anaphylaxis

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A generalized or localized tissue reaction occurring within minutes of an antigen-antibody reaction. Similar reactions elicited by nonimmunologic mechanisms are termed anaphylactoid reactions. In humans, the clinical manifestations of anaphylaxis include reactions of the skin with itching, erythema, and urticaria; the upper respiratory tract with edema of the larynx; the lower respiratory tract with dyspnea, wheezing, and cough; the gastrointestinal tract with abdominal cramps, nausea, vomiting, and diarrhea; and the cardiovascular system with hypotension and shock. Individuals undergoing anaphylactic reactions may develop any one, a combination, or all of the signs and symptoms. Anaphylaxis may be fatal within minutes, or may occur days or weeks after the reaction, if the organs sustained considerable damage during the hypotensive phase.

Anaphylaxis in humans is most often the result of the interaction of specific IgE antibody fixed to mast cells and antigen. Two molecules of IgE are bridged by the antigen, which may be a complex protein or chemical (hapten) bound to protein. The antigen-antibody interaction leads to increased cell-membrane permeability, with influx of calcium and release of either preformed or newly formed pharmacologic mediators from the granules. Preformed mediators include histamine and eosinophilic or neutrophilic chemotactic factors. Newly formed molecules include leukotrienes or slow-reacting substance of anaphylaxis and prostaglandins. The mediator action induces bronchoconstriction, vasodilation, cellular infiltration, and increased mucus production.

Another mechanism for induction of anaphylaxis in humans occurs when antigen binds to preformed IgG antibody and complement components interact with the antigen-antibody complex. The early components of the complement system bind to the antibody molecule, leading to activation of other complement components. During the activation, components known as anaphylatoxins (C3a and C5a) are released which may directly cause bronchoconstriction with respiratory impairment, and vasodilation with hypotension or shock. See also Complement; Eicosanoids.

Anaphylaxis due to IgE mechanisms has been associated with foreign proteins such as horse antitoxins, insulin, adrenocorticotropic hormone (ACTH), protamine, and chymopapain injected into herniated discs; drugs such as penicillin and its derivatives; foods such as shellfish, nuts, and eggs; and venom of stinging insects. Anaphylaxis mediated by IgG is seen in blood-transfusion reactions and following the use of cryoprecipitate, plasma, or immunoglobulin therapy.

After the identification of the inciting agent for the anaphylactic reaction, prevention is the best mode of therapy. Immunotherapy with insect venom and desensitization with certain drugs are effective prophylactic measures. Individuals with recurrent episodes of anaphylaxis, when the etiological cause is unknown and preventive measures are impractical, should be provided with epinephrine in a form that can be self-administered whenever symptoms occur. See also Epinephrine.

The treatment of anaphylaxis is aimed at reducing the effect of the chemical mediators on the end organs and preventing further mediator release. The drug of choice for this is epinephrine given subcutaneously in repeated doses. Additionally, a clear airway and appropriate oxygenation must be maintained; hypotension should be treated, as should any cardiac arrhythmia. See also Antigen-antibody reaction; Hypersensitivity; Shock syndrome.

Hypersensitivity to certain agents, resulting in pain, swelling, and feverishness. A form of anaphylaxis occurs in individuals suffering from nettle rash (urticaria) or asthma, and those who eat foods to which their bodies are allergic (see food allergy).

A condition called exercise-induced anaphylaxis is triggered in some people by combinations of exercise and particular foods. Typically, symptoms occur five minutes into a bout of intense exercise. Itching is the most common symptom, but others include rashes and difficulty in breathing. The most common food associated with exercise-induced anaphylaxis is raw celery, but other foods including shellfish, peaches, grapes, wheat, and alcohol may increase the risk of an attack. Medications, such as aspirin and antibiotics, have also been linked with the condition. In the USA, there have been over 1000 documented cases of exercise-induced anaphylaxis but no reports of death. However, other forms of anaphylaxis can be more serious (see anaphylactic shock).

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.

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 (accessed October 10, 2004).

[Article by: Judith Sims]

A condition that occurs in individuals who are hypersensitive to some substance (e.g. a bee sting) to which they have an abnormal allergic reaction. Histamine, a powerful vasodilator, is released from tissues causing either local or widespread reactions. A severe, widespread reaction can be life-threatening. It is characterized by nausea, lowered blood pressure, irregular heart beat, vomiting, and respiratory distress. See also exercise-induced anaphylaxis.

Resembling anaphylaxis, but not involving an immunological mechanism.

• a. purpura — see anaphylactoid purpura.

A violent allergic reaction characterized by sudden collapse, shock, or respiratory and circulatory failure after injection of an allergen.

