This article was originally published and adapted from Stephen M. Vantassel’s article: “Is Drowning Euthanasia” Wildlife Control Technology Magazine Jan/Feb 2001.  It is owned by https://wildlifecontrolconsultant.com Copying this document is illegal without consent.  ©2001 Stephen M. Vantassel

The Problem of the AVMA

Readers may recall that euthanasia is defined, by the veterinary community, as death without pain or distress. This ideal can be achieved when the animal is rendered  unconscious and therefore unable to feel pain before death occurs. There is little debate concerning this definition of euthanasia. The debate rests on whether drowning is a humane euthanasia technique for killing wildlife.

Traditionally, drowning was viewed as humane because it was believed that the animals were rendered unconscious by CO2 induced narcosis and therefore unable to feel the pain of death by drowning. (Narcosis is defined as a general and nonspecific reversible depression of neuronal excitability, produced by a number of physical and chemical agents, usually resulting in stupor rather an in anesthesia).  This position was argued by F.F. Gilbert and N. Gofton in their 1982 article. “Terminal Dives in mink, muskrat and beaver published in Physiology and Behavior volume 28, pages 835-840. Proponents of drowning argued that drowning can take one of two forms, wet or dry. In wet drowning, water enters the lungs. In dry, drowning, little if any water enters the lungs. Since drowned aquatic animals, such as beaver and muskrat, had dry lungs, it was believed that they died of CO2 induced narcosis. An thus died a humane death.

The Crux of the Debate

The issue, therefore, is whether drowning animals are rendered unconscious by CO2 induced narcosis or not. In a new report published in the Wildlife Society Bulletin, “Drowning is not euthanasia” (1999, 27(3):666-670), the authors (John Ludders of Cornell University, our own Robert Schmidt, F. Joshua Dein of theNationalWildlifeHealthCenter and Patrice Klein HSUS) conclude that drowning is in fact not a good death (euthanasia).

The authors noted that Gilbert and Gofton neglected to take blood samples of the animals used in their terminal dive study. Since the only way to prove an animal died by CO2 narcosis is through blood samples, the authors concluded that they would need to look at euthanasia studies where blood gases were taken from the test animals.  What the authors discovered was that CO2 narcosis can only occur when the CO2  pressure levels rise above 95 millimeters of mercury. They also discovered that true anesthesia (unconsciousness) occurs only when CO2 levels rise above 200 mm Hg.  For example, rats when exposed to 100 % CO2 at various chamber flow rats started to show evidence of narcosis (demonstrated by their loss of coordination) after CO2 levels rose above 123 mm Hg. They became anesthetized (immune to pain) at 332 mm Hg. A study on dogs came to similar conclusions.

Thus the problem was that studies showed that even where animals are exposed to 100 % CO2, it takes a great deal of CO2 in the blood in order to anesthetize them. So if it is that difficult under ideal conditions, how much harder would it be under conditions of drowning where the animal isn’t breathing at all let along breathing CO2? Well as you can guess, it is practically impossible. In studies done with dogs drowned in fresh and salt water, CO2 levels never rose above 70 mm Hg.  Even when dogs were wet drowned the dogs never achieved CO2 levels above 61mm Hg.

The authors also looked at a study on the European beaver (Castro fiber).  The study found that CO2 levels never exceeded 100 mm Hg. In fact the beavers died of anoxia (lack of oxygen) 2-3 minutes before CO2 levels reached 95mm Hg.

So the authors conclude that drowned animals suffer the discomfort and pain of hypoxia (low oxygen) and anoxia (no oxygen) long before the narcotic effects of CO2 kick in, if they kick in at all, before the animal’s death. They believe the evidence of high levels of epinephrine in the blood, which result from stress, support the conclusion that the animals did not die a peaceable death. While some of the epinephrine resulted from the animals’ physiological response to cold water, the authors conclude that the more significant cause of high epinephrine levels was the stress from lack of oxygen.

The authors conclude that all of these studies show that drowning is not euthanasia. They also stated a hope that wildlife management officials use these findings in their development of best management practices for wildlife.

Impact on NWCO’s.

Nwco’s should start preparing for the day when the techniques they learned in fur trapping are no longer legal. If political pressure is brought to bear on wildlife agencies to ban drowning as an option for killing animals, then nwco’s will have to start trapping animals using techniques that won’t necessitate the drowning of animals. This change will have a huge impact on nwco’s that control muskrat, beaver etc. It will be important for NWCO’s not to assume that if drowning is removed as a euthanasia option that the government will provide an alternative. For example, don’t assume that if you can’t use footholds in a drown set, that you will get snares as a replacement and permission to shoot.

Second, I originally thought that the article could be used as evidence that using CO2 gas chambers is also not humane. If my reading of the article is correct, one could argue that the animals placed in CO2 chambers don’t die of CO2 narcosis but in fact die of anoxia which as we have seen is not a painless death. However, in my dialogue with Dr. Ludders, a specialist in veterinary anesthesiology, showed that my view was inaccurate. His original answer to my question was ” Animals placed in 100% CO2 reach a level of  CO2 narcosis rapidly. In drowning animals, CO2 accumulates only through oxygen metabolism…too little, too late for narcosis prior to anoxia.”

Although his answer was definitive on its face, I had more questions which the Dr. was good enough to answer. Let me list our dialogue which has been slightly edited for brevity.

Stephen Vantassel : I understand your point about Co2 narcosis and its anesthetic effects.

My question stems from p. 668 of your article on  drowning is not euthanasia column 2 top paragraph. There you state  that “In rats breathing 100% CO2, plasma norepinephrine increased  significantly and was released from the sympatheitic nervous system and not the adrenal medulla.”

