INTRODUCTION — Anaphylaxis is a sudden, potentially life-threatening allergic reaction. Allergic reactions can be triggered by foods, medications, exercise, latex, or insect stings, or unknown triggers.
Every year, about 500 to 1000 people die from severe anaphylaxis. However, many more people likely experience mild or moderate anaphylaxis and do not seek medical care. As a result, the true frequency of anaphylaxis is unknown.
The severity of anaphylactic reactions can be minimized by recognizing the symptoms early, having the proper medications available for self-treatment, and seeking emergency medical care promptly. It is also important to try to identify the specific trigger for each person, although this is not always possible.
PHYSIOLOGY — Anaphylaxis occurs when a trigger activates immune cells, which then release large amounts of multiple substances, including histamine, into the blood stream. This sets off a number of reactions, including itching, dilated blood vessels (leading to low blood pressure and rapid heart rate), mucus secretion, stimulation of the nervous system, and activation of other cells of the immune system. These reactions cause the symptoms that are commonly associated with anaphylaxis.
In some people with anaphylaxis, abnormal antibodies called IgE (proteins that normally fight infections and protect the body) are made in response to non-harmful things, like food or medicines. These IgE antibodies can trigger a violent immune response when the person is later exposed to that food or medicine. The immune response is so strong and uncontrolled that the reaction itself can be harmful. In other people with anaphylaxis, these abnormal IgE proteins are not found, and the reaction is thought to have been caused by other processes.
SYMPTOMS — Symptoms of anaphylaxis generally begin within 5 to 60 minutes of exposure to a trigger. Some patients may not develop symptoms for several hours.
Anaphylaxis can produce symptoms throughout the body: Skin: Itching, flushing, urticaria (hives), and angioedema (swelling). Eyes: Itching, tearing, and swelling of the tissues around the eyes. Nose and mouth: Sneezing, runny nose, nasal congestion, itching of the mouth, and a metallic taste. Lungs and throat: Difficulty breathing, wheezing, increased airway secretions, swelling of the upper throat and/or tongue, hoarseness, sounds of labored breathing, and a sensation of choking. Heart: Very rapid heartbeat, arrhythmia (an irregular heart beat), low blood pressure, and cardiac arrest (a cessation of the heart's pumping action). Digestive system: Nausea, vomiting, abdominal cramps, bloating, and diarrhea. Nervous system: Dizziness, weakness, fainting, and a sense of impending doom.
The most common symptoms of anaphylaxis are urticaria (hives) and angioedema (swelling of the tissues under the skin), which occur in nearly 90 percent of people who have anaphylaxis. These symptoms usually begin after a period of generalized itching, flushing, and sometimes a growing sense of impending doom.
Respiratory symptoms occur in about 50 percent of people who have anaphylaxis and are especially common in people who also have asthma. Gastrointestinal symptoms occur in 30 percent of people. Anaphylactic shock (extremely low blood pressure) occurs in 30 percent of people who have a reaction. Low blood pressure can cause lightheadedness, dizziness, tunnel vision, and loss of consciousness (passing out). These are serious symptoms.
Less commonly, a person may have biphasic or protracted anaphylaxis. A patient with biphasic anaphylaxis has a reaction that resolves but recurs one to eight hours later; second reactions have occurred as much as 72 hours later. A patient with protracted anaphylaxis has signs and symptoms that persist for up to 48 hours despite treatment.
CAUSES — Anaphylaxis triggers can include: Foods, especially seafood, milk, peanuts and tree nuts Drugs, especially certain antibiotics (such as penicillin), nonsteroidal anti-inflammatory drugs (such as aspirin or ibuprofen), drugs used for chemotherapy, and angiotensin-converting enzyme (ACE) inhibitors (See "Patient information: Allergy to penicillin and other antibiotics") Venom from insects, including bees, wasps, kissing bugs, and fire ants Some substances used during x-ray procedures (radiocontrast media) Transfused blood and blood products Exercise or exertion Latex from natural rubber, used to make gloves, balloons, and some medical products
In some cases, a thorough evaluation by an allergy specialist will not identify any specific trigger. This condition is called idiopathic anaphylaxis and is more common in adults than in children.
