Synergistic lethality induced by the combination of carbon monoxide and cyanide.

Carbon monoxide (CO) and hydrogen cyanide are recognized pyrolytic products of plastic materials in fires. Lethal blood concentrations of CO and cyanide are found in fire victims and considered to be the cause of death. However, there are reports of fire victims with sublethal concentrations of both CO and cyanide and no other attributed reason for their deaths. Thus, the purpose of this study was to investigate lethality induced by low concentrations of CO and cyanide. Male ICR mice were used in these studies. Doses of potassium cyanide (4-9 mg/kg, i.p.) were administered to animals pretreated for 3 min with either air or CO (0.63-0.66%). From these data the LD50 value of potassium cyanide (KCN) was determined in these animals pretreated with either air or CO. A significantly lower LD50 value for KCN was found in CO-pretreated animals as compared to air-pretreated animals. In another series of experiments, animals were pretreated with either saline or KCN (1.00-6.35 mg/kg, i.p.) and then placed in the chamber containing a CO atmosphere (0.325-0.375%). Ten to 20% of saline-pretreated animals were dead at the end of the monitoring period. Sublethal doses of KCN (3.5-6.35 mg/kg, i.p.) produced a synergistic lethality as compared to the saline-pretreated animals. Blood was analyzed for CO and cyanide content to determine if there were any changes that could explain this augmented lethality. There was no difference in CO or cyanide blood concentrations between these treatment groups. From these data there was demonstrated a synergistic lethality induced by the combination of CO and cyanide that could not be explained by altered CO or cyanide blood concentrations.