WASHINGTON—The HSUS welcomes the National Institutes of Health's Office of Laboratory Animal Welfare (OLAW) guidance notice to research institutions regarding the use of carbon dioxide (CO₂) for euthanasia of small laboratory animals.

Carbon dioxide euthanasia is a common practice in research laboratories and is used on millions of animals per year, particularly rats and mice. An HSUS review of scientific literature on carbon dioxide use on animals shows that some studies provide evidence that CO₂ causes pain and distress in animals. The HSUS sent a letter to OLAW in September 2001 requesting that the office alert institutions to the negative effects of carbon dioxide and urge them to use alternatives to CO₂ for euthanasia. In light of this, The HSUS welcomes the attention being drawn to this issue at the federal level and is calling on OLAW to continue to investigate the use of this substance in euthanasia protocols for laboratory animals.

The guidance issued by OLAW last week provides some cautionary guidelines concerning the acceptability of CO₂ use for euthanasia of laboratory animals. Some specific recommendations include a statement that high concentrations of carbon dioxide may be distressful to some species and a warning to pre-fill euthanasia chambers with CO₂ "only under circumstances in which such use has not been shown to cause distress." The document also urges institutions to keep current on literature on carbon dioxide use, to apply this information to their institutional policies, to report to OLAW as a serious non-compliance with Public Health Service policy any instances in which an animal recovers from euthanasia via CO₂, and to remember "the imperative to avoid or minimize discomfort, distress, and pain when consistent with sound scientific practices."

The HSUS's review of the literature on the use of CO₂ as a euthanasia agent and anesthetic on animals found cause for concern. Dr. Andrew Rowan, Ph.D., senior vice president of research, education, and international issues for The HSUS, said, "We found that the results of carbon dioxide studies are all over the map. However, there is an abundance of evidence that CO₂ use does cause pain and distress in animals. In fact, some studies have even used carbon dioxide to intentionally cause pain and/or distress in animals."

The HSUS further discovered that carbon dioxide clearly causes pain in humans. "Institutions are required by Public Health Service policy to assume that if a procedure causes pain and distress in humans, it should be considered to do so in other animals," notes Dr. Rowan. "However, this principle is not being followed by institutions with regards to CO₂ euthanasia."

"The HSUS is pleased that federal attention has now been focused on the issue of carbon dioxide euthanasia," said Dr. Rowan. "However, we would emphasize that additional information and research is necessary in order to determine if the OLAW guidance goes far enough. The conflicting findings in the literature indicate that additional problems with carbon dioxide use are likely to be uncovered. We would like to see this investigated and addressed as soon as possible. And if there is evidence that carbon dioxide causes pain and distress, regardless of the technique used, alternatives should be implemented. Only then will Public Health Service policy truly be followed in regards to this issue."