SUPERStudy: Organophosphate Poisoning

Introduction

Organophosphate poisoning is a potentially life-threatening condition caused by exposure to organophosphate (OP) compounds. These agents irreversibly inhibit acetylcholinesterase, leading to the accumulation of acetylcholine and overstimulation of cholinergic receptors.

Etiology

Sources:

• Agricultural pesticides (e.g., malathion, parathion).
• Chemical warfare agents (e.g., sarin, VX gas).
• Ophthalmologic agents for glaucoma (e.g., echothiophate, isoflurophate).
• Accidental exposure or suicidal ingestion.

Mechanism:

• Irreversible inhibition of acetylcholinesterase.
• Accumulation of acetylcholine causes overstimulation of muscarinic, nicotinic, and CNS receptors.

Epidemiology

• Prevalent in developing countries due to widespread agricultural use.
• Significant cause of morbidity and mortality, particularly in rural areas.
• Common in intentional poisonings (e.g., suicide attempts).

Pathophysiology

1. Inhibition of Acetylcholinesterase: Prevents acetylcholine breakdown at synaptic junctions.
2. Excess Acetylcholine: Leads to overstimulation of muscarinic, nicotinic, and CNS receptors.

Effects by Receptor Type:

• Muscarinic: Bronchoconstriction, bradycardia, increased secretions, miosis.
• Nicotinic: Muscle fasciculations, cramps, flaccid paralysis, tachycardia, hypertension.
• CNS: Seizures, confusion, coma, hallucinations, anxiety.

Clinical Manifestations

1. Muscarinic Symptoms:
   • SLUDGE-M:
     • Salivation
     • Lacrimation
     • Urination
     • Diarrhea
     • Gastrointestinal upset
     • Emesis
     • Miosis
   • Killer B’s: Bradycardia, Bronchorrhea, and Bronchospasm.
   • Hypotension.
2. Nicotinic Symptoms:
   • Muscle weakness, fasciculations, flaccid paralysis.
   • Tachycardia and hypertension (due to adrenal stimulation).
3. CNS Symptoms:
   • Anxiety, confusion, delirium, seizures, coma.

Diagnosis

1. Clinical Presentation: Characteristic symptoms (SLUDGE-M, muscle weakness, CNS involvement).
2. Cholinesterase Activity:
   • Plasma butyrylcholinesterase or pseudocholinesterase levels (decreased in acute poisoning).
   • RBC acetylcholinesterase levels (gold standard).
3. Confirmatory Tests: Detection of OP compounds in blood, urine, or gastric aspirate.

Treatment

1. Emergency Stabilization:
   • Airway protection and oxygenation.
   • Intubation if respiratory failure occurs.
2. Antidotes:
   • Atropine: Blocks muscarinic effects (given until secretions dry up).
   • Pralidoxime (2-PAM): Reactivates acetylcholinesterase (effective if administered early).
3. Supportive Care:
   • Decontamination: Remove clothing and wash skin thoroughly.
   • Activated Charcoal: For ingestion cases.
   • Benzodiazepines: For seizures.

Prognosis

• Mild Cases: Full recovery with prompt treatment.
• Severe Cases: High risk of death due to respiratory failure or multiorgan dysfunction.
• Long-term Effects: Chronic neurological sequelae in survivors of severe poisoning.

SUPERPoint

Organophosphate poisoning leads to a life-threatening cholinergic crisis characterized by muscarinic, nicotinic, and CNS symptoms, requiring rapid administration of atropine and pralidoxime.

References: 

Tintinalli JE, Ma O, Yealy DM, Meckler GD, Stapczynski J, Cline DM, Thomas SH. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 9e. McGraw-Hill Education; 2020.