Anaesthesia and euthanasia
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This document provides background information on assessing and alleviating animal pain during research procedures. It discusses how animal pain can be recognized through behavioral and physiological changes. The importance of adequate post-procedure care like analgesia administration and prevention of complications is outlined. Common anesthetics used in laboratory animals like chloralose, urethane, barbiturates, paraldehyde, magnesium sulfate and ketamine are defined and their typical dosages for species like dogs, cats, rabbits and rats are provided. Factors affecting anesthetic activity and general considerations for anesthesia are also summarized.
Anaesthesia and euthanasia
- 2. BACK GROUND:- • A fundamental responsibility of individuals that use animals in research, teaching or testing is to anticipate and eliminate or minimize any potential that procedures may cause animal pain, distress, or discomfort. • Although animals that are in pain may not behave like humans, (e.g., pain in animals may be accompanied by immobility and silence, in contrast to the groans and cries of human patients), it is assumed that procedures that cause pain in humans cause pain in animals.
- 3. • The presence of pain in animals can be recognized by alterations in animal behavior (e.g., reduced activity, reduced grooming, hunched- up posture, altered gait, changes in temperament, vocalizations, reduced food and water intake, reduced urinary and fecal output), and in physiological variables, (e.g., reduced depth of respiration, increased heart rate, and reduced hydration status). • Animal pain, distress, and discomfort can produce a range of undesirable physiological changes, which may radically alter measured responses to experimental stimuli, as well as the rate of recovery from surgical procedures, hence, its avoidance and alleviation are in the best interest of both the animal and researcher.
- 4. • Reducing post-procedural/post-operative pain, distress, and discomfort is accomplished by good nursing care, (e.g., keeping the animal warm, clean, dry and well padded), and by the administration of analgesic drugs. • In addition to the avoidance and alleviation of pain and discomfort, adequate post-procedural /postoperative animal care also includes efforts to prevent and/or treat post-anesthetic complications, (e.g., aspiration, hypostatic pneumonia, cardiovascular and respiratory depression, dehydration, and infection).
- 5. • The prevention or minimization of animal pain, distress, or discomfort by the proper use of tranquilizers, anesthetics, and analgesics is scientifically and ethically essential to the humane care, use, and treatment of research animals. The use of these classes of drugs must effectively prevent or minimize suffering and discomfort of animals during potentially painful procedures. • The use of these three classes of drugs must be in accordance with currently accepted veterinary medical practice and produce in the subject animal an appropriate level of tranquilization, anesthesia, or analgesia consistent with the protocol or design of the experiment.
- 6. DEFINITIONS:- • Neuroleptic - produces central nervous depression, depression of excitability of the autonomic nervous system, a dulling of consciousness and a reduction of spontaneous motor activity (e.g., tranquilizers/sedatives). • Analgesia - relief from pain. • Preemptive analgesia - managing pain before it begins. • Tranquilization - a state of behavioral change in which the patient is relaxed, unconcerned by its surroundings, and often, indifferent to minor pain. • Sedation - a mild degree of central depression in which the patient is awake but calm; larger doses of sedative may lead to narcosis.
- 7. • Narcosis - a drug-induced state of sedation in which the patient is oblivious to pain. • Local anesthesia - loss of sensation in a limited body area. • Regional anesthesia – loss of sensation in a larger, though limited, body area. • Basal anesthesia - a light level of general anesthesia usually produced by preanesthetic agents; serves as a basis for deeper anesthesia following the administration of other agents. • General anesthesia - complete unconsciousness • Surgical anesthesia - unconsciousness, accompanied by muscular relaxation to such a degree that surgery can be performed painlessly. • Neuroleptanalgesia - a state of central nervous system depression and analgesia usually produced by a combination of a neuroleptic and a narcotic analgesic.
- 8. GENERAL CONSIDERATIONS:- • In order to reduce anesthetic risk and prevent post-anesthetic complications, animals must first be examined for signs of disease or distress including, but not limited to, ruffled, matted or dull hair coat, labored breathing, lack of inquisitiveness, failure to respond to stimuli, abnormal posture/positioning, dehydration, or impaired locomotion. • Acclimatizing animals allows them to adjust physiologically and psychologically to their new environment and provides the opportunity to carefully monitor for any abnormalities. Animals should be acclimatized for a minimum of 7 days.
