Biomedical Engineering Reference
In-Depth Information
Pain management in veterinary medicine is, at the
outset, hampered by the adaptive response of animals to
hide signs of illness, injury, and pain. Signs of pain in
companion animals are hunched posture, vocalization,
decreased activity, restlessness, self-mutilation, increased
respiratory rate, increased heart rate, increased blood
pressure, and decreased appetite. Many of the outwardly
observable signs of pain seen in companion animals may
be absent in nonhuman primates even in instances of
severe trauma, and although vocalization, decreased
appetite, inactivity and grinding of the teeth have been
observed by the authors, these signs are often not noted
until the animals are in critical condition. As laboratory
nonhuman primates are wild animals and prey species, it
must be assumed that the drive to hide injury and pain is
strong, making pain assessment all the more difficult.
Therefore, regardless of whether an animal is showing
outward signs of pain, the assumption should always be
that trauma, inflammation, or other conditions that would
cause pain in a human would also be painful to
a nonhuman primate. Since behavior of animals often
changes immediately when observers enter housing rooms,
it is important to supplement direct monitoring with
remote monitoring using video or telemetry when indi-
cated. Review of the information gleaned by these methods
may provide further insight regarding the pain being
experienced by a particular animal. In treating ill and
injured animals, it is essential to have a general sense for
the severity of pain induced by a given injury or illness. For
example, conditions that are considered to be the most
painful include bone injuries, gastrointestinal inflamma-
tion, and nerve injuries. Moderate pain results from peri-
tonitis, pleuritis, abdominal surgery, infection, and cranial
injuries, whereas skin wounds and pneumonia produce
pain that is less severe (
Rudloff, 2004
).
The physiological response to pain is very similar to
that of shock (
Rudloff, 2004
). Acute pain can result in
increased sympathetic tone, increased risk of cardiac
arrhythmia, decreased gastrointestinal and urinary blood
flow, gastrointestinal ileus, increased blood viscosity,
increased clotting time, and platelet aggregation. The
deleterious effects of chronic pain include increased risk of
thromboembolism, ventilation perfusion mismatch,
hypoxemia, hypercapnia, increased cardiac oxygen
consumption, immunosuppression, and prolonged wound
healing (
Shaffran, 2008; Bonagura and Twedt, 2009;
Looney, 2009
). An important concept that has emerged in
the field of pain management is wind-up, or central sensi-
tization, which occurs in response to chronic pain. When
pain receptors are stimulated chronically and repeatedly,
the nerve fiber threshold is reset and hyperalgesia occurs in
which the intensity of stimulation required in order for pain
perception to occur is reduced. At the same time, nerve
fibers are recruited that normally carry information that is
not related to pain and allodynia occurs in which stimula-
tion that would normally be harmless is now perceived as
painful (
Shaffran, 2008
). Because of the aforementioned
deleterious effects of acute and chronic pain, it is essential
to prevent wind-up by providing adequate analgesia during
the acute period and to maintain analgesia for as long as
pain persists.
As with all other medications administered to
nonhuman primates, the route of administration for anal-
gesics, tranquilizers, sedatives, and anesthetics must be
determined on a case-by-case basis. Administration of
analgesics by the injectable route or by transdermal patch
may be favored in critically ill animals that are obtunded or
unconscious and cannot take oral medication. Once the
acute phase of the illness has passed, it is often more
prudent to administer analgesics via the oral route to
minimize the pain and distress associated with intramus-
cular or subcutaneous injections. Many classes of analge-
sics are administered as constant rate infusions (CRIs) in
the companion animal critical care setting. While CRIs are
advocated as clinically warranted in surgical cases of
prolonged anesthesia or in animals with catheters that are
protected by a jacket and tether system or ambulatory
infusion pump and jacket systems, this option is often
impractical for laboratory nonhuman primates that do not
have ambulatory or tethered chronic catheter access.
Transdermal patches that are used for administration of
analgesics can deliver toxic doses if ingested by the
patient. When used, these patches should be protected by
a bandage and/or jacket, but even these methods cannot
fully eliminate the risk of ingestion. The reader is directed
to Chapter 17 for more detailed information on analgesic
therapy.
The social housing status of critically ill nonhuman
primates should be taken into consideration whenever
analgesic therapy is planned. Sedation and analgesia may
place the treated animal at risk of attack by social partner(s)
because their behavior may change enough to incite
aggression in cagemates. While adequate pharmacological
analgesia is of paramount importance in critically ill and
injured laboratory nonhuman primates, the beneficial
effects of stress reduction must be considered as an adjunct,
and every effort should be made to return animals to their
home cage and social partner(s) as soon as possible. The
clinician must develop an analgesic treatment plan that
provides adequate pain relief while considering psycho-
logical wellbeing.
Transfusion
When delivery of oxygen to the tissues is compromised as
a result of blood loss or hemolysis, and/or a severe coa-
gulopathy is suspected, the transfusion of whole blood or its
principal components may be indicated. Specific conditions
