Anaphylaxis

Symptoms and signs of anaphylaxis

Anaphylaxis is defined as an immediate systems hypersensitivity event produced

by IgE-mediated release of chemicals from mast cells and basophils.
Theoretically, prior exposure to the agent is required and the reaction is
not dose- or route-related, but in practice anaphylaxis to injected antigen
is more frequent, severe, and rapid in onset than following exposure to
oral or topical antigen.
Agents which commonly cause anaphylaxis include:
• drugs — e.g. penicillins, aspirin
• insect stings — e.g. wasp and bee venoms
• food — e.g. nuts.
Urticaria and angioedema are the most common symptoms
and absence of these suggests that the reaction may not be anaphylaxis.
Airways oedema, bronchospasm, and shock are life-threatening and
immediate emergency treatment is usually required.
The onset of symptoms following parenteral antigen (including stings) is
usually within 5–30min. With oral antigen, there is often a delay. Symptoms
usually occur within 2h, but may be immediate and life-threatening.
A late-phase reaction may also occur with recrudescence of symptoms
after apparent resolution. Recurrence is a fairly frequent phenomenon
and healthcare workers should be aware of this. Patients should not be
discharged too quickly as they may require further treatment.
End-of-needle reactions
Some patients may experience an anaphylactic-like reaction during rapid
intravenous (IV) drug administration. This is known as an end-of-needle
reaction. Initial symptoms may suggest anaphylaxis, but in fact this is a
vasopressor effect and can be distinguished from anaphylaxis as bradycardia
occurs which is rare in anaphylaxis. Skin symptoms are also rare
in end-of-needle reactions. Stopping or slowing down the infusion or
injection usually leads to resolution of symptoms,and administration at a
slower rate usually avoids a repeat event.
Signs and symptoms of anaphylaxis
F Urticaria
R Angioedema
E Dyspnoea, wheeze
Q Nausea, vomiting, diarrhoea, cramping abdominal pain
U Flush
E Upper airway oedema
N
T
R Headache
A Rhinitis
R Substernal pain
E Itch with no rash
Seizure