Euthanasia PDF - Veterinary Pharmacology

CHAPTER Requirements Response of -77 of animal euthanasia and confirmation of death...

CHAPTER Requirements Response of -77 of animal euthanasia and confirmation of death EUTHANIZING AGENTS Inhalant gases Inhalant anaesthetics Euthanizing agents Injectable agents Mode of action Barbiturates Classification Miscellaneous agents Chemical methods Physical methods Inhalant agents Unacceptable methods Euthanasia (Greek: eu = good,thanatos = death) is defined as 10. The drug selected for euthanasia should be easily quick and painless death. In other words, euthanasia is the act available and cheap. of inducing humane death in an animal. The practice of euthanasia sfollowed commonly 11. The drug selected for euthanasia should not have human in veterinary medicine to sacrifice anirnals due to multiple reasons abuse potential. such as to relieve pain and suffering of animals in incurable diseases (e.g.cancer), to kill moribund 12. The drug should be easy to admínister and not regquire animals complicate equipments. those are soon going to die and to euthanize animals during the course of an experiment. Irespective ofthe purpose, the euthanasia 13. The drug should not be a threat to environment or pose a sanitationproblem. should always be carried out by inducing minimum pain and distress to animals. The euthanasia should always be induced out by 14. Euthanasia should always be performed in a non-public trained personnel using acceptable area and not in rooms in which animals are housed. techniques in accordance with institutional policies and applicable laws. 15. The euthanasia should be done with the highest degree of respect to animal and must be ethically correct. Requirements of Euthanasia Response of Animal and Confirmation of Death Euthanasia is performed with sole motive of killing the animal without inducing undue pain and distress to the animal. While A variety of behavioural and physiological responses may euthanizing an animal, following points should be kept in mind: be demonstrated by animals while inducing euthanasia. The personnel engaged in euthanizing animal must be well aware of 1. The method adopted should induce euthanasia without all clinical signs and be able to confirm the death on basis of causing apprehension, anxiety,pain and distress to the animal. various reflexes. During the induction process, the animal may 2. The method adopted should cause rapid unconsciousness exhibit signs of pain and/or fear including vocalization, struggling, followed by respiratory and cardiac arrest. escape attempts, agitation, freezing, aggression, fearful postures 3. The method or procedure adopted for euthanasia should or facial expressions. Animal may also exhibit trembling, salivation, be as per the applicable law of the land. urination, defecation, mydriasis, panting and tachycardia. Response 4. The method adopted should be reliable and take minimum to euthanasia procedures such as handling, restraint, confinement, time to induce euthanasia. venipuncture, gas odour, gas chamber noise, etc.may vary among 5. The method adopted should be compatible with the species and among individuals, necessitating careful monitoring Species, age and health status of the animal. of every sign. 6. The method used should not interfere with the Loss ofphysiological function during euthanasia should be Subsequent post-mortem evaluation, examination, or use very cafefully monitored so as to know the exact stage of of tissue. anaesthesia or euthanasia. The desirable stages should occur in The method adopted should be compatible with the the following order to help 7. prevent fear and distress to animal: rapid loss of consciousness> requirement or purpose for which animal is being loss of motor function arrest of > euthanized (e.g. type of experiment or tissue collection). respiratory and cardiac function > loss ofall vital reflexes > death. If loss of motor or respiratory 8. The method or procedure adopted should not have and cardiac function precedes loss emotional effect on the observer(s) or the operator. ofconsciousness, animals becorte fearful and experience distress. Agents those induce muscle 9. The method adopted should be safe for the operating paralysis with out loss of personnel. consciousness are not acceptable as sole agents for euthanasia  1210 ESSENTIALS OF VETERINARYPHARMACOLOGY AND THERAPEUTICS - Sandhu H.S. depolarizing and non-depolarizing muscle relaxants and (e.g. 2. Inhalant anaesthetics magnesium salts) because loss of motor activity alone cannot be e.g. halothane, enflurane, isoflurane, sevoflurane, equated with loss of consciousness and absence of distress. In desflurane, methoxyflurane and ether. some species, tonic immobility may be induced by fear, and care must be taken to not confuse this behavioural response with loss B. Injectable agents of consciousness. 