Anaphylaxis

Definition

Anaphylaxis is a severe, sudden, and potentially fatal allergic reaction to a foreign substance or antigen that affects multiple systems of the body.

Description

Anaphylaxis is a severe, whole-body allergic reaction. After initial exposure to a substance such as wasp sting toxin, the allergic child's immune system becomes sensitized to that allergen. On a subsequent exposure to the specific allergen, an allergic reaction, which can involve a number of different areas of the body, occurs. Anaphylaxis is thought to result from antigen-antibody interactions on the surface of mast cells, connective tissue cells that are believed to contain a number of regulatory, or mediator, chemicals. Specifically, an immunoglobulin antibody protein, IgE, is produced in response to the presence of the allergen. IgE binds to the mast cells, causing them to suddenly release a number of chemicals, including histamine, heparin, serotonin, and bradykinin. Once released, these chemicals produce the bodily reactions that characterize anaphylaxis: constriction of the airways, causing wheezing and difficulty in breathing; and gastrointestinal symptoms, such as abdominal pain , cramps, vomiting , and diarrhea . Shock can occur when the released histamine causes the blood vessels to dilate, which lowers blood pressure; histamine also causes fluids to leak from the bloodstream into the tissues, lowering the blood volume. Pulmonary edema can result from fluids leaking into the alveoli (air sacs) of the lung.

Substances that can trigger an anaphylactic reaction include:

• insect stings from hornets, wasps, yellow jackets, honey bees, or fire ants
• medications, including penicillin, cephalosporin, anesthetics, streptokinase, and others
• foods (ingesting even tiny amounts or simply being near the offending food), including peanuts, tree nuts (such as walnuts or almonds), fish, shellfish, eggs, milk, soy, and wheat
• vaccines, including allergy shots and egg- and gelatin-based vaccines
• hormones, including insulin and possibly progesterone
• rubber latex products
• animal and human proteins, including seminal fluid and horse serum (which is used as snake anti-venom)

Anaphylactoid (meaning "anaphylactic-like") reactions are similar to those of true anaphylaxis but do not require an IgE immune reaction. These are usually caused by direct stimulation of the mast cells. The same chemicals as with anaphylaxis are released, with the same effects, so the symptoms are treated the same way. However, an anaphylactoid reaction can occur on initial exposure to an allergen as well as on subsequent exposures, since no sensitization is required.

There is also a rare kind of food allergy, called exercise-induced allergy, that is caused by eating a specific food and then exercising. It can produce itching , lightheadedness, hives , and anaphylaxis. The offending food does not cause a reaction without exercise , and, alternately, exercise does not cause a reaction without ingesting the food beforehand.

Demographics

Although likely an underestimate, about 10,000 cases of anaphylaxis occur per year in North America, with about 750 fatalities a year. The exact prevalence of anaphylaxis is unknown, because milder reactions may be attributed to asthma attacks or sudden cases of hives, and more serious or fatal episodes might be reported as heart attacks, as the initial symptoms of hives, asthma, and swollen throat can fade quickly.

Causes and symptoms

The symptoms of anaphylaxis may occur within seconds of exposure, or be delayed 15 to 30 minutes and sometimes even an hour or more later, if the allergen is aspirin or other similar drugs. The sooner the symptoms occur after exposure, the more severe the anaphylactic reaction is likely to be.

The first symptoms of an anaphylactic reaction are associated with the skin: flushing (warmth and redness), itching (often in the groin or armpits), and hives. These symptoms are often accompanied by anxiety ; a rapid, irregular pulse; and a sense of impending doom. Then the throat and tongue swell, the voice becomes hoarse, and swallowing and breathing become labored. Symptoms of rhinitis or asthma may also occur, causing a runny nose, sneezing, wheezing, and abnormal high-pitched breathing sounds, further worsening the breathing problems. Gastrointestinal effects may also develop, including vomiting, diarrhea, and stomach cramps. The child may be confused and have slurred speech. In about 25 percent of the cases, the chemicals flooding the blood stream will cause a generalized opening of capillaries (tiny blood vessels), resulting in a drop in blood pressure, lightheadedness, and even a loss of consciousness, which are typical symptoms of anaphylactic shock. The child may exhibit blueness of the skin (cyanosis), lips, or nail beds.