As I read this, it points out that even animals like rats that breath 100% co2 (they aren’t drowning”) still suffer the anxiety of being in an annoxic environment. Wasn’t that the point of this  study that it pointed out that animals suffered in drowning because there wasn’t enough CO2 and this is proven by the fact that animals suffer even when breathing 100 % co2 for they don’t absorb enough in their blood stream to anesticize them before death.

How am I misreading this?

He responded, In our article we specifically mentioned a study reported by Hewett in which rats were exposed to 100% CO2 that was  delivered to the chamber at various flow rates; thus the rats initially  were breathing room air to which 100% CO2 was added over time. A number of studies have shown that inspired carbon dioxide concentrations of 7.5% raise the threshold to pain and higher concentrations are anesthetic. So as more CO2 is added to the chamber, the CO2 concentration progressively increases until the animals become anesthetized (unconscious) which may occur when the CO2 concentration is at 40% or so (at sea level this is a partial pressure of approximately 300 mmHg). Death finally occurs  when one of two events occur the animals stop breathing because the carbon dioxide-induced anesthesia continues to deepen until the respiratory control centersin the brain are very depressed, or the animals are no longer breathing oxygen because it has been displaced by CO2. It’s important to keep in mind that the animals are anesthetized at this stage and, thus,  unconscious and unaware of what is happening to them (this is a crucial pre-requisite for judging whether a technique is judged to be euthanasia or killing).

In studies that have investigated placing rats in a chamber containing 100% CO2, investigators have found that animals such as rats quickly lose consciousness first and then die a short time later.Breathing 100% CO2 quickly raises the CO2 levels in the blood to anesthetic levels (reportedly 25-30 seconds in rats) so that the animals probably are unconscious before they are anoxic (although they are probably hypoxic).

I still had my doubts, So Dr. Ludder’s continued, Stephen – No, you’re not misreading the article or the results. The key here is that the animals are releasing norepinephrine because they are stressed, but at the same time they probably were anesthetized by the CO2 and, thus, were unaware of what was happening to them.

Under anesthesia, the body still can respond to stressors such as hypoxia, anoxia, pain, etc., but because the brain is anesthetized the animal is not aware of these things. As an example, let’s consider a human patient undergoing anesthesia and surgery. During surgery (if everything isdone correctly) the patient is unaware of and does not feel the surgical incision and other surgical manipulations. However, the body still responds to the stresses of anesthesia and surgery and the hormonal indicators of stress do increase.We don’t stop doing surgery, however, because we know that the patients are anesthetized and are not aware of want is happening to them just as was probably true for the rats in the 100% CO2 study.

A drowning animal, on the other hand, does not achieve high enough concentrations of CO2 in the blood to render the brain unconscious. Thus the drowning animal is fully aware of what is happening. Hope this helps John Ludders.

I asked again, “Since animals can’t tell us they were under anesthesia and felt no pain how do we know that the co2 levels were high enough to give them a pain free death even with 100 CO2?”

He Responded: “A very good question and one to which the answers are difficult to obtain (but still possible). The best studies are those  that have instrumented the animals with catheters prior to exposing them to the gas mixture so that blood samples (preferably arterial blood) can be collected while the animals are breathing the gas mixture.

At the same time blood samples are collected the behavior of the animals is noted  and recorded (the Hewett paper that we cited is a good example of this approach). In this way behavior can be correlated with the blood sample results. Other studies have used only behavioral responses as indicatorsof the level of awareness of the animals as they breathe the gas. Certain behaviors such as incoordination and  unconsciousness are fairly easy to  define and characterize, but one does not have the blood gas data to substantiate what the levels of the 2 key gases – oxygen and carbon dioxide – are in the blood and, thus, in the brain.”

So I asked, ” So you are saying that these arterial blood catheter studies show that100% CO2 is humane by your article’s definition?”

He answered, “That particular study showed that the partial pressure of CO2 in  arterial blood progressively increased to the point that the rats became uncoordinated and then anesthetized while they still had  reasonable oxygen  levels so that they were not suffering as a result of  hypoxia or anoxia.  After becoming fully anesthetized, the rats continued to breathe the 100%  CO2 until they developed respiratory paralysis due to very  high levels of  CO2 or due to cerebral anoxia at which time they died.

Third, I didn’t see any investigation in this study regarding the presence of endorphins or pain killing chemicals that may help diminish the suffering of the drowning animals. It could very well be that animal’s fight-flight response creates enough endorphins to counteract the pain.

Finally, we see the coming end of traditional fur trapping. Animal rights activists have been pushing for the end of the foothold for decades. Animal rights activists contended that footholds caused endless suffering. So states likeMassachusetts established laws requiring footholds to be placed in drown sets so the animal wouldn’t suffer for an extended period of time. Now we see that drowning will be off the table. The end of the fur trapper only means one thing for the NWCO, namely more work. It is very likely that if present trends continue that theUnited States will become likeEuropein the development of government trappers.

About the Author

Stephen M. Vantassel, CWCP, ACE, is the owner of Wildlife Control Consultant, LLC. He helps people restore their balance with nature through publishing, training, consulting, and the internet. He has published numerous articles in trade and academic publications available at {Stephen’s Academia.edu Page} along with several books {WCC Store}). Listen to his podcast “Living the Wild Life” at {Pest Geek Podcast}. Please subscribe to {Stephen’s YouTube Channel} He is a sought after speaker and trainer. If you would like to have Stephen speak at your event or use his consultation services, send an e-mail to wildlifecontrolconsultant@gmail.com. Copyright All postings are the property of Stephen M. Vantassel and Wildlife Control Consultant, LLC. Text (not images) may be reprinted in non-profit publications provided that the author and website URL is included. If images wish to be used, explicit and written permission must be obtained from Wildlife Control Consultant, LLC.