1. Barbiturates Before the carcass is disposed death must be by of, verified e.g. thiopental, methohexital and pentobarbital. a means appropriate to the species and the method of euthanasia. 2. Miscellaneous agents Death must be confirmed by examining the animal for cessation of vital signs, such as a heartbeat. The absence of respiration e.g. chloral hydrate, tricaine mesylate,magnesium sulphate does not always indicate death. An animal in deep and potassium chloride. narcosis following administration of an injectable or inhalant agent may II. Physical methods appear dead, but might eventually recover. Euthanasia e.g. captive bolt, gunshot, cervical dislocation, decapitation, frequently results in chemical tissue residues, necessitating proper disposal electrocution, microwave irradiation, exsanguination, of carcass to prevent contamination of the environment or harm maceration, stunning and pithing. to other animals (e.g. scavengers and predators). Selection of an appropriate method and agent of euthanasía is paramount in assuring a painless and humane death. Choice of EUTHANIZING AGENTS the method or agent is normally based on several factors including the species, size, behaviour and physiology of animal, as well as Mode of Action any particular characteristics of the individual animal(s). The There are three basic modes of action for euthanizing agents: setting, available means of animal restraint, skill and knowledge hypoxia/hypoxemia, depression of vital neurons in CNS and of operator, number of animals to be euthanized,and purpose for physical damage to brain tissues. The choice of method depends which the animal(s) is being euthanized are also determining on several factors including the species, age and size of animal, factors inof the methods and/or the agent. In all selection safetyto personnel, ethical considerations and requirement of the circumstances, the euthanasia method should be selected and experiment, if any. used with the highest ethical standards and social conscience. 1. Hypoxia/Hypoxemia Many agents induce death by causing rapid hypoxia or I.CHEMICAL METHODS hypoxemia. These agents act at various sites (lungs or blood) and A. Inhalant Agents can cause loss of consciousness by producing either direct or A large numbers of inhalant gases and inhalant anaesthetics indirecthypoxia/hypoxemia. The symptomsof generalizedhypoxia are used to euthanize animals.These agents act either by inducing depend on its severity and accelerationof onset. Rapid induction rapid hypoxia (e.g. carbon dioxide and carbon monoxide) or by of hypoxia induces unconsciousness, seizures, coma and death. Examples of agents causing death by hypoxia include carbon depressing vital centres in the brajn (e.g. halothane and enflurane). dioxide and carbon monoxide. Inhalant agents can be quick and simple to use thereby decreasing handling-associated stress in animals. They are particularly 2. Depression of vital neurons in CNS valuable in small size animals (e.g. rodents, birds, cats and small A large number of chemical agents induce euthanasia by dogs) in which injections by venipuncture are difficult. Some directly depressing of the brain. This induces the nerve cells inhalant agents irritate respiratory tract and/or induce convulsions unconsciousness followed by death. The onset of euthanasia is prior to loss of consciousness; such agents are unacceptable for equivalent to general anaesthesia and may show initial phases of euthanasia. increased muscle activity, vocalization, etc. resulting in a so called excitementor delirium phase (seefor detail stages ofgeneral Considerations for use ofinhalant agents anaesthesia, Chapter 18).The initial excitatory responses are Following points should be kept in mind while using inhalant generally involuntary and do not appear to be purposeful. Death follows loss of consciousness, and is attributable agents: to cardiac arrest and/or hypoxemia following direct depression of respiratory a. Use of appropriate and recommended conicentration of vasomotor centres. and inhalant gases/agents is must for inducing rapid onset of 3. Physical damage brain unconsciousness and death. gn to physical damage to the brain tissues causing disruption of b. The equipment used to deliver and maintain high brain activities is largely produced concentration of gases must be in good working order. by physical methods. Such methods may induce rapid loss of consciousness and death mainly Leaky or faulty equipment may lead to slow, distressful due to destruction of midbrain centres death and be hazardous to other animals and to operating controlling cardiac, vasomotor ana respiratory activity. Exaggerated muscular activity personnel. loss of can follow consciousness. C. Inhalant gases are generally hazardous to personnel Classification because ofthe risk of hypoxemia (e.g. carbon monoxide), methods CNS depression (e.g. halothane)or health effects resulting e2ol. Chemical from chronic exposure (e.g. nitrous oxide). e290A. Inhalant agents d. Animals with decreased ventilation generally show gases 7o 24 Inhalant agitation and excitement before falling unconscious due dioxide, carbon carbon monoxide, nitrogen e.g. and argon. to slow developing hypoxia. In such cases other non inhalant methodg of euthanasia should be considered.  :EUTHANIZINGAGENTS 17: 1211 Neonatal animals appear to be dry ice, fire extinguishers inhalant agents resistant to hypoxia; so methods such asfrom take longer to induce generatedbyother unacceptable because gas neonates and young (e.g. antacids) is animals. euthanasia in or chemical means act as a t Rapid gas flows precisely. Because CO; can in chambers flow cannot be regulated be kept in may frighten animals. can produce a it is imperative that the animals noise that reversible anacsthetic, If the arrest. G. Animals placed the chamber for several minutes after respiratory together in must be followed with another same species and chambers should be of the animal is not dead, CO, narcosis h preferably of same dislocation, opening of thoracic Chambers should not age. method of euthanasia (cervical be overloaded be taken that chambers are not overcrowded. clean to and necd to be cavity). Care should minimize odour kept ofCO, before that might Some species can tolerate very high concentrations subsequently euthanatized. distress animals i losing consciousness and death. Reptiles, amphibians, anddiving non-flammable and non a great capacity birds and mammalshave Carbon dioxide is inexpensive, for holding as residues. Carbon explosive agent and it does not persist their breath and tissue relatively hence are and resistant to rapidly no specific necropsy lesions developing hypoxia. dioxide poisoning produces ,Inhalant Gases / Inhalant does not distort cellular archítecture. Its use also presents a when adminístered with properly Non-anaesthetics minimal hazard to personnel Inhalantgases largely dioxide is heavier than air so include the designed equipment. Carbon which produce direct or indirect hypoxia non-anaesthetic agents incomplete filling ofeuthanasia chamber may permit tall or climbing hy death. These gases by inhalation followed are rapidly breathed into animals to avoid exposure to the gas. This can be avoided by pre they either displace the lungs where air and cause loss charging the chamber to full capacity. hvpoxia or are diffused of consciousness by into the bloodstream and interfere with OXygen transport system. Carbon monoxide The inhalant gases generally lag period of few show a minutes between the time Carbon monoxide is a colourless, odourless, tasteless and inhale the agent and the animal begins to time it loses non-irritating gas which results from incomplete combustion of these gases must consciousness because require a certain organicmatter.Carbon monoxide is a highly toxic gas as inhaling concentration in the alveoli hefore they can be effective. Euthanasia with inhalant gases is even relatively small amounts of it can lead to hypoxic injury, not recommended alone in animals less than 16 week old because neurological damage and possibly death. The death from carbon neonatal animals are more resistant to monoxide is due mainly to its combination with haemoglobin and hypoxia and it takes longer for them to die. Reptiles,amphibians, diving birds, and diving and formation of carboxyhaemoglobin (COHb).Haemoglobin in this burrowing mammals may also show a prolonged time to loss of form cannot carry oxygen and hence tissues die from oxygen consciousness with inhalant gases. starvation. The affinity of haemoglobin for carbon monoxide is about 200-250times greater than its affinity for oxygen. Death Carbon dioxide occurs rapidly if concentrations of 4 to 6% are used. Carbon Carbon dioxide (CO2) is a heavy, colourless, odourless gas monoxide as euthanizing agent has some advantages like it induces having a acid taste. It is a constituent slightly of atmospheric air loss of consciousness without pain and with minimal discernible in which it exists to an extent of 0.4 per cent. Carbon dioxide is discomfort. Hypoxemia induced by CO is insidious, so that the widely used as euthanizing agents in small animal appears to be unaware. size animals. It largely acts by displacing oxygen from the respiratory Carbon monoxide is extremely hazardous for humans and system and producing CNS depression and death. animals because it is highly toxic and difficult to detect. The signs Carbon dioxide produces variable effects at different and symptoms of