Evaluation of Carbon Dioxide Dissipation within a Euthanasia Chamber

CO2 euthanasia is used widely for small laboratory animals, such as rodents. A common necessity in many animal research facilities is to euthanize mice in sequential batches. We assessed the effects of several variables on the time it took for CO2, to dissipate within a chamber. Using standard euthanasia time, changes in flow rate were compared between a slow 15% fill rate for 7 mm, and a slow 15% followed by a rapid 50% filling for a total of 5 mm. Additional variables assessed included the effects of opening the lid after the completion of chamber filling, turning the chamber over after completion of filling, and the use and removal of a cage from within the chamber. For all trials, CO2, levels in the chambers peaked between 50% and 80%. After the gas was turned off, the concentration of CO2, dropped to below 10% CO2 within 2 min, except when the lid was left on the chamber, where concentration levels remained above 10% after 20 min. CO2 dissipation was significantly faster when the chamber was turned upside down after filling. Significant interaction effects occurred among the factors of cage presence within the chamber, flow rate, and chamber position. Only leaving the lid on the chamber had any practical implication for delaying CO2, dissipation. We recommend that users allow 2 mm for CO2, to clear from the chamber before subsequent euthanasia procedures, unless the chamber is manipulated to increase the dissipation rate.