Insect-sting hypersensitivity — formative SAQs

Question 1 (10 marks)

A nine-year-old boy is stung on the forearm by a wasp at a picnic. Within four minutes he is flushed, wheezy and complaining his throat feels tight, and his lips are swelling. On arrival his oxygen saturation is 91 per cent in air, his respiratory rate is 34 with accessory-muscle use, and his blood pressure is 88/50. Outline your immediate and subsequent management, including the definitive workup and prevention package. ^[2]

Model answer

Immediate recognition and resuscitation (4 marks). This is systemic anaphylaxis to a wasp sting with both respiratory and cardiovascular compromise (Brown grade 3). Call for help, lie him flat with legs raised (he is hypotensive), give high-flow oxygen, and give intramuscular adrenaline into the anterolateral thigh without waiting for any further sign — 300 micrograms (he is around 30 kg). Remove any retained stinger by scraping sideways. Repeat adrenaline every five minutes if there is no response, and give an intravenous crystalloid bolus of 10 mL/kg for shock. Add an inhaled bronchodilator for refractory wheeze after adrenaline. Antihistamines and corticosteroids are adjuncts only. ^{[1] [2]}

Observation and disposition (2 marks). Arrange timed serum tryptase on arrival, at one to two hours, and at baseline at least twenty-four hours later; admit overnight because he has respiratory and cardiovascular compromise and needed resuscitation. Observe for the biphasic reaction, which can recur one to seventy-two hours later. Discharge once fully recovered and stable. ^{[2] [5]}

Definitive workup and prevention (4 marks). Refer to the allergy clinic at four to six weeks for venom-specific immunoglobulin E and skin testing to confirm the culprit (vespid), a baseline serum tryptase to stratify severity and screen for clonal mast-cell disease, and component-resolved diagnostics if double-positive. Refer for venom immunotherapy, which gives around 90 to 98 per cent protection once maintenance is reached over three to five years — indicated because he had a systemic reaction. Discharge with an adrenaline autoinjector (300 micrograms) — prescribe two if rural or remote — a written action plan, medical identification, and family and school education on avoidance and device use. The autoinjector rescues the next reaction; venom immunotherapy prevents it. ^{[3] [4]}