Volume 42 | Issue 2 Article 8

1980 Methods of Euthanasia Kay Schwink Iowa State University

E. L. Egger Iowa State University

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Recommended Citation Schwink, Kay and Egger, E. L. (1980) "Methods of Euthanasia," Iowa State University Veterinarian: Vol. 42 : Iss. 2 , Article 8. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol42/iss2/8

This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. Overall. it is apparent that we need to state. To pursue expansive proposals will reevaluate the current structure of our require the creativeness· and ingenuity of profession in order to deal effectively with the individuals and institutions as well as inertia that will lead to a manpower surplus. aggressive public relations and education to It is obvious that no single solution will demonstrate the quality and the extent of our emerge; instead we need to develop a multi­ training in medicine and other biological faceted approach to the problem. To pursue sciences. We are challenged with a complex any of the restrictive proposals presented here problem, but inherent in this challenge is the or elsewhere will require major alterations in opportunity to advance and improve our an institutional and bureaucratic framework profession. . that is structured for growth instead of steady

Methods of Euthanasia •

Kay Schwink* Dr. E. L. Eggert

The killing of animals is perhaps the most reluctance of people to deal with the situation consistent task faced by veterinCJ.rians in all directly. completely, and honestly. The facets of the profession. In private or in­ authors of this paper believe it should be stitutionalized practice, in almost any area of repugnant for any veterinarian to condone active research, in meat inspection. and in the destruction of any animal by a method pathology and diagnostic services. one that cannot be considered humane. Because common shared activity is the actual or the unconscious animal cannot perceive pain, supervisory killing of animals. The a humane death may be defined as one motivations, methods, and considerations are wherein the animal is rendered unconscious myriad, but the process of inflicting death on (and thus insensitive to pain) as rapidly as a variety of living creatures is an inseparable, possible, with the least possible amount of undeniable part of the veterinary profession. fear and anxiety. Euthanasia is by definitionS the act of The task faced by veterinarians almost inducing death, without pain, to the animal daily throughout their professional lives is the being killed. Various dictionaries add easy, matter of choosing and applying a suitable quiet, and lacking anxiety to the primary method of killing a patient which has been criterion of a euthanasia. which is appointed to die, usually because of a painlessness. Animals killed by and for hopeless or incurable disease condition, or in veterinarians are variously described in the order to diagnose a disease so that other veterinary and human medical literature as animals in similar circumstances can be being sacrificed, destroyed, terminated, successfully treated. The handling of each slaughtered or even harvested. In companion case presented for euthanasia is made unique animal practice, pets may be put down, put by the individual animal and human per­ to sleep, or put out of their misery. Perhaps sonalities involved. this rather vast array of terms to describe a There are many methods which may be single process may be an indication of the employed to reach the same end result. The ideal method should satisfy several criteria: • Ms Schwink is a fourth year • student in the College of 1. It should be painless. Veterinary Medicine, ISU. tDr. Egger is an Assistant Professor of Veterinary clinical 2. It should not cause undue anxiety, Sciences, College of Veterinary Medicine, ISU. alarm, fear, behavior. struggling, vocal-

78 Iowa State Veterinarian ization, muscle spasms, or clinical signs The anesthetic gases may be the agents of of autonomic activation. choice for euthanasia of birds, rodents, cats 3. It should cause unconsciousness in­ and small dogs. These agents cause rapid loss stantaneously and death within minutes. of consciousness and death by hypoxia. 4. It should always cause death when Chloroform, halothane, methoxyfluorane, properly used. enfluorane, and nitrous oxide are, under 5. It should be safe for the properly trained ordinary circumstances, nonflammable and person to use. nonexplosive; cyclopropane and ether are 6. It should be easy for the properly trained both explosive and flammable. Disadvantages person to use. of the inhalant anesthetics for euthanasia are: 7. It should not be a drug attractive for anxiety during induction evoked by irritating abuse in human beings. vapors and initial excitatory action on the 8. It should be aesthetically unobjection­ central nervous system, hazard to the person able. This criterion depends on who the administering the agent, and relatively high observers are. cost. Also, contact of the animal with the 9. It should be practical to use for the liquid before it volatilizes should be avoided particular type of animal to be killed. to prevent undue animal discomfort. 10. It should be economical. Nitrogen gas may be used effectively for 11. It should not create a problem of sanita­ euthanasia of animals over 4 months of age, tion or environmental contamination. provided that equipment is properly con­ 12. It should not cause tissue changes which structed, maintained, and operated. Re­ will alter postmortem examination or search on 360 animals by Fitch et al2 chemical tests. demonstrated that all subjects became un­ It is very unlikely that any agent, either conscious within one minute with no signs of chemical or physical, will ever satisfy all of pain. Some hypoxia-related movement and these criteria for any single euthanasia. The vocalization occurs in the unconscious decision of which of the many available animal, which may be a disadvantage when methods to employ must be based on as many an aesthetic death is important. of these ideals as possible, with the Hydrogen cyanide has been used for veterinarian as well informed as possible on euthanasia and been found very rapid and the characteristics of the agents from which reliable. Because it is extremely irritating to he selects. the respiratory mucosa, produces violent The choice of agents is complicated by the convulsions prior to death, and represents a fact that unconciousness and death do not considerable safety hazard to personnel, it is coincide and that it may be difficult for an not generally recommended for routine observer to know whether an animal is in euthanasia.2•10•13 distress, or is actually unconscious and is Carbon dioxide is odorless, heavier than vocalizing or struggling involuntarily and air, and has a rapid anesthetic effect in without pain. Objective judgments along concentrations greater than 7.5%. Inhalation these lines can be made by studying the of 60% CO2 will cause loss of consciousness multitude of published research monitoring within 45 seconds and stop respiration within electroencephalograms, electrocardiograms, 5 minutes. Research by Croft4 indicates that electromyograms, pulses, and respirations of animals do not detect the presence of high animals dying by various means. CO2 concentrations before its depressant For the purposes of this paper, euthan­ effect occurs. Carbon dioxide is inexpensive, atizing agents will be categorized in one of nonexplosive, nonflammable, and minimally three groups: 1) inhalant, 2) parenteral, or 3) hazardous to personnel when properly main­ physical. tained equipment is used. It does not ac­ Inhalant agents which may be used to kill cumulate in the tissues of food-producing animals include the inhalant anesthetics animals or cause changes in cellular ar­ (ether, chloroform, halothane, methoxyfluo­ chitecture.6 rane, enfluorane, cyclopropane, and nitrous Carbon monoxide can also produce rapid oxide), as well as nitrogen gas, hydrogen painless death without alarm to the animal cyanide, carbon dioxide, and carbon being killed_ Because it is undetectable when monoxide. properly used, people employing CO for

