Anaphylaxis

**Anaphylaxis** is a serious allergic reaction.  It begins suddenly. In some reactions there is a second wave which happens minutes or even hours after the first. It may cause death.  Anaphylaxis has many symptoms (signs of being sick), such as an itchy , throat swelling, breathing problems, and low blood pressure. Common causes include insect bites, foods, and medications.

Anaphylaxis happens when a person eats, breathes in, or ingests an allergen (something they are allergic to).  Their immune system over-reacts.  It sends out special proteins from inside certain white blood cells.  These proteins can start an allergic reaction or make the reaction worse.

Anaphylaxis is diagnosed (found to be sick with something) from a person’s signs and symptoms.  The best treatment is an injection (a shot) of epinephrine (adrenaline).  Sometimes doctors give other medicines along with epinephrine.

Worldwide, about 0.05–2% of people have anaphylaxis at some point in their lives.  Anaphylaxis appears to be getting more common. Half of the people who die of anaphylaxis have had no anaphylactic reaction before.

## History 
Cases of anaphylaxis have been reported since ancient times.

The condition was originally named "aphylaxis" by Charles Richet in 1902.  In 1913, Richet was awarded the Nobel Prize in Medicine and Physiology for his work on anaphylaxis.  The word "anaphylaxis" comes from the Greek words ἀνά (ana), *against*, and φύλαξις (phyla's), *protection.*

## Signs and symptoms 
Anaphylaxis can cause many different signs and symptoms over minutes or hours.  If the anaphylaxis is caused by something that entered the body directly through the bloodstream  symptoms appear within an average of 5 to 30&nbsp;minutes.  If it is caused by a food the person ate symptoms appear up to 2 hours later.
* Itchiness  If a person is having breathing problems, the skin may turn blue because the body is not getting enough oxygen.  This is called cyanosis.

### Cardiovascular symptoms
When a person has anaphylaxis, some of the cells in the heart may release histamine. Histamine is a chemical made by the body. It can cause the heart’s blood vessels to get narrower suddenly (this is called "coronary artery ").
* Syncope (fainting)

In rare cases, very low blood pressure may be the only sign of anaphylaxis. A common cause of harm for babies (especially with new parents) is raw milk or animal milk, which their body can not handle. Breastmilk and Formulae won't cause anaphylaxis.

Allergic reactions are especially dangerous for young children, because they can't talk, or might not know what's happenening. 

### Medication 
Any medication may cause anaphylaxis. The most common are β-lactam antibiotics (such as penicillin), then aspirin and NSAIDs.

### Venom
Venom from stinging or biting insects, like bees and wasps (Hymenoptera) or kissing bugs (Triatominae), may cause anaphylaxis.  If a person has a bad allergic reaction to venom once, they have a greater risk of having anaphylaxis if they are stung or bitten again.  

### Risk factors
Certain diseases, called atopic diseases, can make a person more likely to have allergies.  Atopic diseases include asthma, eczema, and allergic rhinitis.  People with these diseases have a high risk of anaphylaxis from food, latex, and radiocontrast agents.  However, these people do not have a higher risk from injected medications or stings. One study of children with anaphylaxis found that 60% had a history of previous atopic diseases.  More than 90% of children who die from anaphylaxis have asthma. The risk of having another anaphylactic reaction decreases as a person avoids the trigger for longer and longer.
* Bronchoconstriction (where the tubes that carry air to the lungs get narrower)
* Vasodilation (where the blood vessels get wider)
* Fluid leaks out of blood vessels
* The heart muscle does not work as well

## Diagnosis 
Anaphylaxis is diagnosed based on signs, symptoms, and knowing that a person has been exposed to an allergen.  It is very likely that a person has anaphylaxis if any of these three things happen within minutes or hours after they were exposed to an allergen:
# Problems with the skin or mucosal tissue, plus either breathing problems or a low blood pressure
# Two or more of these symptoms:
## Problems with the skin or mucosa
## Breathing problems
## Low blood pressure
## Gastrointestinal symptoms
# Low blood pressure after exposure to an allergen

If a person has a bad reaction to an insect sting or a medication, blood tests for tryptase or histamine might be useful in diagnosing anaphylaxis. However, these tests are not very useful if the cause is food, or if the person has a normal blood pressure.

## Management 
Anaphylaxis is a medical emergency that may require emergency medical treatment.  Some patients need help keeping their airways open so they can breathe.   Other patients need to be given extra oxygen or large amounts of intravenous fluids (fluids given through a needle into a vein).
Epinephrine is the best and first treatment used for anaphylaxis.  It reverses many of the symptoms of anaphylaxis.  It makes the bronchi (the passages to the lungs) get wider. It makes the blood vessels go back to their normal size and it raises blood pressure.

Epinephrine comes in an "auto-injector," usually called an "EpiPen."  Once its safety cap is taken off, the EpiPen just has to be pressed into the thigh, and the right amount of epinephrine will automatically be injected into the person's body.  Doctors can prescribe EpiPens to people who know they have allergies, so they can treat themselves for anaphylaxis.  Many ambulances also carry EpiPens to treat anaphylaxis. The EpiPen is meant to be injected into the thigh muscle, on the outside of the leg, as soon as anaphylaxis is suspected.
* Knowing how to use an EpiPen properly and what the signs of an attack look like
* Parents telling schools about their children's allergies and what to do in case of an anaphylactic emergency
* Wearing a medical alert bracelet that says what the person is allergic to 
* Planning for how to avoid triggers

## Outlook 
If anaphylaxis is diagnosed and the person is treated quickly, there is a good chance that they will recover.  Even if nobody knows what caused the anaphylaxis, the person usually makes a good recovery as long as they get medication to stop the reaction.  Some people die within minutes.

## References