Food allergies in children — Anaphylaxis in children often results from food allergies. Food allergies are most likely to develop in the first three years of life, when many foods are introduced into a child's diet. Allergies to hen's egg, peanuts, cow's milk, soy, fish, and wheat are among the most common food allergies that children develop. In children over the age of three years, peanuts are the most common allergen. Children often outgrow allergies to milk, eggs, and soybeans. However, allergies to peanuts, other tree nuts, fish and seafood tend to persist.
RISK FACTORS — Several factors help to predict which individuals are most likely to experience anaphylaxis and which factors are most likely to trigger anaphylaxis in specific groups of people.
Age — Children are more likely than adults to have anaphylactic reactions to foods. Adults are more likely to have anaphylactic reactions to antibiotics, radiocontrast media, insect stings, anesthetic drugs, and certain intravenous medicines. They are also more likely to have idiopathic anaphylaxis.
Gender — Overall, women are somewhat more likely to experience anaphylaxis.
Asthma — People with asthma are more likely to experience anaphylaxis and to have more severe respiratory problems during anaphylaxis. The combination of food allergy (especially to peanuts and tree nuts) and asthma seems to put people at risk for particularly dangerous attacks of anaphylaxis.
History of anaphylaxis — People who have had an anaphylactic reaction in the past are at increased risk of future anaphylactic reactions. For example, people who have had an anaphylactic reaction to certain antibiotics are four to six times more likely to have another reaction to these antibiotics when compared to the general population. Similarly, 60 percent of people who have had an allergic reaction to a bee or wasp sting have a severe reaction if stung again, and up to 40 percent of people who have had a reaction to radiocontrast media have a repeat reaction if they are given it again (unless they are given medications to prevent a reaction).
Multiple exposures — People who are exposed to several different allergic stimuli at the same time have an increased risk of anaphylaxis. For example, people who receive immunotherapy (regular injections, also called allergy shots) to decrease a their sensitivity to allergens are more likely to have a severe reaction to their injections during the season(s) when natural exposure is greatest (eg, allergy season, usually spring and fall in most regions of the United States).
DIAGNOSIS — The diagnosis of anaphylaxis is usually based upon the presence of characteristics symptoms, particularly if there is an accompanying story of exposure to a potential trigger, such as a new medicine or insect sting.
However, other problems, such as food poisoning, a severe asthma attack, or cardiac events, can sometimes look like anaphylaxis. In such cases, further evaluation by allergists or other specialists may be needed to clarify the diagnosis. In some cases, the diagnosis of anaphylaxis is difficult to establish.
TREATMENT — A patient who has had an anaphylactic reaction should talk with their healthcare provider to design a plan for responding to future reactions. A plan can minimize the severity of an anaphylactic reaction and ensure that the best treatments are given. Many people find that developing a plan is reassuring, even if it is never needed.
Because anaphylaxis can be life-threatening, it should be treated as an emergency. Most people with moderate to severe anaphylaxis are hospitalized for observation, even when emergency treatment brings the symptoms under control. This hospitalization enables prompt treatment if the symptoms reappear several hours later.
Self-treatment — Patients with allergies or who have a history of anaphylaxis should always carry two epinephrine autoinjectors. A full description of epinephrine autoinjectors is available separately. (See "Patient information: Use of an epinephrine autoinjector").
Remove the cause — The trigger for the anaphylactic reaction should be promptly removed, whenever possible. This removal may entail stopping a drug, or in the case of an insect sting, dislodging the stinger with the edge of a credit card or coin. Patients should not attempt to pull the stinger out of the skin.
Respiratory and cardiovascular support — The initial treatment of anaphylaxis addresses any life-threatening respiratory and cardiovascular symptoms. This treatment may require inserting a breathing (endotracheal) tube to keep a person's airways open. Treatment may also include medications to treat low blood pressure and cardiac arrhythmias (irregular heart beat).
