Carbon dioxide

Reformatted from the 2000 Report of the AVMA Panel on Euthanasia –

"Compressed CO₂ gas in cylinders is the only recommended source of carbon dioxide because the inflow to the chamber can be regulated precisely.

"Carbon dioxide generated by other methods such as from dry ice, fire extinguishers, or chemical means (eg, antacids) is unacceptable.

"Species should be separated and chambers should not be overcrowded.

"With an animal in the chamber, an optimal flow rate should displace at least 20% of the chamber volume per minute. Loss of consciousness may be induced more rapidly by exposing animals to a CO₂ concentration of 70% or more by pre-filling the chamber for species in which this has not been shown to cause distress.

"Gas flow should be maintained for at least 1 minute after apparent clinical death. It is important to verify that an animal is dead before removing it from the chamber. If an animal is not dead, CO₂ narcosis must be followed with another method of euthanasia. Adding O₂ to the CO₂ may or may not preclude signs of distress. Additional O₂ will, however, prolong time to death and may complicate determination of consciousness.

"There appears to be no advantage to combining O₂ with carbon dioxide for euthanasia."