1. Severe Allergic Reaction (Anaphylactic Shock) 过敏性休克 Fang Hong 方 红 1st Affiliated Hospital, Zhejiang University

2. Overview Anaphylaxis is a severe allergic reaction that occurs rapidly and causes a life-threatening response involving the whole body. This reaction can lead to difficulty breathing and shock ultimately leading to death. An anaphylactic reaction occurs when the body's immune system overreacts to an antigen, which it recognizes as an "invader" or foreign substance. The reaction usually occurs within seconds to minutes of exposure.

3. Causes Triggers of allergic reactions may include: Drugs, prescription and over-the-counter medication and blood or blood products; Venom of stinging insects; Foods, especially high-protein foods, most commonly, fish, nuts, fruit, wheat, milk, eggs, soy products; Food additives, such as sulfites; Other substances,such as latex (natural rubber); Dyes and contrast materials, used during radiologic procedures or tests; Often, however, the trigger is unknown.

4. Pathogenesis The body's white blood cells produce antibodies as a reaction to that antigen. The antibodies circulate in the bloodstream and attach themselves to mast cells in the body. In an allergic reaction, the antibody is called immunoglobulin E, or IgE. When the antibodies come in contact with the antigen, they signal other cells to produce mediators. Histamine is an one of the mediators. The effects of these mediators on organs and tissues of the body cause the symptoms of the reaction.

5. Symptoms The symptoms of anaphylaxis can vary. In some people, the reaction begins very slowly, but in most the symptoms appear rapidly and abruptly. The most severe and life-threatening symptoms are difficulty breathing and loss of consciousness. Difficulty breathing is due to swelling and/or spasm in the airways. In very rare cases, breathing can stop altogether. Loss of consciousness is due to dangerously low blood pressure, which is called "shock." In the most serious cases, the heart can stop pumping altogether. These events can lead to death from anaphylaxis.

6. Symptoms Generally, a reaction must involve at least two different body systems, such as skin and heart. Skin: Most anaphylactic reactions involve the skin. Wheals (raised bumps): Hives can cause severe itching; Generalized erythema (redness); Swelling in the face, eyelids, lips, tongue, throat, hands, and feet.

7. Symptoms Breathing: Difficulty breathing, wheezing, chest tightness, coughing, hoarseness, nasal congestion, sneezing; Cardiovascular: Blood pressure may drop to dangerously low levels, rapid or irregular heart beat; dizziness, faintness; loss of consciousness, collapse; General: Tingling or sensation of warmth, difficulty swallowing; Nausea, vomiting; Diarrhea, abdominal cramping, bloating; Anxiety, fear, feeling that you are going to die.

8. Medical Care Anaphylaxis is a medical emergency and requires immediate treatment in an emergency department of a hospital. If swelling develops rapidly, particularly involving the mouth or throat, and the patient has trouble in breathing or feels dizzy, light-headed, or faint, go immediately to the nearest emergency department or call an ambulance.

9. Treatment The first priority in the emergency department is to protect the airway (breathing) and maintain adequate blood pressure. The emergency team will make sure that your airway is open and that you are getting adequate oxygen. Oxygen may be given through tubes into the nose or by face mask. In severe respiratory distress, mechanical ventilation may be required.

10. Treatment If blood pressure is dangerously low, medication to increase blood pressure will be given. An intravenous (IV) catheter may be inserted in order to give saline solution to help boost blood pressure. The IV line may also be used to give medication.

11. Treatment Medications include: Epinephrine (0.5ml) should be given by injection into the muscle, through an IV line, or by injection under the skin; H1-receptor blockers/antihistamines: May be given by IV, by injection in the muscle, or by mouth; Inhaled beta-agonists: Used to treat bronchospasm (spasms in the lung) and dilate the airways; Corticosteroids: Help to decrease the severity and recurrence of symptoms; may be given orally, injected in muscle, or by IV line; If low blood pressure does not improve, additional medications, such as dopamine, may be given.

12. Keywords Severe allergic reaction (anaphylactic shock); Allergy; Antibodies, antibody, antigen; Immunoglobulin E, IgE; Epinephrine.

13. Question Please describe your experience with anaphylaxis.