Toxicology, Environmental and Metabolic Emergencies
What the board tests
Toxidrome recognition, antidote choice and dose, and the metabolic emergencies where the first hour of correction changes outcome. Egyptian practice makes organophosphate, scorpion and snake envenomation, paracetamol, methanol and aluminium phosphide exposure high-yield.
Toxidromes and decontamination
- Cholinergic: salivation, lacrimation, urination, diarrhoea, wheeze, bradycardia, pinpoint pupils. Atropine 1-2 mg IV, doubled every 3-5 min until secretions dry, plus pralidoxime 30 mg/kg.
- Anticholinergic, opioid, sympathomimetic and sedative-hypnotic patterns should be recognised from the bedside, not from the history alone.
- Activated charcoal only within 1 h, with a protected airway, and not in caustic or hydrocarbon ingestion.
Antidotes and specific poisons
- Paracetamol: N-acetylcysteine based on the Rumack-Matthew nomogram from 4 h postingestion; treat early if the time is unknown.
- Methanol/ethylene glycol: fomepizole (or ethanol), bicarbonate for acidosis, haemodialysis for severe acidosis or visual loss.
- Salicylate: urinary alkalinisation, dialysis for severe toxicity.
- Carbon monoxide: 100% oxygen; hyperbaric oxygen for syncope, neurological signs, pregnancy or severe carboxyhaemoglobin.
- Methemoglobinaemia: methylene blue 1-2 mg/kg. Cyanide: hydroxocobalamin.
Envenomation and metabolic
- Scorpion sting (Leiurus quinquestriatus): severe cases need antivenom plus supportive care; do not rely on prazosin alone.
- Snake bite: immobilise the limb, avoid incision or suction, give antivenom for systemic or progressive local envenoming; elapid bites may need ventilatory support.
- DKA: isotonic fluid, insulin infusion 0.1 unit/kg/h, potassium replacement once K is under 5.5, and no routine bicarbonate. HHS needs more fluid and lower-dose insulin. Adrenal crisis: hydrocortisone 100 mg before or with fluids. Heat stroke: cool first, transport second.
Worked example
A farmer presents with sweating, salivation, bronchospasm, bradycardia 42/min and pinpoint pupils after spraying. This is organophosphate poisoning. Secure the airway, suction, give atropine 2 mg IV and double the dose every 3-5 min until secretions clear and the chest is dry, give pralidoxime, and observe for intermediate syndrome. Reasoning: atropine is titrated to secretions, not to heart rate or pupil size.
Traps
Under-dosing atropine; giving flumazenil in a mixed overdose; bicarbonate in DKA with a normal pH; waiting for a toxicology screen before antidote; incision or suction at a snake bite site.