Transcript for:
Lecture on Shock

you [Music] all right welcome everybody I want to welcome you to the first lesson in a series of lessons on shock in this lesson we're going to cover the basics of what shock is as well as we're going to do a deep dive into the physiological response that our body goes through when we find ourselves in a state of shock my name is Eddie Watson and I'm going to be presenting this series of lessons and in order to stay up to date on our lessons as we release them make sure and subscribe to our channel below and don't forget to hit that Bell icon in order to be notified as the new lessons become available alright so let's go ahead and dive into the beginning of our lesson to start out we are going to be talking about shock and really what is shock so when we talk about shock it's important to recognize what we're actually talking about is what we call circulatory shock and by this what I mean is that we want to distinguish this from other terms that are commonly used out there typically on TV and in movies and it's it's not a fright or it's not that someone has suffered some sort of post traumatic event those are essentially psychological phenomenon and in the medical context we are talking about circulatory shock and to give you a classical definition of what shock is essentially shock is an acute widespread reduction in affective tissue perfusion and this causes an imbalance of oxygen supply and demand' anaerobic metabolism lactic acidosis cellular and organ dysfunction metabolic abnormalities and if this is prolonged it can cause irreversible organ damage and death so if we talk about shock in its most basic form essentially shock is decreased tissue perfusion and what that really means to us is that our Oh to delivery is going to be less than what our o2 demand is and basically if we were to write that out do two is less than our vo2 so really it's pretty simple shock is essentially a state where your body is not getting enough oxygen to its tissues and really what we're talking about when we're talking about perfusion what we're talking about is how much blood can reach a given amount of tissue over time and as we know that Bloods main responsibility is to carry oxygen and therefore if the amount of blood is decreased then the amount of oxygen delivery is going to be decreased as well and essentially what this tells us is if we end up having a state of decreased perfusion this is going to lead us to a state where we end up in a metabolic acidosis and we're going to talk about this more in depth here in a little bit but essentially when we're in a state of decreased perfusion and decreased oxygen supply that this is going to lead to cell death which will go on to organ failure and ultimately if left to continue that this can lead to death and so the most important takeaway from all of this is that shock is life-threatening and I'm gonna highlight this because it is of utmost importance that you realize this shock is a life-threatening situation and it occurs because the body is not getting enough blood flow due to that lack of blood flow the cells and organs are not getting enough oxygen and nutrients in order to function properly and as a result many organs can be damaged and ultimately the person can end up dying from this and so now that we've covered the the basics of what shock is let's go ahead and move into the physiology of shock and really how our body responds to it okay so I'm gonna bring up a drawing here of some of our anatomy because I think it's important that we cover this stuff first note that this isn't entirely to scale but really just to to give you the understanding of some of the stuff that's going on so let's go ahead and start talking about the the heart here in the middle there's a couple things that I want to point out here the first is going to be our conduction system and importantly just knowing we have our SA node here and our AV node here and we have the bundle of his which branches off into the left and right and goes into our Purkinje fibers and essentially this system controls the electrical conduction through the heart so now moving beyond the heart I want to expand out our vasculature that we have here a little bit and so we know coming out of the left ventricle into the aorta we hit the aortic arch and there's three branches that come off here the first of these is the brachiocephalic which is going to branch off into our right subclavian and a right common carotid which then this is also going to branch off into our internal and external the last of these branches coming off the aorta is our left subclavian and coming off the middle here this is going to be our left common carotid which is gonna again branch into our internal and external and the reason that I drew these out is I want to talk about two different receptor sites that we have and we're going to find these in a couple spots here in our a or tick and arterial vessels and these receptor sites are what we call baroreceptors and chemoreceptors now we're gonna get into talking more about those and what they do here in just a little bit but there are a couple primary locations that you're going to find them the first is we have our baroreceptors here in the aortic arch as well as in our carotid sinus this is going to be both the left and right side and the easy thing to remember is right along with those baroreceptors as well you're also going to have your chemo receptors now moving right up along into the brain there's a couple areas I want to point out the first is going to be this area here and this area here is what we call the medulla oblongata I'm gonna put medulla for short and the next area that I want to talk about is it's actually buried somewhere right up and about here and this is our pituitary gland and while I'm at it let me go back in here and put in some labels that I forgot to do so here's our SA node our AV node and coming off of here and here we have our baroreceptors and our chemoreceptors and so if we work our way all the way down to the bottom we see we have our kidney here and then sitting on top of the kidney we have our adrenal gland and that essentially covers the basics of the anatomy that we need to know right now so now let's talk about what actually happens when we find ourselves in a state of shock I'm gonna hit on a couple things that we had mentioned earlier and explain those