Organophosphate Poisoning 

Description

Organophosphate (OP) poisoning occurs due to ingestion, inhalation, or dermal exposure to organophosphate compounds, which are commonly used as pesticides, insecticides, or nerve agents. Exposure can be:

• Intentional: Parasuicide, self-harm

• Accidental: Farmers, pesticide handlers

• Homicidal or warfare-related

Organophosphates irreversibly inhibit acetylcholinesterase, leading to excessive acetylcholine accumulation at muscarinic, nicotinic, and central nervous system receptors, resulting in a cholinergic crisis.

Carbamates, in contrast, inhibit acetylcholinesterase reversibly and usually cause a shorter duration of toxicity.

Common Sources

• Agricultural insecticides, herbicides, fungicides

• Fertilizers

• Livestock dipping agents

• Shampoos for lice

• Nerve agents (warfare)

Pathophysiology

Excess acetylcholine stimulates:

• Muscarinic receptors: bronchorrhea, bradycardia, miosis, vomiting, salivation, urination, lacrimation

• Nicotinic receptors: muscle fasciculations, weakness, paralysis, hypertension, tachycardia

• CNS effects: confusion, agitation, seizures, coma

Signs and Symptoms

Muscarinic (DUMBBBELS)

• Diarrhea

• Urination

• Miosis (constricted pupils)

• Bronchorrhea

• Bradycardia

• Bronchospasm

• Emesis (vomiting)

• Lacrimation

• Salivation

Nicotinic

• Muscle fasciculations

• Weakness or paralysis

• Tachycardia

• Hypertension

• Anxiety, seizures, coma

CNS / Other

• Confusion, agitation, altered mental status

• Hypoglycemia

• Hypotension

• Type 2 respiratory failure (hypercapnic)

• Intermediate syndrome (proximal muscle weakness, neck flexor weakness, respiratory compromise after 24–96 hours)

Investigations

• Baseline labs: FBC, U&Es, creatinine, LFTs, RBS

• Toxicology: Blood and urine organophosphate levels

• Enzyme assays: Serum or red-cell cholinesterase activity

• ABG: Evaluate respiratory compromise and acid-base status

• Other supportive investigations as clinically indicated

Management

1. Airway and Breathing

• Ensure airway patency

• Oxygen therapy and escalation as needed

• Suction secretions if present

• Mechanical ventilation if respiratory failure

2. Circulation

• Insert 2 large-bore IV lines

• Obtain blood for investigations

• Administer crystalloids for resuscitation and maintenance

• Monitor BP, HR, perfusion

3. Disability / Neurologic Status

• Assess GCS

• Monitor for seizures (manage per seizure protocol)

• Correct hypoglycemia

4. Decontamination

• Remove contaminated clothing

• Wash skin thoroughly with soap and water

• Eye irrigation if ocular exposure

5. Antidotal Therapy

a. Atropine (Muscarinic Antagonist)

• Initial dose: 1–2 mg IV, double every 5 minutes until atropinization endpoint (clearing of bronchial secretions, improvement of oxygenation, resolution of bronchospasm)

• Maintenance infusion: 20% of total atropinization dose over 24 hours

• Monitor for atropine toxicity: confusion, extreme tachycardia, blurred vision, fever, ileus, urinary retention

b. Pralidoxime (2-PAM, Cholinesterase Reactivator)

• Loading dose: 30 mg/kg IV over 20 minutes

• Continuous infusion: 8 mg/kg/hour (max 12 g/day)

• Effective mainly if given early (before “aging” of acetylcholinesterase)

6. Supportive Care

• Mechanical ventilation for respiratory failure

• Correct electrolyte imbalances

• Treat secondary infections (aspiration pneumonia)

• Monitor urine output

• ICU / HDU admission often required

Complications

• Aspiration pneumonitis or pneumonia

• Hypoxic organ injury

• Shock

• Intermediate syndrome (muscle weakness, respiratory compromise)

• Organophosphate-induced delayed polyneuropathy (OPIDP)

• Chronic organophosphate-induced neuropsychiatric disorder (COPIND)

Referral Criteria

• All cases of acute poisoning, even asymptomatic exposures

• Type 2 respiratory failure requiring mechanical ventilation

• Intermediate syndrome

• Persistent cholinergic symptoms despite antidotal therapy

Key Points

• Early recognition and rapid initiation of antidotes (atropine + pralidoxime) save lives.

• Supportive care, especially for airway and respiratory failure, is critical.

• Continuous monitoring in ICU is required for at least 24 hours, often longer.

• Consider psychosocial evaluation for intentional ingestion cases.