Anaphylaxis is a severe allergic reaction to a trigger (most commonly a food, medication, insect sting, or latex) that involves most major body systems.
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's production of an antibody called immunoglobulin E or IgE. When a person who is susceptible to allergies first comes into contact with an allergen, the person's immune system produces IgE antibodies 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 hista-mine 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:
- Foods. Almost any food can cause anaphylaxis in persons who are sensitive to it; however, peanuts, nuts from trees (walnuts, cashews, and Brazil nuts), shellfish, fish, milk, and eggs are the most common offenders.
- Stinging insects. Yellow jackets, honeybees, paper wasps, hornets, and fire ants are the most likely to cause anaphylactic reactions.
- Medications. The drugs most likely to cause problems include 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.
- Latex. Latex is a natural material made from the rubber tree that is 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.
- Exercise. Some people develop anaphylaxis when they exercise within a few hours of eating certain foods.
- Other causes. Although such cases are rare, semen, hormones, and extreme temperatures have been reported to trigger anaphylaxis in some people.
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.
First Aid for Anaphylaxis
There are several steps that friends or bystanders can take if they see someone having an episode of anaphylaxis:
- Call 911 at once for emergency help.
- Check the person to see whether he or she is carrying an EpiPen or similar device for emergency treatment of anaphylaxis. If so, administer the medicine at once.
- Have the person lie flat on his or her back and raise the feet above heart level.
- Try to keep the person calm, as moving unnecessarily or getting panicky can make the anaphylactic reaction worse.
- Cover the person with a blanket to keep warm but do not give him or her anything to drink.
- If the person is vomiting or bleeding from the mouth, gently turn him or her on one side to prevent choking.
- If possible, find out what triggered the reaction and tell the emergency helpers when they arrive.
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'sairway.
Anaphylaxis is considered a whole-body allergic reaction because so many different body systems can be affected:
- Skin: hives, angioedema, redness, itching, rash
- Digestive tract: nausea, abdominal pain or cramping, vomiting, diarrhea, itchy mouth or throat
- Circulation: pale or bluish skin color, weak or rapid pulse, feeling dizzy or lightheaded, low blood pressure, loss of consciousness, shock
- Breathing: wheezing, shortness of breath, throat tightness, cough, difficulty talking, chest pain or tightness, nasal congestion, trouble swallowing
- Psychological: panic, feelings of doom, intense anxiety
Diagnosis of anaphylaxis is based on the patient's symptoms in most cases, particularly if the reaction is sudden. In many cases it will be obvious either from the patient's description or from friends or bystanders what triggered the reaction. The doctor or emergency crew will usually take the patient's pulse, check breathing and blood pressure, and administer adrenaline (epinephrine), a hormone that counteracts the effects of histamine. The patient's heart rate will be monitored and basic life support given until they can be taken to the hospital.
Treatment of anaphylaxis before the patient is taken to the hospital usually consists of checking to see whether the patient's airway is open and administering oxygen or otherwise helping the patient breathe. Intravenous fluids are given if the patient's blood pressure is low. Adrenaline 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.
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.
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's triggers, 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.
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
WORDS TO KNOW
Adrenaline: A hormone that can be used in medicine to open the breathing passages in patients with severe angioedema. It is also called epinephrine.
Allergen: Any substance that can provoke an allergic reaction in susceptible individuals.
Angioedema: The medical term for the swelling of tissues around the eyes, lips, and genitals that sometimes accompanies hives.
Biphasic reaction: A recurrence of the symptoms of anaphylaxis about six to eight hours after the first episode.
Histamine: A compound contained in mast cells that is released during an allergic reaction.
Mast cells: Specialized white blood cells that are found in connective tissue and contain histamine.
Shock: A medical emergency in which there is a drop in blood pressure and a reduced volume of blood circulating in the body.
Jevon, Philip. Anaphylaxis: A Practical Guide. Edinburgh, UK: Butterworth-Heinemann, 2004.
Nagourney, Eric. “Patterns: An Allergic Reaction May Be Tied to Geography.” New York Times, July 17, 2007. Available online at http://www.nytimes.com/2007/07/17/health/17patt.html (accessed May 16, 2008). This is an article about the higher rates of anaphylaxis in the Northeast than in the South or West.
Ray, C. Claiborne. “The Fatal Peanut.” New York Times, December 27, 2005. Available online at http://www.nytimes.com/2005/12/27/science/27qna.html?_r=1&oref=slogin (accessed May 16, 2008). This is a brief question-and-answer column about anaphylaxis and peanut allergy.
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TeensHealth. “Serious Allergic Reactions (Anaphylaxis).”Available online at http://www.kidshealth.org/teen/safety/first_aid/anaphylaxis.html (updated January 2008; accessed May 16, 2008).