After the original symptoms occur, there are three possible outcomes:

• The symptoms may be mild and fade spontaneously or be quickly ended by administering emergency medication. The anaphylactic episode is over for that particular exposure.
• After initial improvement, the symptoms may reoccur after four to 12 hours (a late phase recurrent reaction) and require additional treatment and monitoring. Late phase reactions occur in about 10 percent of cases.
• The reaction may be persistent and severe, requiring extensive medical treatment and hospitalization . This condition occurs in about 20 percent of cases.

When to call the doctor

The child should be given immediate emergency care, if possible, and then taken to the emergency room or the local emergency number (e.g., 911) should be called if symptoms of anaphylaxis develop.

Diagnosis

A child having an anaphylactic reaction will exhibit typical symptoms of anaphylaxis, such as hives and swelling of the eyes or face, blue skin from lack of oxygen, or pale skin from shock. The airway may be blocked, and the child may be wheezing as well as confused and weak. The pulse will be rapid and the blood pressure may be low. Anaphylaxis is an emergency condition that requires immediate professional medical attention.

Once a child has had an anaphylactic reaction, an allergist should be consulted to identify the specific allergen that caused the reaction. The allergist will take a detailed medical history and use blood or skin tests to identify the allergen. The allergist will ask about activities that the child participated in before the event, food and medications the child may have ingested, and whether the child had contact with any rubber products.

Treatment

Because of the severity of these reactions, treatment must begin immediately. The most common emergency treatment involves injection of epinephrine (adrenaline) to stop the release of histamines and relax the muscles of the respiratory tract. The injection is given in the outer thigh and can be administered through light fabric such as trousers, skirts, or stockings. Heavier clothing may have to be removed prior to the injection. After the injection, emergency services or 911 should be called immediately. A child with known severe allergic reactions should be carrying an allergy kit with epinephrine; if not, treatment will have to be delayed until emergency personnel can provide the required medication. For reactions to insect stings or allergy shots, a tourniquet should be placed between the puncture site and the heart; the tourniquet should be released every 10 minutes. If the child is conscious, he or she should lie down and elevate the feet. If trained, the parents or others present should administer CPR if the child stops breathing or does not have a pulse. After 10 to 15 minutes, if symptoms are still significant, another dose of epinephrine can be injected. Even after the reaction subsides, the child should still be taken to the emergency room immediately and monitored for three to four hours, since symptoms can redevelop. Other treatments may be given by medical personnel, including oxygen, intravenous fluids, breathing medications, and possibly more epinephrine. The epinephrine may make the child feel shaky and have a rapid, pounding pulse, but these are normal side effects and are only dangerous to those with heart problems. Steroids and antihistamines may also be given but are usually not as helpful initially as epinephrine. However, they may be useful in preventing a recurrent delayed reaction.

If the child is being treated with beta blocker medications commonly used to treat high blood pressure, angina, thyroid disorders, migraines, or glaucoma, it may be difficult to reverse an anaphylactic reaction.

Prognosis

Anaphylaxis is a severe disorder that has a poor prognosis without prompt treatment. Symptoms are usually resolved with appropriate therapy; therefore, immediate emergency care is essential.

Prevention

For children with known reactions to antibiotics , foods, insect stings, specific foods, or any of the allergens that can induce an anaphylactic reaction, avoidance of the symptom-inducing agent is the best form of prevention.

Specific avoidance measures that are recommended include:

Drugs/medications:

• Parents should advise healthcare personnel of the childs allergies .
• Parents should ask the doctor whether prescribed medications could contain the drug(s) to which the child is allergic.
• The child should take all medications by mouth, if possible, since the risk of anaphylaxis is greater with injections.
• Any child should stay in a doctors office or near medical care for a period of time after receiving injections of an antibiotic or vaccine.

Insect stings:

• The child should avoid areas where insects breed and live.
• The child should not wear bright clothing, perfume, hair spray, or lotions that might attract insects.
• If possible the child should wear long sleeves, long trousers, and shoes when out of doors.

