event is that the heart has a problem and can't pump so when you get this compensatory mechanism that demands more work on an already dysfunctional heart this makes cardiogenic shock worse and ultimately leads to death so as I've summarized on this slide the pathophysiology is a decrease in cardiac output that just gets worse and worse over time some common causes of cardiogenic shock and of course this is not an all-inclusive list it's just some common causes are heart attacks cardiomyopathy myocarditis drug-induced cardiogenic shock so stimulants like cocaine or methamphetamine arrhythmia septal defects or ruptured valves anything the day images the heart either directly or indirectly can cause cardiogenic shock so very very high yield to understand the pathophysiology you see on this slide and very very important to understand that there are several different causes that can all damage the heart and lead to the same end result so let's talk about those up/down arrows that you need to know for test day so our first type of shock is cardiogenic shock and as you see on this slide these are the changes for cardiac output heart rate central venous pressure pulmonary capillary wedge pressure systemic vascular resistance and oxygen saturation so it's cardiogenic so cardiac output is down but the heart rate is increasing an attempt to compensate for the decreased cardiac output central venous pressure will either be not changed or increased pulmonary capillary wedge pressure will be increased because all of that fluid that can't be pumped is just sitting there in the pulmonary capillaries the systemic vascular resistance is increasing as part of the compensation and of course our oxygen saturation is down so that's cardiogenic shock take a little bit of time and rewind the video if you want to hear me explain these up/down arrows once again but if we go back to our flow chart we've already covered one of five of the types of shock that you need to know so cardiogenic shock heart doesn't work done you guys are cruising let's move on to hypovolemic shock and then we'll wrap up at the end with distributive since it actually has three different subtypes so hypovolemic shock what's going on well there's some underlying event that causes a loss of fluid okay so fluid is leaking out of the pipes and that's going to decrease the intravascular volume in the body now when this happens you should think of two different causes a decrease in intravascular volume has two different causes and they're either considered hemorrhagic or non hemorrhagic and what what you should think of if this is too complex for you although I hope it's not is that is the problem due to blood or is the problem due to water so when we lose intravascular volume we can either lose blood or we can lose water so hemorrhagic causes all lose blood so you want to think of things like trauma right somebody gets hit with a baseball bat and you know they get hit in the stomach and all of a sudden their spleen just hemorrhages into their abdomen or maybe someone gets stabbed with a knife right in the heart and all of a sudden they're just squirting blood out of their chest okay so those are hemorrhagic causes of intravascular volume loss the other thing that can happen is GI bleeds so things that anything that will cause a GI bleed whether it's an ulcer or some type of esophageal varices anything along those lines that causes a massive blood loss decreases the intravascular volume and the other big one that you want to keep in mind is postpartum hemorrhage now those are all blood problems right hemorrhagic blood loss but on the other side of the equation you can have a decreased intravascular volume due to water problems so just like you can lose blood on the left you can lose water on the right so how do we lose water well diarrhea vomiting burns salt wasting all of these different types of pathologies cause a decrease intravascular volume due to water problems water loss so in either event the intravascular volume is down and that is how you get hypovolemic shock so now let's talk about some up/down arrows here's where we are with hypovolemic shock so cardiac output is going to be down because there's simply not enough volume and therefore not enough cardiac output to circulate the decreased volume but the heart rate is going to be up to try to compensate central venous pressure will either be unchanged or down because volume is down pulmonary capillary wedge pressure will also be down because there's less fluid sitting in the pulmonary capillaries the SVR systemic vascular resistance will be up because the body's trying to compensate for that hypovolemic shock and oxygen saturation will of course beat down on two major types of shock we had cardiogenic where the heart doesn't work and then hypovolemic where there's low fluid either due to blood loss or water loss now let's talk about the different types of distributive shock so remember that when we talked about distributive shock we had to ask a second question and that second question was what's the underlying problem this can either be an abnormal response to an infection the loss of sympathetic tone or anaphylaxis when we talk about the abnormal response to an infection we're talking about septic shock and in septic shock you have the introduction of a foreign pathogen that causes the release of acute phase reactants and causes massive vasodilation in an inflammatory reaction in loss of sympathetic tone or neurogenic shock there's some injury to either the brain or the spinal cord which decreases the body's ability to use its sympathetic tone aka the body cannot vasoconstrict and if the body cannot vasoconstrict it's going to vasodilate okay and when anything Vaser dilates whether it's septic due to pathogens