Drug therapy — Many different drugs are used to treat anaphylaxis, including epinephrine, asthma medications, antihistamines, and corticosteroids. Intravenous fluids are also frequently used to increase and maintain blood pressure.
Epinephrine is the most effective drug for the treatment of anaphylaxis. It treats all the symptoms of anaphylaxis, and is the most important treatment for the severe symptoms that can occur: low blood pressure, chest tightness or wheezing, and throat closure. (See "Patient information: Use of an epinephrine autoinjector").
Antihistamines can be given by injection or pill, and are almost always given to patients during anaphylaxis. Inhaled medications, such as albuterol, are given during anaphylaxis if a person has difficulty breathing, chest tightness, or coughing. Corticosteroids, such as prednisone, do not work rapidly enough to stop the immediate signs and symptoms of anaphylaxis. However, they may prevent a recurrence in the hours following an anaphylactic reaction and prevent late reactions, such as asthma attacks.
PREVENTION — Anaphylaxis is a frightening experience for the person who suffers the reaction, as well as for the people around him or her. It is normal to worry about future reactions. A few simple measures can reduce this risk.
Allergist evaluation — Anyone who has experienced an anaphylactic reaction should be evaluated by an allergist - a doctor who specializes in the diagnosis and treatment of allergies and related conditions. An allergist may recommend skin tests or blood testing to help identify the stimuli that triggered anaphylaxis. As stated above, a specific trigger cannot be identified in all cases, although an allergist can provide advice about how best to manage this situation as well.
Avoiding triggers — When a trigger can be identified, it can often be avoided. For example, a person with a known food allergy may be able to prevent anaphylactic reactions by carefully eliminating that food from their diet. A healthcare provider can provide strategies for identifying the food in processed products and when dining out.
Eliminating a food requires that a person carefully read food labels on everything they plan to eat, not just the foods that are most likely to contain the allergy trigger. The United States Food Allergen Labeling and Consumer Protection Act (which affects foods labeled on or after January 2006) requires that the nutrition labels on food packages clearly identify eight potential allergy triggers: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, and soybeans. Other potential allergy triggers may be identified with names that are less clear (eg, spices, flavorings, or colorings that may cause an allergic reaction). In addition, "substitute" foods that are used to lower the fat content or replace other components of a food may not remove the allergenic proteins. As an example, some egg substitutes (which are lower in cholesterol) still contain egg white proteins.
People with allergies to bees, wasps, or hornets can wear protective clothing, learn to stay calm around insects, avoid wearing scented sprays or lotions, and take care when outdoors to reduce the likelihood of being stung.
Wear a device identifying the allergy — People who have allergies or have experienced an anaphylactic reaction should wear a bracelet, necklace, or similar alert tag at all times. If another reaction occurs and the person is too ill to explain their condition, this will help responders get the proper care for the person as quickly as possible. This measure is especially important in children.
The alert tag should include a list of known allergies, as well as the name and phone number of an emergency contact. One device, Medic Alert®, provides a toll-free number that emergency medical workers can call to find out a person's medical history, list of medications, family emergency contact numbers, and healthcare provider names and numbers.
Other preventive measures — Other measures to prevent future episodes of anaphylaxis include immunotherapy (injections to reduce sensitivity) for bee and wasp stings, antibiotic desensitization, and premedication with antihistamines and corticosteroids before radiocontrast administration.
WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two patients are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.
This discussion will be updated as needed every four months on our web site (www.patients.uptodate.com). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.
A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable. The National Library of Medicine
(www.nlm.nih.gov/medlineplus/healthtopics.html)
American Academy of Allergy, Asthma, and Immunology
(www.aaaai.org)
Anaphylaxis Foundation and Anaphylaxis Network of Canada
(www.anaphylaxis.org)
The Anaphylaxis Campaign
(www.anaphylaxis.org.uk)
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