Understanding Anaphylaxis
What is anaphylaxis?
Anaphylaxis is an extreme and severe allergic reaction. The whole body is affected, often within minutes of exposure to the allergen but sometimes after hours.
After an initial exposure or "sensitising dose" to an allergen (such as a bee sting) at some point in the person's life, the person's immune system becomes sensitised to that allergen. On a subsequent exposure or "shocking dose", an allergic reaction occurs.
In the United Kingdom, mortality rates for anaphylaxis have been reported as up to 0.05 per 100,000 population, or around 10-20 a year. In 2005 there were 12 deaths associated with severe reaction to foods.1 Anaphylactic reactions requiring hospital treatment appear to be increasing, with authorities in the UK reporting a threefold increase between 1994 and 2004.2
More people are becoming more sensitive to more allergens.
Any allergic reaction, including the most extreme form, anaphylactic shock, occurs because the body's immune system reacts inappropriately in response to the presence of a substance - the allergen - that it wrongly perceives as a threat.
An anaphylactic reaction is caused by the sudden release of chemical substances, including histamine, from cells in the blood and tissues where they are stored. The release is triggered by the reaction between the allergic antibody Immunoglobin E (IgE) and the allergen causing the anaphylactic reaction.
This mechanism is so sensitive that minute quantities of the allergen can cause a reaction. The released chemicals act on blood vessels to cause the swelling in the mouth and airway and anywhere on the skin. There is a fall in blood pressure and, in asthmatics, the effect is mainly on the lungs.
What can cause anaphylaxis?
Common causes include
- 'Nuts' - peanuts, tree nuts (e.g. almonds, walnuts, cashews, Brazils), sesame seeds
- Seafood and shellfish,
- Dairy products and eggs.
- Venom - wasp or bee stings, jellyfish stings
- Non-food causes include natural latex (rubber) and penicillin (or any other drug or injection).
In some people, exercise can trigger a severe reaction, either on its own or in combination with other factors such as food or drugs (e.g. aspirin).
Commonly, most allergens are naturally occurring proteins.
What are the symptoms?
Anaphylaxis can present with many different symptoms due to the systemic effects of histamine release.
The most common areas affected include:
Skin (80% to 90%),
- generalised flushing of the skin
- nettle rash (hives) anywhere on the body
Respiratory (70%),
- swelling of throat and mouth
- difficulty in swallowing or speaking
- severe asthma
Gastrointestinal (30% to 45%),
- abdominal pain, nausea and vomiting
Heart and vasculature (10% to 45%),
- alterations in heart rate
- sudden feeling of weakness (drop in blood pressure)
Central nervous system (10% to 15%).
- collapse and unconsciousness
Symptoms can develop within a few minutes or over several hours, furthermore, an individual may not necessarily experience all of these symptoms3.
What is the treatment for a severe reaction?
Pre-loaded adrenaline auto-injection pens are available on prescription for those believed to be at risk. Adrenaline (also known as epinephrine) acts quickly to constrict blood vessels, relax smooth muscles in the lungs to improve breathing, stimulate the heartbeat and help to stop swelling around the face and lips.
There is no contraindication to administering adrenalin via auto-injector to anyone who is displaying signs of an anaphylactic reaction.
Related Article: The Use of Epi-Pens
Anaphylaxis should always be treated as a medical emergency. It can be fatal unless immediate treatment is available.
Mild cases
- If the person has had a mild reaction with only skin symptoms (itchiness or a rash), adrenaline may not be necessary and they may just need antihistamines and steroids.
- The allergen should be removed if possible.
- The casualty should be sat down on the floor, against a wall, with their knees bent and brought up to:
- Promote fluid drainage from the upper airway,
- Increase blood pressure
- Ease breathing
- Reduce oxygen demand.
Severe cases
- If someone becomes severely ill or collapses soon after an insect bite, eating a particular food or taking medication, call for an ambulance and tell the operator that you think the person has anaphylaxis. Remove the trigger (allergen) if possible.
- An adrenaline injection must be given as soon as a serious reaction is suspected. If the person is carrying an adrenaline injection pen, they may be able to inject themselves or you can help them to use it.
- If there is no improvement within five minutes, a second injection may be needed until the condition improves. Recovery normally occurs fairly quickly once adrenaline has been received.
- If they are unconscious, check their airways are open and clear and check their breathing.
- If they are breathing, put them in the Safe Airway position and continually monitor.
- If the person's breathing stops, cardiopulmonary resuscitation (CPR) should be performed immediately.
Am I at risk from anaphylaxis?4
- If you have suffered a bad allergic reaction in the past – whatever the cause – then any future reaction is also likely to be severe.
- If you have suffered a significant reaction to a tiny dose, or have reacted on skin contact, this might also be a sign that a larger dose may trigger a severe reaction.
- If you have asthma as well as allergies, getting seen by an allergy specialist is particularly important because asthma can put you in a higher risk category.
- Where foods such as nuts, seeds, shellfish and fish are concerned, even mild symptoms should not be ignored because future reactions may be severe.
Further reading:
Managing medicines in Schools and Early Years Settings. Department for Education. 2007
The Medical Conditions at School Website – useful protocols to downlaod for setting up policies for the management of medical conditions in your school
1. Mortality Statistics: 2005. National Statistics Office.. See page 252..
2. A Review of Services for Allergy. Department of Health. 2006. See sections 2.54-55.
