Robert E. Meyer

A review of tribromoethanol anesthesia for production of genetically engineered mice and rats

Tribromoethanol (TBE) is easy and inexpensive to make in the laboratory from readily available reagents, requires no special equipment for its administration, and is not subject to federal or state drug enforcement agency regulations. Intraperitoneal (i.p.) injection of TBE results in the simple and rapid induction of short-term surgical anesthesia; however, recent adverse reports about the efficacy and safety of TBE make its continued routine use as a rodent anesthetic controversial. The authors review the history and use of TBE as an animal anesthetic and conclude that TBE should be relegated to acute terminal studies when administered i.p.

Physiologic Measures of Animal Stress during Transitional States of Consciousness

Simple Summary The humaneness, and therefore suitability, of any particular agent or method used to produce unconsciousness in animals, whether for anesthesia, euthanasia, humane slaughter, or depopulation, depends on the experience of pain or distress prior to loss of consciousness. Commonly reported physiologic measures of animal stress, including physical movement and vocalization, heart rate and ECG, electroencephalographic activity, and plasma and neuronal stress markers are discussed within this context. Abstract Determination of the humaneness of methods used to produce unconsciousness in animals, whether for anesthesia, euthanasia, humane slaughter, or depopulation, relies on our ability to assess stress, pain, and consciousness within the contexts of method and application. Determining the subjective experience of animals during transitional states of consciousness, however, can be quite difficult; further, loss of consciousness with different agents or methods may occur at substantially different rates. Stress and distress may manifest behaviorally (e.g., overt escape behaviors, approach-avoidance preferences [aversion]) or physiologically (e.g., movement, vocalization, changes in electroencephalographic activity, heart rate, sympathetic nervous system [SNS] activity, hypothalamic-pituitary axis [HPA] activity), such that a one-size-fits-all approach cannot be easily applied to evaluate methods or determine specific species applications. The purpose of this review is to discuss methods of evaluating stress in animals using physiologic methods, with emphasis on the transition between the conscious and unconscious states.

Pharmacokinetics and pharmacodynamics comparison between subcutaneous and intravenous butorphanol administration in horses

The study objective was to compare butorphanol pharmacokinetics and physiologic effects following intravenous and subcutaneous administration in horses. Ten adult horses received 0.1 mg/kg butorphanol by either intravenous or subcutaneous injections, in a randomized crossover design. Plasma concentrations of butorphanol were measured at predetermined time points using highly sensitive liquid chromatography-tandem mass spectrometry assay (LC-MS/MS). Demeanor and physiologic variables were recorded. Data were analyzed with multivariate mixed-effect model on ranks (P ≤ 0.05). For subcutaneous injection, absorption half-life and peak plasma concentration of butorphanol were 0.10 ± 0.07 h and 88 ± 37.4 ng/mL (mean ± SD), respectively. Bioavailability was 87%. After intravenous injection, mean ± SD butorphanol steady-state volume of distribution and clearance was 1.2 ± 0.96 L/kg and 0.65 ± 0.20 L/kg/h, respectively. Terminal half-lives for butorphanol were 2.31 ± 1.74 h and 5.29 ± 1.72 h after intravenous and subcutaneous administrations. Subcutaneous butorphanol reached and maintained target plasma concentrations >10 ng/mL for 2 ± 0.87 h (Mean ± SD), with less marked physiologic and behavioral effects compared to intravenous injection. Subcutaneous butorphanol administration is an acceptable alternative to the intravenous route in adult horses.

Principles of carbon dioxide displacement.