Food:

• The child must be instructed to never again eat that kind of food that causes an anaphylactic reaction.
• Parents should carefully read all ingredient labels of foods that the child might eat and be aware of the different terms used for various foods, such as caseinate for milk or albumin for eggs.
• Parents should ask about ingredients in foods while eating out with the child, bring safe substitutes from home, and bring an allergy kit.
• Parents should be aware of possible cross-contamination, such as when an ice cream scoop is used for Rocky Road ice cream, which contains peanuts, and then for vanilla ice cream.
• School kitchen personnel should be notified of the childs condition.
• The child should avoid eating foods that might cross-react with foods that the child is allergic to, for example, if the child is allergic to shrimp, the child may also be allergic to crab or lobster.
• When traveling to other countries, parents should learn the appropriate words for foods that trigger their childs allergy; in addition, parents can request that air carriers serve peanut-free snacks to all passengers when their child is traveling; also the child should avoid eating airline meals.

Latex:

• The child should avoid all latex rubber products.
• If the child has to be hospitalized, the parents should alert the hospital personnel to the childs allergy to latex.
• A child with a latex allergy may also have allergies to kiwi fruit, passion fruit, papayas, bananas, avocados, figs, peaches, nectarines, plums, tomatoes, celery, and chestnuts.

In addition, children with a history of allergic reactions should carry an emergency kit containing injectable epinephrine and chewable antihistamine and be instructed in its use. A child who is not prepared to deal with an anaphylactic reaction is at an increased risk of dying. The allergy kit should include simple instructions on when and how to use the kit; sterilizing swabs to cleanse the skin before and after the injection; epinephrine in a preloaded syringe, as prescribed by the childs doctor in doses appropriate for children; and antihistamine tablets. The expiration date on the medications in the allergy kit should be checked and medications replaced as needed. Also, the epinephrine solution should be clear; if it is pinkish brown, it should be discarded and replaced.

There are many brands of allergy kits. The simplest kit to use is the Ana-kit, which contains a sterile syringe preloaded with two doses of epinephrine with a stop between. Another commonly used kit is the Epi-Pen, which carries a single self-injecting, spring-loaded syringe of epinephrine. Two Epi-Pen kits should be carried, so that two doses are available. Allergy kits should be kept at home, school, and day care ; and the school administrator, teachers, and friends should be made aware of the childs allergies. Adults associated with the child should be trained in giving an injection and have a plan to transport the child to the hospital. Older children should be taught to give self-injections. Children at risk for anaphylaxis should also wear a Medic Alert bracelet or necklace or carry a medical emergency card with them at all times that clearly describes their allergy.

A consultation with an allergist can help to identify the substances that trigger the reaction; the allergist can also provide information on how to best avoid the triggering substance. The allergist may also be able to give allergy shots to children with wasp, yellow jacket, hornet, honey bee, or fire ant allergies. These shots provide 90 percent protection against the first four insect reactions, but less protection against fire ant reactions. Premedication is also helpful in preventing anaphylaxis from x-ray dyes; also there may be alternative dyes available for use that are less likely to cause reactions. Desensitization to medications has also been successful in some cases. The process involves gradually increasing the amount of medication given under controlled conditions. The procedure has worked for sensitivities to penicillin, sulfa drugs, and insulin.

The risk of anaphylaxis sometimes diminishes over time if there are no repeated exposures or reactions. However, the child at risk should also expect the worst and be prepared with preventive medication.

Parental concerns

Parents caring for children who are at risk for life-threatening anaphylactic reactions may experience high stress levels, for they have to maintain vigilance in order to protect the child while creating a sense of normalcy as the child grows up. Parents can reduce their stress by using social support groups, accepting their childs condition, and maintaining a positive attitude.

KEY TERMS

Allergen —A foreign substance that provokes an immune reaction or allergic response in some sensitive people but not in most others.

Allergy —A hypersensitivity reaction in response to exposure to a specific substance.

Epinephrine —A hormone produced by the adrenal medulla. It is important in the response to stress and partially regulates heart rate and metabolism. It is also called adrenaline.

