Neurogenic shock

So, here I have outlined just a general concept of the cardiovascular system. We have the heart over here, the arteries deliver blood to the organs, and the veins deliver blood back from the organs to the heart. So, the reason I'm going to draw this is because the cardiovascular system is critically affected in neurogenic shock. Now, what is neurogenic shock? Neurogenic shock occurs when the nervous system is no longer functioning properly. And this can happen from a number of things. Sometimes, and actually most frequently, it's from trauma, so if the patient has something occur to their spinal cord where it's severed or an epidural goes wrong and some nerves are damaged, that can lead to neurogenic shock, if it's severe enough. Now, what neurogenic shock essentially is is loss of vascular tone and pooling of peripheral blood. So, the nervous system provides tone to the blood vessels and also to the heart. And this tone is known as "sympathetic tone". It's kind of like muscles. If you think about somebody who's flexing versus not flexing, of course there's a certain tightness that the muscles undergo when you flex. Now, that's really happening to the blood vessels at all times, and it's done to really maintain blood pressure. Blood vessels are somewhat tightened and squeezed down a little bit to allow blood to flow through. The idea is, as blood flows through the vascular system, it's going to be maintained in a forward direction by the blood vessels because if it hits up against the wall, the blood vessel bounces it back and pushes the blood forward. If it didn't do this, if there was no vascular tone, blood would run up against the 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 a trampoline, if the trampoline is taut enough, you'll be able to bounce up and down really easily, right? However, if you think about loosening the trampoline, if you loosen the material on the trampoline, you won't be able to bounce as 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 nervous system provides this tone, this vascular tone, to both the arteries and the veins. So, what happens if we shut down this nervous system? Well, the blood vessels will lose their tightness, both the arteries and the veins, so I'm going to go ahead and erase this to show that the blood vessels kind of become floppy. And I'm going to really exaggerate this by making them really wide, so both the arteries and the veins become very floppy. So you can see, if this happens in the arteries, blood is not really going to make it to the organs as well. It's supposed to bounce off and 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 oxygen delivery, decreased tissue perfusion to the organs. And then, blood of course trying to flow back to the heart, won't be able to, it'll just kind of pool. It'll just stay in the venous system and only a minimum amount will return to the heart. So this will actually affect the cardiac output of the heart. Remember blood pressure and tissue 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 to a decrease in blood pressure and tissue perfusion. So, let me actually go ahead and write that out. Blood pressure and O2 delivery. Tissue perfusion is oxygen delivery. So both of these will go down because resistance in the arteries are going down. And now also, the veins aren't able to deliver blood back to the heart. And if you can recall, cardiac output is stroke volume times heart rate. So, if we decrease the amount of blood going back to the heart, that means there's going to be less blood that the heart can squeeze forward, so that means less stroke volume, right? Decreased delivery of blood to the heart leads to decreased stroke volume, which means decreased cardiac output. And that further worsens blood pressure and further worsens oxygen delivery. You're shutting down the cardiovascular system by not being able to maintain vascular tone. Something else that you see in neurogenic shock is, the nervous system, the sympathetic nervous system, controls the heart rate. Now, if you no longer have the input of the nervous system, the heart rate is going to drop. And so, we go back to our equation, heart rate drops, cardiac output drops even further, and blood pressure will drop, and then oxygen delivery will also drop. So this is truly shock. Tissue perfusion is just completely demolished and so is blood pressure. So, the entire cardiovascular system is just not able to maintain blood flow, and that leads to a shut down of oxygen delivery. So, let me go ahead and scroll down so we can think about some of the symptoms. I'm going to keep this somewhat in view so you can still ponder it and think about it. But the symptoms of neurogenic shock will be those of decreased oxygen delivery such as altered mental status, decreased urine output. You think about anything that needs oxygen, any organ that needs oxygen, and think about what would happen if it wasn't getting oxygen; it would start to shut down. So, organ dysfunction can occur... and a major symptom that you see specific to neurogenic shock is bradycardia. Now, this is something you should really be thinking about. This is really the only shock that has bradycardia. Remember, all of the other shocks are going to try to increase heart rate, speed it up, to try to deliver oxygen and deliver blood to the body. But here, we have the heart rate dropping because it's no longer getting input from the nervous system, and so, we have a low heart rate, bradycardia. So, this is a key symptom of neurogenic shock. And, another main symptom that I want to touch on is warm skin. Warm skin occurs because of the dilation of all blood vessels. So these blood vessels in the skin will dilate, they'll enlarge like we were showing up here, so blood can flow through the skin more easily. And that's a problem because it diverts blood away from vital organs such as the brain, the lungs, and the heart. And so, the treatment of neurogenic shock will focus on trying to maintain this blood pressure, so you'll give medication known as "pressers". Pressers allow the blood vessels to clamp back down. If you clamp the vessels down, it directly is affecting the issue in neurogenic shock. And, you'll also give a lot of IV fluids to try to maintain the fluid volume. If you increase the amount of fluid in the vasculature, it's more likely that you'll be able to push it forward and deliver blood to the system. So, IV fluid and pressers help maintain the blood pressure. And a final medication that you'll see is atropine. Atropine works by blocking the parasympathetic nervous system. So, it's like stopping the "rest and relaxation" part of the nervous system, and it increases the "fight or flight". So increasing the fight or flight response, will increase the heart rate. So giving atropine will help raise up the heart rate to increase cardiac output and to improve the pumping of blood throughout the cardiovascular system.