Organophosphate Poisoning

1. Introduction

Organophosphate (OP) poisoning is a medical emergency caused by exposure to organophosphate insecticides, pesticides, or nerve agents. It is a leading cause of morbidity and mortality in developing countries due to its widespread use in agriculture. OP compounds exert their toxicity by irreversibly inhibiting acetylcholinesterase (AChE), leading to excessive acetylcholine (ACh) accumulation at muscarinic, nicotinic, and central nervous system receptors.

2. Pathophysiology

Organophosphates bind irreversibly to acetylcholinesterase (AChE), preventing the breakdown of acetylcholine (ACh). This leads to overstimulation of cholinergic receptors:

✅ Muscarinic Receptors (Parasympathetic System) → SLUDGE Syndrome

• Salivation

• Lacrimation

• Urination

• Diarrhea

• Gastrointestinal cramps

• Emesis

✅ Nicotinic Receptors (Neuromuscular System) → Muscle Weakness & Paralysis

• Fasciculations

• Muscle cramps

• Respiratory failure (diaphragmatic paralysis)

✅ CNS Effects → Seizures & Coma

• Confusion

• Convulsions

• Coma

🔴 Aging:

• OP compounds form an irreversible bond with AChE within 6–48 hours, making reactivation impossible.

• Early treatment with oximes (e.g., pralidoxime) can reverse this before aging occurs.

3. Clinical Features of OP Poisoning

Classic Signs: Cholinergic Crisis (DUMBBELLS Mnemonic)

✅ Diarrhea

✅ Urination

✅ Miosis (Pinpoint pupils)

✅ Bradycardia, Bronchorrhea, Bronchospasm

✅ Emesis (Vomiting)

✅ Lacrimation (Tearing)

✅ Lethargy, Loss of consciousness

✅ Salivation, Sweating

🔴 Severe Toxicity:

• Respiratory failure (excess secretions, bronchospasm, diaphragm paralysis)

• Seizures, coma

• Hypotension or cardiac arrhythmias

4. Diagnosis

✅ Clinical Diagnosis:

• History of exposure (ingestion, inhalation, dermal contact)

• Pesticide smell (Garlic-like odor) on breath and clothing

• Cholinergic symptoms (SLUDGE, DUMBBELLS, Seizures, Respiratory failure)

✅ Laboratory Tests:

• Plasma cholinesterase (Butyrylcholinesterase) ↓

• RBC Acetylcholinesterase ↓ (More specific but takes longer)

🛑 Severity Based on Plasma Cholinesterase Levels:

5. Management of Organophosphate Poisoning

A. Initial Resuscitation (ABCDE Approach)

✅ Airway: Early intubation if excessive secretions or respiratory failure

✅ Breathing: Oxygen therapy, mechanical ventilation if needed

✅ Circulation: IV fluids, monitor BP (risk of bradycardia, hypotension)

✅ Decontamination:

• Remove contaminated clothing

• Wash skin with soap & water (No alcohol-based sanitizers)

• Gastric lavage (if ingestion within 1 hour & airway protected)<controversial>

• Activated Charcoal (1g/kg) if patient presents with 1-2 hours

B. Specific Antidotes

🔴 Key Considerations for Atropine:

• Titrate until bronchorrhea resolves & HR normalizes

• High doses may be needed (Hundreds of mg in severe cases)

🔴 Key Considerations for Pralidoxime:

• Most effective within 6 hours of exposure

• Less useful after enzyme aging (>48 hrs in some OPs)

C. Supportive Management

✅ Mechanical Ventilation if Needed

• Secretions & diaphragmatic paralysis → Intubate early

• Avoid succinylcholine (prolonged paralysis due to AChE inhibition)

✅ Monitoring & ICU Care

• Serial cholinesterase levels (to guide therapy)

• Watch for intermediate syndrome (24-96 hrs after exposure) → Muscle weakness, respiratory failure

✅ Long-Term Follow-Up

• Chronic neuropathy (OP-induced delayed polyneuropathy)

• Neuropsychiatric symptoms (depression, cognitive dysfunction)

6. MCQs on Organophosphate Poisoning

Q1. Which of the following is the best indicator of organophosphate poisoning severity?

A) Pseudocholinesterase levels

B) Glasgow Coma Scale

C) Creatinine

D) Serum Sodium

✅ Answer: A) Pseudocholinesterase levels

Q2. What is the first-line treatment for excessive secretions in OP poisoning?

A) Pralidoxime

B) Atropine

C) Succinylcholine

D) Epinephrine

✅ Answer: B) Atropine

Q3. Why is succinylcholine avoided in OP poisoning?

A) Causes severe bradycardia

B) Exaggerates cholinergic symptoms

C) Prolonged paralysis due to AChE inhibition

D) Causes severe hypertension

✅ Answer: C) Prolonged paralysis due to AChE inhibition