Immunoglobulin E (IgE) —A type of protein in blood plasma that acts as an antibody to activate allergic reactions. About 50% of patients with allergic disorders have increased IgE levels in their blood serum.

See also Allergies.

Resources

BOOKS

Barber, Marianne S. The Parents Guide to Food Allergies: Clear and Complete Advice from the Experts on Raising Your Food-Allergic Child. New York: Owl Books, 2001.

Coss, Linda Marienhoff. How to Manage Your Childs Life-Threatening Food Allergies: Practical Tips for Daily Life. Lake Forest, CA: Plumtree Press, 2004.

Jevon, Philip. Anaphylaxis: A Practical Guide. London, UK: Butterworth-Heinemann, 2004.

Smith, Nicole. Allie the Allergic Elephant: A Childrens Story of Peanut Allergies. San Francisco: Jungle Communications, 2002.

ORGANIZATIONS

American Academy of Allergy, Asthma, and Immunology. 611 E. Wells Street, Milwaukee, WI 53202. Web site: <www.aaaai.org>

Food Allergy and Anaphylaxis Network. 10400 Eaton Place, Suite 107, Fairfax, VA 220302208. Web site: <www.foodallergy.org>

WEB SITES

American College of Allergy, Asthma, and Immunology. Available online at <http://allergy.mcg.edu> (accessed October 10, 2004).

Judith Sims

Anaphylaxis

Definition

Anaphylaxis is a rapidly progressing, lifethreatening allergic reaction.

Description

Anaphylaxis is a type of allergic reaction, in which the immune system responds to otherwise harmless substances from the environment. Unlike other allergic reactions, however, anaphylaxis can result in death. Reaction may begin within minutes or even seconds of exposure, and rapidly progress to cause airway constriction, skin and intestinal irritation, and altered heart rhythms. In severe cases, it can result in complete airway obstruction, shock, and death.

In 2001, more cases of anaphylaxis have been reported, especially in reaction to latex and exotic food antigens. The increased use of latex gloves in hospitals, doctors' offices, dentist offices, and among forensic investigators has also increased exposure to latex allergens.

The broadening of the Western diet, with the incorporation of more exotic foods and increased food processing, also exposes more people to possible food allergens, and at earlier ages. Peanut oil, for example, is often used in fast-food restaurants, and sulfites are used in processed meats and seafood. There is still no labeling for trace amounts of foods or food additives. Unfortunately, problem food allergens can still be present in favorite foods, even if the label does not show it. In some cases, even a small amount can prove fatal in certain individuals.

Causes and symptoms

Causes

Like the majority of other allergic reactions, anaphylaxis is caused by the release of histamine and other chemicals from mast cells, which are a type of white blood cell found in large numbers in the tissues that regulate exchange with the environment: the airways, digestive system, and skin.

On their surfaces, mast cells display antibodies called immunoglobulin type E (IgE). These antibodies are designed to detect environmental substances to which the immune system is sensitive. Substances from a genuinely threatening source such as bacteria or viruses are called antigens. A substance that most people tolerate well, but to which others have an allergic response, is called an allergen. When IgE antibodies bind with allergens, they cause the mast cells to release histamine and other chemicals that spill out onto neighboring cells.

The interaction of these chemicals with receptors on the surface of blood vessels causes the vessels to leak fluid into surrounding tissues, resulting in fluid accumulation, redness, and swelling. On the smooth muscle cells of the airways and digestive system, they cause constriction. On nerve endings, they increase sensitivity and cause itching.

In anaphylaxis, the dramatic response is due both to extreme hypersensitivity to the allergen and its usually systemic distribution. Allergens are more likely to cause anaphylaxis if they are introduced directly into the circulatory system by injection. However, exposure by ingestion, inhalation, or skin contact can also cause anaphylaxis. In some cases, anaphylaxis may develop over time from less severe allergies.

