Forensic and clinical toxicologic studies on blood cyanide concentrations in fire victims

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The aim of this study was to examine the effects of slight methemoglobinemia, typically caused by fire gases, and of the postmortem interval on blood cyanide concentrations in fire victims. The rabbits were sacrificed by intramuscular injection of 1 ml/kg 2% potassium cyanide 5 min after intravenous injection of 0.33 ml/kg of 3% sodium nitrite or physiological saline. Average cyanide concentrations in cardiac blood at the time of death were 47.4 and 3.56 mg/l, respectively. When blood-containing hearts of the rabbits were left at room temperature (20-25℃), cyanide had disappeared almost completely by the end of a storage period of 72 h. Blood cyanide was stable in the hearts left at 4℃. Based on the results of the animal experiments, the formula : C_0=C・e^<0.046t> (C_0=blood cyanide concentration at the time of death, C=blood cyanide concentration detected at autopsy, and t=postmortem interval) was determined. Of twenty-two fire victims with postmortem intervals of 8 to 48 h, five was suspected that blood cyanide concentrations at the time of death had been as high as 5.32-6.47 mg/l. Three showed high saturation (54.7-63.0%) of carboxyhemoglobin and elevated total (free and combined with cyanide) methemoglobin contents (2.6-5.0%). Blood cyanide might have been completely combined with methemoglobin at the time of their death. In the remaining two victims, carboxyhemoglobin saturation was not high (30.9 and 37.9%) and no free methemoglobin was detected. As a result they may have exhibited severe toxic effects of cyanide at the time of their death. Our results suggest that 1) blood cyanide concentrations at the time of death should be estimated using our regression equation and 2) methemoglobin contents as well as carboxyhemoglobin saturation should be determined if toxic effects of cyanide in fire victims are to be properly evaluated.