If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:9:38

Video transcript

hypovolemic shock is a type of shock so low perfusion and low blood pressure that is caused by low volume and this is low volume of the vascular space so to understand hypovolemic shock let's take a look at our cardiovascular system and of course I'm going to start by destroying the heart the heart of course delivers oxygen and vital nutrients to tissues and organs so I'm going to write organs over here and between the heart and organs we have the vascular space so we've got arteries delivering blood to organs and veins returning blood back to the heart from the organs so I've got this oversimplified cardiovascular system right here but this will do the trick to understand hypovolemic shock so hypovolemic shock you've got low amount of blood in the vascular space that is able to return to the heart and the problem the heart runs into is it it tries to pump blood to the organs but the organs are not getting enough oxygen not getting enough blood because the system doesn't have a lot of blood in it so this low return of blood to the heart is known as decreased preload preload is you can essentially think of as loading the heart up with blood it's essentially the filling of the heart another term that's really often interchangeable is left ventricular end-diastolic volume it's essentially saying when you're filling up the heart before it contracts so that's preload you're probably also familiar with the term after load after load is after the heart has already contracted and squeezed out the blood it's how much blood is left in the heart so then it actually stands to reason that preload - after load would equal the stroke volume so think about it how much blood is in the heart just before it contracts and how much blood leaves the heart just after it contracts that's exactly what the stroke volume is that's how much volume the heart has pushed out of it so if you lower preload lower return to the heart you're going to lower stroke volume and that's that's that let's just say afterload doesn't change too much so you lower stroke volume then that means you're going to lower cardiac output as well because cardiac output is stroke volume times heart rate how much blood is squeezed out for B and how many beats there are per minute that gives you the total amount of liters squeezed out of the heart per minute cardiac output so this decrease in cardiac output is what is causing the low tissue oxygenation it's not the hearts problem the heart is trying to beat fiercely that it actually increases heart rate in response to this decreased stroke volume and that's actually remember that's actually one of the cardinal symptoms of shock an increased heart rate tachycardia and of course the blood pressure goes down as well as you can recall the mean arterial pressure the blood pressure is equal to cardiac output times resistance of the vessels systemic vascular resistance so this is kind of just a quick recap of shock in general oh and hey look if we lower cardiac output which we've caused from this hypovolemic shock we still want to try to maintain blood pressure right so what do you think is going to happen the body is going to try to respond by increasing resistance of the blood vessels so that's exactly what happens let me illustrate that right here so there was low blood volume before and the patient has hypovolemic shock so the resistance of the blood vessels will need to increase in response so the body does that by constricting blood vessels vasoconstriction remember when the diameter of a blood vessel decreases we have increased resistance and this increased resistance allows blood to be squeezed forward to return to the heart this will mostly happen in the venous system to return blood to the heart with the hope of increasing preload and also maintaining blood pressure with vascular resistance and remember this vasoconstriction is caused by the nervous system creating a sympathetic response and the sympathetic response is really driven by this low blood pressure if you recall there are things called baroreceptors at key locations in the vasculature that assess the blood pressure when when the blood pressure is low the sympathetic nervous system kicks up and not only will the blood vessels clamp down to increase blood flow to the heart but she'll also be getting sympathetic tone to the heart as well and that's why you see this increased heart rate okay so that gives you a good amount of information about the concept behind hypovolemic shock but what really causes it well what's going to cause low blood volume I've arbitrarily divided it up into really two major concepts blood loss or fluid loss so let's scroll down here so blood loss can be really anything that you can think would cause blood loss a patient vomiting blood urination of blood internal bleeding external bleeding and fluid loss is very similar a patient could be excessively vomiting having severe bouts of diarrhea urinating too much and then some of the less commonly thought of losses of fluid sweating can be a cause if a patient has an issue on the skin so for example if they have a burn fluid can leak out of that burn because the skin normally acts as a protective barrier and when you don't have it fluid can escape the body more easily and then you also have third spacing of fluid so for example ascites ascites is collection of fluid in the abdomen and usually see it with patients who have liver failure proteins are normally created and delivered such as albumin and when the liver no longer can function it no longer creates albumin and when albumin does is maintained blood volume in the intravascular space so if you have low albumin plasma and blood volume can escape and collect as fluid in places such as the abdomen which is ascites so you see the fluid loss is very similar between these two and in fact the symptoms will actually be very similar between these two as well both of them share the Cardinal symptoms of shock such as tachycardia low blood pressure and low flow to organs but also with hypovolemic shock you'll see coole clammy hands and that's from the vasoconstriction that we were showing before blood is actually diverted away from the less essential organs such as the skin and diverted to essential organs such as the brain or the heart or the lungs so because Bloods diverted from the skin it'll feel very cool and next you'll see signs of dryness a patient's mouth they may have a dry tongue or cracked lips from all the dryness and their skin may actually appear very dry too and a final symptom that I want to touch on is the patient may appear very pale this can be especially notice when a patient has a lot of blood loss blood is no longer coloring the skin so they may appear very pale you can look under the eyelids as well which should normally have this very pinkish color but instead it'll be very pale and that's actually known as conjunctival pallor paleness of the conjunctiva okay so what do we do to diagnose and treat this the diagnosis you're going to use your different shock labs of course serum lactate and ABG to assess oxygenation and you might also check a CBC which is a complete blood count and a B G stands for arterial blood gas so you're assessing the oxygenation of a patient and I might as well mention also that serum lactate shows low oxygenation of the tissues as well so for the CBC you might see low hemoglobin or low hematocrit particularly if blood loss is the cause of hypovolemic shock hemoglobin gives you the total amount of hemoglobin hematocrit assesses the percent of total red blood cells in the body and once you suspect hypovolemic shock treatment will be about maintaining blood pressure and blood volume and also blood content so you might be giving IV fluids to replete the blood volume and you might give pressors which helps blood vessels clamp down as we are showing before or you might need to replete the patient's blood content so for example you might want to give them a blood transfusion or they might need platelets or coagulation factors if the patient is bleeding a lot and coagulation factors can be given through fresh frozen plasma fresh frozen plasma is ripe with lots of coagulation factors or you might need to give albumin as we were saying before if the patient's protein blood protein is low albumin is a way to keep blood volume in the vasculature and out of third spaces so you can see treatment focuses on keeping the blood volume up and of course you want to also treat the major problem so for example if a patient is bleeding they may need surgery to repair damaged blood vessels and stop the bleeding