- 9. • When planning to administer drugs, recall that dosage charts for anesthetic and analgesic agents state only the average amount of drug that would be expected to produce a desired level of anesthesia or analgesia under standard conditions. Consequently, animals must be monitored carefully and the dosages tailored to meet each clinical and research situation. • The duration of anesthesia produced by the anesthetic should coincide with the expected duration of the operative procedure.
- 10. ANAESTHESIA:- • The word anaesthesia has been derived from Greek word that means “without perception of insensibility”. • Anesthesia is the act of providing sensation-free relief from pain or pain-producing procedures. • Anesthesia must be performed by a person with knowledge of and familiarity with the drugs to be used in the animal species under consideration.
- 11. FACTORS AFFECT THE ACTIVITY OF ANAESTHETICS • Many factors can affect the activity of anesthetics. The species, strain, sex, age, nutritional and disease status, relative body size, disposition/demeanor, presence of concurrent pain or distress, or medication are known to cause a variation in the amount of drug needed to produce a desired effect in an individual animal.
- 12. Commonly used laboratory anaesthetics There are numerous anesthetics available for use in rodents. Some of the more popular agents include: Chloralose Urethane Barbiturates Paraldehyde Magnesium Sulphate Ketamine Tribromoethanol
- 13. CHLORALOSE • It is a compound of chloral and glucose prepared by heating equal parts of anhydrous glucose and charcoal, when both α- chloralose (active form) and β-chloralose (in active form) are formed. • It is prepared as one percent solution by boiling in 0.9% NaCl or in distilled water, and administered intravenously or intraperitoneally at a temperature of 30-400C before the chloralose comes out of solution.
- 14. Disavantages:- It is suitable only for acute experiments, usually in dogs and cats, inducing surgical anaesthesia for 3-4 hours or longer. Advantages:- It has the advantage of greater constancy of the depth of anaesthesia. The respiration and circulation are not depressed, and the blood pressure is well maintained usually on the higher side. Reflexes are not depressed but may be slightly exaggerated including responses to bilateral carotid occlusion.
- 15. Dog- 1% aq. Solution (hot) 80-120mg i.v. 10% in polyethylene glycol 100mg i.v. Cat- 1% aq. Solution (hot) 80mg i.v. 2% aq. Or saline suspension 80-100mg i.p. 10% in propylene glycol 100mg i.p. Rat- 10% in propylene glycol 80mg i.p.
- 16. URETHANE (Ethyl Carbamate):- It is readily soluble in water giving a neutral solution. Usually 25% solution in water is used. Disadvantages:- • It is suitable only for acute experiments since it has delayed toxic effect on liver, and may also cause agranulocytosis and pulmonary adenomata. • Mice develop an exceptionally high incidence of lung tumours regardless of the route of administration.
- 17. Dog- 25% aq. Solution 1.5g i.v. Cat- 25% aq. Solution 1.0-1.5 g i.v. Rabbit- 25% aq. Solution 0.5 – 1.75g i.v. 50% aq. Solution 1.5-2g i.p Guinea pig- 25% or 50% aq. Solution 1.5g i.p. Rat- 25% aq. Solution 1.25-1.75g i.m. or s.c. 20% aq. Solution 1.5g i.p.
- 18. BARBITURATES • Barbiturates interfere with nerve impulse transmission both in the central nervous system and in the ganglia producing depression of cardiovascular and spinal cord reflexes. • In rabbits pedal reflex (leg retraction) is lost first, then pupillary and finally palpebral reflex.
- 19. Pentobarbital Pentobarbital is a barbiturate and, historically, the most commonly used anesthetic in rodents. Advantages:- At recommended doses, it causes minimal cardiovascular depression. It is also relatively long acting and can provide approximately 45 minutes of surgical anesthesia. Disadvantages:- Pentobarbital is a potent inducer of the hepatic microsomal enzyme system. Causes pronounced respiratory depression as well as hypothermia, particularly when repeated doses are given.
- 20. Pentobarbitone sodium Monkey- 6% solution 25mg i.p. or i.v. Dog and cat 6% solution 30-50mg i.v. or i.p. Rabbit – 6% solution 50-60mg i.v. Guinea pig 1% solution 30-50mg i.p. Rat and mouse 0.6% solution 30-60mg i.p. Frog – 0.6% solution 50mg intraabdominally.
