Resp - Anaphylaxis

Question 1

describe the pathophysiological mechanism leading to anaphylaxis after 1st exposure to an allergen

Answer 1

1. 1st exposure to allergen activates abnormal TH2 response… plasma cell production of Ag-specific IgE (sensitisation).
2. 2nd exposure to Ag causes IgE cross-linking on mast cells… mast cell activation and degranulation… release of histamine, bradykinin and other chemokines.
3. Systemic effects:
   
   • increased vascular permeability and vasodilation… hypotension and cardiovascular collapse
   • epidermal mast cells: generalised urticaria
   • deep dermis mast cells: angioedema (swelling of lips, eyes, tongue and upper resp. airway)
   • lung mast cells: bronchospasms

Question 2

described the symptoms that occur in anaphylaxis

Answer 2

i. generalised itching, itching of palate or EAM
ii. dyspnoea and chest tightness
iii. palpitations
iv. nausea, vomiting and abdo. pain
v. dizziness and sense of impending doom
vi. collapse and loss of consciousness

Question 3

describe the signs of anaphylaxis

Answer 3

1. generalised urticaria
2. stridor (laryngeal oedema) and wheeze (bronchospasm)
3. angioedema (swelling of lips, eyes, tongue and upper resp. tract)
4. hypotension and decreased capillary filling
5. tachycardia

Question 4

how would you manage a pt with severe anaphylaxis

Answer 4

Initial resuscitation:
1. remove trigger, maintain airway, high flow 100% O2

2. lie pt flat, raise legs and fluid resuscitate if hypotensive (e.g. 500-1000 mL 0.9% saline bolus)
3. adrenaline 0.5mg IM (anterolateral middle 1/3 of thigh) - repeat every 5 mins as needed to support CVS

Follow-up:
4. hydrocortisone 200mg IV (corticosteroid may help prevent or shorten protracted reactions)

5. chlorphenamine 10mg IV (antihistamine, may help counter histamine-mediated vasodilation and bronchoconstriction)

If continued respiratory deterioration:
6. nebulised salbutamol (treat bronchospasm) and nebulised adrenaline (treat laryngeal oedema)