MONTH: December 2006
How to do pre-euthanasia sedation
Further to the discussion in your October
article "Could carbon monoxide gas chambers make a comeback,"
I thought I'd wade in on pre-euthanasia sedation.
There is often confusion of terminology.
The word "tranquilizer" and its verb form "tranq"
are used generically. Same with the word "sedation" and "sedate."
Here's what's what:
Tranquilizer usually means phenothiazine-type
drugs such as acepromazine. Tranquilizers reduce alertness and increase
tolerance. They also reduce inhibition and blood pressure and lower the
seizure threshold in some species. Acepromazine is label approved for
dogs, cats and horses.
According to the one and only study on
carbon dioxide euthanasia, acepromazine is recommended for dogs being
put to death in carbon dioxide chambers. It was found to reduce anxiety
response in a significant percentage of dogs.
Sedatives reduce alertness by producing
sleepiness. A typical sedative is xylazine, also used as a short-term
analgesic and muscle relaxant. Brand names include "Rompun"
and "AnaSed." These are label-approved for dogs and cats, at
20 mg/ml concentration, and for horses, deer, and elk at 100 mg/ml concentration.
Adverse effects in dogs and cats include vomiting, reduced blood pressure,
and lowered inhibition.
I do not recommend xylazine as a pre-euthanasia
drug due to its generally poor effect. A dangerous dog or cat is still
dangerous, even if sleepy and muscle relaxed, and the reduction in blood
pressure is significant, a problem when trying to inject intravenously.
For friendly dogs, there is no need to administer xylazine as there is
no anxiety issue.
Anesthesia means loss of sensation, usually
loss of consciousness brought about by the administration of an anesthetic.
To be anesthetized literally means to have no feeling.
The best pre-euthanasia drugs are anesthetics.
Most common and cost-effective is PreMix (5:1 ketamine-xylazine), dosed
at 0.5-0.6 ml per ten pounds. An anesthetized dog or cat is unconscious,
and therefore safe to handle. Adverse effects can be seizures or vomiting.
PreMix is a veterinary compound in use since the mid-1970s, and is not
an FDA approved drug.
Another pre-euthanasia anesthetic is Telazol
(tiletamine-zolazepam), an FDA-approved drug similar in action to PreMix.
Telazol is label-approved for dogs and cats and is, like PreMix, an effective
pre-euthanasia drug when dosed at 0.3-0.6 ml per ten pounds.
There is a fallacy that best practice
is to anesthetize all animals prior to euthanasia. This is simply not
so. Best practice is to administer pre-euthanasia anesthetics when safety
or technical difficulty issues arise. An intramuscular injection of a
stinging medicine, such as either PreMix or Telazol, is in my opinion
counterproductive unless needed.
The use of IV catheters for guardian-present
euthanasia is becoming more prevalent in animal shelters, as well as in
private veterinary practice. I mention their use in my euthanasia-by-injection
I have been euthanizing feral cats for
years, and believe that PreMix or Telazol first is the way to go. Then,
when they are deep enough that they have a negative pinch-withdraw reflex,
I administer the sodium pentobarbital via intracardiac injection, except
for pregnant cats. Then I go IV.
More about pre-euthanasia sedation of cats
For euthanasia pre-sedation, we use telazol,
which combines tiletamine hydrochloride 50 mg/mL, and zolazepam hydrochloride
50. Tiletamine is similar to ketamine, and zolazepam is similar to diazepam
(Valium). The tiletamine stings a bit, the only downside. Tiletamine and
ketamine are dissociative anesthetics, but don't relax muscles. The zolazepam
produces comfortable muscle relaxation and, with the tiletamine, combines
to produce moderate anesthesia and very significant sedation.
The reason we like this combination is
that, unlike with xylazine, the blood pressure doesn't plummet. Low blood
pressure makes finding a vein very tough sometimes.
I also find that with telazol, I see much
less twitching, and less agonal breathing in cats. The twitching and gasping
breaths are spinal reflexes, and don't represent pain, but sure are disconcerting
for the humans. In five years, I have seen two cats become twitchy or
agitated with telazol. One was actually a serval, so who knows? The other
was a very ill cat. The excitement lasted only a few seconds.
Considering how many euthanasias we do,
it is hard to imagine a lower rate of complication. Technical information
about telazol can be verified at <www.vasg.org>. This is a very
good site on animal anesthesia, and I use it all the time.
Telezol is much better for cats than dogs.
I wouldn't use it with dogs, based on what others have told me.
Some people insist that the only way to
euthanize is with an IV catheter in place. We find that the telazol produces
comfortable sedation and such good anesthesia that cats never notice the
second IV injection. To put in a catheter requires restraint, and while
catheters are usually not painful, that is not always true. The telazol/euthanasia
solution combination allows people to be with their cat for the entire
process, and fussing with the catheter is avoided.
I was aghast to learn how executions by
lethal injection are carried out. Apparently they use a paralytic agent,
so if the condemned person is under-sedated, the person could be conscious
for what is essentially a heart attack, chemically-induced with potassium
chloride, or suffocation, because of inability to breathe. Also, the IV
catheters used for human executions are not put in by experts, and the
drugs can easily precipitate if they are accidently mixed. We do better,
much better for our dogs and cats.
--Katherine Schubert, DVM