Organophosphate Poisoning: A Life-Threatening Emergency
Organophosphate compounds are found in pesticides, insecticides, and nerve agents. They cause toxicity by irreversibly inhibiting acetylcholinesterase, the enzyme that breaks down acetylcholine at nerve synapses. This leads to excessive accumulation of acetylcholine, causing overstimulation of muscarinic and nicotinic receptors throughout the body. The resulting cholinergic crisis can be rapidly fatal without treatment.
Recognizing Organophosphate Toxicity: SLUDGE-M and DUMBELS
The classic presentation is remembered by two mnemonics:
- SLUDGE-M: Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis, Miosis (pinpoint pupils)
- DUMBELS: Defecation, Urination, Miosis, Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation
Nicotinic effects include muscle fasciculations, weakness, paralysis, and tachycardia. CNS effects include anxiety, restlessness, seizures, and coma. Death typically results from respiratory failure due to bronchospasm, excessive secretions, and diaphragm paralysis.
Dual Antidote Therapy: Atropine and Pralidoxime
Treatment requires two medications working through different mechanisms:
Atropine blocks the muscarinic effects of acetylcholine excess (secretions, bronchospasm, bradycardia) but does not address the underlying enzyme inhibition or nicotinic effects (muscle weakness). Dose: 2 to 4 mg IV/IM, repeated every 5 to 10 minutes until secretions dry.
Pralidoxime (2-PAM) reactivates acetylcholinesterase by removing the organophosphate molecule from the enzyme before the bond becomes permanent ("aging"). Once aging occurs (typically 24 to 48 hours after exposure, but as little as 2 minutes for some nerve agents), pralidoxime is no longer effective. This is why early administration is critical.
Pralidoxime Dosing
- Adult: 1 to 2 grams IV infused over 15 to 30 minutes, or 1 to 2 grams IM if IV is not available
- Pediatric: 20 to 50 mg/kg IV over 15 to 30 minutes
- Repeat dosing: May repeat in 1 hour if muscle weakness persists
- Rapid IV push can cause hypertension, muscle rigidity, and laryngospasm
Prehospital Considerations
Provider safety is paramount. Wear appropriate PPE including chemical-resistant gloves and respiratory protection. Decontaminate the patient (remove clothing, brush off dry chemicals, flush with water) before providing care in an enclosed space like an ambulance. Administer atropine first to control immediately life-threatening symptoms, then follow with pralidoxime. Early pralidoxime is more effective than delayed administration, so do not wait for hospital arrival if the medication is available.