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Anaphylaxis is a sudden, severe immune response, almost always triggered by an allergen in an atopic individual. The illness progresses rapidly and, in addition to skin symptoms, causes potentially fatal breathing and circulation problems. These symptoms can include airway obstruction due to swelling, bronchoconstriction, hypotension, shock, and tachycardia (fast heartrate). Because onset occurs so quickly, anaphylaxis is a medical emergency.
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Is It Really Anaphylaxis?
Epinephrine should be administered for true anaphylaxis, but not for other sorts of distress such as panic attacks or hives without airway or circulation problems. If a patient is truly experiencing anaphylaxis, the following criteria should be present:
Sudden onset of symptoms that progress rapidly, usually over a period of no more than a few minutes
Life-threatening airway, breathing, or circulation problems (the acronym ABC can be used as a mnemonic)
Skin and/or mucus membrane symptoms, such as rash, hives (urticaria), flushing, swelling
Gastrointestinal symptoms such as cramping and vomiting may or may not be present in anaphylaxis. Exposure to a known allergen in the patient indicates a strong likelihood that a severe reaction really is anaphylaxis.
ABC symptoms alone are not enough to diagnose anaphylaxis. Epinephrine treatment is only appropriate if the other two criteria are present, indicating that anaphylaxis is the true cause of the problem. A confounding factor is that in both anaphylaxis and a panic attack, the patient may experience a sense of great anxiety or impending doom.
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Outside a hospital setting, the first step in treating anaphylaxis is to call for an ambulance so first responders can begin administering care as soon as they arrive. Transporting a patient to the hospital in a civilian vehicle is not recommended because the significant delay in reaching professional treatment can be fatal.
The trigger should be removed from the patient if practical. The patient should be laid flat to improve blood flow to the brain and vital organs and to eliminate the chance of injury in case of fainting. The legs should be elevated to help core blood flow.
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Epinephrine (Adrenaline) and Other Medications
Epinephrine is a hormone normally produced by the adrenal glands. In a healthy person, it is released when the sympathetic nervous system is activated in response to short-term stress. It has a stimulating effect on various body systems, binding to two types of receptors, alpha and beta receptors.
Epinephrine is indicated for anaphylaxis because its various effects all serve to improve the ABC symptoms, albeit temporarily. Its alpha receptor activity reduces swelling and concentrates blood flow to the core body, while its beta receptor activity reduces bronchoconstriction, increases the strength of the heartbeat, and suppresses histamine, an immune system chemical that is prominent in an allergic reaction.
Epinephrine should be administered through an intramuscular injection, not intravenously, except by experienced specialists. Its action is short-term.
The next steps in treatment include providing intravenous fluids and administering medications to reduce the immune system response. Antihistamines such as chlorphenamine target histamine, while steroids such as hydrocortisone target the entire immune system.
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Working Group of the Resuscitation Council (UK), 2008. "Emergency treatment of anaphylactic reactions: Guidelines for healthcare providers" (PDF). London.