Toxicology and Environmental Emergencies
Toxicology rewards pattern recognition and antidote recall. The Board expects toxidrome identification, the antidote, and the toxin where dialysis or urinary alkalinisation changes outcome.
Toxidromes first, drugs second
Opioid: pinpoint pupils, respiratory depression, bradypnoea - titrate naloxone 0.04-0.4 mg IV, then infuse because its half-life is shorter than most opioids. Anticholinergic: hot, dry, flushed, dilated, delirious - physostigmine cautiously, never in tricyclic overdose. Cholinergic (organophosphate): salivation, lacrimation, urination, diarrhoea, bronchorrhoea, bradycardia - atropine in doubling doses until secretions dry, plus pralidoxime. Sympathomimetic: tachycardia, hypertension, sweating, agitation. Sedative-hypnotic: depressed consciousness with stable vital signs.
Toxins with an antidote and a clock
Paracetamol: N-acetylcysteine, nomogram at 4 hours, or treat empirically if the level is unavailable or presentation late. Salicylate: mixed respiratory alkalosis with metabolic acidosis and tinnitus - alkalinise the urine with sodium bicarbonate, dialyse if severe. Methanol and ethylene glycol: raised osmolar gap, profound acidosis, visual or renal injury - fomepizole and dialysis. Tricyclic overdose: QRS above 100 ms predicts seizures and arrhythmia - sodium bicarbonate 1-2 mmol/kg boluses. Carbon monoxide: 100% oxygen, hyperbaric therapy for neurological signs, syncope, pregnancy or severe poisoning. Cyanide: hydroxocobalamin. Digoxin: specific Fab fragments.
Environmental emergencies
Heat stroke is thermoregulatory failure with CNS dysfunction - evaporative and ice-water cooling immediately; dantrolene has no role. Hypothermia: rewarm, remembering that not dead until warm and dead applies. High-altitude illness: descend, dexamethasone, nifedipine for oedema. Drowning: respiratory failure and hypoxic brain injury, where rescue breathing matters most in the first minutes.
Worked example
A young woman presents 3 hours after a mixed overdose with QRS 130 ms, pH 7.30 and a seizure. Give sodium bicarbonate 1-2 mmol/kg as a bolus, target QRS narrowing and pH 7.45-7.55, avoid flumazenil, and treat the seizure with benzodiazepines. The wide QRS is tricyclic sodium-channel blockade, and bicarbonate is the antidote.
Traps
Giving flumazenil in a mixed overdose. Relying on the osmolar gap to exclude methanol - it can be normal late. Giving activated charcoal to a drowsy patient without airway protection. Missing co-ingestion because the first toxidrome explained everything.