Toxicology and Environmental Emergencies
This domain tests toxidrome recognition, decontamination, antidotes, drug overdoses, carbon monoxide, heat illness, and envenomation. The exam focuses on risk assessment and time-critical antidotal therapy.
Core rules
- Toxidromes guide early treatment: opioid (miosis, respiratory depression), anticholinergic (dry, flushed, agitated), cholinergic (salivation, bronchorrhoea, bradycardia), sympathomimetic (tachycardia, hypertension, agitation).
- Paracetamol overdose: use time since ingestion and treatment nomogram; give N-acetylcysteine promptly when indicated.
- Activated charcoal is useful within 1 hour for selected ingestions but is contraindicated in unprotected airway, caustic ingestion, and ileus.
- Salicylate toxicity causes tachypnoea, tinnitus, and mixed acid-base disturbance; urinary alkalinisation and dialysis may be needed.
- Carbon monoxide poisoning: give high-flow oxygen; pulse oximetry may be falsely normal.
Worked example
A 20-year-old presents 6 hours after paracetamol ingestion with a level above the treatment line. Start N-acetylcysteine without waiting for liver enzymes, because early antidote improves outcomes.
Traps
- Do not use naloxone as a substitute for airway support in opioid toxicity.
- Do not give charcoal to a drowsy patient who cannot protect the airway.
- Do not rely on pulse oximetry in carbon monoxide poisoning.
- Do not miss co-ingestants or delayed paracetamol toxicity.