acute CO poisoning are characteristic ofhypoxia concentrations. At a low concentration of 5 percent in air, it and depend upon the concentration of CO inhaled. High exposure produces increased respiration, nausea, giddiness, anxiety and to CO may produce rapid death without significant clinical signs. weakness of muscles. At concentration of 10 percent in air it In low moderate concentrations,varying degree of toxic to signs causes tachypnoea, muscular tremors, sweating, visual may be displayed by the poisoned animal including drowsiness, disturbances, staggering gait and loss of consciousness. A incoordination, weakness, increased respiration and pulse, concentration of 25 to 30 per cent CO, may produce cyanosis, involuntary urination and defecation, and unconsciousness. The convulsion and death from cortical excitability. Very high post-mortem lesions are characteristic of hypoxia and depend on concentrations (>60 per cent) produces immediate insensibility the survival time. followed by death from glottis spasmscausing suffocation. Time Carbon monoxide has been used to euthanatize small animals to loss of consciousness may be further decreased by use of such as mink, chinchillas, birds, reptiles, amphibians and zoo higher concentrations of CO, with an 80 to 100% concentration animals. Carbon monoxide may also be used for individual animal providing anaesthesia. Time to loss ofconsciousness is generally or mass euthanasia is dogs, cats and other small mammals, longer theconcentration is increased slowly rather than exposing provided that commercially CO if compressed is used and proper the animal to the full concentration immediately. Signs of effective safety precautions are taken. Personnel using must be CO Co, anaesthesia are those associated with deep surgical thoroughly acquainted with its use and must understand its anaesthesia, such as loss of withdrawal and palpebral reflexes. hazards and limitations. The CO chambermust be of the highest Carbon dioxide (C0,)is a common agent used for euthanizing quality construction and the CO source and chamber must be rodents and other small animals. Use of a sealed chamber filled located in a well-ventilated environment, preferably out of doors. by a compressed gas cylinder is mostly used. A CO, concentration Carbon monoxide as euthanizing agent is acceptable only for euthanasia.Carbon dioxide equipment is properly designed when of 70% or more is mostly utilized and operated.  1212 ESSENTIALSOF VETERINARY PHAAMACOLOGY AND THERAPEUTICS-SandhWe Nitrogen and Argon euthanasia without causing fear or distress in the animal and Nitrogen (N) and argon (Ar) are colourless, odourless gases without exposing undue risk to the operator. The majority of injectable drugs used as anacsthetic agents which are inert, non-flammable and non-explosive. Nitrogen are acceptable for comprises 78% of atmospheric air, whereas Ar comprises less euthanasia if an adequate overdose is given. The than 1%.Nitrogen (N) and argon may be used to euthanize cats, route is intravenous (1V), preferred and should be restraint, accompanied byadequate small dogs, birds, rodents, rabbits and other small species, and making the animal as comfortable as possible with z00animals. These gases euthanize animals by inducing hypoxia. minimum distress or anxiety. or wild animals can be Aggressive, uncooperative, Euthanasia is induced by placing the animal in a closed container fearful. sedated or given a that has been prefilled with N,or Ar or into which the gas is then immobilizing agent prior to non-paralytic intravenous administration of the rapidly introduced.Unlike carbon monoxide, nitrogen and argon euthanasia agent. When intravenous are less hazardous to euthanizing personnel. However, both gases administrationis considered impractical or impossible, intraperitoneal produce hypoxemia and ventilatory stimulation prior to administration of a non irritating euthanasia agent is acceptable, provided unconsciousness, which could be distressing to some animals. not contain the drug does neuromuscular blocking agents. Therefore, it is recommended that animals may be is acceptable Intracardiac injection sedated prior only when performed to euthanasia. on heavily sedated, anesthetized or comatose animals. Other parenteral routes such as intramuscular, 2. Inhalant Anaesthetics subcutaneous and intrath oracic are not acceptable methods of administering Inhalant anaesthetics have been used to due to the slow and unreliable injectable euthanasiaagents euthanatize many onset of actíon. species of animals including amphibians, birds, cats, dogs, fur bearing animals, rabbits, reptiles, 1. Barbiturates rodents and other small animals, and zooanimals. Inhalant anaesthetics are useful for small animals Barbiturates are an important group of (