Methodology and analysis of gas embolism: experimental models and stranded cetaceans

Abstract

"Gas Bubb!e Disease" or "Decompression like Sickness" was described in stranded beaked whales linked to military sonar (Femandez et al., 2005; Jepson et al., 2003). This hypothcsis raised an important public controversy and a scientific replay in Nature 2004 (Piantadosi and Thalmann, 2004), which clearly disagreed with that interpretation, requiring investigations on analysis of the composition of lhc gas in lhe bubblcs in order to approach a diagnosis of Decompression Sickness (DCS). We have developed and standardized a methodology than enables the evaluation of gas abnndance, gas sampling during in situ necropsies, as well as their storage and transport in vacunm tubes with non-statistical significant changes in gas composition for their final analysis in the laboratory. This methodology was applied to three experimental models: putrefaction, air embolism and compression/decompression model, showing to be effective for the differentiation between putrefaction gases and "in vivo" gas embolism processes. We studied in the same way 93 marine mammals belonging to 18 different species. We found that the presence ofbubbles detected within the cardiovascular system and tissues during the necropsy of stranded cetaceans is a common finding related to "in vivo and / or postmortem" process. To try to avoid these putrefactive masking gases, necropsy and gas sampling must be performed as soon as possible, before 24 hours PM as recommendation but preferably within 12 hours PM. High amounts of gas bubbles in fresh animals were very rare. At necropsy, quantity of bubbles in decomposition codes 1 and 2 stranded cetaceans was found to be more important than the merely presence versus absence of bubbles. Deep divers presented higher abundance of gas bubbles mainly composed of 70% nitrogen and 30% CO2, suggesting a higher predisposition of these species to suffer from decompression.