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Anaphylactic shock

Created by Ian Mannarino.

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Video transcript

- [Voiceover] Anaphylactic Shock is probably one of the shocks that most people are familiar with. It's also known as anaphylaxis. Anaphylactic shock is an allergic reaction that's severe enough to cause shock. And of course shock is decreased tissue perfusion, or in other words decreased oxygenation of tissues. There are a number of different things that can cause an allergic reaction. For example, bee stings can cause an allergic reaction, peanut allergies, food allergies, pollen can cause allergic reactions and so can certain medications as well. Now of course, allergies can be either very mild and seasonal such as hay fever and sometimes allergies can be so severe that it can cause shock. But how does it cause shock? Well first of all to answer that, I want to acknowledge that there are two types of anaphylaxis. Those that are immunologic and those that are non-immunologic. And I'll go ahead and start with immunologic anaphylaxis, because that's actually the most common type. In immunologic anaphylaxis, there's some sort of allergic agent, whether it's poison from a bee sting or a food allergy that somehow gets in to the system. And whatever this material is, it's known as an allergen because it generates an allergic response. So when this allergen first gets into the body, it will interact with B cells, and not B cells like the insect, the bee right up here, but B cells as in the letter B. Now these cells are the antibody creating cells of the immune system, they create antibodies. And antibodies are essentially a little Y shaped protein that is used like a signal marker to find something that's foreign, foreign material. So in this case, the antibodies will be reacting to the allergen. Now antibodies that are created in response to an allergen, are known as IgE. IgE stands for immunoglobulin E. Globulin means protein and immuno just means immune. So really it's immune protein and the classification is E. Now the reason I want to emphasis this, is because IgE specifically docks on to other immune cells which are known as Mast Cells, and these mast cells are mediators of the immune system. So what ends up happening is, once IgE is created, it will dock on to these mast cells. So this all occurs when a person is first exposed to an allergen, and this is called sensitization. The immune system is sensitized to this allergen. So the next time that this allergen comes along, it will create a rapid, allergic response. The allergen will dock on to these antibodies and when they do, the mast cells activate. And when mast cells activate, two main things happen. First of all, mast cells release immune molecules known as cytokines. Cytokines are essentially used for cellular communication. So mast cells communicate with other white blood cells and tell them to come over. So what ends up happening is these white blood cells continue to recruit more white blood cells, and it's a cycle that creates more and more white blood cells being recruited and activated in response to these allergens. Now that activation of both the mast cells and the immune cells, causes release of another molecule known as histamine. Now histamine is a potent vasodilator. In other words, it dilates blood vessels. So here, with the dotted line, I'm showing a blood vessel size before and after histamine, the diameter of the blood vessel increases. Now this is happening in the blood stream in the entire body, and it causes a large drop in blood pressure. So patients lose the function of their circulatory system and are no longer able to distribute oxygen and so that's how an allergy causes shock. And also, let me note that histamine causes blood vessels to become leaky, so fluid escapes the vascular space which causes swelling to occur all throughout the body. So a patient has massive swelling along with a massive drop of blood pressure. Now the second type of anaphylaxis is called non-immunologic. Now non-immunologic anaphylactic shock is essentially the same as immunologic shock, it's just the pathology is slightly different. Instead of mast cells being stimulated by IgE, the allergen specifically targets the receptors on the mast cells. And so you get the same process of histamine release as well as cytokine release, which of course causes the super immunological response as more white blood cells are recruited and then also causes this drop of blood pressure. So what are the symptoms that we see in anaphylactic shock? Well the symptoms are going to be characterized by the actions of histamine. So a patient with anaphylactic shock has this major drop in blood pressure due to vessel dilation. So we'll see flushing of the skin, as blood vessels dilate and blood starts to saturate in the skin. And swelling as fluid is getting outside of the blood vessels. And itchiness, which is also caused by histamine release. So these are all symptoms that you would come to expect from an immune response. You may see other various symptoms such as rhinorrhea, which is a runny nose and this is caused by vessel dilation in the nasal vasculature, so you have an overactive release of fluid. But the symptom that I really want to get to, occurs with the lungs. Histamine not only causes vessel dilation, one of it's most serious symptoms is bronchospasms. Spasms of the bronchi, the main air passages to the right and left lungs. So these bronchospasms make it difficult for a patient to breath. What makes it worse also is that swelling can be occuring in the throat as well, which can close off the airway, making it even more difficult to breath. So a patient comes in whose non-responsive, he's not breathing, and you check and find that the patient has a very low blood pressure. So what do you do? Do you order lab tests? No, that's a terrible idea. This patient is having a severe bout of shock. It should already be apparent based off of the clinical symptoms that this patient has. Especially the low blood pressure, severe low blood pressure should indicate that right away, something needs to be done. So you progress right to treatment. And treatment is based off of the ABC's, airway, breathing and circulation. So number one, you want to establish the airway. If a patient is not breathing, you want to give them 100% oxygen so you can fill up their lungs. And ventilating the patient with a bag mask, to push air into the lungs, may be one of the first ways to respond to a patient who has anaphylactic shock. Along with this, the blood pressure needs to be maintained. And there's one medication that's especially effective at maintaining blood pressure in patient's with anaphylactic shock and that's epinephrine. First of all, of course patients have these very dilated blood vessels. Now epinephrine has strong sympathetic activity, so it acts in a way to constrict blood vessels back down to maintain blood pressure. So this directly counteracts what histamine does to blood vessels. Epinephrine also effects the lungs and causes bronchodilation, so it opens up the airways. So this is important to allow airflow back into the lungs. Now to also maintain blood pressure, IV fluids will help fill up the vascular space. So these are the main ways to treat a patient with anaphylaxis. And along with this, you can give antihistamines to really directly counteract the effects of histamine in the body. But of course, let me emphasize that epinephrine and IV fluids are the mainstay of treatment, because they act to immediately reverse the low blood pressure and restore a patient's circulatory system.