Acute Organophosphate Poisoning

Clinical assessment

Diagnosis is primarily clinical based on history of exposure (often known) and recognition of the characteristic cholinergic toxidrome (especially miosis, excessive secretions, bradycardia, fasciculations). Smell of chemical may be present.

Investigations

• Clinical assessment is key.
• Plasma or Red Blood Cell (RBC) Cholinesterase levels: Can confirm diagnosis and severity (low levels indicate inhibition), but results often not available timely for acute management.
• Monitor: ECG (bradycardia, AV block, QTc prolongation), SpO2, Blood Glucose.
• Rule out other causes of similar symptoms (e.g., carbamate poisoning - similar but shorter duration, other causes of coma/seizures).

Diagnostic criteria

Clinical syndrome (cholinergic toxidrome) following known or suspected exposure to organophosphates. Response to atropine supports diagnosis.

Non-pharmacological management

• Decontamination (CRITICAL, simultaneous with resuscitation, use PPE - gloves, gown): Remove ALL contaminated clothing immediately. Wash contaminated skin thoroughly with copious amounts of soap and water. Irrigate eyes if exposed.
• Airway Management: Aggressive suctioning of excessive secretions is vital. Maintain patent airway (positioning, adjuncts). Endotracheal intubation often required for respiratory failure, inability to clear secretions, or coma.
• Breathing Support: High-flow oxygen. Assisted ventilation (bag-mask or mechanical ventilation) if respiratory failure (due to secretions, bronchospasm, muscle weakness, CNS depression).
• Circulation Support: Establish IV access. IV fluids (Normal Saline) for dehydration, hypovolemia. Monitor BP and HR closely.
• GI Decontamination (Consider risk/benefit, AFTER stabilization/airway secured): Gastric lavage may be considered if massive ingestion within 1-2 hours. Activated charcoal (single dose) may be given within 1-2 hours if airway protected (efficacy debated, aspiration risk high).

Pharmacological treatment

• Antidote (Muscarinic antagonist): Atropine IV. Initial dose: Adult 2-5 mg IV push; Child 0.05 mg/kg IV (minimum dose 0.1mg). Double the dose every 3-5 minutes until signs of atropinization achieved (Endpoint: Drying of pulmonary secretions - clear lungs on auscultation, HR > 80/min, Systolic BP > 80mmHg. Pupil size is NOT a reliable endpoint). Large cumulative doses often needed. Maintain atropinization with repeat boluses or continuous infusion (e.g., 10-20% of total loading dose per hour, titrated). Taper slowly over days once stable.
• Antidote (Cholinesterase reactivator): Pralidoxime (PAM) IV. Indicated for moderate to severe poisoning (esp. muscle weakness, fasciculations, respiratory depression). Most effective if given early (<24-48h). Loading dose: Adult 1-2 g IV over 30 min (or 30 mg/kg); Child 25-50 mg/kg IV over 30 min. Maintenance infusion: Adult 8-10 mg/kg/hr; Child 10-20 mg/kg/hr. Continue for 24-48h or until clinical improvement/off atropine.
• Seizures: Diazepam IV (or Lorazepam) is first line (dose as per general poisoning guidelines).
• Bronchospasm: Nebulized Salbutamol (Adult 5mg; Child 2.5mg). Atropine is primary treatment for bronchospasm/bronchorrhea.
• Avoid: Morphine, succinylcholine, phenothiazines, aminophylline.

Monitoring

Continuous monitoring of: Respiratory status (secretions, breath sounds, rate, effort, SpO2), Cardiovascular status (HR, BP, ECG), Neurological status (GCS, seizures, muscle strength/fasciculations), Degree of atropinization (secretions!). Monitor temperature, blood glucose. Monitor cholinesterase levels if possible to guide duration of PAM therapy.