4/22/2010 The mechanics of euthansia

Vet tip of the Day: Euthanasia - What really happens
Key Words: Barbiturate, gunshot, cerebral cortex

Yesterday's euthanasia stories came straight from the heart.  Today I'd like to take a step back and discuss this difficult topic from a more detached perspective. Much of what will be included in todays' blog was taken directly from the American Veterinary Medical Association Guidelines on Euthanasia published in 2000.  If you want to read them in more detail, they are available on line.

The word euthanasia is derived from two Greek words.  The first, "eu" means "good" and the second, "thanatos" means "death".  Thus the word means "good death" or the act of inducing humane death in an animal.  One of the greatest concerns expressed by owners with respect to euthanasia is their animal's state of consciousness during the transition from life to death.  The AVMA makes it very clear that any appropriate form of euthanasia should result in a rapid loss of consciousness and that the loss of consciousness should occur before, or simultaneously with, loss of motor control.  In most cases, equine euthanasia is performed with an injectable barbiturate, usually sodium pentobarbital.  This drug acts very rapidly, causing central nervous system depression beginning in the cerebral cortex.  The cortex is the center of consciousness, so the first thing that happens when a horse receives a large dose of sodium pentobarbital is an immediate loss of awareness.  The drug then rapidly depresses the lower brain centers, resulting in apnea, or failure to breathe, and cardiac arrest. 

The horse may sink quietly to the ground after the euthanasia injection is administered, but this cannot be guaranteed.  Sometimes the animal becomes rigid and may even fall over backwards.  It can be very disturbing to watch such a large animal hit the ground, but REMEMBER THAT THE HORSE IS UNCONSCIOUS AND UNAWARE.  The physical process of dying may include several gasping breaths, muscle trembling, and voiding.  These activities are natural physical processes that accompany the shutting down of body systems and even though they involve motor activity, or physical movement, they occur AFTER the cortex has stopped functioning and the animal has lost consciousness.

Sometimes owners request that their horse be sedated prior to euthanasia.  If the horse is extremely excited or difficult to handle, this is appropriate.  However, in general I try to avoid sedation if possible.  Sedatives slow the heart rate and decrease cardiac output, thereby slowing the delivery of barbiturate to the brain.  Euthanasia is most often performed on very sick or very old horses, which may already have impaired cardiovascular function.  The goal is to get the largest amount of barbiturate into the horse's brain as quickly as possible to achieve immediate and complete loss of consciousness.  Sedation can compromise this process.

Finally I'd like to address the issue of using firearms to perform euthanasia.  The following is quoted directly from the AVMA Guidelines on Euthanasia (note the term "physical methods" includes firearms and captive bolt pistols):

"When properly used by skilled personnel with well-maintained equipment, physical methods of euthanasia may result in less fear and anxiety and be more rapid, painless, humane and practical than other forms of euthanasia.  Some consider physical methods of euthanasia aesthetically displeasing.  There are occasions, however, when what is perceived as aesthetic and what is most humane are in conflict."

The term "physical methods" includes captive bolt pistols and gunshot.  Most of us have a natural fear of guns and are very upset by the violence associated with the act of shooting an animal, especially one we have loved and cared for. Horses do not share this aversion.  When performed safely and correctly, death by a bullet into the brain is instantaneous and therefore, painless.  It should never be considered unless the person handling the firearm is skilled not only with the weapon, but also absolutely understands the anatomy of the horse's head and how the shot should be placed. 

These are difficult things to think about, but I believe that understanding the process is an important part of making the decision to end a life.  This decision, when you face it, is about the quality of your horse's life.  It is painful, and sad, but it also is part of the responsibility of owning animals.  Now that we have examined the physical realities of euthanasia, tomorrow I will conclude this topic with some more philosophical thoughts on reaching the decision for euthanasia of your horse.


I believe that education is the key to evolution.
I believe that animals are the key to compassion.
I believe the learning never stops.