So, here I have outlinedjust a general concept of the cardiovascular system. We have the heart over here,the arteries deliver blood to the organs, and the veins deliverblood back from the organs to the heart. So, the reason I’m goingto draw this is because the cardiovascular system iscritically affected in neurogenic shock. Now, what is neurogenic shock? Neurogenic shock occurswhen the nervous system is no longer functioning properly. And this can happenfrom a number of things. Sometimes, and actually mostfrequently, it’s from trauma, so if the patient has somethingoccur to their spinal cord where it’s severed or an epiduralgoes wrong and some nerves are damaged, that canlead to neurogenic shock, if it’s severe enough. Now, what neurogenic shockessentially is is loss of vascular tone and poolingof peripheral blood. So, the nervous system providestone to the blood vessels and also to the heart. And this tone is knownas “sympathetic tone”. It’s kind of like muscles. If you think about somebodywho’s flexing versus not flexing, of coursethere’s a certain tightness that the muscles undergo when you flex. Now, that’s really happeningto the blood vessels at all times, and it’sdone to really maintain blood pressure. Blood vessels are somewhattightened and squeezed down a little bit to allowblood to flow through. The idea is, as blood flowsthrough the vascular system, it’s going to be maintainedin a forward direction by the blood vessels because if ithits up against the wall, the blood vessel bounces it backand pushes the blood forward. If it didn’t do this, ifthere was no vascular tone, blood would run up againstthe wall and lose a lot of its energy, it would be really dampened. So, it’s kind of like a trampoline. When you’re bouncing on atrampoline, if the trampoline is taut enough, you’ll be ableto bounce up and down really easily, right? However, if you think aboutloosening the trampoline, if you loosen the materialon the trampoline, you won’t be able to bounceas high, and so that’s the same thing that happens here. When you loosen the blood vessel,it won’t be able to
bounce blood forward as well. So, like I said, the nervoussystem provides this tone, this vascular tone, to boththe arteries and the veins. So, what happens if we shutdown this nervous system? Well, the blood vesselswill lose their tightness, both the arteries and theveins, so I’m going to go ahead and erase this to show thatthe blood vessels kind of become floppy. And I’m going to reallyexaggerate this by making them really wide, so both thearteries and the veins become very floppy. So you can see, if thishappens in the arteries, blood is not really going tomake it to the organs as well. It’s supposed to
bounce offand bounce forward, but that’s not really happening anymore,so it just kind of slowly makes it to the organs, so you have shock, you have decreased oxygendelivery, decreased tissue perfusion to the organs. And then, blood of course tryingto flow back to the heart, won’t be able to, it’ll just kind of pool. It’ll just stay in the venoussystem and only a minimum amount will return to the heart. So this will actually affectthe cardiac output of the heart. Remember blood pressure andtissue perfusion are related to cardiac output and vascular resistance, systemic vascular resistance. So up here in the arteries,we’ve already shown that this system vascular resistance is decreased, so that’s going to lead toa decrease in blood pressure and tissue perfusion. So, let me actually goahead and write that out. Blood pressure and O2 delivery. Tissue perfusion is oxygen delivery. So both of these will go downbecause resistance in the arteries are going down. And now also, t
he veinsaren’t able to deliver blood back to the heart. And if you can recall, cardiacoutput is stroke volume times heart rate. So, if we decrease the amountof blood going back to the heart, that means there’sgoing to be less blood that the heart can squeezeforward, so that means less stroke volume, right? Decreased delivery of blood tothe heart leads to decreased stroke volume, which meansdecreased cardiac output. And that further worsens bloodpressure and further worsens oxygen delivery. You’re shutting down thecardiovascular system by not being able to maintain vascular tone. Something else that yousee in neurogenic shock is, the nervous system, thesympathetic nervous system, controls the heart rate. Now, if you no longer have theinput of the nervous system, the heart rate is going to drop. And so, we go back to ourequation, heart rate drops, cardiac output drops evenfurther, and blood pressure will drop, and then oxygendelivery will also drop. So this is truly shock. Tissue perfusion is justcompletely demolished and so is blood pressure. So, the entire cardiovascularsystem is just not able to maintain blood flow, andthat leads to a shut down of oxygen delivery. So, let me go ahead and scrolldown so we can think about some of the symptoms. I’m going to keep this somewhatin view so you can still ponder it and think about it. But the symptoms of neurogenicshock will be those of decreased oxygen deliverysuch as altered mental status, decreased urine output. You think about anything thatneeds oxygen, any organ that needs oxygen, and thinkabout what would happen if it wasn’t getting oxygen; itwould start to shut down. So, organ dysfunction can occur… and a major symptomthat you see specific to neurogenic shock is bradycardia. Now, this is something youshould really be thinking about. This is really the onlyshock that has bradycardia. Remember, all of the othershocks are going to try to increase heart rate, speed itup, to try to deliver oxygen and deliver blood to the body. But here,
we have the heartrate dropping because it’s no longer getting input fromthe nervous system, and so, we have a low heart rate, bradycardia. So, this is a key symptomof neurogenic shock. And, another main symptomthat I want to touch on is warm skin. Warm skin occurs becauseof the dilation of all blood vessels. So these blood vesselsin the skin will dilate, they’ll enlarge like wewere showing up here, so blood can flow throughthe skin more easily. And that’s a problem becauseit diverts blood away from vital organs such as the brain,the lungs, and the heart. And so, the treatment ofneurogenic shock will focus on trying to maintain this bloodpressure, so you’ll give medication known as “pressers”. Pressers allow the bloodvessels to clamp back down. If you clamp the vesselsdown, it directly is affecting the issue in neurogenic shock. And, you’ll also give alot of IV fluids to try to maintain the fluid volume. If you increase the amountof fluid in the vasculature, it’s more likely that you’llbe able to push it forward and deliver blood to the system. So, IV fluid and pressers helpmaintain the blood pressure.
And a final medication thatyou’ll see is atropine. Atropine works by blockingthe parasympathetic nervous system. So, it’s like stopping the”rest and relaxation” part of the nervous system, and itincreases the “fight or flight”. So increasing the fightor flight response, will increase the heart rate. So giving atropine willhelp raise up the heart rate to increase cardiac outputand to improve the pumping of blood throughout thecardiovascular system.