Anaphylaxis (A&E)

Question 1

Define anaphylaxis.

Answer 1

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

Question 2

What are the two types of anaphylaxis?

Answer 2

• 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)

Question 3

What can trigger anaphylaxis? (3)

Answer 3

• food allergies
• insect stings
• drug reactions (e.g. penicillin, latex)

Question 4

Describe the pathophysiology of anaphylaxis.

Answer 4

Degranulation of mast cells –> histamine release –> systemic vasodilation + bronchospasm –> increased capillary leakage –> anaphylactic shock (tissue oedema affecting larynx, eyelids, tongue, lips)

Question 5

What are some common allergens that can trigger anaphylaxis? (7)

Answer 5

• drugs e.g. penicillin
• latex
• peanuts
• shellfish
• strawberries
• semen
• eggs

Question 6

What can anaphylaxis be caused by in patients with selective IgA deficiency?

Answer 6

Repeat administration of blood products due to formation of anti-IgA antibodies

Question 7

Who is anaphylaxis more common in?

Answer 7

Patients with Hx of atopy

Question 8

What are the clinical features of anaphylaxis? (13)

Answer 8

• acute onset
• airway swelling (angio-oedema)
• stridor (noisy breathing through obstructed airway)
• dyspnoea
• wheezing
• cyanosis
• respiratory arrest
• pale, clammy skin
• hypotension
• tachycardia
• confusion
• urticaria + erythema
• pruritus

Question 9

What might you find on examination in anaphylaxis (overlap with clinical features)? (10)

Answer 9

• tachypnoea
• wheeze / stridor
• cyanosis
• swollen upper airways and eyes
• rhinitis
• conjunctival infection (bilateral)
• urticarial rash
• erythema
• hypotension
• tachycardia

Question 10

What are some risk factors for anaphylaxis? (3)

Answer 10

• 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

Question 11

How is anaphylaxis usually diagnosed?

Answer 11

Clinical diagnosis

Question 12

What is the main blood test done in anaphylaxis?

Answer 12

Mast cell tryptase - may remain elevated for up to 12 hours after acute episode

(Sample taken during, 4h and 12h post reaction)

Question 13

What are some other useful investigations for a medical emergency like anaphylaxis? (3)

Answer 13

• ECG
• U&Es
• ABG

Question 14

What investigations can be done following acute anaphylaxis to identify allergens? (2)

Answer 14

• allergen skin testing - IDs allergen
• IgE immunoassays - IDs food-specific IgE in serum

Question 15

What are some differential diagnoses for anaphylaxis? (13)

Answer 15

• septic shock
• cardiogenic shock
• hypovolemic shock
• vasovagal reaction
• asthma
• acute COPD exacerbation
• hereditary angio-oedema
• vocal cord dysfunction syndrome
• foreign body aspiration
• carcinoid syndrome
• postmenopausal hot flushes
• panic disorder
• food poisoning

Question 16

What is the management plan for anaphylaxis?

Answer 16

• first step: remove trigger + call for help
• ABCDE approach + high-flow oxygen (15L/min non-rebreathe mask)
• IM 500 micrograms (0.5mL) adrenaline for adults >12y into anterolateral aspect of medial thigh
  
  • repeat at 5-minute intervals according to response
  • 500mcg dose of 1:1000 IM adrenaline
• after IM adrenaline: cetirizine PO 10-20mg (or IV chlorphenamine 10mg) + IV hydrocortisone 200mg

Question 17

How do we manage bronchospasm in anaphylaxis?

Answer 17

Salbutamol +/- ipratropium (SABA + SAMA)

Question 17

How do we manage anaphylaxis post-attack? (6)

Answer 17

• admit to ward and monitor ECG
• measure mast cell tryptase 1-6h after (sample taken during, 4h and 12h post reaction)
• continue cetirizine/chlorphenamine
• suggest MedicAlert bracelet with name of trigger
• teach about self-injected adrenaline (EpiPen)
• skin prick tests showing specific IgE to help identify allergens to avoid

Question 18

What is refractory anaphylaxis (and how do we treat it)?

Answer 18

• anaphylaxis persists despite 2 doses IM adrenaline
• treat with IV adrenaline + IV fluid bolus

Question 19

What are some complications of anaphylaxis? (4)

Answer 19

• shock
• organ damage (from shock)
• MI
• recurrence

Question 20

Describe the prognosis of anaphylaxis.

Answer 20

Outlook will depend on success of immunotherapy, allergen avoidance, and compliance with carrying their adrenaline auto-injectors

Question 21

Why are patients admitted and monitored in hospital setting for up to 6h post initial-anaphylaxis?

Answer 21

Sometimes occurs as biphasic reaction, with second reaction 4-6h after initial

Young children particularly at risk

Question 22

What doses of IM adrenaline are given to different ages in anaphylaxis? (4)

Answer 22

• <6m: 100-150mcg
• 6m-6y: 150mcg
• 6-12y: 300mcg
• > 12y: 500mcg