• Afflictions and Conditions - anaphylaxis: acute, allergic reaction to substance to which person has been previously sensitized, resulting in faintness, palpitations, loss of color, difficulty in breathing, and shock

Anaphylaxis
Classification and external resources
Angioedema of the face such that the boy is unable to open his eyes. This reaction was due to an allergen exposure.
ICD-10	T78.2
ICD-9	995.0
DiseasesDB	29153
MedlinePlus	000844
eMedicine	med/128
MeSH	D000707

Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death".^[1] It typically results in a number of symptoms including an itchy rash, throat swelling, and low blood pressure. Common causes include insect bites, foods, and medications.

On a pathophysiologic level, anaphylaxis is due to the release of mediators from certain types of white blood cells triggered either by immunologic or non-immunologic mechanisms. It is diagnosed based on the presenting symptoms and signs. The primary treatment is injection of epinephrine, with other measures being complementary.

Worldwide 0.05–2% of people are estimated to have anaphylaxis at some point in their life and rates appear to be increasing. The term comes from the Greek words ἀνά ana, against, and φύλαξις phylaxis, protection.

Contents 1 Signs and symptoms 1.1 Skin 1.2 Respiratory 1.3 Cardiac 1.4 Other 2 Causes 2.1 Food 2.2 Medication 2.3 Venom 2.4 Risk factors 3 Pathophysiology 3.1 Immunologic 3.2 Non-immunologic 4 Diagnosis 4.1 Classification 4.2 Allergy testing 4.3 Differential diagnosis 4.4 Post-mortem findings 5 Prevention 6 Management 6.1 Epinephrine 6.2 Adjuncts 6.3 Preparedness 7 Prognosis 8 Epidemiology 9 History 10 Research 11 References 12 External links

Signs and symptoms

Signs and symptoms of anaphylaxis.

Anaphylaxis typically presents with many different symptoms over minutes or hours^[2][3] with an average onset of 5 to 30 minutes if exposure is intravenous and 2 hours for foods.^[4] The most common areas affected include: skin (80–90%), respiratory (70%), gastrointestinal (30–45%), heart and vasculature (10–45%), and central nervous system (10–15%)^[3] with usually two or more being involved.^[5]

Skin

Hives and flushing on the back of a person with anaphylaxis

Symptoms typically include generalized hives, itchiness, flushing or swelling of the lips.^[6] Those with swelling or angioedema may describe a burning sensation of the skin rather than itchiness.^[4] Swelling of the tongue or throat occurs in up to about 20% of cases.^[7] Other features may include a runny nose and swelling of the conjunctiva.^[8] The skin may also be blue tinged due to a lack of oxygen.^[8]

Respiratory

Respiratory symptoms and signs that may be present, including shortness of breath, wheezes or stridor.^[6] The wheezing is typically due to spasms of the bronchial muscles^[9] while stridor is related to upper airway obstruction secondary to swelling.^[8] Hoarseness, pain with swallowing, or a cough may also occur.^[4]

Cardiac

Coronary artery spasm may occur with subsequent myocardial infarction, dysrhythmia, or cardiac arrest.^[3][5] Those with underlying coronary disease are at greater risk of cardiac effects from anaphylaxis.^[9] The coronary spasm is related to the presence of histamine-releasing cells in the heart.^[9] While a fast heart rate due to low blood pressure is more common,^[8] a Bezold–Jarisch reflex has been described in 10% of cases, where a slow heart rate is associated with low blood pressure.^[10] A drop in blood pressure or shock (either distributive or cardiogenic) may result in the feeling of lightheadedness or loss of consciousness.^[9] Rarely very low blood pressure may be the only sign of anaphylaxis.^[7]

Other

Gastrointestinal symptoms may include crampy abdominal pain, diarrhea, and vomiting.^[6] There may be confusion, a loss of bladder control or pelvic pain similar to that of uterine cramps.^[6][8] Dilation of blood vessels around the brain may cause headaches.^[4] A feeling of anxiety or of "impending doom" has also be described.^[5]

Causes

Anaphylaxis can occur in response to almost any foreign substance.^[11] Common triggers include venom from insect bites or stings, foods, and medication.^[10][12] Foods are the most common trigger in children and young adults while medications and insect bites and stings are more common in older adults.^[5] Less common causes include: physical factors, biological agents such as semen, latex, hormonal changes, food additives such as monosodium glutamate and food colors, and topical medications.^[8] Physical factors such as exercise (known as exercise-induced anaphylaxis) or temperature (either hot or cold) may also act as triggers through their direct effects on mast cells.^[5][13] Exercise induced events are frequently associated with the ingestion of certain foods.^[4] During anesthesia, neuromuscular blocking agents, antibiotics, and latex are the most common causes.^[14] The cause remains unknown in 32-50% of cases, referred to as "idiopathic anaphylaxis".^[15]

