Biomedical Engineering Reference
In-Depth Information
cerebral edema because these drugs will increase cerebral
blood flow and brain volume, exacerbating the edema.
When immobilizing an animal with suspected cerebral
edema the goal is to prevent a further rise in intra-cranial
pressure (ICP) and this can be difficult to achieve.
Manual restraint can be stressful and lead to increased
ICP, and ketamine can increase cerebral blood flow (and
therefore ICP) and therefore may induce seizures. Mid-
azolam alone (or if necessary with a low dose of alpha-2
adrenoceptor agonist that is antagonized once an intra-
venous cannula is placed) can be used for immobiliza-
tion, particularly if the animal already shows signs of
reduced responsiveness. Although alpha-2 adrenoceptor
agonists lead to initial hypertension followed by hypo-
tension, which is undesirable, unlike ketamine they can
be antagonized and so may provide a better choice for
combination with midazolam in this circumstance. It
must be remembered however that any sedative
(including benzodiazepines) can depress respiration, lead
to hypercapnia, and increase brain volume, hence place-
ment of an endotracheal tube, measurement of expired
carbon dioxide, and the availability of mechanical
ventilation are strongly advised.
applicable) should be available for administration to the
fetus (
Table 17.4
).
Pediatric Anesthesia
The priority in pediatric anesthesia is maintenance of heart
rate because cardiac output is rate dependent. For this
reason the routine prophylactic use of muscarinic antago-
nists such as atropine or glycopyrrolate is a sensible option.
A stable ECG signal is easily achieved even in very small
animals and where possible this should be combined with
peripheral pulse monitoring to ensure adequate peripheral
perfusion. Multi-parameter monitoring is possible
(
Figure 17.6
) with suitably sensitive monitors and appro-
priately sized equipment, but values obtained should
always be interpreted in this context. Due to their small size
and low fat reserves, pediatric patients are prone to anes-
thetic induced hypothermia. Use of a forced warm air
blanket is the most effective way of counteracting this
effect. Drugs that undergo a large degree of liver metabo-
lism should be avoided if possible, as hepatic microsomal
enzyme systems are immature. Mask induction with
a volatile agent, either with or without prior sedation, is
suitable for the majority of pediatric nonhuman primates.
Sevoflurane is probably the agent of choice for mask
induction because it is the least pungent and unlikely to
result in airway irritation. Very young animals should not
be fasted before anesthesia but an orogastric tube can be
passed following induction to empty the stomach of milk if
needed.
Obstetric Anesthesia
The same considerations for obstetric anesthesia in other
species apply to nonhuman primates. A number of physi-
ological changes occur during pregnancy that may impact
anesthetic management. Changes in respiratory function
mean that supplemental oxygen should be given prior to,
during, and immediately following anesthesia, as the
patient will desaturate quickly if apnea occurs. Direct
(increase in progesterone levels) and indirect (changes to
ventilation and the volume of distribution) effects lead to
a reduced anesthetic requirement for both inhaled and
injectable agents, and alterations in inhaled agent concen-
tration will have more rapid affect. The priority in obstetric
anesthesia is maintenance of maternal blood pressure
because uteroplacental perfusion is pressure dependent and
does not autoregulate. Maternal blood pressure should be
continuously monitored (see “Cardiovascular function”
above) and steps taken to maintain normotension (intra-
venous fluid restoration and the use of vasopressors if
needed) should problems arise. In order to avoid the
hypotension associated with high doses of inhaled agent,
a balanced anesthetic technique, using a combination of
agents, should be employed. Positioning of the animal
should avoid compression of the abdominal aorta and
caudal vena cava by the gravid uterus and portable suction
should be available in case vomiting, caused by delayed
gastric emptying, occurs. Effects of maternal drugs on the
fetus should be considered, and if cesarean section is per-
formed anesthetic and analgesic reversal agents (where
POSTANESTHETIC CARE
Extubation
Extubation should be performed following cessation of
anesthesia and once the animal can maintain blood
oxygen saturation
>
95% and an end tidal CO
2
<
50 mmHg when breathing room air. As a general guide,
if saturation is maintained for longer than two minutes
after oxygen is discontinued, it is safe to continue and
extubate the animal when its jawtone and airway
protective reflexes begin to return. Once extubation has
been performed and until the animal is able to sit up it
must be directly observed to ensure that the airway
remains patent and blood oxygen saturation remains
>
95%. All animals will require some degree of special
attention in the postoperative period, but this care can be
hampered when dealing with nonhuman primates by the
aggressive nature of some animals. Arousal of
a nonhuman primate quickly follows the return of
protective airway reflexes. Extubation just before these
reflexes return will therefore allow for safe handling of
the animal if problems occur such as vomiting. Vomiting
