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Organophosphate insecticide poisoning — MRCEM SBA MCQ

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HardToxicology and environmental emergenciesOrganophosphate insecticide poisoningMRCEM SBA

A 42-year-old greenhouse worker is brought to the emergency department after spilling a concentrated organophosphate insecticide over his clothing. His contaminated clothing has been removed and his skin washed. He has received oxygen, airway suction and two intravenous doses of atropine. He remains alert and protects his airway; an anaesthetist is present. His pulse has risen from 54 to 118 beats/min and his pupils are dilated, but he still has copious bronchial secretions and widespread wheeze. His blood pressure is 116/72 mmHg and SpO₂ is 95% on a reservoir mask. Fasciculations are visible in both calves. He is being monitored and a critical care bed is being arranged. Which antidote strategy is most appropriate now?

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Correct answer: E — Repeat intravenous atropine boluses to clear bronchial secretions and arrange early pralidoxime.

The labelled exposure, bronchorrhoea, wheeze and fasciculations indicate clinically significant organophosphate poisoning. Although atropine has increased his heart rate and dilated his pupils, the persistent wet chest shows that its crucial respiratory effect has not yet been achieved. Repeat intravenous boluses should be titrated to improvement in bronchial secretions and bronchospasm, alongside suction, oxygen and readiness to ventilate. Pralidoxime should be arranged early as an adjunct; it does not replace atropine for the immediate control of muscarinic airway effects. A maintenance infusion may be useful after effective initial atropinisation, but starting one without further boluses leaves his current bronchorrhoea inadequately treated. B addresses acetylcholinesterase inhibition and may help neuromuscular effects, but wrongly substitutes pralidoxime for urgently needed atropine. C mistakes tachycardia for proof that atropinisation is complete; the chest findings are the decisive discriminator. D would delay treatment for a confirmatory investigation despite a characteristic exposure and ongoing respiratory toxicity. His protected airway and maintained oxygen saturation permit continued antidote treatment under close monitoring, but deterioration would require immediate ventilatory support.

Reference: HSE Labelling Handbook Volume 2, Appendix 8: Organophosphate compounds with anticholinesterase activity (November 2020) — https://www.hse.gov.uk/pesticides/assets/docs/Lab-HB-Vol-2-Professional.pdf NHS England Clinical Guidelines for Use in a Major Incident: CBRN Guidelines—Nerve Agents (8 January 2020) — https://www.england.nhs.uk/wp-content/uploads/2018/12/B0128-clinical-guidelines-for-use-in-a-major-incident-v2-2020.pdf