- 21. Phenobarbitone sodium Phenobarbitone sodium and barbitone sodium are used for prolonged experiments. Dog and cat – 10% aq. Solution 180-200mg i.p.
- 22. Tiopentone sodium Thiopentone sodium (pentothal) is used for surgical operations of short duration. It produces rapid induction with minimum excitation. Dog – 2.5% fresh solution. 12-16 mg i.v. (for brief duration) 20-26mg i.v. (for longer duration)
- 23. PARALDEHYDE: Advantages:- It has a wide margin of safety because it depresses only the cerebrum and not the medullary centres. Intravenous injection is likely to produce cardiac dilatation and pulmonary congestion and oedema. Disadvantages:- Under its influence the basal blood pressure as well as the response to vasopressor and depressor drugs are low. Bilateral carotid occlusion produces poor pressor response or even a depressor response. Dog – 6% solution 1.2ml i.p Cat – 6% solution 2.1ml i.m.
- 24. MAGNESIUM SULPHATE:- A 20% magnesium sulphate solution 5ml/kg intravenously produces anaesthesia for about an hour. Calcium gluconate intravenously will counteract its depressant effect immediately. Its principal use is in producing euthanasia.
- 25. Tribromoethanol Advantages:- In most rodents, tribromoethanol produces good surgical anesthesia, with good skeletal muscle relaxation and only a moderate degree of respiratory depression. It is relatively inexpensive and not a controlled agent. Disadvantages:- It is a potential for causing peritonitis. When exposed to either light or temperatures >400C, tribromoethanol degrades into two byproducts: hydrobromic acid and dibromoacetaldehyde. Both of these compounds are highly irritating when administered IP and result in peritonitis and visceral adhesions which may be fatal.
- 26. Ketamine hydrochloride Ketamine hydrochloride, a dissociative anesthetic, disrupts pain transmission and suppresses spinal cord activity with some action at opioid receptors. Visceral pain is not abolished with dissociative anesthetics and there is poor muscle relaxation and analgesia. Disadvantages:- Ketamine is a poor anesthetic when used alone, but is more often combined with other agents. When combined with other drugs, it is usually administered IP. Ketamine is acidic, can be irritating, and cause muscle necrosis when administrated IM. Ketamine-induced nerve damage can cause selfmutilation in rodents. Ketamine is a controlled substance. Store in a locked cabinet and maintain a log of its use.
- 27. EUTHANASIA:- • The term euthanasia is derived from the Greek terms eu meaning good and thanatos meaning death. A “good death” would be one that occurs with minimal pain and distress. In the context • Euthanasia is the act of inducing humane death in an animal. “Sacrificing the experimental animal after use by gentle procedure causing minimum of physical and mental suffering is called euthanasia (Painless killing).
- 28. Objectives of euthanasia:- • The primary criteria for euthanasia in terms of animal welfare are that the method be painless, achieve rapid unconsciousness and death, require minimum restraint, avoid excitement, is appropriate for the age, species, and health of the animal, must minimize fear and psychological stress in the animal, be reliable, reproducible, irreversible, simple to administer (in small doses if possible) and safe for the operator, and, so far as possible, be aesthetically acceptable for the operator.
- 29. Methods of Euthanasia:- Methods of euthanasia fall into two broad categories. • Chemical methods. • Physical methods. chemical methods • Inhalant agents:- Ex – ether, halothane, methoxyflurane, isoflurane, enflurane, chloroform, nitrogen, nitrous oxide, carbon di oxide, carbon monoxide, argon, hydrogen cyanide. • Injectable agents:- Ex – barbiturates, chloral hydrate, ethanol, ketamine, magnesium sulphate, potassium chloride, neuromuscular blocking agents.
