--- module: 059-02 language: en chapter: 59 title: "Poisoning, Overdose, Envenomation, and Environmental Exposure" module_title: "Toxicokinetics, pattern recognition, antidotal logic, and environmental emergencies" source_sha256: 1d3a60f0e5ca9fbc8ac36d4ec3898da1619abc766b9326fd09421299d83aca50 --- # Toxicokinetics, patterns, antidotes, environment ## Exposure control first ### Identification often arrives late ### Protect rescuers, remove clothing #### Brush off dry powder before irrigation #### Prevent secondary exposure ### Stabilise airway, ventilation, circulation ### Looking well does not exclude toxicity #### Delayed release or accumulating metabolite #### Observe to expected kinetics ## Toxicokinetics ### Toxicity is dose reaching target over time ### Absorption: route, formulation, gastric emptying ### Distribution: binding, lipid solubility, volume ### Metabolism may create toxic products #### Paracetamol, methanol, ethylene glycol ### Saturation, cycling, bezoars prolong toxicity ## History and toxidromes ### Seek maximum plausible dose #### Records and scene may beat tablet counts ### Low stated intent does not reduce dose ### Opioids: depressed ventilation, miosis ### Sympathomimetic versus antimuscarinic #### Sweating versus dry skin, retention, ileus ### Cholinergic: muscarinic secretions #### Nicotinic fasciculation then weakness ## Electrocardiogram and decontamination ### Early electrocardiogram reveals channel effects ### Wide QRS predicts seizure and dysrhythmia #### Bicarbonate raises sodium and pH ### QT: correct potassium and magnesium ### Charcoal benefit depends on timing and airway ### Corrosives not neutralised #### Exothermic reaction worsens injury ## Paracetamol and salicylate ### Paracetamol silent while glutathione consumed ### Nomogram only for single timed ingestion ### N-acetylcysteine helps even after injury ### Salicylate: mixed alkalosis and acidosis ### Serial levels, single fall misleading ### Acidaemia drives salicylate into brain ### Alkalinisation needs potassium correction ### Intubation hazardous #### Preserve pre-intubation minute ventilation #### Abnormal adaptation may keep patient alive ## Opioid, sedative, serotonergic antidote logic ### Opioid death is ventilatory failure #### Ventilate before or with naloxone ### Titrate naloxone to breathing, not alertness ### Long-acting opioids outlast naloxone ### Flumazenil removes anticonvulsant protection ### Serotonin toxicity: rapid, clonus, hyperreflexia ### Neuroleptic syndrome: slower, severe rigidity ### Muscle heat may need paralysis ## Toxic alcohols, digoxin, lithium ### Alcohol dehydrogenase makes toxic metabolites #### Osmolar gap falls as anion gap rises #### Fomepizole blocks metabolism ### Digoxin: bradyarrhythmias and tachyarrhythmias #### Antibody fragments for life threat #### Total level uninterpretable afterwards ### Lithium: tremor, ataxia, altered consciousness #### Dialysis decided beyond concentration #### Charcoal does not adsorb lithium ## Gases, organophosphates, corrosives ### Oximetry reads carboxyhaemoglobin as oxygenated #### Late low level underestimates peak ### Atropine to secretions and perfusion ### Oximes act before enzyme ageing ### Late weakness needs respiratory surveillance ### Mild oral findings do not exclude injury ### Button battery: rapid necrosis, urgent removal ## Envenomation and environment ### Identify by geography, syndrome, progression ### Antivenom only for significant envenomation ### Heat stroke: cool immediately #### Antipyretics fail, not prostaglandin fever ### Hypothermia can mimic death ### Smoke: carbon monoxide and cyanide ### Drowning: ventilate, not drain water ## Consultation and discharge ### Confirm formulation and antidotes with poisons service ### Discharge after predicted peak passes ### Antidote improvement may be temporary ### Psychosocial plan and restricted access ### Check household and co-workers