a little bit more so as we talked about when you find yourself in a state of hypoperfusion and as we know hypoperfusion means low oxygen delivery and so what's going to happen is our cells which are normally working in anaerobic fashion robic metabolism they are going to transition to what we call anaerobic and so if we remember to aerobic respiration and what happens there essentially your cells are taking oxygen that's delivered they're utilizing them in the electron transport chain and the end result is that we get ATP or the energy for our cells and so it happens is when we're in a state of hyper perfusion and that oxygen is not available the cells have to switch to an anaerobic process and unfortunately this process isn't anywhere as efficient as the aerobic process and so this means that we end up with less ATP and ultimately this leads to cell death another one of the issues with the anaerobic process is that one of the byproducts that comes from that is something that we call lactic acid and as its name suggests it's acidic and due to our state of hypoperfusion we're gonna see a buildup of lactic acid and other waste products including co2 and ultimately we're going to find ourselves in a state of a metabolic acidosis so now let's talk about what's going on with our body and some of these key areas of anatomy that we pointed out here and so as we have the blood that's coming out of the heart here for whatever reason there can be multiple causes which we will get into in future lessons here but you end up with a decreased mean arterial pressure or a decreased map and what happens when you have a decreased map that that is going to lead to a decreased and baroreceptor firing what's happening is our baroreceptors our stretch receptors typically we find ourselves with a normal blood pressure which causes pressure against the baroreceptors which causes them to stretch out and when they stretch out it signals them to fire and so as our blood pressure drops it causes less stretching of these baroreceptors and therefore a decreased amount of firing and so what happens is you have a couple nerves that go from our baroreceptor and chemo receptor sites and go up to the medulla that we talked about so the first of these nerves goes from our bare receptors on the air erratic arch and this is our vagus nerve or cranial nerve 10 and then we also have another nerve that is on our Bayer receptor and chemo receptor sites here in the carotid sinuses and these go up to the medulla as well and this is via the glossopharyngeal nerve or cranial nerve nine so now within the medulla there's a couple areas that we really want to focus on the first of these is what we call the cardio regulatory Center and the other one is what we call the vasomotor Center and so the cardio regulatory center as you can probably figure out is responsible for regulating the heart and there's two primary areas for this the first of these is the cardioinhibitory is the cardio acceleration and so as you can probably figure out the cardioinhibitory Center inhibits our cardiac activity and it has a responsibility and lowering our heart rate and if you think about this in terms of our sympathetic and parasympathetic responses this is going to be our parasympathetic yesterday the cardio accelerator II is activating our cardiac response this is really twofold we're gonna see an increased heart rate as well as an increased stroke volume and we actually have a really good lesson within our hemodynamic series that i'm going to link to up above that really covers cardiac output and these components and how they impact it and so as we mentioned with the cardioinhibitory being a part of the parasympathetic response the cardio accelerator is going to be a part of our sympathetic and so if we go back to our pathway the cardioinhibitory is gonna go actually along the efferent vagus nerve and is going to come down to the regulatory center conduction center of the heart and it's going to inhibit or reduce our heart rate all the while the cardio accelerator is going to come via the sympathetic nerve which actually travels down our spinal cord this is eventually going to come out of one of our thoracic sympathetic nerves it's going to come down and innervate the heart and our conduction system and again this is accelerating or activating which is going to lead to that increased heart rate and stroke volume now like we talked about when we find ourselves in a state with a low map we're gonna have decreased baroreceptor firing those are gonna be transmitted up to the medulla and what happens when it gets in there when it goes to when that signal gets to the cardio regulatory center is we are actually going to inhibit the inhibitory center and so we're gonna essentially be inhibiting the decreasing heart rate and within the cardio acceleration er we're gonna activate that Center and essentially this is going to activate our sympathetic response increasing our heart rate and our stroke volume and ultimately leading to an increased cardiac output therefore increasing our mean arterial pressure and in addition to activating the cardio accelerator we're also going to activate the vasomotor Center and the activation of this vasomotor Center is also going to be one of our sympathetic responses and so again we're going to travel down the sympathetic nerve in the spinal column we're gonna eventually come out at a lower level but another thoracic sympathetic nerve and that's gonna go down and synapse with our adrenal gland and more importantly the adrenal medulla and what this is going to do is this is going to trigger the release of adrenaline and noradrenaline and these two catecholamines play a very important role in vasoconstriction and this is going to take place both in our arteries as well as our veins so again we're going to have the release of these chemicals which as we've said our adrenaline and noradrenaline and these catecholamines are gonna buying inside of the vessels to our alpha receptors and this is going to cause our vasoconstriction which is going to lead to an increase in our systemic vascular resistance and ultimately an increase in our mean arterial pressure one important thing to note with these catecholamines and that vasoconstriction is we're not going to see it within the heart and we're not going to see it in the brain because the body actually wants to increase our blood flow