Anaphylaxis

Anaphylaxis

Definition

Anaphylaxis is a severe allergic reaction to a trigger (most commonly a

food, medication, insect sting, or latex) that involves most major body

systems.

Description

Anaphylaxis is a reaction that occurs in people who are severely allergic to

certain foods or other substances. People with individual or family histories

of hay fever, asthma, eczema, or food allergies are at increased risk

of having an anaphylactic reaction at some point in their lives. People

with asthma are particularly likely to have an anaphylactic reaction to

food at some point. Anaphylaxis is an overreaction to an allergen caused

by the body

IgE. When a person who is susceptible to allergies first comes into contact

with an allergen, the person

that are specific to that allergen. The IgE antibodies then attach

themselves to the surface of mast cells, which are specialized cells that lie

within the connective tissue near the blood vessels. The next time the

person encounters that specific allergen, the IgE antibodies trigger the

release of a compound called histamine from the mast cells. The histamine

in turn causes the tissue swelling, difficult breathing, and other

symptoms of anaphylaxis.

Some people have a recurrence of symptoms about six to eight hours

after an episode of anaphylaxis. This recurrence is called a biphasic or

delayed reaction.

Some substances are more likely to trigger anaphylactic reactions

than others. The most common triggers are:

•

sensitive to it; however, peanuts, nuts from trees (walnuts, cashews,

and Brazil nuts), shellfish, fish, milk, and eggs are the most common

offenders.

Foods. Almost any food can cause anaphylaxis in persons who are

•

and fire ants are the most likely to cause anaphylactic reactions.

Stinging insects. Yellow jackets, honeybees, paper wasps, hornets,

•

penicillin and other antibiotics; antiseizure medicines; fluids given

after surgery; antibodies made from horse serum; blood and blood

products; radiocontrast dyes used in certain types of imaging studies;

and morphine or similar pain medications.

Medications. The drugs most likely to cause problems include

•

often used to make surgical gloves and other medical products.

The greatest danger of anaphylaxis caused by latex occurs when the

rubber material touches moist areas of the body or internal surfaces

during surgery, because the allergen in latex can be absorbed by the

body much more quickly.

•

when they exercise within a few hours

of eating certain foods.

Exercise. Some people develop anaphylaxis

•

semen, hormones, and extreme temperatures

have been reported to trigger anaphylaxis

in some people.

Other causes. Although such cases are rare,

Demographics

The exact number of cases of anaphylaxis in the

United States each year is unknown, partly

because some doctors use the term to refer to relatively

mild allergic reactions while others use it to

describe only those severe enough to be considered

life-threatening. About 30,000 people are

taken to hospital emergency rooms with an anaphylactic

reaction in an average year. A commonly

cited statistic is that about 15 percent of the general

population is at risk of anaphylaxis, with

one percent of the population at specific risk

of anaphylaxis caused by medications and

another one percent allergic to latex. It is estimated

that there are between 500 and 1,000

deaths from anaphylaxis each year in the

United States; fifty of these deaths are caused

by insect stings. People of all races, both sexes,

and all age groups are equally at risk of anaphylaxis.

Elderly people, however, are more likely

than younger people to die from anaphylaxis because they often suffer

from other diseases or medical conditions. Research conducted at Harvard

in 2007 suggests that there may be geographical differences in the

rates of anaphylaxis in the United States, with a higher proportion of

cases in the Northeast and lower rates in the West and South. The

researchers are not certain of the reasons for these differences, however.

Causes and Symptoms

Anaphylaxis results from the release of histamine from mast cells in

response to the presence of an allergen. Histamine causes the blood vessels

to dilate (expand), which lowers blood pressure. It also causes fluid to leak

from the bloodstream into the tissues, which in turn causes the itchy skin

swellings known as hives, and also lowers blood volume. These effects can

lead to shock. Fluid can also leak into the air sacs in the lungs and make it

difficult to breathe. Angioedema, or hivelike swelling of the tissues around

the eyes or in the throat and mouth, can be severe enough to block the

patient

Anaphylaxis is considered a whole-body allergic reaction because so

many different body systems can be affected:

’s airway.

•

Skin: hives, angioedema, redness, itching, rash

•

diarrhea, itchy mouth or throat

Digestive tract: nausea, abdominal pain or cramping, vomiting,

•

dizzy or lightheaded, low blood pressure, loss of consciousness,

shock

Circulation: pale or bluish skin color, weak or rapid pulse, feeling

•

difficulty talking, chest pain or tightness, nasal congestion, trouble

swallowing

Breathing: wheezing, shortness of breath, throat tightness, cough,

•

Psychological: panic, feelings of doom, intense anxiety

Diagnosis

Diagnosis of anaphylaxis is based on the patient

cases, particularly if the reaction is sudden. In many cases it will be

obvious either from the patient

what triggered the reaction. The doctor or emergency crew will

usually take the patient

administer adrenaline (epinephrine), a hormone that counteracts the

effects of histamine. The patient

life support given until they can be taken to the hospital.

’s symptoms in most’s description or from friends or bystanders’s pulse, check breathing and blood pressure, and’s heart rate will be monitored and basic

Treatment

Treatment of anaphylaxis before the patient is taken to the hospital

usually consists of checking to see whether the patient

and administering oxygen or otherwise helping the patient breathe. Intravenous

fluids are given if the patient

and antihistamines are also given to help open the airway, relieve hives

and other skin reactions, and restore normal blood pressure. Once in the

hospital, the patient may be given further treatment, including emergency

surgery to open the airway if he or she is still having trouble

breathing. Steroid medications may be given in the hospital to lower the

risk of a delayed or biphasic reaction, and the patient will usually be kept

in the hospital for a few hours to make sure there will not be such a reaction

after returning home.

Prognosis

The prognosis for anaphylaxis is very good if the person carries and uses

an EpiPen or similar device, or receives prompt emergency treatment. In

some cases, however, people die from low blood pressure, shock, or cardiac

arrest. The elderly are at higher risk for death from anaphylaxis.

Prevention

People who have had a severe allergic reaction even once should consult

an allergist for evaluation and advice about preventive measures. This

precaution is particularly important if the patient does not know what

caused the anaphylaxis. The allergist can determine the patient

prescribe an EpiPen or TwinJect for self-treatment, advise the patient

about any medications that may increase the risk of anaphylaxis, and in

some cases give the patient allergy shots to decrease sensitivity to insect

stings or antibiotic medications. Other preventive measures that people

can take include: Wear a MedicAlert or similar tag that identifies the

allergy for bystanders or emergency rescuers. Learn to read food labels

carefully and asking restaurant staff about food ingredients when eating

out. Lower the risk of insect stings by wearing long-sleeved clothing and

avoiding bright colors and perfumes that attract insects. Be careful when

drinking sweetened beverages outdoors. Avoid walking barefoot in the

grass. If stinging insects appear, stay calm and avoid slapping or swatting

at them; move away from them slowly.

’s triggers,

The Future

Experts believe that the number of anaphylactic reactions in the United

States will rise in the future because of the increased number of potential

allergens to which people are exposed.

SEE ALSO Asthma; Eczema; Hay fever; Hives’s airway is open’s blood pressure is low. AdrenalineLatex. Latex is a natural material made from the rubber tree that is’s production of an antibody called immunoglobulin E or’s immune system produces IgE antibodies