a while ago, we compared intraperitoneal pentobarbital as a euthanasia technique with carbon dioxide overdose in rats. we expected, naively, that this would serve as an appropriate gold standard but were disappointed to find considerable variety in its effects, including a fairly high misinjection rate. the misinjection rate has been documented before, in rats and mice e.g. Corey-Avila et al. 2007 Lab Anim 36:25-30.
we wondered if the variability in effect could be improved, if not the misinjection rate. so we compared a fairly standard dose of pentobarbital with a high dose and a larger volume of the standard dose. time to loss of consciousness was shorter with both high dose and high volume approaches and similar with each technique; however, the time to death was substantially faster in the high dose group (5 times faster than the standard dose and 3 times faster than the high volume group). thus, the higher dose shortens the time to death, limiting any period of suffering that might exist. additionally, because of the reduced variability, we were able to suggest guidelines for when a misinjection has occurred i.e. if loss of consciousness does not occur within 2.5 minutes of injection. these findings should improve both the speed and predictability of euthanasia in rats when using an intraperitoneal pentobarbital injection technique.
this project was the work of katie zatroch, who is now an anesthesiology resident. the resultant paper has been published in BMC Vet Research (DOI: 10.1186/s12917-017-0982-y).