What is it?

• Anaphylaxis is a severe, potentially life-threatening allergic reaction. It can occur within seconds or minutes of exposure to something you're allergic to, such as the venom from a bee sting or a peanut.
• The flood of chemicals released by your immune system during anaphylaxis can cause you to go into shock; your blood pressure drops suddenly and your airways narrow, blocking normal breathing. Signs and symptoms of anaphylaxis include a rapid, weak pulse, skin rash, and nausea and vomiting. Common triggers of anaphylaxis include certain foods, some medications, insect venom and latex.
• Anaphylaxis requires an immediate trip to accident and emergency, and an injection of epinephrine. If anaphylaxis isn't treated right away, it can lead to unconsciousness or even death.

Symptoms

An anaphylactic reaction is most likely to occur in susceptible people who've been stung by an insect, eaten something they're allergic to, or taken a medication that they are sensitive to. Even if you've only had a mild allergic reaction in the past, you still may be at risk of anaphylaxis.

Anaphylaxis symptoms usually occur within minutes of exposure to an allergen. In rare cases, anaphylaxis occurs more than half an hour after exposure. Anaphylaxis symptoms include:

• Skin reactions including hives and itching, flushed or pale skin (almost always present with anaphylaxis)
• Constriction of the airways and a swollen tongue or throat, which can cause wheezing and trouble breathing
• A weak and rapid pulse
• Nausea, vomiting or diarrhoea
• Dizziness or fainting

Causes

Your immune system produces antibodies that defend against foreign substances. This is good when a foreign substance is harmful (such as a bacterium or virus). But some people's immune systems overreact to substances that shouldn't cause an allergic reaction. When this occurs, your immune system sets off a chemical chain reaction, leading to allergy symptoms. In most people, allergy symptoms are not life-threatening. But some people have a severe allergic reaction that can lead to anaphylaxis.

A number of allergens can trigger anaphylaxis, depending on what you're allergic to.

Common anaphylaxis triggers include:

• Certain medications, especially penicillin
• Foods such as peanuts, tree nuts (walnuts, pecans), fish, shellfish, milk and eggs
• Insect stings from bees, yellow jackets, wasps, hornets and fire ants

Less common causes of anaphylaxis include:

• Latex
• Muscle relaxants used in general anesthesia
• Exercise

Anaphylaxis triggered by exercise varies from person to person. In some people, aerobic activity such as jogging triggers anaphylaxis. In others, less intense physical activity such as yard work can trigger a reaction. Eating certain foods before exercise or exercising when the weather is hot, cold or humid has also been linked to anaphylaxis in some people.

Anaphylaxis symptoms are sometimes caused by aspirin, other nonsteroidal anti-inflammatory drugs — such as ibuprofen and naproxen— and the intravenous (IV) contrast used in some X-ray imaging tests. Although similar to allergy-induced anaphylaxis, this type of reaction isn't triggered by allergy antibodies.

If you don't know what triggers your allergy attack, your doctor may do tests to try to identify the offending allergen. In some cases, the cause of anaphylaxis is never identified. This is known as idiopathic anaphylaxis.

How is anaphylaxis Diagnosed?

Your doctor will ask you questions about your allergies or any previous allergic reactions you've had. This evaluation will include questions about:

• Whether any particular foods seem to cause a reaction
• Any medications you take, and if certain medications seem linked to your symptoms
• Whether you've had allergy symptoms when your skin has been exposed to latex
• Whether stings from any particular type of insect seem to cause your symptoms

To help confirm the diagnosis:

• You may be tested for allergies with skin tests or blood tests
• You may also be asked to keep a detailed list of what you eat or to stop eating certain foods for a time

How do you treat anaphylaxis?

During an anaphylactic attack, an emergency medical team may perform cardiopulmonary resuscitation (CPR) if you stop breathing or your heart stops beating. You may be given medications including:

• Epinephrine (adrenaline) to reduce your body's allergic response
• Oxygen, to help compensate for restricted breathing
• Intravenous (IV) antihistamines and cortisone to reduce inflammation of your air passages and improve breathing
• A beta agonist (such as ventolin) to relieve breathing symptoms

What to do in an emergency

If you're with someone who is having an allergic reaction and shows signs of shock caused by anaphylaxis, act fast. Signs and symptoms of shock caused by anaphylaxis include pale, cool and clammy skin, weak and rapid pulse, trouble breathing, confusion, and loss of consciousness. Even if you're not sure symptoms are caused by anaphylaxis, take the following steps immediately:

• Call 999 or emergency medical help.
• Check the person's pulse and breathing and, if necessary, administer CPR or other first-aid measures.
• Give medications to treat an allergy attack, such as an epinephrine autoinjector or antihistamines, if the person has them.

Using an autoinjector

• Many people at risk of anaphylaxis carry an autoinjector. This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh. Always be sure to replace epinephrine before its expiration date, or it may not work properly.

Long-term treatment 

If your anaphylactic reaction is triggered by insect stings, you may be able to get a series of allergy shots (immunotherapy) to reduce your body's allergic response and prevent a severe reaction in the future.

Unfortunately, in most other cases there's no way to treat the underlying immune system condition that can lead to anaphylaxis. But you can take steps to prevent a future attack — and be prepared in the event one does occur.

• Avoid your known allergy triggers as much as you can.
• You may need to carry self-administered epinephrine. During an anaphylactic attack, you give yourself the drug using an autoinjector (EpiPen).
• Your doctor may recommend taking prednisone or antihistamines. 

Living with anaphylaxis

Having a potentially life-threatening reaction is frightening, whether it happens to you or to your child. Developing an anaphylaxis emergency action plan may help put your mind at ease. Work with your or your child's doctor to develop this written step-by-step plan of what to do in the event of a reaction. That way, you'll know exactly what you need to do if anaphylaxis occurs, and you'll have a written plan that you can share with teachers, baby sitters and other caregivers so that they'll know what they need to do, too.

Prevention

The best way to prevent anaphylaxis is to avoid substances that you know cause this severe reaction. Follow these steps:

• Wear a medical alert necklace or bracelet to indicate if you have an allergy to specific drugs or other substances.
• Alert your doctor to your drug allergies before having any medical treatment. If you receive allergy shots, always wait at least 30 minutes before leaving the clinic so that you can receive immediate treatment if you have a severe reaction to the allergy shot.
• Keep a properly stocked emergency kit with prescribed medications available at all times. Your doctor or Pharmacist can advise you on the appropriate contents. This may include an epinephrine autoinjector. Make sure your autoinjector has not expired. These medications generally last 18 months.
• If you're allergic to stinging insects, exercise caution when they're nearby. Wear long-sleeved shirts and pants. Avoid bright colors and don't wear perfumes or colognes. Stay calm if you are near a stinging insect. Move away slowly and avoid slapping at the insect.
• Avoid wearing sandals or walking barefoot in the grass if you're allergic to insect stings.
• If you have specific food allergies, carefully read the labels of all the foods you buy and consume. Manufacturing processes can change, so it's important to periodically recheck the labels of foods you commonly eat. When eating out, ask about ingredients in the food, and ask about food preparation because even small amounts of the food you're allergic to can cause a serious reaction.

References:

http://en.wikipedia.org/wiki/Anaphylaxis
http://www.anaphylaxisireland.ie/?page_id=7
http://www.irishanaphylaxis.org
http://allergy-ireland.ie/anaphylaxis-the-basic-facts/
http://www.mayoclinic.org/diseases-conditions/anaphylaxis/basics/definition/con-20014324
http://www.nlm.nih.gov/medlineplus/ency/article/000844.htm
http://www.medicinenet.com/anaphylaxis/article.htm