or neurogenic due to a spinal cord injury and subsequent loss of sympathetic tone all changes in vasodilation will cause a change in the distribution of fluid and that's why this is a type of distributive shock now in anaphylaxis you're obviously having an anaphylactic reaction and this is an IgE mediated type one hypersensitivity reaction that causes changes in histamine and mast cells which also leads to a massive vasodilation but this is mediated because of a type 1 hypersensitivity reaction again in all three of these types of distributive shock the underlying problem is technically functionally the same you're having either a vasodilation or an inability to vasoconstrict causing an indirect vasodilation and in all of those scenarios you're changing the distribution of fluid in the body hence the name distributive shock so now let's go back to these really high yield up/down arrows what you'll notice for the different types of distributive shock is that in septic shock the cardiac output is actually going to be up because remember this is a response to an inflammatory reaction and therefore the body is trying to compensate for that by dispersing more blood throughout the body to fight and eradicate said infection also heart rate will be up for the same reason now central venous pressure is going to be unchanged or down because as the body continued leave azo dilates then that central venous pressure will drop and likewise the pulmonary capillary wedge pressure will drop because less blood is sitting in the pulmonary capillaries since the body is undergoing massive vasodilation systemic vascular resistance is obviously down and of note systemic vascular resistance will be down in all three types of distributive shock because the common commonality between them is that all three of these distributive types of shock feature vasodilation or indirectly vasodilation by inability to vasoconstrict oxygen saturation is actually up in septic shock and we'll come back to this exception in just a moment now in neurogenic shock the cardiac output is down and the heart rate is down in this case it's the inability to use sympathetic tone and because sympathetic tone is a major driver and mediator of cardiac output and heart rate both of those factors are down central venous pressure is unchanged or down because you simply don't have the sympathetic drive to maintain your cardiac output so there's not enough pressure in the system because there's not enough pressure in the system there's less circulating free blood which means that the pulmonary capillary wedge pressure is also down because this is an inability to vasoconstrict and therefore you're indirectly vasodilating your systemic vascular resistance is down and like all of the types of shock with the exception of septic which again we'll come back to in just a second oxygen saturation is down let's wrap up with the up/down arrows for anaphylactic shock now this is again a type 1 hypersensitivity reaction mediated by IgE with also some help by the mast cells and histamine and all that stuff that you learned in immunology in this case cardiac output is down it simply cannot keep up with the demand due to the massive vasodilation heart rate however will compensate there's no problem with sympathetic tone in anaphylactic shock in neurogenic shock you do have a problem with sympathetics and therefore heart rate cannot compensate but an anaphylactic shock heart rate is certainly compensating central venous pressure and pulmonary capillary wedge pressure and systemic vascular resistance are all down because the anaphylactic shock is still a vase dilatory process and therefore when that vasodilation occurs you have less blood in your central venous system less blood in your pulmonary capillaries and obviously SVR is down because you're simply bays are dilating oxygen saturation is also down now I told you that an exception to the rule with oxygen saturation was in septic shock and this is beyond the purpose of this discussion you don't really need to know this for USMLE and comlex but just briefly oxygen saturation will be up but oxygen delivery will be down so even though there's more oxygen saturation and this is a byproduct of any inflammatory process the actual delivery of that oxygen to target tissues is down but when you're looking at a chart you'll see that arrow going up because oxygen saturation itself is increased the way that you should memorize this is to remember that septic equals Sat just match up those s's septic shock is the one where Sat is up so septic is set just remember that septic goes with Sat and you'll remember that it's the exception to this rule the other exception that you should take close pay close attention to is neurogenic shock with heart rate being down in all of these types of shock heart rate is up because it's trying to compensate but in neurogenic shock you don't have the sympathetic tone required to drive that heart rate to compensate for the decreased cardiac output and because of that you can remember this as saying neurogenic has no heart rate compensation so just like we matched those s's for septic and sat for neurogenic we match those ends for neurogenic and know now let me pause for a second because this is the end of the video this is incredibly high yield and I hope that you understand this discussion and can reason through these up/down arrows if you're taking your test and have trouble recalling these I think that the best way to go about this is not to memorize it but rather to reason through it ask yourself what's gonna happen if the heart you know tears a hole in it how a cardiac output change how will heart rate change etc etc and if you reasoned through it it should make sense good luck and keep getting those points