Anaphylaxis - Anaphylactic reaction; Anaphylactic shock; Shock - anaphylactic
Anaphylaxis is a sudden, severe, potentially fatal, systemic allergic reaction that can involve various areas of the body (such as the skin, respiratory tract, gastrointestinal tract, and cardiovascular system). Symptoms occur within minutes to two hours after contact with the allergy-causing substance, but in rare instances may occur up to four hours later. Anaphylactic reactions can be mild to life-threatening. Anaphylaxis is a severe and potentially life-threatening allergic reaction to such allergy-causing substances as insect venoms, latex, foods and medications.
Your immune system produces antibodies that defend against foreign substances, including allergens. These antibodies release chemicals that may cause symptoms such as watery eyes and a runny nose. Anaphylaxis occurs when your immune system severely overreacts to an allergen. The flood of chemicals in your body makes your blood pressure drop suddenly, and your bronchial tubes narrow, causing difficulty breathing or even unconsciousness and death. You may have an anaphylactic response within seconds or minutes of exposure to an allergen such as a bee sting or an ingested peanut.
Although anaphylaxis is the most dangerous type of allergic reaction, it's also the least common. Still, hundreds of Americans die of anaphylactic shock each year.
Fortunately, you can be prepared to respond quickly and effectively to an allergic emergency. It's equally important to do all you can to prevent exposure to life-threatening allergens.
DefinitionAnaphylaxis is a life-threatening type of allergic reaction.
Causes, incidence, and risk factors
Anaphylaxis is an severe, whole-body allergic reaction. After an initial exposure to a substance like bee sting toxin, the person's immune system becomes sensitized to that allergen. On a subsequent exposure, an allergic reaction occurs. This reaction is sudden, severe, and involves the whole body.
Tissues in different parts of the body release histamine and other substances. This causes constriction of the airways, resulting in wheezing, difficulty breathing, and gastrointestinal symptoms such as abdominal pain, cramps, vomiting, and diarrhea.
Histamine causes the blood vessels to dilate (which lowers blood pressure) and fluid to leak from the bloodstream into the tissues (which lowers the blood volume). These effects result in shock. Fluid can leak into the alveoli (air sacs) of the lungs, causing pulmonary edema.
Hives and angiedema (hives on the lips, eyelids, throat, and/or tongue) often occur. Angiedema may be severe enough to block the airway. Prolonged anaphylaxis can cause heart arrhythmias.
Some drugs (polymyxin, morphine, x-ray dye, and others) may cause an anaphylactoid reaction (anaphylactic-like reaction) on the first exposure. This is usually due to a toxic reaction, rather than the immune system mechanism that occurs with "true" anaphylaxis. The symptoms, risk for complications without treatment, and treatment are the same, however, for both types of reactions.
Anaphylaxis can occur in response to any allergen. Common causes include insect bites/stings, horse serum (used in some vaccines), food allergies, and drug allergies. Pollens and other inhaled allergens rarely cause anaphylaxis. Some people have an anaphylactic reaction with no identifiable cause.
Anaphylaxis occurs infrequently. However, it is life-threatening and can occur at any time. Risks include prior history of any type of allergic reaction.
Symptoms develop rapidly, often within seconds or minutes. They may include the following:
Signs and tests
Examination of the skin may show hives and swelling of the eyes or face. The skin may be blue from lack of oxygen or may be pale from shock. Angiedema in the throat may be severe enough to block the airway.
Listening to the lungs with a stethoscope may reveal wheezing or indicate fluid (pulmonary edema). The pulse is rapid, and blood pressure may be low. Weakness, pale skin, heart arrhythmias, mental confusion, and other signs may indicate shock.
Testing for the specific allergen that caused anaphylaxis (if the cause is not obvious) is postponed until after treatment.
Anaphylaxis isn't a common condition. However, if you have a history of allergies or asthma, you may be at increased risk — especially if you've had prior anaphylactic reactions. Future reactions may be more severe than the first.
Screening and diagnosis
See a specialist in allergies and immunology if you've experienced an episode of anaphylaxis or think you've experienced some of the signs and symptoms associated with it. An evaluation typically includes questions about:
You may be tested for allergies with skin tests or blood tests. The specialist can provide you instructions on how you might prevent future anaphylactic reactions and how to self-administer medication if you do have a reaction. You may also be asked to keep a detailed list of what you eat or to stop eating certain foods for a time.
Adrenaline (epinephrine) is the drug most commonly used to treat anaphylactic reactions. It can be self-administered with an autoinjector, a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh. Your doctor may recommend that you carry epinephrine and show you how to use the autoinjector. Make sure the people closest to you know how to administer the drug — if they're with you in an anaphylactic emergency, they could save your life. Medical personnel called in response to a severe anaphylactic reaction also may give you epinephrine.
A doctor or emergency medical team may perform cardiopulmonary resuscitation (CPR). They may also inject you with antihistamines and cortisone to reduce inflammation of your air passages and improve your breathing.
If you're with someone who has experienced anaphylaxis and shows signs of shock — pale, cool, and clammy skin, weak and rapid pulse, shallow breathing, dilated pupils, weakness, confusion, anxiety — follow these steps:
If the person isn't breathing or has no pulse, perform CPR.
The best way to prevent anaphylaxis is to avoid substances that you know cause this severe reaction. Follow these steps to help ensure your well-being: