Lecture: Anesthesia, pain management and euthanasia
Anesthesia
Anesthesia = a situation during which harmful events are not experienced, that can be
reversed and is under control. We want to minimize the animal suffering in our animals.
There are two different ways of anesthetizing an animal during a surgical or any other
painful intervention:
- General anesthesia: complete unconsciousness
- Local anesthesia: only the place where the procedure will take place but needs
good restraining of the animal. For local anesthesia it is very important to put
some to provide the researcher with more freedom to operate, more time and
makes the procedure mentally less stressful when you know the animal is not
having any pain due to the procedure.
You can reach the level of surgical anesthesia by using a:
- (Mono-anesthetic) à only one compound
Al the compounds have advantages/strengths and disadvantages/weaknesses. If
you use one compound and you want to reach full anesthetic depth but you also
need to analgesia your animal, this means you have to give relatively speaking a
large dose to your animal. This is going to increase the risks that come with your
compound.
Pentobarbital was used as a mono-anesthetic for a long time but barbiturates
are used as sleeping pills. They have an increased analgesia effect but they have a
very narrow dose range; so they easily reach toxicity levels and they really
depress the cardiovascular and respiratory system.
Pentobarbital is deadly easy to use (because you just need to inject a dose) but
the animals are easily dead; because you have a very narrow dose range before
this compound becomes toxic.
Pentobarbital is a very nice compound for euthanasia. The animals are very
rapidly anesthetized but this also easily leads to death.
- Balanced anesthetic à several compounds combined
With combined anesthesia you are going to use the strengths of several
compounds in their lowest dose to utilize the strengths of these compounds
but not their disadvantages. This way you only have the good end-points of
your compounds and less adverse effects due to your low dose (AE).
For example you combine an analgesic (pain relief aspects) with another
compound that will lead your animal to obtain unconsciousness but without
increasing the dose.
What do we want to reach during an anesthetic protocol; what are the key elements?
- Reach mental block à loss of consciousness during this harmful event
- Reach sensory block à loss of pain during this harmful event
- Reach motor block since ideally the animal will try to run away à prevent the
animal from escaping from the harmful event. When you want to open the
abdominal cavity you want the muscles to be relaxed otherwise if they are
contracted you can’t open the abdomen. That’s why you also need a motor block.
- Autonomous block especially during abdominal surgery to prevent a vagal
reflex that could affect the cardiovascular system in a negative way.
Saif Haify Laboratory Animal Science – Summary 6-November-2015
,Different phases during anesthesia; first you have the analgesia phase where your
animal is still conscious and has a normal breathing pattern followed by excitement that
is most of the time skipped. If you move higher you’ll see that breathing pattern will
change until you reach the surgical anesthesia phase where your animal loses
consciousness and has an increased relaxed muscle tone.
Anesthetic phases: (1) induction; (2) excitation; (3) surgery à reflexes and (4) recovery
Saif Haify Laboratory Animal Science – Summary 6-November-2015
, There are two important questions you have to ask your self before anesthetizing the
animal:
- Do we need to fast our animal?
When we all go to surgery we are advised not to eat and come sober to the
hospital but we are allowed to drink. This is said because of the reflexes that can
occur during surgery and because some of these compounds they trigger
vomiting and if you vomit during autonomic block, then you can inhale this vomit
and get pneumonia.
Most animals can be fasted before surgery except the rabbit! If a rabbit doesn’t
eat for a while it will develop dysbacteriosis due to a shift in the bacterial flora
and die.
- Should we already give this animal some analgesic, yes or no? Should we give it
atropine in order to get rid of this autonomous block, yes or no?
These are already questions you should ask yourself and think carefully about before
you start.
Isoflurane is a gas anesthetic used during surgical procedures. Usually you induce with
5% isoflurane and then you maintain anesthetic at 1-3% isoflurane. Most of the time you
perform surgery on your own and because you are stressed due to the surgery, you
might forget your isoflurane levels and sometimes this can be too much for your animal
and you overdose your animal. You will see that in the breathing frequency of your
animal.
Fasting
All animals should have access to water 60 minutes before surgery.
- All carnivores, ferrets and pigs
o No food 8-12h before surgery
- Large to medium sized birds
o No food 6-12h before surgery
- Small birds
o No food 2h before surgery
- Fish
o No food 1-2 days before surgery
- Rabbits and rodents
o Beside the fact that it is too dangerous to fast your rodents and rabbits
prior to surgery, it is also unnecessary to do so. You cannot empty the GI-
tract of these animals since they are caecotrophic!
Never fast pregnant animals before surgery and also when performing abdominal
surgery, you have to monitor post-operative food intake to see whether they start
eating and defecate. Because when you touch the abdominal organs, this can trigger
post-operative ileus à no peristaltic behavior of the animal’s GI-tract anymore! The
animal will feel full and blown and it will also not defecate. So always check for post-
operative ileus before feeding your animal after abdominal surgery.
Saif Haify Laboratory Animal Science – Summary 6-November-2015
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