Anaphylaxis most often results from allergens in foods, drugs, latex, and insect venom. Specific causes include, but are not limited to:

• fish, shellfish, and mollusks
• peanuts, tree nuts, and seeds
• eggs
• milk
• insulin in vegetables and processed foods
• stings of bees, wasps, and hornets
• preservatives, especially sulfites and parabens
• vaccines (e.g. flu, measles, rabies, chicken pox, and diphtheria-tetanus-pertussis) prepared with a gelatin base made from pork products

• antibiotics, including penicillin and its derivatives, cephalosporins, streptomycin, tetracycline, and sulphonamides
• gamma globulin and human serum albumin
• hormones like insulin, ACTH, and glucocorticoids
• anti-inflammatory drugs such as aspirin, ibuprofen, and other NSAIDs
• anti-venoms
• antiseptics such as mercurochrome
• allergy immunotherapy vaccines
• radiopaque dyes used in diagnostic studies (radiocontrast media)
• latex from exam gloves, catheters, tubing, condoms, etc.
• local anesthetics
• dyes (erythrosine and resorcinol, used in hair dyes)

Exposure to cold or exercise can also trigger anaphylaxis in some individuals.

Symptoms

Symptoms may include:

• flushing of face, head, or hands
• urticaria (hives)
• swelling and irritation of the tongue or mouth
• swelling of the sinuses
• difficulty breathing
• wheezing
• cramping, vomiting, or diarrhea
• anxiety or confusion
• strong, very rapid heartbeat (palpitations)
• drop in blood pressure
• chest pain
• loss of consciousness

Not all symptoms may be present, and some may be more severe than others. Symptoms usually occur immediately or within 20 minutes of exposure. On occasion, with food anaphylaxis, symptoms may not appear for several minutes or even hours. As a general guideline, the slower the onset of symptoms comes on, the less serious the episode. Symptoms may also reappear several hours later, sometimes in a more severe form.

Diagnosis

Anaphylaxis is diagnosed based on the rapid development of symptoms in response to a suspected allergen. Identification of the cause may be done with RAST testing, a blood test that identifies IgE reactions to specific allergens. Skin testing can also be done, but with care. Food challenges should be avoided.

Sometimes, the offending allergen is not readily apparent, and the diagnosis of anaphylaxis could be overlooked. Also, some of the symptoms resemble other conditions such as cardiac arrhythmia, myocardial infarction, seizure disorder, insulin reaction, and pulmonary embolism.

A detailed medical history taken of the patient before medical or surgical procedures may help in diagnosis if symptoms manifest. Often, the only evidence of anaphylactic reaction is anecdotal or self-reported surveys.

Treatment

Emergency treatment of anaphylaxis involves injection of adrenaline (epinephrine), which constricts blood vessels and counteracts the effects of histamine. Oxygen may be given, as well as intravenous replacement fluids. Antihistamines may be used for skin rash, and aminophylline for bronchial constriction. If the upper airway is obstructed, the insertion of a breathing tube or tracheotomy tube may be needed.

Treatment should be administered immediately. Epinephrine injected directly into muscle tissue is quick and extremely effective. Intravenous injections require specific calculations regarding the dilution of adrenaline in order for it to be administered. Epinephrine inhalers are not as effective, as are short-acting b-agonist inhalers used by persons suffering from asthma. These can prove fatal because they delay effective treatment.

Self-administered epinephrine devices such as EpiPen and EpiE-Z are life-saving tools. Patients must be properly trained in their use and instructed to keep these devices updated and close at hand.

Patients should also be monitored for 24 hours after the symptoms have subsided. Symptoms have been known to return several hours later when the patient has returned home from the hospital.

Prognosis

The rapidity of symptom development is an indication of the likely severity of reaction: the faster symptoms develop, the more severe the ultimate reaction. Prompt emergency medical attention and close monitoring reduces the likelihood of death. Nonetheless, death is possible from severe anaphylaxis. For most people who receive rapid treatment, recovery is complete.

Health care team roles

All medical personnel should be trained to recognize the symptoms of anaphylaxis and to use the proper emergency procedures. Nurses and physicians assistants need to ask patients about their history of allergy when preparing them for a doctor's visit or before invasive procedures. Physicians, lab personnel, and nurses need to routinely ask whether a person is allergic to medications and latex. Inquiries about food allergies can be very helpful when preparing to administer vaccinations or medications. A patient's allergy history may have changed since the last doctor's visit. Even a small reaction like a rash on initial exposure to an allergen can be an indicator that a patient may have a more serious reaction on subsequent encounters with the agent.

