Biomedical Engineering Reference
In-Depth Information
(where re-breathing circuits are used, see section
“Endotracheal intubation” below). For more detail on
the maintenance and testing of anesthetic machines see
Vogler 2008 .
analgesic agents can therefore facilitate the production
of a steady state of anesthesia and by reducing intra-
operative stimulation of pain pathways may lead to an
overall reduction in postoperative pain. It has been
shown in animals that analgesic drugs are more effective
if given pre-emptively, i.e. before surgery begins
( Dickenson and Sullivan, 1987; Lascelles et al., 1994,
1995 ) and hence should be given as soon as is practical
following immobilization. Although the degree of
increase in postoperative pain relief associated with pre-
emptive analgesia remains controversial, there is general
agreement that the administration of analgesics in the
preoperative period has been shown to be without harm
in normal, healthy laboratory animals. There is also
general agreement that ensuring analgesics are acting
effectively prior to recovery of consciousness provides
more effective pain management. See the main section
“Analgesia” for more detail on analgesia.
The muscarinic antagonists atropine and glyco-
pyrrolatearecommonlyusedbothtoreduceunwanted
oral secretions and vagally-induced bradyarrythmias
during the period of anesthesia. These drugs affect a wide
variety of physiological functions in addition to their
target effects and may predispose the animal to tachyar-
rythmias. For these reasons they are rarely used routinely
in modern day clinical practice. The use of muscarinic
antagonists is therefore better restricted to those situa-
tions where there is a particular risk of bradycardia (see
sections
Clinical Evaluation and Preparation
Before anesthetizing a primate, the animal should be
examined for signs of ill health, its behavior and tempera-
ment should be assessed, and its body weight recorded.
Animals on food or water restriction that are not obtaining
their normal ad-lib intake should preferably have the
restriction discontinued for 1 e 2 days prior to anesthesia.
Care should be taken to prevent gorging of either food or
water during this period as this can predispose the animal to
gastrointestinal bloat. Similarly, during recovery from
anesthesia, a delay in return to ad-lib feeding may be
desirable to prevent gorging, abnormal fluid balance, and so
forth.
Both Old World and New World nonhuman primates
may vomit on induction of anesthesia, so it is advisable to
withhold food for 12 e 16 hours and water for 2 hours before
induction of anesthesia. Because of their high metabolic
rate and propensity for hypoglycemia, the smaller primates
(
2 kg) should only have food withheld for 4 e 6 hours
before induction of anesthesia.
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Preanesthetic Drugs
Sedatives
In other species, light sedative medication may be
administered before anesthesia is induced, in order to
calm the animal. However because administration of drugs
to the conscious nonhuman primatecanbebothstressful
for the animal and dangerous for the handler, the anes-
thetic protocol usually begins with administration of
a drug or drugs that immobilize the animal and induce
a state of deep sedation or light anesthesia (see section
“Immobilization/deep sedation/light anesthesia” below).
For this reason, it is relatively rare for drugs to be
administered in the preanesthetic period, and although
adjunct drugs may be administered before immobilization
is induced they would more usually be administered very
shortly after.
“Neurosurgery”
and “Pediatric
anesthesia”
below).
In cases of nonelective anesthesia, such as for necessary
medical treatment, the antiemetic metoclopromide may be
given 30 e 60 minutes beforehand to help reduce the like-
lihood of vomiting and increase gastric emptying via
increased small intestinal peristalsis. It is helpful to have
suction available during induction of anesthesia in this
circumstance so that if the animal does vomit the oral
cavity can be cleared efficiently.
Corticosteroids such as dexamethasone or methylpred-
nisolone may be given perioperatively, e.g. to reduce
cerebral edema during craniotomy. As the use of both
corticosteroids and nonsteroidal antiinflammatories
(commonly used analgesic agents), particularly in combi-
nation, has been associated with gastrointestinal side
effects in many species, the concurrent use of gastro-
protectant drugs such as H 2 histamine receptor antagonists
(e.g. ranitidine), proton pump inhibitors (e.g. omeprazole),
or prostaglandin E 1 analogs (e.g. misoprostol), possibly in
conjunction with cytoprotectants (e.g. sucralfate), is
advised. There is little detailed information regarding the
clinical efficacy of many of these drugs in nonhuman
primates, but the agents have been used safely in laboratory
studies.
For a guide to drug doses see Table 17.1 .
Adjunct Drugs
Depending on the experimental protocol and condition of
the animal there are a variety of nonanesthetic drugs that
may be given before or very shortly after immobilization so
that those drugs can be clinically active before surgery
begins.
Many of the drugs used to maintain anesthesia
have poor analgesic properties. The additional use of
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