Food

Many foods can trigger anaphylaxis; this may occur upon the first known ingestion.^[10] Common triggering foods vary around the world. In Western cultures, ingestion of or exposure to peanuts, wheat, tree nuts, shellfish, fish, milk, and eggs are the most prevalent causes.^[3][5] Sesame is common in the Middle East, while rice and chickpea are frequently encountered as sources of anaphylaxis in Asia.^[5] Severe cases are usually the result of ingesting the allergen,^[10] but some people experience a severe reaction upon contact. Children can outgrow their allergies. By age 16, 80% of children with anaphylaxis to milk or eggs and 20% who experience isolated anaphylaxis to peanuts are able to tolerate these foods.^[11]

Medication

Any medication may potentially trigger anaphylaxis. The most common are β-lactam antibiotics (such as penicillin) followed by aspirin and NSAIDs.^[3][16] Other antibiotics are implicated less frequently and the reactions to NSAIDs are agent specific meaning that if one is allergic to one NSAID they can typically tolerate a different one.^[16] Other relatively common causes include chemotherapy, vaccines, protamine and herbal preparations.^[5][16] Some medications (vancomycin, morphine, x-ray contrast among others) cause anaphylaxis by directly triggering mast cell degranulation.^[10]

The frequency of a reaction to an agent partly depends on the frequency of its use and partly on its intrinsic properties.^[17] Anaphylaxis to penicillins or cephalosporins only occurs after they bind to proteins inside the body with some agents binding more easily than other.^[4] Anaphylaxis to penicillin occurs once in every 2,000 to 10,000 courses of treatment, with death occurring in less than one in every 50,000 courses of treatment.^[4] Anaphylaxis to aspirin and NSAIDs occurs in about one in every 50,000 persons.^[4] If someone has a reaction to penicillins their risk of a reaction to cephalosporins is greater but still less than one in 1000.^[4] The old radiocontrast agents caused reactions in 1% of cases while the newer lower osmolar agents cause reactions in 0.04% of cases.^[17]

Venom

Venom from stinging or biting insects such as Hymenoptera (bees and wasps) or Triatominae (kissing bugs) may induce anaphylaxis in susceptible people.^[3][18] Previous systemic reactions, which are anything more than a local reaction around the site of the sting, are a risk factor for future anaphylaxis;^[19][20] however, half of fatalities have had no previous systemic reaction.^[21]

Risk factors

People with atopic diseases such as asthma, eczema, or allergic rhinitis are at high risk of anaphylaxis from food, latex, and radiocontrast but not injectable medications or stings.^[5][10] One study in children found that 60% had a history of previous atopic diseases, and of those who die from anaphylaxis more than 90% have asthma.^[10] Those with mastocytosis or of a higher socioeconomic status are at increased risk.^[5][10] The longer the time since the last exposure to the agent in question the lower the risk.^[4]

Pathophysiology

Anaphylaxis is a severe allergic reaction of rapid onset affecting many body systems.^[1][22] It is due to the release of inflammatory mediators and cytokines from mast cells and basophils, typically due to an immunologic reaction but sometimes non-immunologic mechanism.^[22]

Immunologic

In the immunologic mechanism, immunoglobulin E (IgE) binds to the antigen (the foreign material that provokes the allergic reaction). Antigen-bound IgE then activates FcεRI receptors on mast cells and basophils. This leads to release of inflammatory mediators such as histamine. These mediators subsequently increase the contraction of bronchial smooth muscles, trigger vasodilation, increase the leakage of fluid from blood vessels, and cause heart muscle depression.^[4][22] There is also an immunologic mechanism that does not rely on IgE, but it is not known if this occurs in humans.^[22]

Non-immunologic

Non-immunologic mechanisms involved substances that directly cause the degranulation of mast cells and basophils. These include agents such as contrast medium, opioids, temperature (hot or cold), and vibration.^[13][22]

Diagnosis

Anaphylaxis is diagnosed based on clinical criteria.^[5] When any one of the following three occurs within minutes/hours of exposure to an allergen there is a high likelihood of anaphylaxis:^[5]

1. Involvement of the skin or mucosal tissue plus either respiratory difficulty or a low blood pressure
2. Two or more of the following symptoms:-

   a. Involvement of the skin or mucosa

   b. Respiratory difficulties

   c. Low blood pressure

   d. Gastrointestinal symptoms

3. Low blood pressure after exposure to a known allergen

During an attack, blood tests for tryptase or histamine (released from mast cells) might be useful in diagnosing anaphylaxis due to insect stings or medications. However these tests are of limited utility if the cause is food or if the person has a normal blood pressure,^[5] and they are not specific for the diagnosis.^[11]