In the case of latex allergy in the wake of a surgical procedure, medical personnel will need to strip the operating room or the procedure room of all latex items. Some patients are so sensitive to latex in any form that even inhaling a latex particle in the air could be life threatening.

Prevention

Avoidance of the allergic trigger is the only reliable method of preventing anaphylaxis. For insect allergies, this requires recognizing likely nest sites, wearing long sleeves, and using insect repellant. Preventing food allergies requires knowledge of the prepared foods or dishes in which the allergen is likely to occur, reading labels, and carefully questioning about ingredients when dining out. Use of a Medic-Alert tag detailing drug allergies is vital to prevent inadvertent administration during a medical emergency. In addition, patients with latex sensitivity need to avoid using latex products of all kinds and must notify medical and dental personnel of their latex allergy.

People prone to anaphylaxis should carry an Epipen or Ana-kit, which contains an adrenaline dose ready for injection. They also should be carefully trained in its use.

KEY TERMS

Allergen— A substance that causes an allergic reaction.

Adrenocorticotropic hormone (ACTH)— A hormone normally produced by the pituitary gland, sometimes taken as a treatment for arthritis and other disorders.

Antibody— An immune system protein that binds to a substance from the environment.

Histamine— A substance produced by the immune system in response to an allergen.

NSAIDs— Non-steroidal anti-inflammatory drugs, including aspirin and ibuprofen.

Tracheostomy tube— A tube that is inserted into an incision in the trachea (tracheotomy) to relieve upper airway obstruction.

Resources

BOOKS

Lawlor Jr., G.J., T.J. Fischer, and D.C. Adelman. Manual of Allergy and Immunology. Boston/New York/Toronto/London: Little, Brown and Co., 1995.

PERIODICALS

Davis, Blanca Rosa. "Perioperative Care of Patients with Latex Allergy." AORN Journal 72 no. 1 (July 2000): 47.

Jurewizc, Mary Ann. "Anaphylaxis: When the Body Overreacts." Nursing 30 no. 7 (July 2000): 58.

Neugut, Alfred I., Anita T. Ghatak, and Rachel L. Miller. "Anaphylaxis in the United States: An Investigation into Its Epidemiology." Archives of Internal Medicine 161 no. 1 (January 8, 2001): 15.

Socjerer, Scott H., Joel A. Forman, and Sally A. Noone. "Use Assessment of Self-Administered Epinephrine among Food-allergic Children and Pediatricians." Pediatrics 105 no. 2 (February 2000): 359.

ORGANIZATIONS

American College of Allergy, Asthma, & Immunology. 85 West Algonquin Road, Suite 550, Arlington Heights, IL 60005. 〈http://www.allergy.mcg.edu〉.

OTHER

Merck Manual On-line. 〈http://www.merck.com/pubs/mmanual/〉.

Anaphylaxis

Definition

Anaphylaxis is a rapidly progressing, life-threatening allergic reaction.

Description

Anaphylaxis is a type of allergic reaction, in which the immune system responds to otherwise harmless substances from the environment. Unlike other allergic reactions, however, anaphylaxis can kill. Reaction may begin within minutes or even seconds of exposure, and rapidly progress to cause airway constriction, skin and intestinal irritation, and altered heart rhythms. In severe cases, it can result in complete airway obstruction, shock, and death.

Causes and symptoms

Causes

Like the majority of other allergic reactions, anaphylaxis is caused by the release of histamine and other chemicals from mast cells. Mast cells are a type of white blood cell and they are found in large numbers in the tissues that regulate exchange with the environment: the airways, digestive system, and skin.

On their surfaces, mast cells display antibodies called IgE (immunoglobulin type E). These antibodies are designed to detect environmental substances to which the immune system is sensitive. Substances from a genuinely threatening source, such as bacteria or viruses, are called antigens. A substance that most people tolerate well, but to which others have an allergic response, is called an allergen. When IgE antibodies bind with allergens, they cause the mast cell to release histamine and other chemicals, which spill out onto neighboring cells.

