Anesthesia, analgesia, and euthanasia of invertebrates

Invertebrate animals have long played an important role in biomedical research in such fields as genetics, physiology, and development. However, with few exceptions, scientists, veterinarians, and technicians have paid little attention to the anesthesia, analgesia, and euthanasia of these diverse creatures. Indeed, some standard research procedures are routinely performed without anesthesia. Yet various chemical agents are available for the immobilization or anesthesia of invertebrates, ranging from gases or volatile liquids that can be pumped into either an anesthetic chamber (for terrestrial species) or a container of water (aquatic species), to benzocaine and other substances for fish. Many invertebrates are not difficult to immobilize or anesthetize and the procedures recommended in this article appear to be safe; however, none should be considered totally risk-free. Analgesia of invertebrates is as yet a largely unexplored field; until scientific data are available, other measures can promote the well-being of these animals in the laboratory. For euthanasia, various methods (physical or chemical or a combination of both) have been recommended for different taxa of invertebrates, but most have not been properly studied under laboratory conditions and some can be problematic in the context of research procedures and tissue harvesting. Furthermore, relevant data are scattered, sometimes available only in languages other than English, and there is no international approach for seeking and collating such information. In this article I review various methods of anesthesia, analgesia, and euthanasia for terrestrial and aquatic invertebrates, as well as areas requiring further research.     

Carbon dioxide for euthanasia: concerns regarding pain and distress, with special reference to mice and rats

Carbon dioxide (CO2) is the most commonly used agent for euthanasia of laboratory rodents, used on an estimated tens of millions of laboratory rodents per year worldwide, yet there is a growing body of evidence indicating that exposure to CO2 causes more than momentary pain and distress in these and other animals. We reviewed the available literature on the use of CO2 for euthanasia (as well as anaesthesia) and also informally canvassed laboratory animal personnel for their opinions regarding this topic. Our review addresses key issues such as CO2 flow rate and final concentration, presence of oxygen, and prefilled chambers (the animal is added to the chamber once a predetermined concentration and flow rate have been reached) versus gradual induction (the animal is put into an empty chamber and the gas agent(s) is gradually introduced at a fixed rate). Internationally, animal research standards specify that any procedure that would cause pain or distress in humans should be assumed to do so in non-human animals as well (Public Health Service 1986, US Department of Agriculture 1997, Organization for Economic Cooperation and Development 2000). European Union guidelines, however, specify a certain threshold of pain or distress, such as 'skilled insertion of a hypodermic needle', as the starting point at which regulation of the use of animals in experimental or other scientific procedures begins (Biotechnology Regulatory Atlas n.d.). There is clear evidence in the human literature that CO2 exposure is painful and distressful, while the non-human literature is equivocal. However, the fact that a number of studies do conclude that CO2 causes pain and distress in animals indicates a need for careful reconsideration of its use. Finally, this review offers recommendations for alternatives to the use of CO2 as a euthanasia agent.     

实验动物饲养和运输的伦理与福利

本文提出实验动物福利是人类应当给予实验动物的良好条件（正面因素）,主要体现在动物的饲养和运输等过程,以“5F”为基本理论;伦理则是人类给予动物实验处理（负面因素）时应遵循的原则,主要体现在动物实验过程中,以“3R”为基本理论.同时总结了实验动物饲养和运输过程的实际经验,从环境、笼具、垫料、密度、饲料和饮水、社会和行为需要、安乐死、运输等方面,介绍了保障实验动物福利的具体做法.     

