Addressing the safety of postanesthesia euthanasia for scavengers
The article “Use of potassium chloride for low-residue euthanasia of anesthetized California sea lions (Zalophus californianus) and northern elephant seals (Mirounga angustirostris) with life-threatening injury or disease” by Witmer et al1 addresses an important aspect of euthanasia. In the case of wild species, or animals that must be humanely euthanized in areas where rendering facilities do not exist, options other than barbiturates need to be available. This paper clearly demonstrates the effectiveness of potassium chloride as one of these choices. An additional important issue is the potential for environmental contamination from drugs used to induce the pre-euthanasia anesthesia that is required for techniques such as intracardiac potassium chloride to be humane.
In their discussion, the authors do address residues of xylazine, ketamine, and midazolam in tissues left after euthanasia. In doing so, they reference our paper, “Drug residues after intravenous anesthesia and intrathecal lidocaine hydrochloride euthanasia in horses.”2 However, in their conclusions, they mischaracterize the point of our research by saying “Aleman et al measured tissue concentrations of xylazine, ketamine, midazolam, and lidocaine in horses following euthanasia and detected levels that could cause sedation in scavengers that consumed sufficient quantities of tissue.” This misses our most relevant finding: while these compounds can be detected in muscle tissue of horses following euthanasia, they are in parts-per-billion concentrations (nanograms/gram of tissue) and therefore pose no threat to carnivores or scavengers that may ingest the carrion. To demonstrate this, we calculated the amount of tissue that a carnivore would have to eat to cause sedation. One example from the article is that a 15-kg coyote would require 150 kg of meat to get enough xylazine to sedate it even mildly. Similarly, large amounts would be required for ketamine, midazolam, or lidocaine to have an effect.
If practitioners get the spurious message that a carcass from postanesthesia euthanasia is unsafe, they will be reluctant to use such effective and humane techniques as potassium chloride injection or intrathecal lidocaine when euthanizing suffering animals in remote areas. It is true that some small amount of anesthetic drug is introduced into the environment and the exact effect of these agents is not known. However, the concentration of such contaminants, as well as the rarity of their use, needs to be taken into consideration. If the goal is to completely avoid the introduction of anesthetic chemicals into the environment, the only real alternative would be gunshot or captive bolt euthanasia, which carry with them issues of safety, availability, and a negative public perception, despite being humane alternatives based on AVMA guidelines.3
References
- 1. ↑
Whitmer ER, Trumbull EJ, Harris HS, Whoriskey ST, Field CL. Use of potassium chloride for low-residue euthanasia of anesthetized California sea lions (Zalophus californianus) and northern elephant seals (Mirounga angustirostris) with life-threatening injury or disease. J Am Vet Med Assoc 2021;259(2):197–201.
- 2. ↑
Aleman M, Davis E, Knych H, Guedes A, Smith F, Madigan JE. Drug residues after intravenous anesthesia and intrathecal lidocaine hydrochloride euthanasia in horses. J Vet Intern Med 2016;30(4):1322–1326.
- 3. ↑
AVMA guidelines on euthanasia. AVMA. Accessed June 5, 2021. https://olaw.nih.gov/sites/default/files/Euthanasia2007.pdf
Authors respond:
The authors thank Dr. Davis for his comments and agree with his characterization of the low risk of secondary intoxication to scavengers.
Emily R. Whitmer, DVM
Emily J. Trumbull, DVM
Heather S. Harris, DVM, MPVM
Sophie T. Whoriskey, DVM
Cara L. Field, DVM, PhD
The Marine Mammal Center
Sausalito, California
Future-proofing the profession
I was pleased to see the recent letter1 expressing support for the Veterinary Futures Commission, which was jointly established by the AVMA and the American Association of Veterinary Medical Colleges (AAVMC) in 2018.2
Futuristic thinking is not new to the veterinary profession. Since the 1970s, there have been numerous forward-thinking studies; however, there has been little progress as a result.3,4 With the multitude of rapidly occurring changes both within the profession and in society in general, we can and must do better.
A year of planning has been lost because of the COVID-19 pandemic. I strongly urge the leaders of the AVMA and AAVMC to reengage and reenergize the Veterinary Futures Commission as quickly as possible. Ongoing systematic analysis of the market for veterinary services and educational opportunities will be essential if the veterinary profession is to make its optimal contribution to society in the future.
Ted Cohn, DVM, AVES (Hon)
Past President, AVMA (2014–2015)
Lone Tree, Colorado
