Cyanide poisoning — smoke inhalation antidote viva

Mechanism. Cyanide binds Fe³⁺ of cytochrome a3 (complex IV) → stops oxidative phosphorylation → anaerobic lactate with high venous O2 (histotoxic hypoxia).^[2]

Empiric trigger. Fire + unconscious + lactate ≥10 mmol/L → treat for CN before any level returns.^[1][4]

Antidotes. Hydroxocobalamin 70 mg/kg (adult 5 g) IV over 15 min (binds CN → cyanocobalamin, excreted in the urine; a second 5 g dose may follow if severe toxicity persists). Add sodium thiosulfate 12.5 g IV (50 mL of the 25 per cent solution, NITHIODOTE label) for severe cases. 100% oxygen throughout; early intubation for inhalation injury.^[3]

Avoid nitrites in smoke victims — metHb worsens coexistent CO. Dicobalt edetate risks serious cobalt toxicity when CN absent (anaphylactic shock, hypotension, ventricular arrhythmias among recorded serious effects — IPCS antidote monograph).^[4]

CO parallel. Continue high-flow/FiO2 1.0 oxygen (CO half-life from ~5 hours to ~1 hour); consider HBO criteria (LOC, neuro, pregnancy, high COHb — HBO shortens the half-life to ~20 minutes).^[5]