To the editors: I am writing to comment and expand on the physical principles governing carbon dioxide displacement rates for ferret euthanasia recently described by Fitzhugh and coworkers1, where ferrets were placed into cages that were either prefilled with carbon dioxide or filled at a displacement rate of 10%, 20% or 50% of the cage volume per min. Prefilling the cage or filling it at a rate of 50% volume per min for 3 min resulted in less time to recumbency and to last breath than did filling the cage at a slower displacement rate. By converting the chamber displacement rate into a time constant (τ), one can demonstrate the interaction between time and inflow rate on the gas concentration achieved within any enclosed space2. The change in gas concentration within an enclosed space involves two components: (i) the physical process of wash-in of new gas (or wash-out of existing gas); and (ii) the time constant required for that change to occur within the container for a known flow rate. These components are commonly combined in the practice of anesthesia to predict how quickly a change in concentration of an inhaled anesthetic will occur within a circle rebreathing circuit. As the authors state, the 2000 AVMA euthanasia guidelines recommend a carbon dioxide displacement rate of 20% of the chamber volume per min as optimal for euthanasia3. This recommendation is based on the work of Hornett and Haynes, which examined the effect of various carbon dioxide gas flow rates on the behavior and death of rats4. In that study, a carbon dioxide flow rate of 19.5% of the chamber volume per min was empirically determined to achieve a quiet delivery into unconsciousness, with death occurring 6–9 min after beginning flow. Smith and Harrap reported similar findings in rats using a carbon dioxide flow rate equivalent to 22% of the chamber volume per min (ref. 5). The physical principles underlying the choice of this particular flow rate were not described in the sources cited above3–5. The rate of change of gas concentration within any enclosed space is a special form of non-linear change known as an exponential process, and as such can be derived from the wash-in and washout exponential functions6. For the wash-in exponential function, the quantity under consideration rises towards a limiting value at a rate that progressively decreases in proportion to the distance it still has to rise. In theory, the concentration approaches, but never reaches, 100%. Conversely, for the wash-out exponential function, the quantity under consideration falls at a rate that progressively decreases in proportion to the distance it still has to fall; again, in theory, the quantity approaches, but never reaches, zero. The exponential wash-in and wash-out equations are used to derive the time constant (τ) for an enclosed volume or space. This constant is mathematically equal to the enclosed volume or space undergoing wash-in or wash-out divided by the rate of flow, or displacement, into that space, where τ = volume / flow rate (refs. 6, 7). Thus, the time constant represents the time at which the wash-in or wash-out process would have been complete had the initial rate of change continued as a linear function rather than an exponential function6. As such, the time constant is similar in concept to the half-life, although they are neither identical nor interchangeable7. For the wash-in function, 1τ is required for the concentration of the inflowing gas to rise to 63.2%, 2τ is required for the concentration to rise to 86.5%, and 3τ is required for the concentration to rise to 95% of the inflowing gas concentration, with ∞(τ) required for the gas concentration to rise to 100% (ref. 6). Conversely, for the washout function, 1τ is required for the remaining gas concentration to fall to 36.8% of the original value, 2τ is required for gas concentration to fall to 13.5%, and 3τ is required for gas concentration to fall to 4.98%, with ∞(τ) required for gas concentration to fall to zero6. The flow or displacement rate therefore determines the time constant for any given enclosed volume, such that increasing the flow rate will result in a proportional reduction of the wash-in and wash-out time constants for any size chamber (and vice versa). According to the above , i t can be show n that the AVMA-recommended carbon dioxide inflow rate of 20% of the chamber volume per min represents a τ value of 5 min (chamber volume / (0.2 × chamber volume / 1 min)) regardless of chamber volume. Thus, a carbon dioxide inflow rate equivalent to 20% of the chamber volume per min is predicted to increase carbon dioxide concentration within any enclosed space from 0 to 63.2% in 5 min (1τ), to 86.5% in 10 min (2τ) and to 95% in 15 min (3τ). An examination of the experimental data of Smith and Harrap5 confirms this: in their study, carbon dioxide supplied at an inflow rate of 22% chamber volume per min increased carbon dioxide concentration to approximately 64% in 4.5 min (1τ in this case). Applying these concepts to the study by Fitzhugh and coworkers1 illustrates the interaction between gas flow rate, wash-in time and subsequent gas concentration. The time constants (τ) for the studied inflow rates of 10%, 20% and 50% of the chamber volume per min are 10 min, 5 min and 2 min, respectively. Each of these inflow rates is predicted to raise carbon dioxide concentration from 0 to 63.5% within 1τ, but wash-in times will be considerably shorter at higher flow rates (Table 1).

CFD Simulation of Gas Mixing for Evaluation of Design Alternatives for On-Farm Mass Depopulation of Swine in a Disease Emergency

In the event of a foreign animal disease outbreak in the United States, a rapid and humane method for on-farm swine depopulation will be required. Given the extraordinary number of animals involved, and the design of currently used swine confinement buildings, methods relying on the handling and restraint of individual animals will prove much too slow to stem the spread of disease. For example in the case of foot-and-mouth disease (FMD), infected animals are to be humanely euthanized and disposed of within 24 hours of diagnosis to limit viral replication and subsequent disease spread, and all susceptible animals on adjacent farms within a specified radius are to be humanely euthanized and disposed of within 48 hours. Implementation of such emergency methods will require proactive establishment of protocols ensuring humane conditions while conserving resources and protecting personnel. Hence the objective of the current project is to identify, evaluate, and disseminate efficient practical methods to mass depopulate swine on farms in a local, regional, or national emergency. This involves evaluating the application of carbon dioxide (CO2 ) supplied by a bulk liquid CO2 tanker trucks as well as the possibility of generating CO2 on-site such as from locally purchased dry ice. In this effort, the use of Computational Fluid Dynamics (CFD) has proved to be a very powerful tool for evaluating transient CO2 concentrations during wash-in and wash-out of the euthanization chambers. Also CFD has been used to evaluate the need for plenums for CO2 distribution and the effect on CO2 distribution within the chambers including stratification due to CO2 density. The CFD simulation method involved the following general procedure.

Evaluation of carbon dioxide administration for on-site mass depopulation of swine in response to animal health emergencies.

apid methods for on-site swine depopulation are re-quired in the event of an animal health emergency in North America. The term animal health emergency, as used in this context, includes a wide range of poten-tial situations such as disease outbreaks, contamination with chemicals (eg, dioxin) or radionuclides (eg, cesi-um-137), and adverse animal welfare conditions creat-ed by transportation restrictions that severely limit feed deliveries and animal movement. As described by the AVMA, mass depopulation refers to methods by which large numbers of animals must be destroyed quickly and efficiently with as much consideration given to the welfare of the animals as practicable, but where the cir -cumstances and tasks facing those performing depopu-lation are understood to be extenuating.