Classification

There are three main classifications of anaphylaxis. Anaphylactic shock is associated with systemic vasodilation that results in low blood pressure which is by definition 30% lower than the person's baseline or below standard values.^[7] Biphasic anaphylaxis is the recurrence of symptoms within 1–72 hours with no further exposure to the allergen.^[5] Reports of incidence vary, with some studies claiming as many as 20% of cases.^[23] The recurrence typically occurs within 8 hours.^[10] It is managed in the same manner as anaphylaxis.^[3] Pseudoanaphylaxis or anaphylactoid reactions are a type of anaphylaxis that does not involve an allergic reaction but is due to direct mast cell degranulation.^[10][24] Non-immune anaphylaxis is the current term use by the World Allergy Organization^[24] with some recommending that the old terminology no longer be used.^[10]

Allergy testing

Skin allergy testing being carried out on the right arm

Allergy testing may help in determining the trigger. Skin allergy testing (such as patch testing) is available for certain foods and venoms.^[11] Blood testing for specific IgE can be useful to confirm milk, egg, peanut, tree nut and fish allergies.^[11] Skin testing is available to confirm penicillin allergies but is not available for other medications.^[11] Non-immune forms of anaphylaxis can only be determined by history or exposure to the allergen in question, and not by skin or blood testing.^[24]

Differential diagnosis

It can sometimes be difficult to distinguish anaphylaxis from asthma, syncopy, and panic attacks.^[5] Asthma however typically does not have itching or gastrointestinal symptoms, syncope presents with pallor rather than a rash, and a panic attack may have flushing but does not have hives.^[5] Other conditions that may present similarly include: scrombroidosis and anisakiasis.^[10]

Post-mortem findings

In a person who died from anaphylaxis, autopsy may show an "empty heart" attributed to reduced venous return from vasodilation and redistribution of intravascular volume from the central to the peripheral compartment.^[25] Other signs are laryngeal edema, eosinophilia in lungs, heart and tissues, and evidence of myocardial hypoperfusion.^[26] Laboratory findings could detect increased levels of serum tryptase, increase in total and specific IgE serum levels.^[26]

Prevention

Avoidance of the trigger of anaphylaxis is recommended. In cases where this may not be possible, desensitization may be an option. Immunotherapy with Hymenoptera venoms is effective at desensitizing 80–90% of adults and 98% of children against allergies to bees, wasps, hornets, yellowjackets, and fire ants. Oral immunotherapy may be effective at desensitizing some people to certain food including milk, eggs, nuts and peanuts; however adverse effects are common. Desensitization is also possible for many medications, however it is advised that most people simply avoid the agent in question. In those who react to latex it may be important to avoid cross-reactive foods such as avocados, bananas, and potatoes among others.^[5]

Management

Anaphylaxis is a medical emergency that may require resuscitation measures such as airway management, supplemental oxygen, large volumes of intravenous fluids, and close monitoring.^[3] Administration of epinephrine is the treatment of choice with antihistamines and steroids often used as adjuncts.^[5] A period of in hospital observation for between 2 and 24 hours is recommended for people once they have returned to normal due to concerns of biphasic anaphylaxis.^{[10][23][27][4]}

Epinephrine

An old version of an EpiPen auto-injector

Epinephrine (adrenaline) is the primary treatment for anaphylaxis with no absolute contraindication to its use.^[3] It is recommended that an epinephrine solution be given intramuscularly into the mid anterolaterial thigh as soon as the diagnosis is suspected. The injection may be repeated every 5 to 15 minutes if there is insufficient response.^[5] A second dose is needed in 16 to 35% of episodes^[10] with more than two doses rarely required.^[5] The intramuscular route is preferred over subcutaneous administration because the latter may have delayed absorption.^[28] Minor adverse effects from epinephrine include tremors, anxiety, headaches, and palpitations.^[5]

People on β-blockers may be resistant to the effects of epinephrine.^[10] In this situation if epinephrine is not effective intravenous glucagon can be administered which has a mechanism of action independent of β-receptors.^[10]

If necessary, it can also be given intravenously using a dilute epinephrine solution. Intravenous epinephrine however has been associated both with dysrhythmia and myocardial infarction.^[29] Epinephrine autoinjector used for self-administration typically in two doses, one for adults or children who weight more than 25 kg and one for children who weigh 10 to 25 kg.^[30]

