Co and N2 Are No Humane Alternatives to Co2 Euthanasia in Rats.

Abstract

Carbon dioxide (CO2) is commonly used for euthanasia of laboratory animals but has potential negative side effects. There is an urgent need to identify alternatives causing minimal distress while providing a fast and reliable loss of consciousness (LOC). We evaluated different CO2 concentrations (30% and 70%) and explored carbon monoxide (CO) and nitrogen (N2) as alternatives for a more humane euthanasia in rats. Isoflurane anesthesia was included as a reference. We assessed relevant physiological parameters in rats using a multifaceted approach combining EEG, ECG, telemetry, EMG, respiration, behavior, biochemical stress parameters, and lung histopathology. 70% CO2 resulted in rapid LOC and a faster death compared to 30% CO2 thus minimizing the time of consciousness in which distress and eventually pain can be experienced. Nevertheless, a higher amount of distress (e.g. gasping, arrhythmia or seizures) experienced until LOC might outweigh the benefits of a faster LOC. CO and N2 resulted in longer times to LOC, induced seizures before LOC, increased stress levels and caused higher lung damage. Therefore, CO and N2 are no humane alternatives to CO2 and should not be used for euthanasia of rodents. However, combining CO2 with anesthetic gases might be suitable to induce a more humane euthanasia.