ASPHYXIA DUE TO OXYGEN DEFICIENCY BY GASEOUS SUBSTANCES

The determination of the cause of death in asphyxiation gas cases is v ery difficult because of the variation in circumstances surrounding su ch deaths. To clarify the cause of death and to identify the factors i nvolved in asphyxia, the symptoms during asphyxia, the concentration o f gases at the respiratory arrest, the time to death and the concentra tion of the gaseous substances in the tissues were studied using rats and six gases. Three inhalations were used: (1) rapid asphyxia (2-3 mi n) in the exposure chamber in which the oxygen was depleted completely , (2) prolonged asphyxia (20-25 min) by gradually depleted oxygen, and (3) asphyxia by the inhalation of gases saturated with a critical gas concentration, maintaining the O-2 at 20% (60 min). In the rapid asph yxia groups, respiratory arrest occurred within 30 to 40 s, followed b y cardiac arrest 2 or 3 min thereafter. Severe convulsions were observ ed only with the use of nitrogen. In the prolonged asphyxia groups, re spiratory arrest occurred at the concentration of 4-5% O-2 with non-to xic gases (N-2, CH4, N2O, and propane). The toxic gases CO2 and Freon- 22 produced respiratory arrest at the concentration of 6.6-8.0% O-2 (6 0-67% CO2) and 13-14% of O-2 (30-35% Freon-22), respectively. Variatio ns in the concentrations of the gases among the tissues was observed a ccording to the type of asphyxia, type of gas and the duration of expo sure. The concentration of the fat-soluble gases in the adipose tissue showed marked variation according to the duration of the exposure. Th e distribution pattern of methane was different from those of the othe r gases, in which the variation of concentrations among the tissues ex cept lung were little in both rapid and prolonged asphyxia, These phen omena were considered to be attributable to the solubility of the gase ous substances in blood and tissues. Atrophy in the alveoli was observ ed after the rapid asphyxia with CO2 and N2O. Local hemorrhaging in th e lungs was also observed, especially in CO2 asphyxia, The risks of ox ygen-depletion asphyxia are the rapid reaction of loss of consciousnes s and respiratory and cardiac arrest. This paper presents valuable fin dings for the diagnosis of the cause of death and estimating the situa tion of the accident in cases of asphyxia. (C) 1998 Elsevier Science I reland Ltd. All rights reserved.