Adjuncts

Antihistamines (both H1 and H2), while commonly used and assumed effective based on theoretical reasoning, are poorly supported by evidence. A 2007 Cochrane review did not find any good-quality studies upon which to base recommendations^[31] and they are not believed to have an effect on airway edema or spasm.^[10] Corticosteroids are unlikely to make a difference in the current episode of anaphylaxis, but may be used in the hope of decreasing the risk of biphasic anaphylaxis. Their prophylactic effectiveness in these situations is uncertain.^[23] Nebulized salbutamol may be effective for bronchospasm that does not resolve with epinephrine.^[10] Methylene blue has been used in those not responsive to other measures due to its presumed effect of relaxing smooth muscle.^[10]

Preparedness

People prone to anaphylaxis are advised to have an "allergy action plan", and parents are advised to inform schools of their children's allergies and what to do in case of an anaphylactic emergency.^[32] The action plan usually includes use of epinephrine auto-injectors, the recommendation to wear a medical alert bracelet, and counseling on avoidance of triggers.^[32] Immunotherapy is available for certain triggers to prevent future episodes of anaphylaxis. A multi-year course of subcutaneous desensitization has been found effective against stinging insects, while oral desensitization is effective for many foods.^[3]

Prognosis

In those in whom the cause is known and prompt treatment is available, the prognosis is good.^[33] Even if the cause is unknown, if appropriate preventative medication is available, the prognosis is generally good.^[4] If death occurs, it is usually due to either respiratory (typically asphyxia) or cardiovascular causes (shock),^[10][22] with 0.7–20% of cases resulting in death.^[4][9] There have been cases of death occurring within minutes.^[5] Outcomes in those with exercise-induced anaphylaxis are typically good, with fewer and less severe episodes as people get older.^[34]

Epidemiology

The incidence of anaphylaxis is 4–5 per 100,000 persons per year,^[10] with a lifetime risk of 0.5–2%.^[5] Rates appear to be increasing: incidence in the 1980s was approximately 20 per 100,000 per year, while in the 1990s it was 50 per 100,000 per year.^[3] The increase appears to be primarily for food-induced anaphylaxis.^[35] The risk is greatest in young people and females.^[3][10]

Currently, anaphylaxis leads to 500–1,000 deaths per year (2.4 per million) in the United States, 20 deaths per year in the United Kingdom (0.33 per million), and 15 deaths per year in Australia (0.64 per million).^[10] Mortality rates have decreased between the 1970s and 2000s.^[36] In Australia, death from food-induced anaphylaxis occur primarily in women while deaths due to insect bites primarily occur in males.^[10] Death from anaphylaxis is most commonly triggered by medications.^[10]

History

The term "aphylaxis" was coined by Charles Richet in 1902 and later changed to "anaphylaxis" due to its nicer quality of speech.^[11] He was subsequently awarded the Nobel Prize in Medicine and Physiology for his work on anaphylaxis in 1913.^[4] The phenomenon itself however has been described since ancient times.^[24] The term comes from the Greek words ἀνά ana, against, and φύλαξις phylaxis, protection.^[37]

Research

There are ongoing efforts to develop sublingual epinephrine to treat anaphylaxis.^[10] Subcutaneous injection of the anti-IgE antibody omalizumab is being studied as a method of preventing recurrence, but it is not yet recommended.^[5][38]