- 30. Physical methods:- • PENETRATING CAPTIVE BOLT • EUTHANASIA BY A BLOW TO THE HEAD • GUNSHOT • CERVICAL DISLOCATION • DECAPITATION • ELECTROCUTION • MICROWAVE IRRADIATION • THORACIC (CARDIOPULMONARY, CARDIAC) COMPRESSION • KILL TRAPS • MACERATION • ADJUNCTIVE METHODS • Exsanguination • Stunning • Pithing
- 31. PENETRATING CAPTIVE BOLT:- A penetrating captive bolt is used for euthanasia of ruminants, horses, swine, laboratory rabbits, and dogs. Its mode of action is concussion and trauma to the cerebral hemisphere and brainstem. Advantages— the penetrating captive bolt is an effective method of euthanasia for use in slaughterhouses, in research facilities, and on the farm when use of drugs is inappropriate. Disadvantages— (1) It is aesthetically displeasing. (2) Death may not occur if equipment is not maintained and used properly.
- 32. EUTHANASIA BY A BLOW TO THE HEAD • Euthanasia by a blow to the head must be evaluated in terms of the anatomic features of the species on which it is to be performed. The anatomic features of neonatal calves, however, make a blow to the head in this species unacceptable. • Personnel performing euthanasia by use of a blow to the head must be properly trained and monitored for proficiency with this method of euthanasia, and they must be aware of its aesthetic implications.
- 33. GUNSHOT A properly placed gunshot can cause immediate insensibility and humane death. In some circumstances, a gunshot may be the only practical method of euthanasia. Advantages—(1) Loss of consciousness is instantaneous if the projectile destroys most of the brain. (2) Given the need to minimize stress induced by handling and human contact, gunshot may at times be the most practical and logical method of euthanasia of wild or free-ranging species. Disadvantages—(1) Gunshot may be dangerous to personnel. (2) It is aesthetically unpleasant. (3) Under field conditions, it may be difficult to hit the vital target area.
- 34. CERVICAL DISLOCATION Cervical dislocation is a technique that has been used for many years and, when performed by well trained individuals, appears to be humane. However, there are few scientific studies to confirm this observation. Advantages—(1) Cervical dislocation is a technique that may induce rapid loss of consciousness. (2) It does not chemically contaminate tissue. (3) It is rapidly accomplished. Disadvantages—(1) cervical dislocation may be aesthetically displeasing to personnel. (2) Cervical dislocation requires mastering technical skills to ensure loss of consciousness is rapidly induced. (3) Its use is limited to poultry, other small birds, mice, and immature rats and rabbits.
- 35. DECAPITATION:- Decapitation can be used to euthanatize rodents and small rabbits in research settings. It provides a means to recover tissues and body fluids that are chemically uncontaminated. Advantages—(1) Decapitation is a technique that appears to induce rapid loss of consciousness. (2) It does not chemically contaminate tissues. (3) It is rapidly accomplished. Disadvantages—(1) Handling and restraint required to perform this technique may be distressful to animals. (2) The interpretation of the presence of electrical activity in the brain following decapitation has created controversy and its importance may still be open to debate.
- 36. ELECTROCUTION:- • Electrocution, using alternating current, has been used as a method of euthanasia for species such as dogs, cattle, sheep, swine, foxes, and mink. Electrocution induces death by cardiac fibrillation, which causes cerebral hypoxia. However, animals do not lose consciousness for 10 to 30 seconds or more after onset of cardiac fibrillation. • Advantages—(1) Electrocution is humane if the animal is first rendered unconscious. (2) It does not chemically contaminate tissues. (3) It is economical. • Disadvantages—(1) Electrocution may be hazardous to personnel. (2) When conventional single-animal probes are used, it may not be a useful method for mass euthanasia because so much time is required per animal.
- 37. MICROWAVE IRRADIATION:- Heating by microwave irradiation is used primarily by neurobiologists to fix brain metabolites in vivo while maintaining the anatomic integrity of the brain. Microwave instruments have been specifically designed for use in euthanasia of laboratory mice and rats. • Advantages—(1) Loss of consciousness is achieved in less than 100ms, and death in less than 1 second. (2) This is the most effective method to fix brain tissue in vivo for subsequent assay of enzymatically labile chemicals. • Disadvantages—(1) Instruments are expensive. (2) Only animals the size of mice and rats can be euthanatized with commercial instruments that are currently available.
