United States Animal Protection Case Against Use of Carbon Monoxide


CASE AGAINST THE CONTINUED USE OF CARBON MONOXIDE AS AN INHALATIONAL AGENT FOR EUTHANASIA Background Gassing pound animals with carbon monoxide began when the American SPCA took over the New York City animal control contract in 1895. The use of gas stopped what was then considered the inhumane practice of drowning strays in the Hudson River. Carbon monoxide gassing subsequently gained acceptance across the U.S. and became one of the more commonly used methods of euthanasia in animal control facilities. However, the method of carbon monoxide gassing, while inexpensive and effective, was never evaluated as a humane method by veterinarians. Therefore, the physiological and psychological effects of this method on individual animals were a matter of speculation. AVMA Guidelines On Euthanasia In 1972, at the request of the American Veterinary Medical Association (AVMA) Council on Research, the Executive Board of the AVMA convened a Panel on Euthanasia. The task assigned to this Panel was to define euthanasia as it applies in veterinary medicine; survey any veterinary and scientific literature on the various methods of euthanasia; and provide guidance on agents and methods to veterinarians who (presumably) would be performing or directing these procedures. Included in this mandate was to comment on the possible effects of each particular method on the physiology and behavior of animals. The Panel was not directed to obtain was firsthand (practice) knowledge of the individual methods, or distinguish methods which were more humane than others. Additionally, the Panel did not distinguish humane methods that could easily be performed by non-veterinarians in animal control settings. The Panel on Euthanasia issued its report on March 1, 1972 in the AVMA Journal. The Panel on Euthanasia was reconvened in 1978, 1986, 1993, 2000 and 2007. Following the 2007 session, the title of the final document was changed to the 2007 AVMA Guidelines on Euthanasia. While more references were cited, clarifying language was used and summary tables were provided, the Guidelines still did not provide a comparative assessment of humane methods that might be used by non-veterinarians in animal control settings. These Guidelines also neglected to discuss newer veterinary drugs that facilitated a multiple modality approach to euthanasia. When the General Considerations in the AVMA Guidelines are compared with the discussions on the use of inhalational methods of carbon monoxide for euthanasia, several glaring dichotomies become evident. Among the 12 General Considerations, seven do not substantially conform to the letter and intent of the Guidelines. Specifically, the (1) ability to induce loss of consciousness and death without causing anxiety, apprehension, distress or pain (2) the time required to induce loss of consciousness, (3) reliability, (4) safety for personnel, (7) emotional effect on observers or operators, (10) compatibility with species, age and health status and (11) ability to maintain equipment in proper working order are stringent requirements that are difficult to manage and are highly variable with the inhalational use of carbon monoxide. The following point-by-point discussion of the problems associated with the General Considerations is relevant. Discussion Of AVMA Guidelines The ability of inhalational agents to be used for euthanasia is considered humane “if the animal is rapidly exposed to a high concentration of the agent.” However, the AVMA Guidelines recognize that carbon monoxide is explosive in concentrations above 10% in air, which also increases the risk of acute toxicity in humans. Based upon this presumption of hazard, the Guidelines recommend “commercially prepared gas” at concentration of approximately 6% be used. The ability of carbon dioxide to cause rapid loss of consciousness without anxiety, apprehension, distress or pain is questionable based upon the few scientific studies performed in animals and the anecdotal information from human exposure. In a carefully controlled study using 6% carbon monoxide in dogs, the actual time to loss of consciousness could not be determined. But it was recorded that abnormal brain waves which occurred 20-25 seconds before loss of consciousness was associated with agitation and vocalization. A subsequent study by the same investigators demonstrated that the pre-euthanasia administration of tranquilizers reduced, but did not eliminate agitation and vocalization. Other scientific studies demonstrate that cats can have tremors and convulsions prior to loss of consciousness and pigs demonstrate pre-narcosis agitation and vocalization. An important consideration in assessing the acute effects of carbon monoxide exposure of animals are the symptoms reported by humans who recover from carbon monoxide toxicosis. Among the commonly reported symptoms of “early carbon monoxide toxicosis are headache, dizziness, and weakness. As concentrations of (carbon monoxide) carboxyhemoglobin increase, these signs may be