The interaction of these chemicals with receptors on the surface of blood vessels causes the vessels to leak fluid into surrounding tissues, causing fluid accumulation, redness, and swelling. On the smooth muscle cells of the airways and digestive system, they cause constriction. On nerve endings, they increase sensitivity and cause itching.

In anaphylaxis, the dramatic response is due both to extreme hypersensivity to the allergen and its usually systemic distribution. Allergens are more likely to cause anaphylaxis if they are introduced directly into the circulatory system by injection. However, exposure by ingestion, inhalation, or skin contact can also cause anaphylaxis. In some cases, anaphylaxis may develop over time from less severe allergies.

Anaphylaxis is most often due to allergens in foods, drugs, and insect venom. Specific causes include:

• Fish, shellfish, and mollusks
• Nuts and seeds
• Stings of bees, wasps, or hornets
• Papain from meat tenderizers
• Vaccines, including flu and measles vaccines
• Penicillin
• Cephalosporins
• Streptomycin
• Gamma globulin
• Insulin
• Hormones (ACTH, thyroid-stimulating hormone)
• Aspirin and other NSAIDs
• Latex, from exam gloves or condoms, for example.

Exposure to cold or exercise can trigger anaphylaxis in some individuals.

KEY TERMS

ACTH— Adrenocorticotropic hormone, a hormone normally produced by the pituitary gland, sometimes taken as a treatment for arthritis and other disorders.

Antibody— An immune system protein which binds to a substance from the environment.

NSAIDs— Non-steroidal antiinflammatory drugs, including aspirin and ibuprofen.

Tracheostomy tube— A tube which is inserted into an incision in the trachea (tracheostomy) to relieve upper airway obstruction.

Symptoms

Symptoms may include:

• Urticaria (hives )
• Swelling and irritation of the tongue or mouth
• Swelling of the sinuses
• Difficulty breathing
• Wheezing
• Cramping, vomiting, or diarrhea
• Anxiety or confusion
• Strong, very rapid heartbeat (palpitations )
• Loss of consciousness.

Not all symptoms may be present.

Diagnosis

Anaphylaxis is diagnosed based on the rapid development of symptoms in response to a suspect allergen. Identification of the culprit may be done with RAST testing, a blood test that identifies IgE reactions to specific allergens. Skin testing may be done for less severe anaphylactic reactions.

Treatment

Emergency treatment of anaphylaxis involves injection of adrenaline (epinephrine) which constricts blood vessels and counteracts the effects of histamine. Oxygen may be given, as well as intravenous replacement fluids. Antihistamines may be used for skin rash, and aminophylline for bronchial constriction. If the upper airway is obstructed, placement of a breathing tube or tracheostomy tube may be needed.

Prognosis

The rapidity of symptom development is an indication of the likely severity of reaction: the faster symptoms develop, the more severe the ultimate reaction. Prompt emergency medical attention and close monitoring reduces the likelihood of death. Nonetheless, death is possible from severe anaphylaxis. For most people who receive rapid treatment, recovery is complete.

Prevention

Avoidance of the allergic trigger is the only reliable method of preventing anaphylaxis. For insect allergies, this requires recognizing likely nest sites. Preventing food allergies requires knowledge of the prepared foods or dishes in which the allergen is likely to occur, and careful questioning about ingredients when dining out. Use of a Medic-Alert tag detailing drug allergies is vital to prevent inadvertent administration during a medical emergency.

People prone to anaphylaxis should carry an "Epi-pen" or "Ana-kit," which contain an adrenaline dose ready for injection.

Resources

OTHER

The Meck Page. February 20, 1998. 〈http://www.merck.com〉.

Anaphylaxis

Anaphylaxis is a violent allergic reaction of the whole body which can result in death. During anaphylaxis, the allergic person's throat swells so much that she or he cannot breath, while internal organs may start to shutdown. The immune system's attempt to rid the body of a particular substance actually turns against the body itself.

