Anaphylaxis (A&E) Flashcards
Define anaphylaxis.
Severe, generalised or systemic hypersensitivity reaction, characterised by rapidly developing life-threatening airway and/or breathing and/or circulation problems usually associated with skin and mucosal changes
Acute, life-threatening type 1 hypersensitivity reaction due to IgE-mediated mast cell activation
What are the two types of anaphylaxis?
- immunogenic: IgE-mediated or immune complex/complement-mediated (food, insect, stings, drugs) - sometimes a cofactor is required (NSAIDs, alcohol)
- non-immunogenic: anaphylactoid reaction - mast cell/basophil degranulation without antibody involvement (vancomycin, codeine, ACEi)
What can trigger anaphylaxis? (3)
- food allergies
- insect stings
- drug reactions (e.g. penicillin, latex)
Describe the pathophysiology of anaphylaxis.
Degranulation of mast cells –> histamine release –> systemic vasodilation + bronchospasm –> increased capillary leakage –> anaphylactic shock (tissue oedema affecting larynx, eyelids, tongue, lips)
What are some common allergens that can trigger anaphylaxis? (7)
- drugs e.g. penicillin
- latex
- peanuts
- shellfish
- strawberries
- semen
- eggs
What can anaphylaxis be caused by in patients with selective IgA deficiency?
Repeat administration of blood products due to formation of anti-IgA antibodies
Who is anaphylaxis more common in?
Patients with Hx of atopy
What are the clinical features of anaphylaxis? (13)
- acute onset
- airways welling (angio-oedema)
- stridor (noisy breathing through obstructed airway)
- dyspnoea
- wheezing
- cyanosis
- respiratory arrest
- pale, clammy skin
- hypotension
- tachycardia
- confusion
- urticaria + erythema
- pruritus
What might you find on examination in anaphylaxis (overlap with clinical features)? (10)
- tachypnoea
- wheeze / stridor
- cyanosis
- swollen upper airways and eyes
- rhinitis
- conjunctival infection (bilateral)
- urticarial rash
- erythema
- hypotension
- tachycardia
What are some risk factors for anaphylaxis? (3)
- Hx atopy/asthma
- exposure to common sensitiser:
- celery, crustacean, fish, egg, legume, milk, mustard, nuts, sesame, soya
- Abx, anaesthetics, NSAIDs, ACEi, aspirin, contrast, chlorhexidine
- venoms (hypenoptera)
- latex
- exercise
- hot/cold exposure
- previous anaphylaxis
How is anaphylaxis usually diagnosed?
Clinical diagnosis
What is the main blood test done in anaphylaxis?
Mast cell tryptase - may remain elevated for up to 12 hours after acute episode
(Sample taken during, 4h and 12h post reaction)
What are some other useful investigations for a medical emergency like anaphylaxis? (3)
- ECG
- U&Es
- ABG
What investigations can be done following acute anaphylaxis to identify allergens? (2)
- allergen skin testing - IDs allergen
- IgE immunoassays - IDs food-specific IgE in serum
What are some differential diagnoses for anaphylaxis? (13)
- septic shock
- cardiogenic shock
- hypovolemic shock
- vasovagal reaction
- asthma
- acute COPD exacerbation
- hereditary angio-oedema
- vocal cord dysfunction syndome
- foreign body aspiration
- carcinoid syndrome
- postmenopausal hot flushes
- panic disorder
- food poisoning