A Survey of Veterinarians’ Attitudes toward Euthanasia of Companion Animals in Japan

This study investigated veterinarians’ attitudes toward euthanasia of companion animals in Japan. A nationwide survey was conducted with 932 veterinarians in small animal practices. It examined the number of times they administered euthanasia, their moral criteria for choosing euthanasia for animals, and their behavioral criteria for suggesting euthanasia to owners. According to the data analyses, on average the veterinarians administered euthanasia 2.48 times a year. For many veterinarians, two conditions were necessary to justify euthanasia for animals: “the animals are incurable and suffering” and “the owners request to euthanize the animals.” In the absence of either condition, the veterinarians were inclined to disapprove of choosing euthanasia. If the owners requested further treatment, 67% showed clear disapproval of choosing euthanasia for animals with serious medical conditions. Meanwhile, more than 76% showed clear disapproval of euthanizing healthy animals when the owners requested it. These results indicate that the owners’ request takes precedence over the animals’ condition for suffering animals, but not for healthy animals. For animals with serious medical conditions, 56% of the veterinarians answered that they would or might suggest euthanasia to the owners even though the owners requested further treatment. In this situation, for some veterinarians, the animals’ condition rather than the owners’ request might become a determinant in suggesting euthanasia to owners, even if their moral judgments were against choosing euthanasia for the animals. A decrease in the owners’ or the animals’ quality of life and the owners’ inability to pay were not primary factors in choosing or suggesting euthanasia. Having an experience of euthanizing their own animals was a key factor for the veterinarians which increased not only the number of times they administered euthanasia but also the degree of their moral approval of choosing euthanasia and their behavioral willingness to suggest it to owners.     

Managing intentions: the end-of-life administration of analgesics and sedatives, and the possibility of slow euthanasia

There has been much debate regarding the 'double-effect' of sedatives and analgesics administered at the end-of-life, and the possibility that health professionals using these drugs are performing 'slow euthanasia.' On the one hand analgesics and sedatives can do much to relieve suffering in the terminally ill. On the other hand, they can hasten death. According to a standard view, the administration of analgesics and sedatives amounts to euthanasia when the drugs are given with an intention to hasten death. In this paper we report a small qualitative study based on interviews with 8 Australian general physicians regarding their understanding of intention in the context of questions about voluntary euthanasia, assisted suicide and particularly the use of analgesic and sedative infusions (including the possibility of voluntary or non-voluntary 'slow euthanasia'). We found a striking ambiguity and uncertainty regarding intentions amongst doctors interviewed. Some were explicit in describing a 'grey' area between palliation and euthanasia, or a continuum between the two. Not one of the respondents was consistent in distinguishing between a foreseen death and an intended death. A major theme was that 'slow euthanasia' may be more psychologically acceptable to doctors than active voluntary euthanasia by bolus injection, partly because the former would usually only result in a small loss of 'time' for patients already very close to death, but also because of the desirable ambiguities surrounding causation and intention when an infusion of analgesics and sedatives is used. The empirical and philosophical implications of these findings are discussed.     

Influence of euthanasia method on blood and gill variables in normoxic and hypoxic Gulf killifish Fundulus grandis

In many experiments, euthanasia, or humane killing, of animals is necessary. Some methods of euthanasia cause death through cessation of respiratory or cardiovascular systems, causing oxygen levels of blood and tissues to drop. For experiments where the goal is to measure the effects of environmental low oxygen (hypoxia), the choice of euthanasia technique, therefore, may confound the results. This study examined the effects of four euthanasia methods commonly used in fish biology (overdose of MS‐222, overdose of clove oil, rapid cooling and blunt trauma to the head) on variables known to be altered during hypoxia (haematocrit, plasma cortisol, blood lactate and blood glucose) or reflecting gill damage (trypan blue exclusion) and energetic status (ATP, ADP and ATP:ADP) in Gulf killifish Fundulus grandis after 24 h exposure to well‐aerated conditions (normoxia, 7·93 mg O₂ l^?1, c. 150 mm Hg or c. 20 kPa) or reduced oxygen levels (0·86 mg O₂ l^?1, c. 17 mm Hg or c. 2·2 kPa). Regardless of oxygen treatment, fish euthanized by an overdose of MS‐222 had higher haematocrit and lower gill ATP:ADP than fish euthanized by other methods. The effects of 24 h hypoxic exposure on these and other variables, however, were equivalent among methods of euthanasia (i.e. there were no significant interactions between euthanasia method and oxygen treatment). The choice of an appropriate euthanasia method, therefore, will depend upon the magnitude of the treatment effects (e.g. hypoxia) relative to potential artefacts caused by euthanasia on the variables of interest.     

