Air embolism or putrefaction? Gas analysis findings and their interpretation

Gas was detected in the hearts of 111 necropsy cases. The gas was quantified and then analyzed by gas chromatography. In 70 cases H2, a clear marker of putrefaction, could be identified in the samples. After critical consideration, air embolism was accepted in 36 of the remaining cases. In nearly all instances, severe skull trauma or stab wounds to the neck or clavicular region gave rise to the air embolism. When the gas analysis data were compared, clear-cut differences were found between the two groups of putrefaction and air embolism. CO2 concentrations below 15%, N2 concentrations above 70%, and a CO2/N2 ratio below 0.2 proved to be good criteria to determine an air embolism. However, gas volumes, O2 concentrations, and CO2/O2 ratios largely overlapped in the two groups. Air embolism samples consistently had lower O2 concentrations and higher CO2 concentrations than atmospheric air, and this was evidently independent from incipient putrefaction. We suggest that these deviations result from a gas exchange between the venous blood and the embolized air volume taking place in the right heart ventricle. The dimensions of the concentration shifts may be understood from severe agonal hypoxia and hypercapnia.