References

1. ^ ^{a b} Tintinalli, Judith E. (2010). Emergency Medicine: A Comprehensive Study Guide (Emergency Medicine (Tintinalli)). New York: McGraw-Hill Companies. pp. 177–182. ISBN 0-07-148480-9. 
2. ^ Oswalt ML, Kemp SF (May 2007). "Anaphylaxis: office management and prevention". Immunol Allergy Clin North Am 27 (2): 177–91, vi. doi:10.1016/j.iac.2007.03.004. PMID 17493497. "Clinically, anaphylaxis is considered likely to be present if any one of three criteria is satisfied within minutes to hours" 
3. ^ ^{a b c d e f g h i j k l} Simons FE (October 2009). "Anaphylaxis: Recent advances in assessment and treatment". J. Allergy Clin. Immunol. 124 (4): 625–36; quiz 637–8. doi:10.1016/j.jaci.2009.08.025. PMID 19815109. https://secure.muhealth.org/~ed/students/articles/JAClinImmun_124_p0625.pdf. 
4. ^ ^{a b c d e f g h i j k l m n o} Marx, John (2010). Rosen's emergency medicine: concepts and clinical practice 7th edition. Philadelphia, PA: Mosby/Elsevier. p. 15111528. ISBN 978-0-323-05472-0. 
5. ^ ^{a b c d e f g h i j k l m n o p q r s t u v w x} Simons, FE; World Allergy, Organization (2010 May). "World Allergy Organization survey on global availability of essentials for the assessment and management of anaphylaxis by allergy-immunology specialists in health care settings.". Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology 104 (5): 405–12. doi:10.1016/j.anai.2010.01.023. PMID 20486330. http://www.csaci.ca/include/files/WAO_Anaphylaxis_Guidelines_2011.pdf. 
6. ^ ^{a b c d} Sampson HA, Muñoz-Furlong A, Campbell RL, et al. (February 2006). "Second symposium on the definition and management of anaphylaxis: summary report—Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium". J. Allergy Clin. Immunol. 117 (2): 391–7. doi:10.1016/j.jaci.2005.12.1303. PMID 16461139. 
7. ^ ^{a b c} Limsuwan, T; Demoly, P (2010 Jul). "Acute symptoms of drug hypersensitivity (urticaria, angioedema, anaphylaxis, anaphylactic shock).". The Medical clinics of North America 94 (4): 691–710, x. doi:10.1016/j.mcna.2010.03.007. PMID 20609858. http://smschile.cl/documentos/cursos2010/MedicalClinicsNorthAmerica/Acute%20Symptoms%20of%20Drug%20Hypersensitivity%20(Urticaria,%20Angioedema,%20Anaphylaxis,%20Anaphylactic%20Shock).pdf. 
8. ^ ^{a b c d e f} Brown, SG; Mullins, RJ, Gold, MS (2006 Sep 4). "Anaphylaxis: diagnosis and management.". The Medical journal of Australia 185 (5): 283–9. PMID 16948628. 
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10. ^ ^{a b c d e f g h i j k l m n o p q r s t u v w x y z} Lee, JK; Vadas, P (2011 Jul). "Anaphylaxis: mechanisms and management.". Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology 41 (7): 923–38. doi:10.1111/j.1365-2222.2011.03779.x. PMID 21668816. 
11. ^ ^{a b c d e f g} Boden, SR; Wesley Burks, A (2011 Jul). "Anaphylaxis: a history with emphasis on food allergy.". Immunological reviews 242 (1): 247–57. doi:10.1111/j.1600-065X.2011.01028.x. PMID 21682750. 
12. ^ Worm, M (2010). "Epidemiology of anaphylaxis.". Chemical immunology and allergy 95: 12–21. doi:10.1159/000315935. PMID 20519879. 
13. ^ ^{a b} editors, Marianne Gausche-Hill, Susan Fuchs, Loren Yamamoto, (2007). The pediatric emergency medicine resource (Rev. 4. ed. ed.). Sudbury, Mass.: Jones & Bartlett. pp. 69. ISBN 978-0-7637-4414-4. http://books.google.ca/books?id=lLVfDC2dh54C&pg=PA69. 
14. ^ Dewachter, P; Mouton-Faivre, C, Emala, CW (2009 Nov). "Anaphylaxis and anesthesia: controversies and new insights.". Anesthesiology 111 (5): 1141–50. doi:10.1097/ALN.0b013e3181bbd443. PMID 19858877. 
15. ^ editor, Mariana C. Castells, (2010). Anaphylaxis and hypersensitivity reactions. New York: Humana Press. pp. 223. ISBN 978-1-60327-950-5. http://books.google.ca/books?id=bEvnfm7V-LIC&pg=PA223. 
16. ^ ^{a b c} Volcheck, Gerald W. (2009). Clinical allergy : diagnosis and management. Totowa, N.J.: Humana Press. pp. 442. ISBN 978-1-58829-616-0. http://books.google.ca/books?id=pWZLkZB7EW8C&pg=PA442. 
17. ^ ^{a b} Drain, KL; Volcheck, GW (2001). "Preventing and managing drug-induced anaphylaxis.". Drug safety : an international journal of medical toxicology and drug experience 24 (11): 843–53. PMID 11665871. 
18. ^ Klotz, JH; Dorn, PL, Logan, JL, Stevens, L, Pinnas, JL, Schmidt, JO, Klotz, SA (2010 Jun 15). ""Kissing bugs": potential disease vectors and cause of anaphylaxis.". Clinical infectious diseases : an official publication of the Infectious Diseases Society of America 50 (12): 1629–34. doi:10.1086/652769. PMID 20462351. 
