Study of relationship between Metahemoglobin, Carboxihemoglobin and Hydrogen Cyanide in fire victims: interpretation of finding and confrontation with other episodes.

FERRARI L., GIANNUZZI L.

Geneva, Suiza

Congreso; The International Association of Forensic Toxicologists. TIAFT. 47 th International Meeting.; 2009

The International Association of Forensic Toxicologists. TIAFT.

In a previuos work in order to evaluate the contribution of Carbon monoxide (CO) and hydrogen cyanide (HCN) as toxic agent in fire causalities to the diagnosis of cause of death, a lethal index for CO and HCN was defined (LICO and LIHCN). In the prent work Carboxihemoglobin (COHb), Hemoglobin (Hb), Methahemoglobin (MeHb) and hydrogen cyanide (HCN) were quantified in victims blood to elucidate the cause of the death. We analysed bood samples of forensic autopsy cases in a tragic polyurethane mattress fire provoked death of 32 convicts in a prison ( Magdalena, Penitenciary Service of Buenos Aires Province, Argentina) in 2006. The cadaveric blood samples were gently drawn by puncturing femoral vein and analyzed by CO-oximeter systems. Blood alcohol (ethanol), cyanide and drugs were examined by gas chromatography. Saturation of COHb ranged from 10% to 43%, Hb between 2-19.7%, MetHb beetween 0.10 to 35.7% and HCN between 0.24 to 15 mg/L. These latter values were higher than the lethal levels reported in literature. Other toxic components routinely measured (ethanol, methanol, aldehydes and other volatile compounds) gave negative results on the 32 cases. Neither drugs of abuse nor psychotropics were detected.  The results indicated that death in the 32 fire victims was probably caused by HCN, generated during the extensive polyurethane decomposition provoked by a rapid increase of temperature. For other way, statistical analysis showed that %COHb and %MetHb in blood concentration were not independent variables with c2 = 11.12 (theoretic c2 = 4.09, degrees of freedom = 12, a=0.05). Aiming to obtain a relationship between these two variables, different ratios were analyzed. The most probable ratio between concentration of COHb and Met-Hb for our 32 cases was exponential decay model :  where a and b are constants. With a non-linear regression model, the value of a and b was estimated through the representation of [CO-Hb/MetHb] as a function of MetHb. A good fitting with the experimental data was achieved using the proposed equation. The values of a=107.28±4.79, b=0.935±0.06 and determination coefficients r2 =0.958.  This is the first report that calculated  the relationshif between COHb and MetHb in forensic blood samples.