to these areas and as an overview the sympathetic activation that we see as a result of the decreased baroreceptor firing is all part of the early phase of our body's response to shock now as our body continues to persist in this state of shock there are a couple of mid-to-late responses that we're also going to see the first of these is we're going to see an increase in renin production from the adrenal gland and as that renin enters the bloodstream there's a few interesting things that are going to happen so I'm going to bring this over so we're going to see an increase in renin this is really where a cascade of some very interesting combinations take place the first of these is going to be an interaction with a precursor called angiotensinogen so as you know we have our liver that's roughly over here and the liver is responsible for making this angiotensinogen and when these two combine they're gonna form what we call angiotensin 1 and angiotensin 1 is really not all that interesting but an interesting thing of what happens is the angiotensin 1 which is floating around in the blood when it makes its way over to our lung there happens to be a high concentration of an enzyme that we call angiotensin converting enzyme or ACE and when angiotensin 1 and ace interact with each other we end up getting angiotensin 2 there's a couple of very interesting things that angiotensin 2 is going to do for us first it's going to increase our thirst this is potentially to to bring in more fluid volume in order to increase our mean arterial pressure it's also going to increase our vasoconstriction but in addition to that it's going to work its way through the blood and when it gets to our adrenal cortex over here this is going to trigger the release of aldosterone so once again we're gonna have aldosterone being released here it's gonna make its way into our blood and so when the aldosterone makes its way into our kidney which is going to lead to an increase in our sodium reabsorption and as we know water follows sodium so we're gonna see an increase in our water reabsorption and this is ultimately going to lead to an increase in our circulating plasma volume and ultimately an increase in our mean arterial pressure and this increased intravascular volume leads to an increase in the venous return to the heart basically our preload which ultimately will lead to increased cardiac output and thus increased March mean arterial pressure again covered in the cardiac output lesson within the hemodynamic series now finally the last bit that goes on that I'm going to talk about is in our posterior pituitary is it's gonna recognize an increased osmolality due to that increase in our sodium that we have over here and that's going to lead to the release of the antidiuretic hormone and the antidiuretic hormone is another way for our body to be able to increase the reabsorption of sodium and thus water and ultimately leading to that increased mean arterial pressure so we've covered a lot here in terms of our physiological response of our body to shock and what all is happening and the point of this isn't for you to memorize every single step of this but I want you to understand when we start talking about some of the responses that we're expecting to see why exactly we would see them so now that we've got that a lot of the way let's just go ahead and quickly cover some of the signs that we would expect to see on a patient who is in shock so the first of these and probably the most obvious is we're gonna see a decreased blood pressure and again we'll talk about some of the causes and the reasons for this but there can be multiple things that are going on but the end result is a low blood pressure typically you're gonna find yourself in a state where you have an increased heart rate but there is one form of shock that we will talk about later that this doesn't happen in so it's important to know that this is not always gonna be seen but usually will be you're gonna have a weak and thready pulse so you have rapid breathing and increased respiratory rate and it's also going to be shallow you may also notice pallor and your patient you may have either absent or decreased bowel sounds and a couple signs that we would see when we're looking at end organ damage and a couple things reach this point would be confusion and lethargy another sign would be a reduced or absent urine output also you would see cold clammy mottled skin another sign that you would see indicating an organ damage would be St elevation now these are not obviously all of the signs that you would see in shock and organ damage but these are some of the major ones that you really should be on the lookout for and finally I just want to talk about some of the lab values that you can expect to see the first of these that you'll see is an elevated lactate and this is going to be a direct result of that switch from aerobic respiration to anaerobic you're going to see a decreased pH also what we call acidosis and this is specifically going to be a metabolic acidosis you'll see an elevated B UN and creatinine you also see an elevated ALT and ast indicating shock liver you'll see elevated troponin also it decreased pao2 and this is a result of the decreased perfusion leading to less oxygen making its way into the blood and finally one of the things that you'll see is an altered svo2 and depending which shock here in this can either be elevated or decreased and again we'll talk about that in future lessons all right and that concludes this first lesson on shock we've covered a lot in this lesson going over the basics of what shock is as well as a deep dive into the physiology and the body's response to shock as well as covering the signs and labs that you would see with a patient who is currently in shock and with that said I do want to thank you for for watching today I hope this lesson was informative for you if you liked this video and you found it useful make sure and hit the like button it really helps get the word out about our Channel and in the comments below tell us your favorite part of the video feel free to ask us any questions that you might have finally check out the next lesson in this series covering the stages of shock as well as a brief overview of the different causes of shock or you can also check on another one of our great series of lessons on hemodynamics thanks for watching and have a great day