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At my veterinary school graduation, my classmates and I
took an oath to alleviate pain and suffering in animals.
Unfortunately, the recognition and treatment of pain in animals has
been overlooked or underestimated by veterinarians.
Thankfully, this is changing. Over the last ten years the
veterinary community has undergone a transformation in how animal pain is
viewed and interpreted, with incredible gains being made in our
recognition, understanding, and treatment of pain.
Pain sensation is difficult to measure objectively,
especially in animals, as they cannot communicate to us verbally.
They cannot express where the pain is, or use descriptors such as
throbbing, dull, sharp, or stabbing.
Thus, an animal’s pain is what we interpret it to
be. We must rely on
behavioral cues which can sometimes go unnoticed or be misinterpreted.
Achieving effective analgesia in cats is especially challenging, as they
tend to mask their suffering. In addition, many of our analgesics may not
be suitable for cats.
Strategies for Pain Management
Currently, we have two main strategies: pre-emptive
analgesia and multi-modality therapy.
Pre-emptive analgesia
means giving pain
medication before the patient is exposed to the painful procedure.
Introduced in recent years, the concept has gained acceptance as a
cost-effective means of controlling post-operative pain and improving
overall outcome, especially for elective procedures such as spaying and
neutering.
The second strategy, multi-modality therapy, has
become the cornerstone of effective pain management in animals.
This involves the combined administration of several different
analgesic drug classes or techniques.
The reasoning behind multi-modality therapy is the knowledge that
various classes of analgesic drugs have additive or synergistic effects
when administered together. After pain receptors are stimulated, several steps must occur
physiologically before pain is perceived.
The rationale behind multi-modality therapy is to combine drugs
that disrupt the development of pain at the various individual steps
Classes of drugs
There are several pharmacologic classes of drugs available
to treat pain. Opioids,
alpha-2 agonists, non-steroidal anti-inflammatory drugs, local
anesthetics, and adjuvant analgesic agents have all been
employed in controlling animal pain. Unfortunately, cats are particularly
susceptible to exhibiting adverse effects from classes of drugs,
especially the opioids (confusion, agitation, anxiety), alpha-2 agonists
(vomiting), and NSAIDS (this group includes aspirin and acetaminophen,
both of which can be harmful, and even lethal, to cats). One particular
opioid, called fentanyl, is becoming a very popular method of achieving
excellent pain control in cats.
Fentanyl Patches
The relatively new
science of transdermal drug administration (delivering drugs into the
bloodstream via application of gels or patches) is becoming more
commonplace in veterinary medicine. The fentanyl patch has probably
become the most commonly used transdermal drug in veterinary medicine.
Fentanyl is a synthetic opioid that is 75 to 100 times more
potent than morphine. Given
intravenously, it has a short duration of action (30 to 60 minutes),
requiring frequent dosing or expensive pumps that allow a slow, constant
intravenous infusion. The
development of a transdermal fentanyl patch, however, has allowed fentanyl
to be administered at a constant rate without the need for expensive
equipment. After clipping the hair and gently cleaning the skin, a 25
microgram patch is applied to the skin.
In dogs, patches are usually applied on the back of the neck, while
in cats, the patch adheres better to the side of the chest, and bandaging
is seldom required. Application of a fentanyl patch incorporates both pain
management strategies: applied several hours before surgery, it achieves
pre-emptive analgesia; afterward, it serves as one component of a
multiple-drug post-operative pain management protocol.
Several years ago, a study reported in the Journal of the
AVMA suggested that for cats undergoing declaw surgery, administration of
butorphanol (an opioid) the day of surgery and the first full day after
surgery provides very effective analgesia. I had been utilizing
butorphanol in this manner (i.e. both pre-emptively and post-operatively)
ever since. In 1998, the AVMA Journal published results of a clinical
trial showing that a 25 microgram fentanyl patch, applied 6 hours before
declawing, was safe and effective.
A
recent report, again in the Journal of the AVMA, compared transdermal
fentanyl with butorphanol for pain management in cats undergoing declawing.
The verdict: there was no difference between fentanyl and
butorphanol. Both drugs
provided equal, effective analgesia.
Advantages of the fentanyl patch is that repeated administration of
the drug is not required. Disadvantages
are the increased cost: transdermal fentanyl can cost 3 to 5 times as much
as butorphanol. Depending on
individual circumstances, I use both methods.
Two decades ago, the concept of pain, as it related to our
patients, barely registered a blip on the radar screen of most veterinary
academicians and practitioners, believing that pain perception in animals
was somehow different from pain experienced by humans. We now recognize that animals perceive pain much the same way
that humans do, and that we have a moral obligation to protect pets from
pain and suffering. Our
understanding of animal behavior and animal physiology is increasing and
evolving, allowing us to develop more practical and potent methods of
providing analgesia for our patients.
Updated 2/9/06 |
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