What are the effects and signs?
What is anaphylaxis?
Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction that is characterised by rapidly developing life-threatening respiratory and/or circulation problems. It is usually associated with skin and mucosal (lip, mouth or gut) changes.
The symptoms of anaphylaxis, for example in peanut allergy, are caused by the effects of an inappropriate immunological response to peanut protein. Pre-formed anti-peanut IgE is present in the circulation, skin and elsewhere. The IgE recognises peanut protein and activates cells in the body. These cells release inflammatory chemicals such as histamine. These chemicals cause blood vessels to dilate and become more permeable to fluid. The effect of this is best seen in the skin, which becomes red or swollen or raised. The effect may be described by a parent as flushing or a rash. Anaphylaxis develops when swelling in the airway causing difficulty in breathing, or loss of fluid from the circulation and dilation of blood vessels cause reduction in blood pressure and loss of consciousness.
Symptoms and signs of anaphylaxis
Typical symptoms include onset of the following symptoms within 30min of exposure to an allergen -:
- A sense of impending doom
- Swelling inside the throat (laryngeal oedema)
- Wheezing and difficulty breathing
- Collapse
- Loss of consciousness
- Severe abdominal pain and diarrhoea
In children, anaphylaxis is most commonly characterised by respiratory difficulty rather than sudden collapse due to reduced blood pressure.
Other features of an allergic reaction may be present but do not in themselves indicate that anaphylaxis has occurred -:
- Swelling of the lips or mouth
- Nausea/vomiting
- Hives – a skin rash also known as urticaria (looks very similar to a stinging nettle rash) – may be all over the body as part of a generalised allergic reaction or be a local effect e.g. touching a peanut with the hand.
- Rhinitis – runny nose
- Conjunctivitis – red, inflamed itchy or watery eyes
Potentially life threatening symptoms may not be listed in the medical evidence but simply be referred to as anaphylaxis or an episode of anaphylaxis. Anaphylaxis is under and over diagnosed by non-specialists. If there is doubt about whether anaphylaxis has occurred or whether there is a risk of anaphylaxis – always rely on the opinion of the consultant allergist.
Anaphylaxis risk assessment
Peanut allergy is the commonest cause of anaphylaxis in children and provides a useful model for risk assessment. The clinical severity of reactions to peanut varies from mild to severe (anaphylaxis) both between individuals and within individuals over time. Further accidental reactions are usually of similar severity or less severe than the original reaction. Child reactions usually do not become more severe or more frequent, providing they receive appropriate advice. The severity of any reaction and whether the child develops anaphylaxis will depend on the dose of allergen, the route of exposure and the state of health of the child at the time. For example consuming a meal that contained peanut would usually cause a more severe reaction than skin contact. Uncontrolled asthma increases the risk of anaphylaxis.
There is a large number of children who have the potential to develop anaphylaxis, for example all those with peanut allergy, however in reality anaphylaxis rarely occurs. It can be difficult to identify those children at significant risk but anaphylaxis is most likely to occur amongst -:
1. Those who have previously had an anaphylactic reaction
2. Those with poorly controlled asthma (defined by a doctor)
3. Those who react to trace amounts of allergen
Anaphylaxis is the most severe type of allergic reaction covered in this guidance. Milder reactions via the same mechanism may occur, for example, the only allergic reactions experienced so far may have been lip swelling and hives/urticaria. Such reactions are not serious in themselves but they are a marker of allergy and may indicate a risk of anaphylaxis.
Types of allergies and allergens
IgE mediated allergies are diverse, many are mild with few symptoms and others are severe. Examples of mild IgE mediated reactions include mild hay fever and mild asthma. An example of more severe allergy is the presence of nut allergy with a history of anaphylaxis. Children with more severe allergies often have several allergic conditions, for example, they will usually have a food allergy and eczema and asthma. This guidance is specifically designed to cover those children with severe allergies who have either had or are at risk of anaphylaxis. A small number of conditions can induce anaphylaxis independently of IgE, these are described below. Other conditions related to allergy such as eczema and asthma are covered elsewhere in guidance. It may be difficult to work out which cases are severely affected by allergy and which are not and which sections of guidance should be used. The link to ‘Guidelines for which guidance to use’ below will help you to decide to what category a case belongs and which guidance is most relevant. Several sections of guidance may need to be used to assess a case with severe allergies because the allergy has caused a range of problems or effects, for example, eczema and asthma and a history of anaphylaxis.
