Emergency Medicine · Toxicology
The facts most likely to be tested
Organophosphates cause irreversible inhibition of acetylcholinesterase, leading to a life-threatening cholinergic crisis.
The classic clinical presentation is defined by the DUMBELS mnemonic: Diarrhea, Urination, Miosis, Bronchospasm/Bradycardia, Emesis, Lacrimation, and Salivation.
Atropine is the first-line treatment to reverse muscarinic effects, specifically targeting bronchorrhea and bradycardia.
Pralidoxime is the specific antidote used to regenerate acetylcholinesterase by removing the phosphate group, but it is only effective if administered before aging occurs.
Nicotinic toxicity manifests as muscle fasciculations, weakness, and paralysis, which are not reversed by atropine.
Skin decontamination is the critical first step in management to prevent ongoing dermal absorption and protect healthcare providers from secondary exposure.
Miosis (pinpoint pupils) is a highly sensitive and classic physical exam finding that helps distinguish cholinergic excess from other toxidromes.
Vignette unlocked
A 45-year-old farm worker is brought to the emergency department after being found confused in a greenhouse. On physical exam, he is noted to have profuse salivation, lacrimation, and pinpoint pupils. His heart rate is 48/min, and lung auscultation reveals diffuse wheezing and crackles. He exhibits visible muscle fasciculations in his upper extremities. His clothes are noted to have a strong chemical odor.
What is the most appropriate initial pharmacologic intervention for this patient's respiratory symptoms?
Atropine
The patient is in a cholinergic crisis; atropine is the priority to dry up life-threatening bronchorrhea and reverse bradycardia, addressing the 'B' in DUMBELS.
Full handout
High yield triage
Etiology / Epidemiology
Common in agricultural workers exposed to pesticides; inhibits acetylcholinesterase leading to cholinergic crisis.
Clinical Manifestations
Presents with SLUDGE syndrome and DUMBELS; miosis and bronchorrhea are classic findings.
Diagnosis
Diagnosis is clinical; RBC cholinesterase levels confirm exposure if time permits.
Treatment
First-line is atropine to dry secretions, followed by pralidoxime to reverse enzyme inhibition.
Prognosis
Monitor for respiratory failure; death usually results from bronchospasm or muscle paralysis.
Full handout
Epidemiology & Etiology
Primarily affects farmers and industrial workers via dermal, inhalation, or ingestion routes. It is a frequent cause of suicidal ingestion in rural settings. Exposure to nerve agents like Sarin represents a high-stakes bioterrorism risk.
Pertinent Anatomy
The toxin targets the synaptic cleft of the neuromuscular junction and autonomic ganglia. It disrupts the parasympathetic nervous system and somatic motor endplates.
Pathophysiology
Organophosphates irreversibly bind and inhibit acetylcholinesterase, causing massive accumulation of acetylcholine at synapses. This leads to continuous overstimulation of both muscarinic and nicotinic receptors. The process is known as aging when the bond becomes permanent, rendering pralidoxime ineffective.
Clinical Manifestations
Patients present with the DUMBELS mnemonic: Diarrhea, Urination, Miosis, Bronchorrhea/Bradycardia, Emesis, Lacrimation, and Salivation. Respiratory failure is the primary cause of death due to excessive secretions and diaphragmatic paralysis. Nicotinic effects include muscle fasciculations and weakness.
Diagnosis
Diagnosis is strictly clinical; do not delay treatment for labs. RBC cholinesterase is the most specific test, while plasma pseudocholinesterase is more sensitive but less specific. Levels <50% of normal are diagnostic.
Treatment
Initial management requires aggressive airway protection and decontamination. Administer atropine until bronchorrhea resolves; do not use atropine for nicotinic symptoms like muscle weakness. Follow with pralidoxime to regenerate the enzyme, ideally within 24-48 hours before aging occurs.
Prognosis
Patients require prolonged observation for rebound toxicity. Monitor for delayed neuropathy occurring 1-3 weeks post-exposure. Mechanical ventilation is often required for severe cases.
Differential Diagnosis
Carbamate poisoning: shorter duration of action, no aging
Opioid overdose: miosis present but lacks SLUDGE secretions
Cholinergic mushroom toxicity: rapid onset, usually lacks nicotinic symptoms
Nerve agent exposure: rapid onset, high mortality, requires immediate PPE
Organochlorine poisoning: presents with seizures and tremors, not cholinergic crisis