- 38. THORACIC (CARDIOPULMONARY, CARDIAC) COMPRESSION:- • Thoracic (cardiopulmonary, cardiac) compression is used to euthanatize small- to medium-sized free ranging birds when alternate techniques described in these guidelines are not practical. Advantages—(1) This technique is rapid. (2) It is apparently painless. (3) It maximizes carcass use for analytical/contaminant studies. Disadvantages—(1) It may be considered aesthetically unpleasant by onlookers. (2) The degree of distress is unknown.
- 39. KILL TRAPS:- • Mechanical kill traps are used for the collection and killing of small, free-ranging mammals for commercial purposes (fur, skin, or meat), scientific purposes, to stop property damage, and to protect human safety. • Advantage—Free-ranging small mammals may be killed with minimal distress associated with handling and human contact. • Disadvantages—(1) Traps may not afford death within acceptable time periods. (2) Selectivity and efficiency is dependent on the skill and proficiency of the operator.
- 40. MACERATION:- • Maceration, via use of a specially designed mechanical apparatus having rotating blades or projections, causes immediate fragmentation and death of day-old poultry and embryonated eggs. Advantages—(1) Death is almost instantaneous. (2)The method is safe for workers. (3) Large numbers of animals can be killed quickly. Disadvantages—(1) Special equipment is required. (2) Macerated tissues may present biosecurity risks.
- 41. ADJUNCTIVE METHODS • Stunning and pithing, when properly done, induce loss of consciousness but do not ensure death. Therefore, these methods must be used only in conjunction with other procedures, such as pharmacologic agents, exsanguination, or decapitation to euthanatize the animal. Exsanguination • Exsanguination can be used to ensure death subsequent to stunning, or in otherwise unconscious animals. Because anxiety is associated with extreme hypovolemia, exsanguination must not be used as a sole means of euthanasia. Animals may be exsanguinated to obtain blood products, but only when they are sedated, stunned, or anesthetized.
- 42. Stunning • Animals may be stunned by a blow to the head, by use of a non- penetrating captive bolt, or by use of electric current. Stunning must be followed immediately by a method that ensures death. • Blow to the head—Stunning by a blow to the head is used primarily in small laboratory animals with thin craniums. A single sharp blow must be delivered to the central skull bones with sufficient force to produce immediate depression of the central nervous system. When properly done, consciousness is lost rapidly.
- 43. Non-penetrating captive bolt— A non-penetrating captive bolt may be used to induce loss of consciousness in ruminants, horses, and swine. Signs of effective stunning by captive bolt are immediate collapse and a several second period of tetanic spasm, followed by slow hind limb movements of increasing frequency. Other aspects regarding use of the non-penetrating captive bolt are similar to the use of a penetrating captive bolt, as previously described.
- 44. Electrical stunning—Alternating electrical current has been used for stunning species such as dogs, cattle, sheep, goats, hogs, fish and chickens. Experiments with dogs have identified a need to direct the electrical current through the brain to induce rapid loss of consciousness. In dogs, when electricity passes only between fore- and hind limbs or neck and feet, it causes the heart to fibrillate but does not induce sudden loss of consciousness. For electrical stunning of any animal, an apparatus that applies electrodes to opposite sides of the head, or in another way directs electrical current immediately through the brain, is necessary to induce rapid loss of consciousness.
- 45. Pithing:- • In general, pithing is used as an adjunctive procedure to ensure death in an animal that has been rendered unconscious by other means. For some species, such as frogs, with anatomic features that facilitate easy access to the central nervous system, pithing may be used as a sole means of euthanasia, but an anesthetic overdose is a more suitable method.
- 46. REFERENCES:- • Practical pharmacology and clinical pharmacy by S.K.Kulkarni, Vallabh publications, Page no- 21. • Essentials of medical pharmacology by KD Tripathi, 6th edition, jaypee brothers medical publishers (p ) ltd, page no – 351, 365. • Modern pharmacology with clinical applications Charles R. Craig, fifth edition, Page no-291. • Laboratory animals: Rodent Anesthesia & Analgesia by Kathleen A. Murray. • Guidelines on anesthesia and analgesia in laboratory animals, University of South Florida provides the following guidelines for use by IACUC- certified faculty and staff. • AVMA Guidelines on Euthanasia (Formerly Report of the AVMA Panel on Euthanasia) June 2007. • Euthanasia of animals used for scientific purposes by J.S.Reilly, Second edition.
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