Investigation of oxyhemoglobin and carboxyhemoglobin ratios in right and left cardiac blood for diagnosis of fatal hypothermia and death by fire

Few large-scale investigations have looked at the oxyhemoglobin ratio (%O₂-Hb) or the carboxyhemoglobin ratio (%CO-Hb) in fatal hypothermia and death by fire as applicable to forensic medicine. We therefore retrospectively examined right and left cardiac blood samples for both %O₂-Hb and %CO-Hb in 690 forensic autopsy cases. We therefore sought to establish reference values for the above forensic diagnoses, to compare %O₂-Hb in fatal hypothermia with or without cardiopulmonary resuscitation (CPR), and to compare the relationship between %CO-Hb and smoking history. All %O₂-Hb and %CO-Hb data were obtained during or immediately after autopsies using a portable CO-oximeter. Death by carbon monoxide (CO) intoxication and death by fire were excluded from the analysis involving smoking history.

In fatal hypothermia, %O₂-Hb in the left cardiac blood was significantly higher than that in the right cardiac blood, providing important evidence for fatal hypothermia. Furthermore, %O₂-Hb in the left cardiac blood increases with CPR but that in the right cardiac blood increases in parallel. No correlation was observed between rectal temperature and %O₂-Hb in the right and left cardiac blood, indicating that it is unlikely that postmortem cooling increases %O₂-Hb in cardiac blood. %CO-Hb in smokers was significantly higher than that in non-smokers, although the number of cigarettes smoked did not appear to be significant. When assessing death by fire, we identified that %CO-Hb of >10% was a reliable marker of antemortem CO inhalation, regardless of smoking history.