Organophosphate Poisoning Management

[Last updated on 2nd August 2024]

Clinical features:

Muscarinic effects:

SLUDGE/BBB: Salivation, Lacrimation, Urination, Diarrhoea, Gastric Emesis, Bronchorrhea, Bronchospasms, Bradycardia

Nicotinic effects:

Fasciculations, Muscle weakness, Paralysis, Respiratory depression, Seizures, Coma

Intermediate syndrome:

Occurs in 10-40%, after 24 to 96 hours, Neck flexion weakness, Decreased deep tendon reflexes, Cranial nerve abnormalities, Proximal muscle weakness, Respiratory insufficiency

Overview of Management

1. Decontamination

  • For topical exposure with potential dermal absorption
  • Remove patient’s clothes
  • Vigorously irrigate affected areas

2. Supportive Care and ABCs

  • If markedly low GCS, give 100% oxygen and immediate tracheal intubation (avoid succinylcholine)
  • Adequate volume resuscitation with isotonic crystalloid

3. Atropine

  • Recommended for all patients with cholinergic toxicity from organophosphate or carbamate poisoning (Grade 1A) (1).
  • Indications to start atropine:
    • Systolic blood pressure < 80 mmHg
    • Pulse rate < 80 / min
    • Wheezes and crackles
    • Small pupils
    • Excessive sweating in the axilla
  • Dosing:
    • Adults: Start with 2 to 5 mg IV bolus; Children: 0.05 mg/kg IV bolus
    • Assess the response in 3 to 5 minutes, with the following targets.
      • SBP > 80 mmHg
      • Pulse rate > 80 / min
      • Clear chest
      • Pupils no longer pinpoint
      • Dry axillae
    • The endpoint for atropinisation is dried pulmonary secretions and adequate oxygenation. Tachycardia and mydriasis must not be used to limit or to stop subsequent doses of atropine. The main concern with organophosphate toxicity is respiratory failure from excessive airway secretions (2).
    • If inadequate atropinisation after 3 to 5 minutes give a repeat IV atropine bolus, doubling the initial dose. (e.g.: if initially given 3 mg, then give the next dose 6 mg)
    • Continuous reassess in every 3 to 5 minutes and if adequate atropinisation is not achieved, give repeated atropine boluses doubling the previous doses (e.g.: 3 mg, 6 mg, 12 mg, …)
    • Continue atropine boluses repeatedly until adequate atropinisation achieves.
    • The main objective of using atropine is to improve cardiorespiratory parameters in patients dealing with organophosphate toxicity. Assessment of heart rate, blood pressure, and respiratory status is more crucial than pupil size and skin moisture (3).
  • After atropinisation achieved, start an IV atropine infusion as follows.
    • Calculate the total cumulative dose which was given as boluses.
    • Start atropine infusion 20% from the total cumulative bolus per hour.
    • Monitor vital parameters pulse rate and blood pressure and monitor lung sounds.
    • Reduce the atropine infusion rate every 30 minutes keeping SBP > 80 mmHg, PR > 80 / min and clear lungs.
    • The endpoint for atropinisation is dried pulmonary secretions and adequate oxygenation. Tachycardia and mydriasis must not be used to limit or to stop subsequent doses of atropine. The main concern with organophosphate toxicity is respiratory failure from excessive airway secretions (2).
    • Patients with severe poisoning may require the administration of hundreds of milligrams of atropine, either as bolus doses or continuous infusion, over the course of several days to weeks until the patient shows improvement (3).
    • Features of atropine toxicity:
      • Confusion
      • Pyrexia
      • Absent bowel sounds
      • Urinary retention
    • If atropine toxicity develops hold atropine infusion and once the toxicity features disappeared start IV atropine infusion 80% from the previous rate.

4. Oxime Therapy

  • Atropine does not bind to nicotinic receptors and ineffective in treating neuromuscular dysfunction.
  • Pralidoxime is effective in treating muscarinic and nicotinic symptoms.
  • Always administer with concurrent atropine.
  • Suggested for all patients with:
    • Evidence of cholinergic toxicity
    • Neuromuscular dysfunction
    • Exposure to organophosphorus agents causing delayed neurotoxicity (Grade 2C).
  • WHO recommendation:
    • Adults: IV bolus of at least 30 mg/kg, administered slowly over 30 minutes
    • Children: 25-50 mg/kg, administered slowly over 30 minutes

5. Seizure Treatment

  • Treat with benzodiazepine
  • Prophylactic diazepam (e.g., 10 mg IV) to reduce neurocognitive dysfunction after poisoning

References:

  1. Organophosphate and carbamate poisoning – UpToDate [Internet]. [cited 2024 Jul 8]. Available from: https://www.uptodate.com/contents/organophosphate-and-carbamate-poisoning
  2. Organophosphate Toxicity Medication: Anticholinergic agents, Antidotes, OP poisoning, Benzodiazepines [Internet]. [cited 2024 Jul 8]. Available from: https://emedicine.medscape.com/article/167726-medication#2
  3. Robb EL, Regina AC, Baker MB. Organophosphate Toxicity. 2023 Nov 12 [cited 2024 Jul 8]; Available from: https://www.ncbi.nlm.nih.gov/books/NBK470430/