Anaphylaxis

Question 1

Define anaphylaxis.

Answer 1

An acute, systemic and life-threatening allergic response to a trigger caused by the release of immune and inflammatory mediators from basophils and mast cells. At least two organ systems are involved, such as the skin, the upper and lower airways, and the cardiovascular, neurological, and gastrointestinal systems, in this order of priority or in combination.

Question 2

Explain the aetiology/risk factors of anaphylaxis.

Answer 2

Exposure to allergen in pre-sensitised individuals is the cause of immune-mediated anaphylaxis. Common allergens include drugs, foods, and insect stings, but exercise with or without the presence of an allergen may also be a trigger. Sometimes, a cofactor (such as an NSAID, alcohol, or another food) is required to provoke food-associated and exercise-induced anaphylaxis.
The most common trigger (up to ⅓ of cases) is food.

Question 3

Summarise the epidemiology of anaphylaxis.

Answer 3

Anaphylaxis is under-reported and it is difficult to estimate as study definitions and criteria are not always comparable. The incidence of food allergic reactions that are coded as anaphylaxis is highest in young children. In children, food allergy is most prevalent in the industrialised world and the emerging economies of southeast Asia, possibly due to an increased exposure to processed food.

Question 4

Recognise the presenting symptoms of anaphylaxis.

Answer 4

Rapidly progressive upper airway obstruction
Rash
Bronchospasm
Hypotension or cardiovascular collapse

Question 5

Recognise the signs of anaphylaxis on physical examination.

Answer 5

The patient appears agitated, confused, and either flushed or pale. Neurological manifestations also include dizziness, visual disturbances, tremor, disorientation, syncope, and seizures.
Wheezing, an over-inflated chest, the use of accessory muscles, and preference for the forward-leaning position point to bronchoconstriction. Cardiovascular collapse may occur in addition to hypotension.
Nearly all adults will show skin manifestations of systemic mediator release, such as rash, erythema, or urticaria. These features might be overshadowed by the more dramatic respiratory and cardiovascular symptoms. Abdominal pain, nausea, vomiting, and diarrhoea are common symptoms.

Question 6

Identify appropriate investigations for anaphylaxis and interpret the results.

Answer 6

During the anaphylactic shock, no investigations are useful as they take too long.
Serum tryptase level.

Question 7

Generate a management plan for anaphylaxis. Identify the possible complications of anaphylaxis and its management.

Answer 7

INITIAL
Cardiorespiratory assessment + supportive measures
IM adrenaline (epinephrine)
Assess and secure airway
IV normal saline

Cardiopulmonary arrest
CPR and IV adrenaline (epinephrine)

Severe hypotension
IV adrenaline (epinephrine)
IV glucagon

Persistent respiratory symptom
Inhaled beta-2 agonist

Symptomatic hives and rhinorrhoea
H1 antagonist and H2 antagonist

Post-emergency stabilisation
Corticosteroids

Question 8

Summarise the prognosis for patients with anaphylaxis.

Answer 8

Individuals with previous reactions are at higher risk for recurrence. However, the severity of the previous reaction does not necessarily predict the severity of a subsequent reaction.