Carbon Dioxide Euthanasia for Rats and Mice (BU ASC Guidelines)

“Euthanasia” is a term meaning “good death”.

The goal of euthanasia is to provide a rapid, painless, stress-free death. Carbon dioxide (CO2) overdose causes rapid unconsciousness followed by death. The CO₂ flow rate should displace 30% to 70% of the cage volume per minute.

Exposure to CO2 without removing animals from their home cage is a rapid and humane method of euthanasia, because the animals are not stressed by handling or being moved to a new environment.

Exposure to CO2 can cause deep narcosis that can appear to be, but is not, death. In such cases, animals that superficially appear to be dead may eventually awaken; this arousal can occur after the disposal of carcasses into refrigerators or freezers. Presumed death after exposure to carbon dioxide must be confirmed based on careful assessment of the animal for unambiguous signs of death, such as cardiac arrest or fixed, dilated pupils. CO₂ narcosis must be followed with secondary method of euthanasia (i.e. cervical dislocation, thoracotomy, etc.).



Standard Size Caging

Flow rate calculation


Step 1


Step 2


Step 3


Step 4


Step 5


Step 6


Step 7


Step 8


Step 9


Step 10


Step 11


Step 12


Step 13

BU IACUC Approved October 2008, Revised May 2019

CO2 Euthanasia Procedure

Information For...

Back to Top