Makindo Medical Notes

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☠️ Organophosphate (OP) Toxicity — the “classic” nerve agent poisoning. OPs inhibit acetylcholinesterase → ↑ acetylcholine at synapses → cholinergic crisis: salivation, miosis, bronchorrhoea, paralysis. 💡 Death is usually from respiratory failure.

📌 About

• Common in pesticides (e.g., malathion, fenthion) and chemical warfare agents (sarin, soman, tabun, cyclosarin).
• Onset can be rapid (minutes) depending on dose/route.
• Pathology: irreversible phosphorylation of acetylcholinesterase → accumulation of ACh → hyperstimulation of muscarinic, nicotinic & CNS receptors.

⚙️ Pathophysiology

• Normal: Acetylcholine is broken down by acetylcholinesterase into acetate + choline.
• OPs bind irreversibly to the enzyme’s active site → persistent ACh activity at synapses.
• Results in muscarinic overstimulation (secretions, bradycardia), nicotinic effects (fasciculations → paralysis), and CNS toxicity (seizures, coma).

🧩 Clinical Features

• Intermediate Syndrome (24–96h): Respiratory/muscle weakness → ventilation often required.
• Delayed Polyneuropathy (2–3wks): Distal sensory-motor neuropathy, prolonged recovery.

🧪 Investigations

• Erythrocyte cholinesterase activity = best marker (serum pseudocholinesterase less reliable).
• ABG: hypoxia, hypercapnia if respiratory failure.
• Other labs: electrolytes, lactate, CXR for aspiration.

🚑 Management

• Decontamination: Isolate patient, remove clothing, wash skin with soap/water. Staff wear PPE 🧤.
• Airway & Breathing: O₂, suction secretions, prepare for advanced airway. ❌ Avoid succinylcholine (prolonged paralysis).
• Atropine: 1–3 mg IV (adults), repeat q5–10 min until secretions dry & HR >70 bpm. ⚠️ Tachycardia ≠ contraindication.
• Pralidoxime (2-PAM): 30 mg/kg IV over 20 min. Reactivates acetylcholinesterase (best given early, before “aging” of enzyme occurs).
• Diazepam: 5–10 mg IV for seizures or agitation.
• Supportive: Fluids for diarrhoea/vomiting, ICU admission for severe poisoning.

💡 Clinical Pearls

• Deaths are usually due to airway compromise (secretions, bronchospasm, paralysis, CNS depression).
• Always suspect in farmer with pinpoint pupils + secretions + muscle fasciculations.
• ⚠️ Atropine endpoint = drying of secretions, not HR or pupil size.
• Give atropine + diazepam immediately in unresponsive flaccid patients — seizures may be occult.
• Consider intermediate syndrome — patients can deteriorate even after initial improvement.

📚 Reference

• Organophosphate (OP) Poisoning – OpenAnesthesia

Cases — Organophosphate (OP) Toxicity

• Case 1: A 36-year-old male farmworker collapses while spraying pesticides. Pinpoint pupils, copious secretions, fasciculations, and bradycardia (HR 48). Management: Decontamination (clothes removed, skin washed), high-flow O₂, IV atropine titrated until secretions dry, IV pralidoxime. Outcome: Extubated after 2 days in ICU, discharged on day 5 with occupational health follow-up.
• Case 2: A 4-year-old boy ingests insecticide stored in a soft-drink bottle. Presents with vomiting, drooling, bronchospasm, fasciculations, and hypotension. Management: Intubated, IV atropine boluses then infusion, IV pralidoxime, benzodiazepines for seizures. Safeguarding team notified. Outcome: Full recovery within a week, no neurological sequelae. Environmental health arranged safe chemical storage.
• Case 3: A 29-year-old woman presents after deliberate ingestion of a large quantity of organophosphate pesticide. She is unresponsive, hypotensive, bradycardic, with copious airway secretions. ECG shows prolonged QTc. Management: Intubation and mechanical ventilation, repeated high-dose atropine infusions, pralidoxime infusion over 5 days, and vasopressor support. Developed intermediate syndrome with proximal muscle weakness requiring prolonged ventilation. Psychiatry referral initiated once medically stable.
  Outcome: Weaned from ventilator after 3 weeks, discharged to psychiatric care. Residual mild proximal weakness at 2-month review, but no further seizures or respiratory compromise.

Teaching Commentary 🧑‍⚕️

These three cases illustrate the spectrum of OP toxicity: 1) Occupational exposure with prompt recognition and good recovery, 2) Accidental ingestion in a child — highlights safeguarding and public health, 3) Severe deliberate overdose — often requiring prolonged ICU stay and prone to “intermediate syndrome” (delayed muscle weakness after initial recovery). Management principles remain consistent: decontamination, atropine, pralidoxime, seizure control, and ICU support. Outcomes hinge on exposure dose, treatment delay, and respiratory support. Always involve psychiatry in intentional cases.