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Anaphylaxis: The Basic Facts

Anaphylaxis is a severe allergic reaction — the extreme end of the allergic spectrum. The whole body is affected, often within minutes of exposure to the allergen. Nut allergies are frequently severe and for that reason have received widespread publicity. Other causes of anaphylaxis also include other foods, insect stings, latex and drugs. On rare occasions there may be no obvious trigger.

What is going on when anaphylaxis occurs?

Any allergic reaction, including the most extreme form, anaphylactic shock, occurs because the body’s immune system reacts inappropriately in response of a presence 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 (IgE) with the substance (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 swelling in the mouth and anywhere on the skin. There is a fall in blood pressure and there may be an asthmatic effect on the lungs.

Why does adrenaline (epinephrine) work?

During anaphylaxis, blood vessels leak, bronchial tissues swell and blood pressure drops, causing choking and collapse. Adrenaline 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 (angioedema).

Signs and symptoms may include.

General flushing of the skin. / Nettle rash (hives) anywhere on the body. Sense of impending doom. / Swelling of the throat and mouth. / Difficulty in swallowing or speaking. / Alterations in heart rate. / Severe asthma. / Abdominal pain, nausea and vomiting. / Sudden feeling of weakness (drop in blood pressure). Faint / Collapse and unconsciousness 

The EpiPen

The EpiPen Auto-injector is a self-injecting syringe that automatically delivers a single 0.3 ml dose of 1:1000 epinephrine. A paediatric version, EpiPen Jr, dispenses 0.3 rnL of 1:2000 epinephnne.

This device is popular among patients who are uncomfortable injecting themselves. It has been useful in schools and daycare facilities, where trained personnel may not be available. It is simple to use and requires a force of only about 31b to the tip to trigger the injection mechanism. However, caution must be used to avoid accidental injection. The 22-gauge needle is propelled by a spring that generates 16lbs of force; this could be problematic if the needle were to hit solid tissue such as bone.