followed by decreased visual acuity, tinnitus, nausea, progressive depression, confusion, and collapse. Because carbon monoxide stimulates motor centers in the brain, loss of consciousness may be accompanied by convulsions and muscular spasms.” It is clear from these descriptions that use of carbon monoxide does not prevent anxiety, apprehension, or distress, let alone pain (headache, convulsions and muscle spasms) before narcosis is attained. While the reliability of carbon monoxide to produce death in animals is not questioned, the capability to produce humane death is clearly questionable in the scientific literature and in anecdotal information received from observers and operators of gassing chambers. Both sources report the clinical signs described in the discussion above prior to the loss of consciousness among many species. Safety of personnel is clearly a problem with carbon monoxide. Above a 10% concentration, this gas is potentially explosive. The Material Safety Data Sheet (MSDS) describes this agent as extremely hazardous for personnel because it is highly toxic and difficult to detect. Acute exposure to concentrations in concentrations as low as 0.2% of inspired air can produce signs of carbon monoxide toxicosis. Chronic exposure to very low concentrations of carbon monoxide as little as 0.05% of inspired air may be a health hazard in cardiovascular disease and have teratogenic effects. Gas chambers must be surrounded by an efficient exhaust or ventilation system to prevent accidental exposure of humans. There is a high incidence of negative emotional effect on observers and operators associated with the use of carbon monoxide gas used for euthanasia. Many operators report that they simply “turn on the gas and walk away,” which does not fulfill the AVMA Guideline to observe animals until they lose consciousness and ensure that individual animals are dead (euthanized). The only study that indicated The ability to determine the compatibility of carbon monoxide euthanasia with animal species, different ages of animals and the health status of individual animal requires knowledge of taxonomy, neonatology and some ability to perform a clinical evaluation of individual animals. Carbon monoxide is contraindicated in reptiles, amphibians, diving birds and mammals that have a great capacity for holding their breath and/or living with anaerobic metabolism. Use of carbon monoxide in neonatal animals less than 16 weeks of age is contraindicated because of residual fetal hemoglobin in their blood. And lastly, animals with impaired respiratory function may not be able to assimilate carbon monoxide rapidly through respiration. A carbon monoxide chamber requires a special site, ventilation and construction. Operation requires thorough maintenance, strict operating procedures and a stringent requirement for training operators on maintenance, procedures and hazards. These requirements under the AVMA Guidelines impose difficult and in some circumstances conflicting limitations on reliably performing humane euthanasia with carbon monoxide. The AVMA Guidelines state the chamber should (preferably) be located outside, must constructed from the highest quality materials, must be cleanable and should allow for separation of individual animals. If a chamber is located inside a building, there is a requirement for a carbon monoxide monitoring system. A not well understood feature of these chambers is that they have to be safely vented to the outside in a manner that allows displacement of air inside the chamber with the carbon monoxide gas. They cannot be air tight to function properly. The Guidelines also require a chamber to be well lit and have view a port to allow the direct observation of animals. All lights and mechanical apparatus must be explosion proof because of the combustibility of carbon monoxide. Operation procedures require thorough cleaning between uses to minimize odors (pheromones) that would cause anxiety, apprehension and distress in animals subsequently euthanatized. Loading of the chamber permits only animals of the same species in a manner that precludes overcrowding. In introducing the carbon monoxide gas into the chamber, the flow rate should be adequate to rapidly achieve a uniform concentration of at least 6% carbon monoxide inside the chamber, but should be so rapid as to produce noise that causes agitation. And finally, all personnel using carbon monoxide chambers must be instructed thoroughly on all the above Guidelines and must understand the hazards and limitations. It is also mandatory that carbon dioxide be used in compliance with all Federal (NIOSH/OSHA, EPA) and state regulations. Based upon the above considerations, the operation of a carbon monoxide chamber to cause humane euthanasia by anyone other than a veterinarian who could judge a malfunction of the apparatus, or an untoward physiological or behavior problem with an individual animal, is not reasonable. United States Animal Protection Dr. Robert Hopkins Dawn Taylor Bechtold


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