EM · Cyanide poisoning

Cyanide poisoning

Also known as Cyanide toxicity · Histotoxic hypoxia · Smoke inhalation cyanide · Cytochrome oxidase poisoning

Cyanide poisoning — the histotoxic toxin that halts cellular respiration by binding the ferric iron of cytochrome c oxidase (complex IV), shutting oxidative phosphorylation and forcing every tissue into anaerobic metabolism. The emergency source is the enclosed-space house fire (cyanide released from burning plastics, wool and polyurethane), and the patient is the unconscious fire survivor with soot in the mouth, a high lactate and a metabolic acidosis out of proportion to the carboxyhaemoglobin level — co-existing carbon monoxide is the rule. The clinical signs are rapid collapse, seizure and coma, an initial hypertension then bradycardic cardiovascular collapse, and the rare cherry-red skin from venous oxygen that the tissues cannot extract. Management is 100 per cent oxygen, empirical hydroxocobalamin 70 mg per kilogram (adult 5 g) intravenously — the preferred antidote because it does not cause hypotension or methaemoglobinaemia — and sodium thiosulfate intravenously. The smoke-inhalation kit (amyl or sodium nitrite) is avoided because methaemoglobinaemia worsens the co-existent carbon monoxide poisoning. ACEM-primary, globally tagged.

Checked against its sources on 5 Sept 2026