ACP Broadsheet No 142: November 1993. Measurement of carbon monoxide and cyanide in blood.

Introduction Carbon monoxide and hydrogen cyanide are often found in fire atmospheres. These gases can incapacitate rapidly and thus render the victim unable to escape from the fire. High concentrations of carbon monoxide and hydrogen cyanide found in the blood of fire victims indicate a degree of survival in the toxic fire atmosphere. Concentrations may be sufficiently high in the blood to attribute death to carbon monoxide or hydrogen cyanide poisoning. The measurement of these substances in blood is quite straightforward but changes after death may raise or lower the cyanide concentration in the blood significantly. It is the impact of these processes that renders the cyanide level so difficult to interpret in many situations. This uncertainty in cyanide concentration may be responsible for the lack of correlation between cyanide and carboxyhaemoglobin concentrations in the blood of fire victims. Carbon monoxide deaths may also occur following inhalation of exhaust fumes and cyanide deaths may follow ingestion of cyanide salts. The concentrations in blood and tissue in these circumstances may greatly exceed those encountered in fire death situations.