Issue No.2, 1980 79 euthanasia must be aware of potential nonviolent and outwardly aesthetic death, it hazards to themselves. Automobile exhaust as should be remembered that death is due to a source of carbon monoxide is acceptable paralysis of respiratory muscles followed by only if the exhaust fumes are adequately hypoxia and suffocation. There is no cooled and filtered and the engine is depressant action on the brain, and con­ operating efficiently with a rich fuel-air sciousness has been shown to remain for 2 to 3 mixture. minutesl3 following paralysis. The use of Parenteral pharmacologic agents are the these drugs alone to kill animals is unac­ most commonly used euthanatizing methods ceptable, although in some instances they employed in the Iowa State University may be used to immobilize an animal prior to teaching hospital and in student laboratory the administration of other agents when exercises. For tractable, nonvicious animals, restraint itself is a dangerous, painful, or these are the agents of choice because of their traumatic procedure. reliability and rapidity of action. The Other parenteral agents include nicotine, preferred route of administration is usually magnesium sulfate, chloral hydrate, and the intravenous, although in some situations, combination of choral hydrate, magnesium intraperitoneal or intracardiac injections are sulfate, and sodium pentobarbital. These will more feasible. not be discussed here except to state that the Barbituric acid derivatives depress the latter combination is suggested as a suitable central nervous system rapidly, producing means of euthanatizing large animals. 12 unconsciousness within seconds,8 followed by The final category of euthanatizing death due to depression of the respiratory methods is the physical agents, which include center of the medulla. Advantages are gunshot, captive bolt, electrocution, rapidity of action, aesthetic induction when microwaves, and cranial disarticulation. properly administered, and lack of disturbing Gunshot and captive bolt are, when unconscious behavior prior to death. properly applied, rapid and effective, killing Disadvantages include discomfort and dis­ the animal by direct concussion of the brain. turbing induction when intravenous injection Gunshot is frequently used to kill large is not achieved, and the attractiveness of these animals, especially by practitioners in the agents for human abuse. It is the recom­ field. Tissue changes do not occur except for mendation of the A VMA Panel on the obvious ones to the brain itself; this Euthanasias that the advantages of the destruction of the brain frequently makes barbituric acid derivatives far outweigh the these methods impractical because post­ disadvantages. For nervous or intractable mortem examination of the brain may be subjects, preinduction use of tranquilizers or desired. The use of microwaves to humanely sedatives may be considered. kill small rodents has been reportedl4 and In order to eliminate the disadvantage of appears promising, although not yet ready for using a controlled substance for euthanasia, general use. commercial euthanatizing solutions are Decapitation and cervical dislocation are available. An example is T-6P, which is often used to kill lab animals and birds. These attractive because it eliminates the necessity methods are effective and acceptable pro­ of locked cabinets and careful record­ vided that rapid deliberate application of the keeping. Although research indicates that the technique is accomplished to prevent undue animal's sensation during induction and animal discomfort. 5 death may be markedly similar to those using Another physical means of rendering live barbiturates, many observers have been animals dead is electrocution. Electricity can disturbed by the frequency of unaesthetic kill animals in two ways.15.17 A small electric reactions. If T-61 is injected too rapidly current passing through the body paralyzes (except in the horse), animals may appear to muscles of respiration and causes death from experience distress and pain prior to un­ asphyxiation. A larger electric current conscIOusness. passing through the body causes ventricular While the use of the curariform drugs fibrillation. Research suggests that con­ (curare, succinylcholine, pancuronium, gly­ sciousness can remain for 12 to 20 seconds ceryl fenesin, and other neuromuscular after the onset of extemely painful blocking agents) appears to produce a very fibrillation. l