When research on the immune system was progressing in the 1800s, most scientists thought that the body's reactions to invaders were always protective. While researching experimental smallpox innoculations in 1798, Edward Jenner (1749-1823) observed that patients given a second shot often suffered violent reactions. Despite this risk, people were more afraid of the disease than possible inoculation side effects. Jenner's experimentation, which included inoculating subjects with both cowpox and smallpox, eventually led to the development of a successful—and safe—smallpox vaccine.

The first complete study and description of negative immune responses was produced by two Frenchmen, physiologist Charles Richet and physician Paul Portier (1866-1962). During a scientific cruise on the yacht of Prince Albert of Monaco (a small principality on the Mediterranean Sea), Albert suggested that Portier and Richet study the poison (toxin) produced by the tentacles of the Portuguese man-of-war, a jelly-fish. Back in France, the two men continued their studies with extracts of toxin from a sea anemone (a flower-like marine creature). While looking for a toxic dose level, they injected dogs with sea anemone venom. Dogs that survived were given time to recover and then reinjected. Richet expected that the first exposure to the toxin would create a certain amount of immunity in the dogs, the same way that getting a virus gives someone immunity to another encounter with the same disease. Instead, the initial exposure made the dogs hypersensitive. A second, much smaller dose of toxin quickly killed them. Since this result was the opposite of a protective immune response, or prophylaxis, Richet named the hypersensitive reaction anaphylaxis. Richet's identification of anaphylaxis won him the 1913 Nobel Prize for medicine.

After further research, it was discovered that many substances people are allergic to, particularly foods and toxins from animals (such as bee venom), can cause strong reactions. This knowledge provided a valuable warning to physicians engaged in serum (anti-poison) therapy. The researchers began checking patients for possible sensitization before injecting potentially toxic amounts of serum. Those patients with an initially severe reaction to an allergen (or allergy-causing agent) were advised to carry epinephrine (an artificial hormone) to inject immediately if they had a severe reaction.

[See also Hormone ]

Anaphylaxis

Anaphylaxis is a severe allergic reaction. The symptoms appear rapidly and can be life threatening.

The symptoms of anaphylaxis include the increased output of fluid from mucous membranes (e.g., passages lining the nose, mouth, and throat), skin rash (e.g., hives), itching of the eyes, gastrointestinal cramping, and stiffening of the muscles lining the throat and trachea. As a result of the latter, breathing can become difficult. These symptoms do not appear in every case. However, some sort of skin reaction is nearly always evident.

Anaphylaxis results from the exposure to an antigen with which the individual has had previous contact, and has developed a heightened sensitivity to the antigen. Such an antigen is also known as an allergen. The allergen binds to the specific immune cell (e.g., immunoglobulin E, also known as IgE) that was formed in response to the initial antigen exposure. IgE is also associated with other specific cells of the immune system that are called basophils and mast cells. The basophils and mast cells react to the binding of the allergen- IgE complex by releasing compounds that are known as mediators (e.g, histamine , prostaglandin D2, trypase). Release of mediators does not occur when IgE alone binds to the basophils or mast cells.

The release of the mediators triggers the physiological reactions. For example, blood vessels dilate (become larger in diameter) and fluid can pass across the blood vessel wall more easily. Because the immune system is sensitized to the particular allergen, and because of the potent effect of mediators, the development of symptoms can be sudden and severe. A condition called anaphylactic shock can ensue, in which the body's physiology is so altered that failure of functions such as the circulatory system and breathing can occur. For example, in those who are susceptible, a bee sting, administration of a penicillin-type of antibiotic, or the ingestion of peanuts can trigger symptoms that can be fatal if not addressed immediately. Those who are allergic to bee stings often carry medication with them on hikes.

Anaphylaxis occurs with equal frequency in males and females. No racial predisposition towards anaphylaxis is known. The exact number of cases is unknown, because many cases of anaphylaxis are mistaken for other conditions (e.g., food poisoning). However, at least 100 people die annually in the United States from anaphylactic shock.

See also Allergies; Immunoglobulins and immunoglobulin deficiency syndromes