Allergies Clinics of London

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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.

·         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, fish and shellfish.  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 the food essence can trigger a reaction (as in a Restaurant when the person at the next table is eating fish).

Allergy to venom from wasp stings can cause anaphylaxis as can allergy to latex and drugs such as penicillin, codeine and aspirin. Bee Allergy is less common in the UK.
 

In the hospital context, the majority of anaphylactic reactions are to medicines such muscle relaxants, antibiotics 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.

Sometimes we never find the cause of the anaphylactic reaction and in 1978 the term "Idiopathic" Anaphylaxis was coined to describe this group of people.

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 which 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 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 may even need a short course of cortisone tablets.

If you have had a previous and severe anaphylactic reaction, make sure you use the Adrenaline Injector straight away with any future reactions – as any delay puts you at far greater risk for collapse and dying.  Although many people carry an Epipen, the most common cause of death is failure to use it.  There are two types of injector, one for children and another for adults.  The injector is easy to use and is activated by pressing firmly against the front of the thigh muscle.  Your doctor should issue you with a “trainer” Epipen to practice self-administration.

If you have always experienced milder attacks with minimal or no breathing difficulties we usually recommend that you immediately take antihistamine medication and monitor the situation for a few minutes before giving adrenaline.  Milder symptoms then usually resolve over the next half hour.  Always make sure you have someone with you who knows about your condition and who can seek further help if necessary.

Make sure that you do not exert yourself, have a hot bath or get hot, rather remain cool, as increased circulation can lead to more severe and rapid allergic reactions

All people who have had anaphylaxis should go to the local hospital Emergency Unit for further observation. This is because when the adrenaline wears off they may need further treatment, such as antihistamines, corticosteroids and occasionally oxygen and intravenous fluid therapy. We would also recommend that you go to your local hospital and introduce yourself to the medical team so that they are aware of your anaphylactic tendency.  There is a risk of developing a delayed reaction some hours after the initial reaction and you should remain in the Emergency Unit for at least 4 hours for observation.

When referred to an allergy clinic, the specialist will take an extensive “allergy history” to try and clearly identify the cause of the anaphylaxis.  They will then perform allergy tests on a blood sample using the updated RAST test called a Cap RAST.  This test measures specific IgE antibodies in the patient’s blood to the suspected allergens.  Skin Prick Testing is not recommended for diagnosing anaphylaxis as these tests run the risk of triggering an allergic reaction.  Blood  RAST tests are completely safe and the recommended method of testing for the cause of anaphylaxis.  In some situations, patients may have what looks appears to be an anaphylactic reaction - but which is in fact a fainting spell or sudden drop in blood pressure.  In this situation, we recommend a blood test which measures Mast Cell Tryptase a protein released in the body during anaphylaxis.  This is measured in the blood even hours after the reaction and can usefully confirm that anaphylaxis has indeed occurred. Methyl Histamine can also be measured in the urine of patients after suspected anaphylaxis.

First aid measures
Emergency care for someone with suspected anaphylaxis

·         If the person is conscious and having breathing difficulties, help them to sit up.  If they are shocked with low blood pressure, they are better off lying flat with their legs raised.

·         If the person is unconscious, check their airways and breathing and lie them in the recovery position.

·         If you know that the person is susceptible to anaphylaxis, check if they carry a preloaded adrenaline syringe (EpiPen). If necessary, help the person to inject it into the muscle of the thigh. This can be administered through clothing.

·         Dial 999 for an ambulance and tell the controller that you think the person may have anaphylaxis. If available, antihistamine and steroid tablets should also be given.

How can we prevent anaphylaxis?
If you have ever had an anaphylactic reaction, you must be referred to an Allergy Clinic for full assessment so as to identify the cause of the reaction.

The following precautions need to be taken to prevent future anaphylactic reactions.

You must have at least two preloaded adrenaline auto-injectors called an Epipen, carry one on your person and keep the other accessible at work or school.

·         Never forget to carry your Epipen with you at all times

·         Other people at home, work or college must be informed about your allergy, where you keep your Medication and how to use it.

·         Make sure that your medication is always easily accessible and that the “expiry date” has not passed.

You must also wear a prominent Medic Alert bracelet or necklace engraved with information for emergency medical workers about your specific anaphylactic condition.

 Don't put yourself at risk

If you have one anaphylactic reaction there is no predicting how severe the next reaction might be. Future reactions may be identical, more severe or less severe.   You are however unlikely to ever completely outgrow the allergy and need to take constant precautions.  Never assume that you will be all right just because you have not had a reaction for some time.

·         Check for 'hidden' ingredients on food labels and be very carefully with restaurant food. Foods such as nuts and eggs may have a variety of different names and may be added to processed foods.

·         It is wise to seek the advice of an experienced dietician for help with excluding the offending allergen from your diet.

Certain non-allergic conditions can mimic anaphylaxis

Systemic Mastocytosis is a rare condition where a person has an over-abundance of Mast Cells in the skin or internal organs - these cells can suddenly release large amounts of Histamine and Tryptase after minimal provocation. The result is a reaction that mimics a full blown anaphylactic reaction.  The serum Tryptase levels remain highly elevated even between attacks. Systemic Mastocytosis sufferers may have deeply freckled skin (Urticaria Pigmentosa) and associated flushing, headaches, urticaria, asthma, diarrhoea, organ and bone pain (a bone biopsy is used in the diagnosis)..

Hereditary Angioedema is a familial condition that occurs in 1 in 80 000 people.  The typical symptoms begin in adolescence (often females).  The angioedema (tissue swelling) lasts for 2-3 days and involves the face, neck and limbs with debilitating non-itchy swelling and breathing difficulties. There is a deficiency or under-activity of the C1 Esterase Inhibitor enzyme and very low serum Complement C4 on blood testing. This condition responds to Danazol and not to conventional antihistamine medication.

Carcinoid Syndrome can mimic Anaphylaxis but there is usually considerable flushing, diarrhoea, wheezing and an associated  right heart murmur with high levels of Hydroxy Indole Acetic Acid (5HIAA) in the urine.

Sometimes  Panic Attacks, Hysteria, Aspiration of Foreign substances, Seizures, Scrombo-toxicity, Lung clots (Pulmonary Embolism), Low blood sugar, Fainting spells and Heart Attacks  can closely resemble anaphylactic reactions.

Dr Adrian Morris    Click here for the Surrey Allergy Clinic.

September 2006