Long have veterinarians tried to reduce active signs of death during pet euthanasia. A quiet death, with minimal to no movement from the pet’s body, is always preferred. Seeing a pet’s body move in unusual ways during their last breaths can leave owners wondering what their pet is experiencing. Are they in pain? Are they resisting death in some way? The answer to both questions is no, however veterinarians are always looking for ways to prevent body movement during a pet’s euthanasia.

Active signs of death refer to the movements a body makes while physiologic death is occuring. It’s different from what a pet patient may exhibit while a euthanasia injection is being administered. It’s important to recognize that body changes during death (a cascade of events) are normal and expected. The body is a very dynamic thing, full of forces that can be challenging to comprehend. When an animal dies, they go through a series of large energy alterations that can be seen by observers. These include agonal breaths, opisthotonus stretches, myoclonic twitching, and even urination/defecation. Let’s look at why these even occur in the dying body and then how to reduce them if possible.

1. Agonal breaths – no oxygen is reaching the brain. This reflexive breathing pattern emerges to fix the problem. It’s not true breathing but rather a signal that death is coming. To observers, it looks like the body is gasping for air and suffocating, however the mind is unaware of the movement. 
2. Opisthotonus – a dramatic abnormal posture due to spastic contraction of the extensor muscles of the neck, trunk, and lower extremities that produces a sometimes severe backward arching from head to tail. There is an imbalance between neurologic pathways innervating muscle groups. It is possible that the secretion of inhibitory neurotransmitters, such as glycine and gamma-aminobutyric acid (GABA) plays a role (note that pentobarbital euthanasia solution is GABA potentiating). Whether the patient dies naturally or through euthanasia, opisthotonus stretches are commonly seen.
3. Myoclonus and muscle twitching – brief muscle spasms seen throughout various parts of the body due to a lack of normal innervation during death. They may be the result of euthanasia drugs directly affecting nerve fibers, a result of ATP energy changes in the muscle fibers themselves, and cellular acidosis. Muscle twitches can be strong enough to move a paw or ear, or be more subtle like tiny muscle fasciculations along the body. Whisker and lip twitching are quite common in my experience.
4. Urination and defecation – the bladder and bowel release due to contracting muscles during death, and sphincter relaxation. Like the others, urination and defecation are seen during natural death and euthanasia.

For some pet owners, witnessing active signs of death can be a good thing. It reinforces the truth that their pet has died, and can help them acknowledge this new reality, as sad as it is. And I’ve actually tried to increase signs of death when other pets are in the room. To me, an obvious passing can improve the chances that other pets will understand that death has arrived. If you’ve ever seen a pet lift its head and look over as another pet takes an agonal breath, you know what I mean. I’ve seen living companion pets walk over to their dying friend and howl over the top of them at the exact moment of death. If there is something to perceive, I want them to perceive it.

This said, ultimately what veterinary teams want is to have death be less active when loved ones are watching. Can this be done, you ask? It can, and it hinges on the use of pre-euthanasia anesthesia, the type of euthanasia drug, and the speed of administration. As a general longstanding rule, anesthetized patients will pass more quietly than those who are awake or sedated. Anesthesia leads to complete unconsciousness and has already quieted the nervous system. Using propofol before injecting pentobarbital euthanasia solution is a good example of what veterinary teams do to reduce active signs of death in pet patients. Intravenous propofol induces anesthesia and unconsciousness first. Another example is the administration of ketamine and tiletamine drug protocols under the skin or in the muscle. They quiet the nervous system before anything else happens. 

In my experience, the big game changer is the speed and type of euthanasia solution administration. When using pentobarbital, the most common euthanasia drug in North America, it must be given very fast to awake animals (intravenously in this instance). The rate is 1 ml or more per second. This moves patients rapidly through all anesthetic stages (pentobarbital is an anesthetic itself) to achieve death in around 60 seconds. In awake patients, rapid administration is key. However, when they are heavily sedated or anesthetized, evidence suggests that cutting this rate down to 0.1 ml per second uses pentobarbital to induce deeper anesthesia before overdose, thus reducing active signs of death. The worst thing to do is give pentobarbital slowly to an awake animal. That is most likely to bring about the agonal breathing, opisthotonus stretching, and muscle tremors. While there is no recent research to fully support this information, veterinarians report the same as what I’ve seen over the years. Perhaps research in this area is around the corner. Non-pentobarbital euthanasia drugs tend to lead to more active signs of death too. Examples include potassium chloride, magnesium sulfate, and lidocaine. 

In closing, active signs of death can be a good thing but most people wish to avoid them. It is ok to embrace what the body does naturally and to let it do its thing. As long as loved ones and witnesses know what to expect and what’s normal, they should be allowed to remain present with their pet and observe these bodily changes. I anticipate that as the human-animal bond grows and veterinary teams get better at euthanasia, more and more people will accept what death looks like, active or quiet, and find beauty in all of it.

Want to learn more about pet euthanasia? Keep an eye out for CAETA euthanasia research articles and take our Peaceful Euthanasia Certification program.

References

1. Beckerman, J. Ed. What to Know About Agonal Breathing. 2023. https://www.webmd.com/heart-disease/what-to-know-agonal-breathing
2. Lee, J. The Use of Propofol During Euthanasia in Veterinary Medicine. 2020. https://vetgirlontherun.com/the-use-of-propofol-during-euthanasia-in-veterinary-medicine-vetgirl-veterinary-continuing-education-blog/
3. Shahade A, De Jesus O. Opisthotonus. [Updated 2023 Aug 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. 
4. Shedge R, Krishan K, Warrier V, et al. Postmortem Changes. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.