Euthanasia of rats with carbon dioxide--animal welfare aspects

A method of inducing euthanasia by carbon dioxide (CO2) inhalation in the home cage of an animal is described and tested for distress by behavioural as well as by hormonal measures. The animals were maintained in their home cage while CO2 was induced at a flow of 6 l/min. The behaviour of the animals was measured continuously as were the serum concentrations of glucose, ACTH and corticosterone 30, 75 and 120 s after the CO2 was introduced into the cage. In order to test for distress, two groups of rats were pre-treated with acepromazine (orally) and pentobarbiturate (i.p. injection) respectively, in order to reduce possible distress caused by CO2 euthanasia, and were compared with control groups. There were no signs of distress by behavioural or by hormonal changes. All changes seen could be attributed to experimental effects and, especially as there was no difference between the pre-treated and the control groups of rats, it must be assumed that the described method of euthanasia is in concordance with animal welfare, it leads to rapid death without severe distress or pain, and it seems therefore to be 'humane'.     

Veterinary science student preferences for the source of dog cadavers used in anatomy teaching

Live animals and cadavers are integral to veterinary education. In the year of this survey (2008), and in at least the five preceding years, cadavers obtained by euthanasia of healthy pound dogs and ex-racing greyhounds were dissected by students, during their veterinary anatomy classes at the University of Queensland School of Veterinary Science. Students may have ethical concerns about this. An alternative approach was to use donated dog cadavers. These are owned pet dogs that have died of natural causes or have been euthanised for medical reasons, and have been donated by their owners for the purposes of veterinary education. Veterinary students at the School were surveyed in 2008, in order to determine their preferences for cadaver source. Data from 406 questionnaires were analysed. Third-year and fifth-year veterinary students were more likely than first-year students to prefer pound-dog/greyhound cadavers over donated cadavers for anatomy dissection (p ≤ 0.002). Between 32% and 45% of the students had no preference for either source of cadaver. These findings are consistent with the hypothesis that veterinary students become more accepting of the euthanasia of unwanted healthy animals for education as they progress through the veterinary programme, in contexts such as the current study. This could occur due to increased acceptance of the euthanasia of healthy animals generally, a decline in moral development, desensitisation, and/or the belief that healthy animal cadavers offer a superior learning experience.     

EUTHANASIA AFTER THE HOLOCAUST – IS IT POSSIBLE?: A REPORT FROM THE FEDERAL REPUBLIC OF GERMANY

The author theorizes that eugenically-related killings before and during the Nazi era have made it more difficult to discuss euthanasia in modern West Germany and have influenced public policy on this issue. Opinion polls reveal that over 50% of West Germans favor active euthanasia, a proportion identical to that in corresponding U.S. polls. However, official opinion is strongly opposed to legalizing any kind of euthanasia except nontreatment of those in the irreversible process of imminent death. Even legally acceptable treatment refusal may be easily overridden by declaring the patient incompetent. Kottow cites poor medical treatment of the mentally ill and 38% public acceptance of proposals to kill them as evidence of dormant tendencies which support the view that the "times are not yet ripe for innovative legislation."     

Understanding Animal Companion Surplus in the United States: Relinquishment of Nonadoptables to Animal Shelters for Euthanasia

Relinquishing a nonhuman animal to a shelter is a complex decision that, it is often believed, ultimately may represent a breakdown of the human-animal bond. The result of such a breakdown is an animal companion surplus in the United States, which is no better evidenced than by the statistics documenting the millions of animals euthanized at shelters every year. This research examined the companion animals who are relinquished by their owners to shelters for adoption and compared them specifically to those relinquished for euthanasia. The study also compared the owner characteristics of the animals in these two groups. Although the majority of dogs and cats relinquished are clearly adoptable, a sizable number of these pets presented to shelters for euthanasia have problems precluding their adoptability: old age, illness, and refractory behavior.     