19. ^ Bilò, MB (2011 Jul). "Anaphylaxis caused by Hymenoptera stings: from epidemiology to treatment.". Allergy 66 Suppl 95: 35–7. doi:10.1111/j.1398-9995.2011.02630.x. PMID 21668850. 
20. ^ Cox, L; Larenas-Linnemann, D, Lockey, RF, Passalacqua, G (2010 Mar). "Speaking the same language: The World Allergy Organization Subcutaneous Immunotherapy Systemic Reaction Grading System.". The Journal of allergy and clinical immunology 125 (3): 569–74, 574.e1-574.e7. doi:10.1016/j.jaci.2009.10.060. PMID 20144472. 
21. ^ Bilò, BM; Bonifazi, F (2008 Aug). "Epidemiology of insect-venom anaphylaxis.". Current opinion in allergy and clinical immunology 8 (4): 330–7. doi:10.1097/ACI.0b013e32830638c5. PMID 18596590. 
22. ^ ^{a b c d e f} Khan, BQ; Kemp, SF (2011 Aug). "Pathophysiology of anaphylaxis.". Current opinion in allergy and clinical immunology 11 (4): 319–25. doi:10.1097/ACI.0b013e3283481ab6. PMID 21659865. 
23. ^ ^{a b c} Lieberman P (September 2005). "Biphasic anaphylactic reactions". Ann. Allergy Asthma Immunol. 95 (3): 217–26; quiz 226, 258. doi:10.1016/S1081-1206(10)61217-3. PMID 16200811. 
24. ^ ^{a b c d} Ring, J; Behrendt, H, de Weck, A (2010). "History and classification of anaphylaxis.". Chemical immunology and allergy 95: 1–11. doi:10.1159/000315934. PMID 20519878. http://media.wiley.com/product_data/excerpt/42/04708611/0470861142.pdf. 
25. ^ Anaphylaxis, Author: Stephen F Kemp, MD, FACP; Chief Editor: Michael A Kaliner, MD;http://emedicine.medscape.com/article/135065-overview#showall
26. ^ ^{a b} Da Broi, U; Moreschi, C (2011 Jan 30). "Post-mortem diagnosis of anaphylaxis: A difficult task in forensic medicine.". Forensic Science International 204 (1-3): 1–5. doi:10.1016/j.forsciint.2010.04.039. PMID 20684869. 
27. ^ "Emergency treatment of anaphylactic reactions – Guidelines for healthcare providers" (PDF). Resuscitation Council (UK). January 2008. http://www.resus.org.uk/pages/reaction.pdf. Retrieved 2008-04-22. 
28. ^ Simons, KJ; Simons, FE (2010 Aug). "Epinephrine and its use in anaphylaxis: current issues.". Current opinion in allergy and clinical immunology 10 (4): 354–61. doi:10.1097/ACI.0b013e32833bc670. PMID 20543673. 
29. ^ Mueller, UR (2007 Aug). "Cardiovascular disease and anaphylaxis.". Current opinion in allergy and clinical immunology 7 (4): 337–41. doi:10.1097/ACI.0b013e328259c328. PMID 17620826. 
30. ^ Sicherer, SH; Simons, FE, Section on Allergy and Immunology, American Academy of, Pediatrics (2007 Mar). "Self-injectable epinephrine for first-aid management of anaphylaxis.". Pediatrics 119 (3): 638–46. doi:10.1542/peds.2006-3689. PMID 17332221. 
31. ^ Sheikh A, Ten Broek V, Brown SG, Simons FE (August 2007). "H1-antihistamines for the treatment of anaphylaxis: Cochrane systematic review". Allergy 62 (8): 830–7. doi:10.1111/j.1398-9995.2007.01435.x. PMID 17620060. 
32. ^ ^{a b} Martelli, A; Ghiglioni, D, Sarratud, T, Calcinai, E, Veehof, S, Terracciano, L, Fiocchi, A (2008 Aug). "Anaphylaxis in the emergency department: a paediatric perspective.". Current opinion in allergy and clinical immunology 8 (4): 321–9. doi:10.1097/ACI.0b013e328307a067. PMID 18596589. 
33. ^ Harris, edited by Jeffrey; Weisman, Micheal S. (2007). Head and neck manifestations of systemic disease. London: Informa Healthcare. pp. 325. ISBN 978-0-8493-4050-5. http://books.google.ca/books?id=31yUl-V90XoC&pg=PA325. 
34. ^ editor, Mariana C. Castells, (2010). Anaphylaxis and hypersensitivity reactions. New York: Humana Press. pp. 223. ISBN 978-1-60327-950-5. http://books.google.ca/books?id=bEvnfm7V-LIC&pg=PA223. 
35. ^ Koplin, JJ; Martin, PE, Allen, KJ (2011 Oct). "An update on epidemiology of anaphylaxis in children and adults.". Current opinion in allergy and clinical immunology 11 (5): 492–6. doi:10.1097/ACI.0b013e32834a41a1. PMID 21760501. 
36. ^ Demain, JG; Minaei, AA, Tracy, JM (2010 Aug). "Anaphylaxis and insect allergy.". Current opinion in allergy and clinical immunology 10 (4): 318–22. doi:10.1097/ACI.0b013e32833a6c72. PMID 20543675. 
37. ^ "anaphylaxis". merriam-webster.com. http://www.merriam-webster.com/dictionary/anaphylaxis. Retrieved 2009-11-21. 
38. ^ Vichyanond, P (2011 Sep). "Omalizumab in allergic diseases, a recent review.". Asian Pacific journal of allergy and immunology / launched by the Allergy and Immunology Society of Thailand 29 (3): 209–19. PMID 22053590. 

