What clue suggests cyanide poisoning in a patient from a fire incident?

• A. Coloured skin yellow.
• B. Slow progression over hours with no metabolic acidosis.
• C. Normal venous blood color.
• D. Rapid onset of dizziness, headache, confusion, metabolic acidosis; bright red venous blood; treat with high-flow O2 and hydroxocobalamin if available.

Answer: (D)

Cyanide poisoning from smoke exposure causes histotoxic hypoxia—cells can’t use the oxygen carried in blood, so oxygen delivery looks normal, but tissues starve and lactic acid builds up. That makes the picture quick and dramatic: sudden dizziness, headache, and confusion as the brain is affected, along with metabolic acidosis from anaerobic metabolism. A telltale sign is the venous blood appearing bright red because it remains highly oxygenated since tissues aren’t extracting it. In management, give high-flow oxygen promptly and administer an antidote like hydroxocobalamin if available, which binds cyanide to form cyanocobalamin.

The other clues don’t fit cyanide poisoning as well. Yellow skin isn’t typical and points elsewhere; a slow progression with no metabolic acidosis contradicts the rapid, acid-producing nature of cyanide effects; normal venous blood color would clash with the expected histotoxic hypoxia and high venous oxygen content.