Biomedical Engineering Reference
In-Depth Information
apparatus in marmosets, tamarins, and squirrel monkeys,
but a range of devices are now available that can function
successfully in animals weighing only 200 e 300 g. Anes-
thetic records should note monitored physiological
parameters at regular intervals (e.g. every 5 min) to facil-
itate monitoring of trends across time during the procedure
and to make notes on the progress of the procedure,
administration of drugs, or any variations in the anesthetic
protocol. Such records can prove vital as a base of evidence
for future refinements to anesthetic and or procedural
protocols.
Respiratory Function
Clinical observation of respiratory rate and pattern is
relatively straightforward, but can be complicated by
placement of surgical drapes, especially in smaller
primates. In these smaller species, the anesthetic breathing
system will not normally contain a reservoir bag, so
observation of bag movements cannot be used to monitor
respiration. Placement of a respiratory monitor in the
airway overcomes this problem, and also has advantages in
larger species as it frees the anesthetist to attend to other
tasks. Simple thermistor-operated devices generally func-
tion well in all nonhuman primates. Where signal pro-
cessing equipment is available, an accelerometer may be
used to monitor chest wall movements, a method that is
particularly useful for small species ( Devonshire et al.,
2009 ). If electronic monitoring is unavailable, an eso-
phageal stethoscope can be used in all but the smallest
animal. This allows appreciation of both lung and heart
sounds, but does require the operator to assess these
continuously unless the device is attached to an amplifier
and speaker.
In common with other species, the pattern, rate, and
depth of respiration varies both with anesthetic depth and
with the anesthetic regimen used. With inhalant anesthetics
and the majority of injectable regimens respiratory rate
falls. As with many other variables, gradual changes in rate,
rather than a sudden reduction, are more usual, so keeping
a note of trends in the anesthetic record is strongly
recommended.
The adequacy of oxygenation (and pulse rate) can be
assessed using a pulse oximeter ( Figures 17.5, 17.6 ). A
monitor with an upper limit of at least 350 bpm is prefer-
able when anesthetizing small primates such as marmo-
sets, and successful operation may also depend upon the
type of probe used. The pulse oximeter signal may be
disrupted by environmental light, patient movement, or any
condition that causes patient peripheral hypoperfusion. It is
advisable to try several instruments, probes, and probe
positions to find the combination that is most reliable, and
also to ensure that conditions such as hypothermia and
hypotension are avoided. In the authors' experience,
a signal can usually be obtained from across the hind foot
FIGURE 17.6 Intubated 6-day-old macaque connected to a low dead
space connector with side stream capnography port. The VitalStore
multi-parameter monitor (Vetronic Services Ltd) measures end tidal
carbon dioxide of 35 mmHg, inspired carbon dioxide of 2 mmHg,
a spontaneous respiratory rate of 54 bpm, inspired and expired oxygen
levels of 93 and 91% respectively and inspired and expired sevoflurane
levels of 2.9%, via the sample line attached to the capnography port. The
capnography trace does not demonstrate the plateau that would be
expected when monitoring an animal with a lower respiratory rate (more
time for gas mixing to stabilize) and therefore a large manual breath was
used to confirm that the end tidal carbon dioxide reading was the true peak
value. A pulse oximeter probe is positioned on the hind foot and measures
blood oxygen saturation of 87% and a pulse rate of 189 bpm. The relatively
low oxygen saturation reading was found to be due to poor probe
placement. The probe was removed, the foot massaged, and the probe
replaced with a small amount of conductive gel on its surface and resul-
ted in values above 95%. An oscillometric blood pressure cuff is positioned
on the forearm and a rectal
temperature probe placed (values not
displayed).
that adequate padding protects them from pressure injury.
During prolonged periods of anesthesia (
3 e 4 h), the
animals' limbs should be periodically repositioned and
massaged at appropriate, convenient points during the
procedure, to reduce the risk of dependent edema and
damage to muscles and joints.
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Intraoperative Monitoring
It is particularly important to provide high standards of
perioperative care with primates in a research setting, not
only because problems such as hypothermia prolong
recovery, but also because they cause widespread physio-
logical effects that may interfere with particular research
protocols. Use of electronic monitoring devices can be of
considerable value, particularly during prolonged anes-
thetics. The type of monitoring used should be selected
based on the size and species of primate, the duration of
anesthesia, type of surgery, and assessment of the degree of
risk of complications or emergencies. Small body size and
consequent low signal strength can limit the use of some
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