Biomedical Engineering Reference
In-Depth Information
long term effects on the animal that could interact with later
use in a research protocol. It is therefore important to
establish appropriate responses to the situations described
below as part of the overall plan of perioperative care.
For a guide to drug doses see
Table 17.4
.
hypotension should include a reduction in the amount of
anesthetic being administered (with provision of additional
analgesia if needed) and intravenous fluid administration to
expand circulating volume. In most situations these
changes would be sufficient. If hypotension persists,
however, or worsens, sympathomimetic (vasopressor)
drugs such as adrenaline or dopamine can be used.
Every effort should be made to minimize blood loss,
especially in smaller primates. If blood loss occurs, whole
blood or plasma volume expanders (e.g. colloid solutions)
can be given. Whole blood should be collected from
a donor animal and immediately mixed with acid-citrate-
dextrose (ACD) at a rate of 1 part ACD to 4 parts blood.
Blood from most species can be stored at 4
C for several
days until required. Cross-matching of blood is advisable if
repeated transfusions are required. Red blood cells from the
donor animal are washed, mixed with the recipient's serum,
and observed for clumping. In an emergency, an initial
transfusion can usually be given safely as naturally occur-
ring isoantibodies to erythrocyte antigens do not occur
(
Socha et al., 1982
). Alternatively, blood (
Respiratory Depression and Respiratory
Arrest
To assist ventilation if the animal has not been intubated,
the head and neck should be extended, the tongue pulled
forward, and the chest compressed. If the animal has been
intubated, then respiration can be assisted relatively easily
using the anesthetic breathing system either by intermit-
tently occluding the gas outflow (e.g. when using an
Ayre's T piece breathing circuit) or by compressing the
reservoir bag. It is preferable to use a reservoir bag as this
minimizes the risk of inadvertently over-inflating the
lungs. Attempting to assist ventilation using a facemask is
often unsuccessful and may result in inflation of the
stomach. Doxapram, a centrally acting respiratory stimu-
lant, can be administered to stimulate ventilation and
should always be administered if mechanical ventilation is
not already being provided.
Gradual onset of respiratory depression commonly
precedes complete respiratory arrest. If this is detected,
then the potential causes should be identified and corrective
action taken, However, the depression in respiratory func-
tion may simply be an almost inevitable side-effect of
producing a deep plane of surgical anesthesia. This can be
managed easily by use of intermittent positive pressure
ventilation, either by using a mechanical ventilator (see
“Ventilation” above) or by manually compressing the
reservoir bag in the breathing system whilst the dose of
anesthetic agent is reduced.
10%) can be
withdrawn from the animal a week or so before surgery,
mixed with anticoagulant and stored until
<
the day of
surgery.
If cardiac arrest occurs, then external cardiac massage
and emergency drugs such as epinephrine can be used to try
to resuscitate the animal. The success of resuscitation
largely depends on the underlying cause of cardiac arrest
but also on the type and timeliness of resuscitation applied.
However, survival is not the only aim for laboratory animal
procedures, as induction of unintended abnormalities such
as focal ischemia may render the animal unsuitable for
study. Therefore it is advised that standard texts are used to
identify appropriate emergency interventions
for
the
particular study,
in advance of
the administration of
anesthesia.
Hypotension, Hemorrhage, and Cardiac
Arrest
Methods for supporting the circulation or treating cardiac
arrest are similar in most species, but correct use of these
techniques requires considerable experience. It is always
preferable to try to anticipate impending problems, and
prevent them.
Hypotension can result from the direct (drug induced
vasodilation and myocardial depression or surgical
manipulation) or indirect (acid-base and electrolyte
disturbances or hypovolemia) effects of anesthesia and
surgery. Although many nonhuman primate species appear
to tolerate low blood pressure well compared to other
animal species, a mean arterial pressure of less than
60 mmHg in many species may be too low to maintain
perfusion of
SPECIAL CONSIDERATIONS
Imaging
As with other species, placement of primates in imaging
devices can introduce a number of complications to an
anesthetic regimen. These problems may be magnified to
the extent that many imaging protocols will require long
scan durations.
Whilst imaging of the nonanesthetized nonhuman
primate is possible, anesthesia is often required to reduce
the stress of prolonged immobility. Use of neuromuscular
blocking agents to immobilize animals for imaging is not
an acceptable technique. One obvious problem when
imaging anesthetized patients is that with most modalities
the animal is hidden from view, meaning access may be
restricted and direct clinical monitoring is impossible or
the vital organs.
Initial
treatment of
