Bias in Rating of Rodent Distress during Anesthesia Induction for Anesthesia Compared with Euthanasia

Selection of an appropriate method of euthanasia involves balancing the wellbeing of the animal during the procedure with the intended use of the animal after death and the physical and psychologic safety of the observer or operator. The recommended practices for anesthesia as compared with euthanasia are very disparate, despite the fact that all chemical methods of euthanasia are anesthetic overdoses. To explain this disparity, this study sought to determine whether perception bias is inherent in the discussion of euthanasia compared with anesthesia. In this study, participants viewed videorecordings of the anesthesia of either 4 rats or 4 mice, from induction to loss of consciousness. Half of the participants were told that they were observing anesthesia; the other half understood that they were observing euthanasia. Participants were asked to rate the distress of the animals by scoring escape behaviors, fear behaviors, respiratory distress, and other distress markers. For mice, the participants generally rated the distress as high when they were told that the mouse was being euthanized, as compared with the participants who were told that the mouse was being anesthetized. For rats, the effect was not as strong, and the distress was generally rated higher when participants were told they were watching anesthesia. Because the interpretation of distress showed bias in both species-even though the bias differed regarding the procedure that interpreted as distressing-this study demonstrates that laboratory animal professionals must consider the influence of potential perception bias when developing policies for euthanasia and anesthesia.