80 Iowa State Veterinarian Studies performed between 1950 and 1954 case. Roger Hatch, In his chapter on by Croft and Roberts resulted in the con­ euthanatizing agents in a well-known text­ clusion that in order to avoid pain during book of veterinary pharmacology, 8 suggests electrocution, it is essential first to make the that perhaps we should all hold on to our animal unconscious by passing a current emll)tions, sentiment, and empathy for ani­ directly through the brain, from side to side. 1 mals, lest we kill them as dispassionately as we Only after this has been done, and a classical sometimes kill each other. His point is well convulsive pattern, the electroplectic fit, is taken. produced, should the current be passed through the whole body to cause death by ventricular fibrillation and circulatory References I. Carding T: Euthanasia of Dogs and Cats: An 2 collapse. The use of two leads (a single Analysis of Experience and Current Knowledge with circuit), attached to the lip or ear and to the Recommendations fOT Research, Elsevier Scientific tailor anus, paralyzes the animal, creates Publishing Co. Amsterdam. 1977. severe muscular pain and suffocation, but 2. Carding T: Euthanasia of dogs and cats, Animal Regulation Studies 1:5-21.1977. does not render the animal immediately 3. Critchley. M. (ed): Butterworths Medical Die· unconscious. 17 tionary. ed. 2. 1978, Butterworth Pub. Inc .. Boston In 1954, the British Veterinary Associ­ 19 Cummings Park, Woburn. Mass 08101. ation condemned all existing methods of 4. Croft PG: Anesthesia and euthanasia. In: UFA W electrocution, because equipment to trans­ Handbook on the Care and Management of Laboratory Animals, ed. 3. Baltimore. Williams and cranially stun animals before applying the Wilkins Co. 1967. pp.160-172. lethal current did not exist. Special cabinets 5. Croft PG: Electrical euthanasia of unwanted dogs. are now manufactured which satisfy the In: Humane Destruction of Unwanted Animals, humane specifications of unconsciousness Herts. England. Potters Bar. The Universities Federation for Animal Welfare. 1976. prior to actual killing. Electrocution can be 6. Feldman DB. Gupta BN: Histopathological changes recommended for euthanasia only when such in laboratory animals resulting from various methods equipment is employed. This is the opinion of of euthanasia. Lab Anim Sci, 26:218-221. 1976. the AVMA Panel on Euthanasial3 and the 7. Glen JB. Scott WN: Carbon dioxide euthanasia of Humane Practices Committee of the Canadi­ cats. British Veterinary Journal. 129:471-479. 1973. 8. Hatch RC: Euthanatizing agents. In Jones LM. an Veterinary Medical Association,16 as well Booth NH. McDonald LE (ed): Veterinary Phar­ as that of various humane societies and macology and Therapeutics. Ames. Iowa State animal welfare organizations across the globe. University Press. 1977. pp. 1289-1296. The Canadian committee further condemns 9. Hicks T, Bailey EM Jr.: Succinylcholine chloride as an euthanatizing agent in dogs. Am J Vet Res, 39(7) electrocution by any technique of any animal 1195-1197.1978. whose cranial sutures are still cartilaginous, 10. Hume CW: Letter to the editor. Vet Rec. 73.33. because these sutures interfere with efficient 196I.p.812. current flow across the brain. II. Lumb WV. Doshi K. Scott RJ: Euthanasia in dogs: Another physical method used for eutha­ comparison of T·61 and pentobarbital. JA VMA 172:2149-152.1978. nasia is rapid decompression. This subject has 12. Lumb WV. Jones E: Veterinary Anesthesia. been the center of some controversy and will Philadelphia. Lee and Febiger. 1973. not be discussed here because its use is not 13. McDonald LE. Booth NH. Lumb WV. Redding widespread among veterinarians at the RW. Sawyer DC. Stevenson L. Wass WM: Report on the AVMA panel on euthanasia. JAVMA, 173:1, present time. 1978. pp. 39-72. 14. Schmidt MJ. Schmidt DE. Robins GA: Cyclic Conclusions: adenosine monophosphate in brain areas: microwave Euthanasia is a broad and controversial irradiation as a means of tissue fixation. Science. topic, certainly one which cannot be covered 173: 1143-1144. 1971. 15. Simpson HN. Derbyshire AJ: Electrical activity of comprehensively in a work such as this. Each the motor cortex during cerebral anemia. Am"1 method has advantages and disadvantages, PhysioII09:99. 1934. proponents and opponents. Many available' 16. Stonehouse RW et al: The euthanasia of dogs and methods have not been mentioned. cats. a statement of the humane practices committee Euthanasia should be performed as of the Canadian Veterinary Medical Association. Canadian Veterinary Journal. 19:6.164-168.1978. professionally and compassionately as possible 17. Sugar P. Gerard RW: Anoxia and brain potentials. J under the individual circumstances of each Physiol(London) 1:558.1938.

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