Anaphylaxis and anaphylactic shock
Anaphylaxis, or anaphylactic shock, is a sudden catastrophic allergic reaction that involves the whole body. It usually occurs within minutes of exposure to the offending allergen (insect stings, nuts and medicines being the commonest causes).The first documented case of anaphylaxis was in 2641 BC, when King Menes of Egypt died from a Wasp sting. While the first fatal reaction to peanuts was described by a Canadian researcher Dr Evans in 1988.
Approximately 1 in 500 people attending hospital Emergency Units come because of some form of anaphylactic reaction and the number of new cases in developed countries seem to be rapidly increasing. Possible changes in our diet and environment have been implicated (nut anaphylaxis was first documented only 20 years ago)
What causes Anaphylaxis?
Why some people develop anaphylaxis and others not, is difficult to explain. But it usually happens to people who are known to have allergies and particularly those who suffer with brittle asthma.The most common cause of anaphylaxis in the community is from eating a food to which you are allergic such as nuts, peanuts, eggs, mammalian milk, soya, wheat, fish and shellfish. These 8 foods account for 90% of cases of food induced anaphylaxis. Peanuts and tree nuts (such as Brazil nuts, Hazelnuts, Almonds and Walnuts) are the foods most likely to provoke a reaction.
Even eating a tiny amount of a particular food can cause anaphylaxis. Some people are so sensitive that breathing in the food essence can trigger a reaction (as in a Restaurant when the person at the next table is eating fish or kissing a person who has recently eaten peanuts).
Allergy to venom from wasp stings can cause anaphylaxis as can allergy to latex and drugs such as penicillin, codeine and aspirin. Bee sting allergy is less common in the UK.
In the hospital context, the majority of anaphylactic reactions are to medicines such as muscle relaxants, antibiotics, xray contrast medium and injectable medications including anaesthetic agents. Latex allergy and anaphylaxis is becoming an ever increasing problem, particularly in health workers and children who have frequent operations and are sensitised by exposure to Latex in surgical gloves, drip sets and catheters.
Some people may develop anaphylaxis after eating certain foods such as celery, shrimps, wheat, apple, hazelnut, squid and chicken and then exercising shortly after ingesting the food - triggering Exercise Induced Anaphylaxis.
Often we never find the cause of the anaphylactic reaction and in 1978 the term "Idiopathic" Anaphylaxis was coined to describe this group of people which accounts for about half of all cases of anaphylaxis. However new and previously unrecognised allergens such as lupin flour and celeriac should be considered.
Symptoms of Anaphylaxis
Anaphylaxis comprises a group of symptoms and features, which in combination lead to a generalised severe allergic reaction with respiratory difficulties and circulatory shock.The initial reaction is swelling and itching of the area where the allergen has entered. Food for example, initially causes swelling and itching of the mouth and throat while a wasp sting will cause intense itching and swelling at the sting site.
A generalised reaction then rapidly follows with an itchy rash that spreads over the whole body. The face and soft tissues begin to swell and breathing becomes difficult. The scalp, palms and soles of feet become intensely itchy.
The person becomes very agitated with a “feeling of impending doom”, tightening of the throat and chest occur, while the blood pressure may begin to drop and the victim then loses consciousness.
These symptoms develop very rapidly within a few minutes of coming into contact with the allergen. Most anaphylactic reactions occur within an hour of exposure to the causative allergen.
Treatment
Anaphylaxis needs to be treated as a matter of urgency as the symptoms of respiratory obstruction and shock develop rapidly. Emergency treatment consists of an injection of a drug called adrenaline or epinephrine, which raises blood pressure, relieves breathing difficulties and reduces swelling. Once adrenaline has been given, people normally recover very quickly. They should also immediately take a dose of antihistamine and will need a short course of cortisone (steroid) tablets.read more