Understanding Animal Companion Surplus in the United States: Relinquishment of Nonadoptables to Animal Shelters for Euthanasia

Relinquishing a nonhuman animal to a shelter is a complex decision that, it is often believed, ultimately may represent a breakdown of the human-animal bond. The result of such a breakdown is an animal companion surplus in the United States, which is no better evidenced than by the statistics documenting the millions of animals euthanized at shelters every year. This research examined the companion animals who are relinquished by their owners to shelters for adoption and compared them specifically to those relinquished for euthanasia. The study also compared the owner characteristics of the animals in these two groups. Although the majority of dogs and cats relinquished are clearly adoptable, a sizable number of these pets presented to shelters for euthanasia have problems precluding their adoptability: old age, illness, and refractory behavior.     

Success of intracoelomic radiotransmitter implantation in the treefrog (Hyla versicolor)

Concern about the effects of habitat modification on the natural movements and behavior of amphibians has led researchers to devise several methods to follow individual animals as they migrate among seasonal resources; one such method is the surgical insertion of radiotransmitters. Intracoelomic implantation has come into general use despite the relative lack of specific procedural guidelines and information about the effects of transmitter insertion and removal. The author outlines the surgical implantation procedures used on a small amphibian (gray treefrog) and provides insight into the effects of multiple major surgical invasions on the long-term survival of amphibians. Multiple survival surgeries were successful in this study and may be an alternative to euthanasia in some instances.     

There for You: Attending Pet Euthanasia and Whether this Relates to Complicated Grief and Post-Traumatic Stress Disorder

ABSTRACT

Recognizing the deep relationship between grief and the loss of a companion animal, veterinarians and mental health practitioners often find themselves consoling pet owners both prior to and in the aftermath of pet euthanasia. Yet how does euthanasia influence this bereavement process? To explore this we examined, using a survey, the correlations between pet euthanasia, Complicated Grief (CG), and Post-Traumatic Stress Disorder (PTSD) amongst a diverse range of pet owners from the state of Hawaii. Participants (n = 236) completed a 37-item questionnaire, the Inventory of Complicated Grief Revised Short Form (ICG-R-SF), and the PTSD Checklist (PCL). Of the participants, 3.4% and 4.7% met the criteria for CG and PTSD, respectively. This paper explores and subdivides respondents into those who attended their companion animal’s euthanasia and those who did not. Our results indicate that physically attending a companion animal’s euthanasia is not correlated with CG or PTSD. As the experience of pet loss itself may be more indicative of psychological distress than whether or not the owner was present at the moment of euthanasia, veterinary staff need not dissuade pet owners from sharing their pet’s final moments.     

A comparative analysis of carbon dioxide displacement rates for euthanasia of the ferret

Though carbon dioxide asphyxiation is a common method of euthanasia for laboratory animals, species-specific guidelines have not been established for this procedure in the domestic ferret (Mustela putorius furo). The authors investigated the efficacy and stress effects of carbon dioxide euthanasia in 24 ferrets that had participated in previous experimental protocols. They euthanized ferrets by placing them in cages that were either prefilled with carbon dioxide or gradually filled at a displacement rate of 10%, 20% or 50% of the cage volume per min. Blinded observers subjectively evaluated ferret distress. Prefilling the cage or filling it at a rate of 50% volume per min resulted in less time to recumbency and to last breath than did filling the cage at a slower displacement rate. Slower carbon dioxide displacement rates also caused an increase in ferret blood glucose concentrations, which may indicate distress. Overall, observers found that prefilling the euthanasia cage caused the least stress to ferrets.     

