--- module: 059-01 language: en chapter: 59 title: "Poisoning, Overdose, Envenomation, and Environmental Exposure" module_title: "Foundations" source_sha256: 3103f21e16fcc374acd6b221dcad3f5f47f73882e6c20f1050d3a53aa3b3f256 --- # Toxicology foundations ## Orientation and immediate approach ### Physiology applied under uncertainty #### Histories incomplete, products mixed ### Protect staff and stop exposure #### Remove clothing, brush off dry chemicals ### Stabilise airway, breathing, circulation ### Normal early findings do not exclude delay #### Delayed release, metabolites, hepatic toxicity ### History: substance, maximum amount, time, route ### Self-poisoning: psychosocial review after stabilisation #### Low intent does not reduce dose ## Toxidromes ### Opioid: low consciousness, slow breathing, small pupils ### Sedative-hypnotic: no unique pupil pattern ### Sympathomimetic: agitation, mydriasis, sweating ### Antimuscarinic: mydriasis with dry flushed skin #### Reduced bowel sounds, urinary retention ### Cholinergic: secretions, bronchospasm, small pupils ### Serotonin toxicity: hyperreflexia, clonus, heat ### Neuroleptic malignant syndrome: slower, rigid ### Malignant hyperthermia: anaesthetic-triggered ## Testing and decontamination ### Paracetamol measured despite no symptoms ### QRS widening: sodium-channel blockade ### QT prolongation: polymorphic ventricular tachycardia ### Urine screens: treat the patient, not the screen ### Charcoal: early, cooperative, protected airway #### Aspiration can be catastrophic #### Poor binding of alcohols, metals, corrosives ### Whole-bowel irrigation for selected cases ## Paracetamol and salicylate ### Paracetamol saturates conjugation #### Reactive metabolite depletes glutathione ### Nomogram only for single timed ingestion ### N-acetylcysteine replenishes glutathione ### Salicylate uncouples and stimulates respiration #### Early respiratory alkalosis, later acidosis ### Toxicity can worsen as serum level falls ### Avoid intubation, preserve hyperventilation ## Opioids, sedatives, antidepressants ### Ventilation is the priority ### Naloxone titrated to breathing #### May wear off before the opioid ### Flumazenil can precipitate seizure ### Tricyclics block fast sodium channels #### Bicarbonate treats cardiovascular toxicity ### Serotonin reuptake inhibitors often milder ## Stimulants and hyperthermia ### Catecholamine excess: agitation, vasospasm, heat ### Benzodiazepines reduce central activation ### Rapid external cooling, not antipyretics ### Serotonin toxicity: stop, sedate, cool ### Neuroleptic malignant syndrome: stop, support ### Malignant hyperthermia: immediate dantrolene ## Alcohols and gases ### Ethanol intoxication is a diagnosis of exclusion ### Methanol: formic acid, vision, basal ganglia ### Ethylene glycol: acidosis, kidney, oxalate ### Fomepizole blocks alcohol dehydrogenase ### Carbon monoxide: pulse oximetry can look normal #### High oxygen, co-oximetry, hyperbaric advice ### Cyanide blocks electron transport #### Lactic acidosis, prompt antidote ## Pesticides, metals, corrosives ### Organophosphates inhibit acetylcholinesterase #### Atropine to secretions and perfusion #### Weakness after apparent recovery ### Lead: children and pregnancy vulnerable #### Remove source, chelate by level and symptoms ### Acids coagulate, alkalis penetrate ### Oropharynx does not predict oesophagus ## Envenomation and bites ### Record time, place, progression ### Keep still, immobilise, pressure guidance #### No cutting, sucking, freezing, tourniquet ### Antivenom by syndrome, ready for anaphylaxis ### Bites: irrigate, tetanus, rabies, antibiotics #### Hand and fist injuries: urgent surgery ## Heat, cold, immersion ### Heat exhaustion lacks neurological dysfunction ### Heat stroke: encephalopathy, organ injury #### Cold-water immersion, do not delay ### Hypothermia: bradycardia, coagulopathy #### Handle gently, rewarm by severity ### Drowning: ventilation and oxygenation first