External links

Wikimedia Commons has media related to: Anaphylaxis

• Anaphylaxis at the Open Directory Project

v t e Consequences of external causes (T66–T78, 990–995) Temperature/radiation elevated temperature: Hyperthermia · Heat syncope reduced temperature: Hypothermia · Immersion foot syndromes (Trench foot • Tropical immersion foot • Warm water immersion foot) · Chilblains · Frostbite · Cold intolerance • Acrocyanosis • Erythrocyanosis crurum radiation: Radiation poisoning · Radiation burn · Chronic radiation keratosis • Eosinophilic, polymorphic, and pruritic eruption associated with radiotherapy • Radiation acne • Radiation cancer • Radiation recall reaction • Radiation-induced erythema multiforme • Radiation-induced hypertrophic scar • Radiation-induced keloid • Radiation-induced morphea Air Hypoxia/Asphyxia · Barotrauma (Aerosinusitis, Decompression sickness) · High altitude (Altitude sickness/Chronic mountain sickness, HAPE) Food Starvation Maltreatment Physical abuse · Sexual abuse · Psychological abuse Emesis Motion sickness · Seasickness · Airsickness · Space adaptation syndrome Adverse effect Hypersensitivity (Anaphylaxis, Angioedema, Allergy, Arthus reaction) Adverse drug reaction Other Electric shock · Drowning · Lightning injury Ungrouped skin conditions resulting from physical factors Dermatosis neglecta • Pinch mark • Pseudoverrucous papules and nodules • Sclerosing lymphangiitis • Tropical anhidrotic asthenia  • UV-sensitive syndrome environmental skin conditions: Electrical burn • frictional/traumatic/sports (Black heel and palm • Equestrian perniosis • Jogger's nipple • Pulling boat hands • Runner's rump • Surfer's knots • Tennis toe • Vibration white finger • Weathering nodule of ear • Wrestler's ear • Coral cut  • Painful fat herniation ) • Uranium dermatosis iv use (Skin pop scar • Skin track • Slap mark • Pseudoacanthosis nigricans • Narcotic dermopathy)

v t e Immune disorders: hypersensitivity and autoimmune diseases (279.5–6) Type I/allergy/atopy (IgE) Foreign Atopic dermatitis · Allergic urticaria · Hay fever · Allergic asthma · Anaphylaxis · Food allergy (Milk, Egg, Peanut, Tree nut, Seafood, Soy, Wheat), Penicillin allergy Autoimmune none Type II/ADCC (IgM, IgG) Foreign Pernicious anemia · Hemolytic disease of the newborn Autoimmune Cytotoxic Autoimmune hemolytic anemia · Idiopathic thrombocytopenic purpura  · Bullous pemphigoid  · Pemphigus vulgaris · Rheumatic fever · Goodpasture's syndrome "Type 5"/receptor Graves' disease · Myasthenia gravis Type III (Immune complex) Foreign Henoch–Schönlein purpura · Hypersensitivity vasculitis · Reactive arthritis · Farmer's lung · Post-streptococcal glomerulonephritis · Serum sickness · Arthus reaction Autoimmune Systemic lupus erythematosus · Subacute bacterial endocarditis · Rheumatoid arthritis Type IV/cell-mediated (T-cells) Foreign Allergic contact dermatitis · Mantoux test Autoimmune Diabetes mellitus type 1 · Hashimoto's thyroiditis · Guillain–Barré syndrome  · Multiple sclerosis  · Coeliac disease · Giant-cell arteritis GVHD Transfusion-associated graft versus host disease Unknown/ multiple Foreign Hypersensitivity pneumonitis (Allergic bronchopulmonary aspergillosis) · Transplant rejection · Latex allergy (I+IV) Autoimmune Sjögren's syndrome · Autoimmune hepatitis · Autoimmune polyendocrine syndrome (APS1, APS2) · Autoimmune adrenalitis · Systemic autoimmune disease M: LMC cell/phys/auag/auab/comp, igrc imdf/ipig/hyps/tumr proc, drug(L3/4)

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