 Hello, and welcome to EM Ottawa video series. The next patient you're seeing has just eaten some peanuts and immediately had an itchy rash on her body. You've been asked to see her. She says that she has a nut allergy and her rash is really, really itchy. How would you manage her? In this video, we'll discuss anaphylaxis in the emergency department. Specifically, we'll discuss its pathophysiology, presentation, and management. Allergic reaction occurs when the body reacts to a previously sensitized allergen. It can occur in different body systems. It can range from mild to severe. The worst form of allergic reaction is anaphylaxis. In anaphylaxis, multiple systems are involved. Anaphylaxis is a medical emergency. Let's step back and take a look at its pathophysiology. What causes an allergic reaction? In a very simplified way, the previously sensitized allergen causes production of IgE antibodies. These IgE antibodies go on to bind mass cells and basophils, causing them to degranulate, leaking chemicals from inside their cells. These chemicals include histamine, leukotriens, and prostaglandins, among others. All the symptoms of allergic reaction and anaphylaxis are caused by these chemical mediators. The treatment of allergic reaction and anaphylaxis is directed to, one, supportive care, and two, inhibiting these chemical mediators. Let's see how these mediators can affect different parts of the body. In anaphylaxis, multiple body systems are involved. They can include the lungs, the circulatory system, the skin, and the gut. In the lungs, these mediators cause bronchoconstriction and mucous production. In the circulatory system, it causes vasodilation. In the gut, it can cause diarrhea and cramping. In the skin, they cause swelling. It can be superficial, such as hives, or it can be deep, such as angioedema. Based on the above, how should we approach a patient with anaphylaxis? Well, like most, potentially, sick patients in an emergency apartment, we start with ABC. In the next few slides, we'll first discuss the assessment and then the treatment. Practically, both prongs will be happening at the same time. First, airway. In a patient with anaphylaxis, there can be lots of airway swelling, both what we can see and what we cannot. Starting with what we can see, we assess the oropharynx and the mouth for swelling of the tongue, lips, and mucous membrane. Other parts of the upper airway can also swell, but we cannot see. We assess that by first asking about difficulty swallowing or tightness in the throat. We also listened for strider that signals upper airway obstruction. It can sound something like this. Mostly, it will be during inspiration. However, sometimes you can hear it during expiration as well. If the airway is obstructed, the main treatment is epinephrine. It is usually given intramuscularly. The dose is 0.3 to 0.5 cc of a 1 in 1000 epinephrine solution. We then monitor the airway closely. The same dose of epinephrine can be given repeatedly after 5 to 10 minutes if the symptoms do not subside. If the swelling does not decrease, or if it gets worse, we might need to establish a definitive airway. We typically do this by intubation. It will potentially be a very difficult airway because of the edema. In patients with airway obstruction, early epinephrine is key. Next, breathing. Remember how the mediators cause mucus production and bronchoconstriction? That usually leads to wheezes. Just like in an asthma attack. It may sound something like this. You might also see signs of respiratory distress, such as in-drawing, tracheotugging, abdominal breathing, or tripotting postures. How do we treat this? Just like in an asthma attack. We give subcutimal for bronchodilation. If you have used epinephrine, it will also bronchodilate the patient as well. Patients also receive oxygen if they are hypoxic. Next, circulation assessment and treatment. Since the mediators cause vasodilation, they can cause hypotension and syncope. They can also cause decreased contractility, leading to more hypotension and potentially arrhythmia. We will want to put the patient on a cardiac monitor. We should also ask for an EKG as well. How do we treat this? We give intravenous fluids. Often, we start with 1 to 2 liters of intravenous fluids. If after 1 to 2 liters of fluids the patient is still hypotensive, we will often start a vasopressor. It could be something like dopamine or epinephrine. If we are using epinephrine, we often use a 1 in 10,000 concentration as an infusion. The dose is 0.5 to 1 cc over about 10 to 15 minutes. That translates to about 50 to 100 micrograms of epinephrine. Be careful what kind of epinephrine you order. There are two concentrations of epinephrine available. Do not give the more concentrated the 1 in 1001 intravenously. Once ABC is stabilized, we can start targeting those mediators. The main treatment targets histamines with anti-histamine medications. There are two kinds of anti-histamines, H1 blocker and H2 blockers. The H1 blocker we use is diphenhydramine. It is given as 50 milligrams every 4 hours. Can be given IV, PO or IM. The H2 blocker we use is renitidine. It is given as 150 milligrams PO or 50 milligrams IV. These medications will take longer to work than epinephrine. Therefore, even though in a patient with mild symptoms, these H1 and H2 blocker might suffice. In a patient with anaphylaxis, so reactions that involve different systems, give epinephrine early before giving these anti-histamines. In some patients, there is a phenomenon known as a second phase reaction. That is, after the first reaction, the patients can have a recurrence of their symptoms, even though they did not get exposed to the same allergen again. This can happen between 6 to 72 hours after the first reaction. It can be the same reaction, worse symptoms or less. The thought is that steroids might decrease the occurrence of the second phase reaction and make the symptoms less if it does happen. However, the evidence for this is not conclusive and therefore it is up to your clinicians the discretion to prescribe them. If they are prescribed, they are often perenosome 50 milligrams oral daily for a few days. Once the patient feels better, they are observed to ensure the symptoms are indeed subsiding. When they do go home, they are often described a few more days of the anti-histamines and steroids if they are used. Patients should also be given an EpiPen and learn how to use it in case they have another reaction in the future and they cannot reach the hospital in time. Of course, the patients should stay away from the allergen if they know what it is. If it is unknown, we should refer the patient for outpatient allergy testing. To summarize, we discussed the pathophysiology of anaphylaxis, the ABC approach and management, including epinephrine and intubation for airway, bronchodilators for breathing, fluids and epinephrine IV for circulation and hypotension and supplemented with anti-histamines for patients who are having an anaphylaxis reaction. We hope you enjoy it and thank you for watching.