Important: Whatever you do, do one or more dry runs without the animal first. Practice the procedures until you are comfortable performing them without mishap before doing anything involving your pet.
Since 2003, when this site when up, I have had numerous reports of success and only one report of failure from someone who had no idea what might have gone wrong and who apparently was unable to understand the instructions provided. The lesson would seem to be: know your limitations.
Some non-believers in science question the need for experimentation, but I am quite sure that the procedures detailed above could not have been developed without some experimentation, by others and myself, and that to guess without testing would have been grossly irresponsible. Accordingly I wish to acknowledge the invaluable contributions of eight wild house mice, uninvited and destructive guests, who would otherwise have met their end in a mousetrap (sorry but allowing mice around our house in the country attracts way too many rattlesnakes, and I have a family to consider). Fortunately all I had to do was to verify that my methods, based on the research of others, were producing the same results as reported by real scientists who did all the real work. When I could put a wild, stress-out mouse to sleep without any apparent added distress, I ended my experiments. (Some mice, not partially confined by shredded paper and with room to wander, acted drunk, and staggered about for about 20 seconds before becoming unconscious—not a pretty sight, but they appeared more confused and disoriented than in pain).
Dry ice is used by some labs for CO2 euthanasia. Dry ice is a potentially hazardous substance. It is obtainable, but not readily available, and may not be obtainable at all when actually needed. The rate of sublimation in air is too slow, and adding dry ice to water results in violent, possibly explosive, boiling. It is difficult to control the rate of flow. Cold burns to you or your pet are a real hazard. Dry ice is not something you want to fool with at home.
While all vets should know how to perform humane euthanasia properly, some may not want to bother. If possible, do go to a vet, but make sure you observe the procedure, and if the vet doesn't want you to observe, go elsewhere. The preferred method (with small mammals) is to induce anesthesia using an inhalant such as Halothane or Isoflurane, followed by lethal injection or overdose of the inhalant. Some vets, when not being observed, may skip the first step and just inject something lethal into the body cavity.
At-home use of inhalant anesthesia is advocated by some as the best method of do-it-yourself euthanasia. Halothane, Isoflurane, Methoxyflurane, and other inhalant anesthetics are controlled substances obtainable (so far as I know) only by licensed veterinarians or researchers and are not legally available to the public. Some are being abused by a few recreational drug users, so it might be possible to obtain them, but even if you could, they are not appropriate for home use. First, with the exception of Methoxyflurane which is no longer available in the USA, inhalant anesthetics can only be used properly with an anesthesia machine capable of delivering them at the proper concentration (5% initially), and rate. Second, for your safety, you would also need a gas scavenger to protect yourself from fumes. Inhalant anesthesia is not a practical method for most pet owners.
Some claim that CO2 euthanasia is inhumane and should never be considered. This is based on the mistaken belief that CO2 acts only by inducing asphyxiation. Using it is likened to smothering your pet to death with a pillow; however it is a well established fact that carbon dioxide is a rapid depressant and powerful anesthetic. My observation is that CO2 acts as quickly and with even less excitation than Isoflurane (yes I tried it, given to me by a country vet who doesn't think I'm crazy and who has better things to do than euthanize small animals), perhaps because it is nearly odorless. At high concentration CO2 does indeed kill the animal by hypoxia, but only after induction of anesthesia. Even within the scientific literature you can find some misinformation. Procedures often call for precharging the euthanasia chamber with concentrated CO2 because this will cause the most rapid death. This is true, but speed is not the most important consideration. It is now realized that high concentrations of CO2 are noxious and inflict pain before induction of anesthesia. A gradual increase in concentration avoids this.
Some vets are concerned that CO2 euthanasia is ineffective in causing death and that some additional procedure is required to be sure death has occurred. This is an odd concern, at least with rodents, because respiration during the anesthesia phase is quite obvious as is the cessation of all respiration shortly after the high concentration CO2 is introduced. Neither mice nor men can stop breathing for 10 minutes and then revive (except in cases of hypothermia or animals that have evolved extraordinary breath holding abilities). If you have any concerns, wait 30 minutes or longer. The AVMA doesn't seem to have this concern.
I have received requests for a method that would be suitable for larger pets. Chicken producers are offering 'humanely slaughtered' chickens using CO2 which means it appears to work, even though chickens exceed the 2 lb. limit. I have recently become aware of the helium/nitrogen bag method of euthanasia advocated by right to die groups like Final Exit. This method of at home euthanasia for humans works by asphyxiation, but reportedly without causing distress. Helium is readily available for filling party balloons, and so this would be a practical method, but one I have not tried. Some oxygen may now be added to retail helium to avoid "misuse" so purity may be questionable.
I am glad to have this highly effective and practical method of at-home euthanasia, and hope others will make good and responsible use of it should the unfortunate need arise. Finally, I would like to thank all of those who have written to me to express their appreciation for the information in this paper, and for letting me know that much pointless suffering has been prevented. An unexpected result has been that much human suffering as may be caused by watching helplessly as a beloved pet dies has been reduced as well.
1. Report of the AVMA Panel on Euthanasia, JAVMA, Vol. 218, No.5, March 1, 2001
2. Hackbarth H, Kppers N, Bohnet W. Euthanasia of rats with carbon dioxide--animal welfare aspects. Lab Anim 2000;34:91-96
3. Leake CD, Waters RM. The anesthetic properties of carbon dioxide. Curr Res Anesthesiol Analg 1929;8:17-19
4. Niel L, Stewart SA, Weary DM. Effect of flow rate on aversion to gradual-fill carbon dioxide exposure in rats. Appl Anim Behav Sci 2008. 109:77–84.
5. Niels Lombolt, M.D. THE USE OF CARBON DIOXIDE ANAESTHESIA BEFORE SLAUGHTER, Assistant Professor, Dpt. of Pharmacology, University of Copenhagen