Anaphylaxis

Question 1

What is anaphylaxis?

Answer 1

Acute, life-threatening, type 1 hypersensitivity reaction due to IgE-mediated mast cell activation

Question 2

Explain the aetiology of anaphylaxis

Answer 2

Food allergies, insect stings, drug reactions (eg. penicillin, latex) → Degranulation of Mast Cells → Massive Histamine Release → Systemic Vasodilation → Increased Capillary Leakage into bloodstream to multiple organs→ Anaphylactic Shock (swelling, edema & tissue injury)

Question 3

What are the risk factors for anaphylaxis?

Answer 3

History of atopy (genetic tendency to develop allergic diseases)

Question 4

What presenting symptoms are associated with anaphylaxis?

Answer 4

• Acute Onset
• Airway Swelling (Angio-Oedema)
• Stridor, Dyspnoea, Wheezing, Respiratory Arrest, cough
• Pale, Clammy skin, Hypotension, Tachycardia, Confusion, loss of consciousness
• Urticaria, Erythema, Pruritus
• Abdo cramps, vomiting, diarrhoea
• Can recur hours later (biphasic)
• can last for days (protracted)

Question 5

What investigations are used to monitor and diagnose anaphylaxis?

Answer 5

1. Lab tests: increase in histamine, tryptase and IgE
   (Mast-Cell Tryptase → may remain elevated for up to 12hrs after acute episode)
2. ECG, U&Es, ABG → all useful investigations for a medical emergency

Question 6

How is anaphylaxis managed?

Answer 6

1. ABCDE + High flow oxygen (15L/min non-rebreathe mask)
2. Remove the Trigger (+ Call for Help)
3. Give ASAP → Intramuscular Adrenaline (one 500 MICROgram (mcg) dose of 1:1000 IM adrenaline for adults >12yrs old into anterolateral aspect of medial thigh):
   - Give IM even if patient has IV access
   - Refractory Anaphylaxis ⇒ persists despite 2 doses of IM adrenaline (Tx with IV adrenaline and IV fluid bolus)
4. After Adrenaline → IV chlorphenamine (anti-histamine) 10mg + IV hydrocortisone 200mg

Question 7

How does epinephrine (adrenaline) work to combat anaphylaxis?

Answer 7

1. Blood vessel constriction
2. increases heart contractility & heart rate
3. Relaxes smooth muscle

Question 8

What complications are associated with anaphylaxis?

Answer 8

recurrence, cardiac arrest, distributive shock

Question 9

What antihypertensive drug should be avoided with an epipen, for a patient with anaphylaxis?

Answer 9

Adrenaline has both alpha and beta- adrenergic effects which lead to vasoconstriction and vasodilation respectively. Non- cardioselective beta blockers like labetalol used in conjunction with adrenaline could lead to unopposed alpha- adrenergic vasoconstrictive effects, leading to a hypertensive crisis. Hence, labetalol should be avoided in anaphylaxis.