The effect of mouse euthanasia technique on subsequent lymphocyte proliferation and cell mediated lympholysis assays

The purpose of this study was to determine the effects that specific euthanasia methods have on mitogen induced lymphocyte proliferation (LP) and the induction of alloantigen specific cytolytic T-lymphocytes (CTL). Mice were euthanatized by cervical dislocation (CD), or anesthesia with methoxyflurane or pentobarbital followed by CD (M-CD or P-CD respectively), CO2 overexposure (CO2-OD) or halothane overexposure (H-OD). Mitogenic lymphoproliferation was increased in cells derived from mice euthanatized by M-CD and P-CD. In contrast, the cytolytic profile of CTL derived from mice euthanatized by P-CD, CO2-OD and H-OD was decreased. The results of this study show that euthanasia techniques involving the use of methoxyflurane, pentobarbital, CO2 and halothane affect in vitro lymphoproliferation and CTL function. We conclude that the method of euthanasia influences certain immunologic parameters and selection of a particular technique should be given careful consideration.     

Regional distribution of glutamate in the central nervous system of rat terminated by carbon dioxide euthanasia

Carbon dioxide euthanasia is an established method for the termination of small laboratory animals. It has also been employed by the authors in neurobiological research on the post-mortem glutamate concentration in the structures of rat brains. The following investigations were aimed at optimizing the termination procedure based on the CO2 saturation rate of the inhaled air. Two rates of CO2 flow were applied, and the higher one significantly augmented the glutamate level in the hippocampus and cerebellum. The relationship between this finding and signs of central fear reaction is discussed. The authors conclude that lower rather than higher CO2 flow in euthanasia procedures is gentler and is therefore preferable for use with laboratory animals.     

Rates of euthanasia and adoption for dogs and cats in Michigan animal shelters

Estimates of canine and feline euthanasia at U.S. animal shelters—largely based on voluntary surveys with low response rates—make it difficult to estimate the population from which the euthanized animals derive. Estimates of euthanasia rates (animals euthanized per unit of population) have varied widely and been available only sporadically. This study used requirements of Michigan state law (Pet Shops, Dog Pounds, and Animal Shelters Act, 1969) for animal shelters to collect admission and discharge data for all 176 Michigan-licensed animal shelters. In 2003, Michigan shelters discharged 140,653 dogs: Of these, 56,972 (40%) were euthanized; 40,005 (28%) were adopted. This annual euthanasia rate is 2.6% of the estimated 2003 Michigan dog population. Michigan shelters discharged 134,405 cats in 2003: 76,321 (57%) by euthanasia and (24%) by adoption. The estimated ratio of euthanized cats to cats who had owners was 3.1%. Small shelters and privately owned shelters were associated with higher adoption rates. Comparison with historical information from the past 10 to 20 years suggests the number of companion animals being euthanized in shelters has decreased and that progress has been made in reducing the companion animal overpopulation problem.     

On euthanasia: exploring psychological meaning and attitudes in a sample of Mexican physicians and medical students

Euthanasia has become the subject of ethical and political debate in many countries including Mexico. Since many physicians are deeply concerned about euthanasia, due to their crucial participation in its decision and implementation, it is important to know the psychological meaning that the term 'euthanasia' has for them, as well as their attitudes toward this practice. This study explores psychological meaning and attitudes toward euthanasia in 546 Mexican subjects, either medical students or physicians, who were divided into three groups: a) beginning students, b) advanced students, and c) physicians. We used the semantic networks technique, which analyzed the words the participants associated with the term 'euthanasia'. Positive psychological meaning, as well as positive attitudes, prevailed among advanced students and physicians when defining euthanasia, whereas both positive and negative psychological meaning together with more ambivalent attitudes toward euthanasia predominated in beginning students. The findings are discussed in the context of a current debate on a bill proposing active euthanasia in Mexico City.     

Comparative physiological responses to stressors in animals.

1. The species-specific experimental response to stressors (SSERTS) analysis has been applied to a number of species under varied short and long term conditions. 2. The measure provides quantitative data relating to the physiological responses of animals when exposed to stressors and results are presented comparing these for different methods of immobilization, euthanasia, etc. at intra- and inter-species level. 3. It is suggested that the SSERTS measure is of greater value for measuring the responses of animals to stressors than is the measurement of the concentration of single blood variables.