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Preop
evaluation
Parenteral
anesthetics
Inhalation
agents
Intraoperative
monitoring
Special
considerations
Postoperative
care
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Splenectomized or
immunosuppressed Macaca fascicularis
are at added risk for developing anemia due to naturally occurring malarial
infections. They compensate by increasing cardiac output and heart rate, and
anesthesia may drop these and adversely affect tissue oxygen delivery. Anemia may
reduce the solubility of volatile anesthetics and consequently, accelerate
the rate at which the alveolar concentration can be increased or decreased. |
| NHPs
with hypertension may not tolerate repeated ketamine doses; inhalation
anesthetics are preferred. |
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Common practice
to fast animals for 12 hours except in the case of Callitrichidae
and other small species; generally fast for 6-8 hours to avoid hypoglycemia |
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Prolonged
withholding of water is unnecessary; 3 hours is sufficient |
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Addition of H2
antagonists before induction has shown to protect against aspiration
pneumonia in Papio spp.
Ranitidine (preferred because it doesn't affect cytochrome P450) or
cimetidine given preop decrease histamine-induced gastric fluid secretion. |
Anticholinergic
Drugs
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In
neonatal NHPs, cardiac output is heart-rate dependent. Therefore,
bradycardia is very dangerous. Glycopyrrolate is
twice as potent and has a longer duration of action than atropine. |
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Atropine
possesses arrhythmogenic properties and may predispose nonhuman primates to
ventricular tachycardia and bigeminal patterns. |
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1. Dissociatives
Ketamine
| Animals retain pharyngeal,
laryngeal, and palpebral reflexes |
| Tonic-clonic movements or
psychotomimetic emergence reactions have been reported in NHPs. |
| Does not alter the magnitude of
many endocrine responses |
Ketamine-Xylazine
| Provides muscular relaxation
and analgesia sufficient for minor surgical procedures |
| Xylazine-induced bradycardia
and hypotension are common |
| Xylazine overrides the
stimulatory effects of ketamine |
Ketamine-Medetomidine
Used in Pan
troglodytes to produce rapid induction, stable immobilization, excellent
relaxation and calm recovery. In Saimiri sciureus, medetomidine given
alone facilitates mask induction and can be reversed. Combined with ketamine,
medetomidine produced excellent sedation and muscle relaxation in Chlorocebus
and Papio.
Capuano evaluated medetomidine alone at
several doses in rhesus macaques, and found that it was unsuitable for
sedation due to variable response. Medetomidine causes initial increases in
respiratory rate followed by a decrease, decreased heart rate, drop in blood
pressure and body temperature, and inconsistent sedation, analgesia and muscle
relaxation{4192}.
Ketamine-Diazepam
IM injection
of diazepam may be painful with unreliable absorption and multiple doses may
lead to prolonged recovery due to its long elimination half-life. Nonetheless,
its use has been reported in Papio, Saimiri, and Callithrix.
Ketamine-Midazolam
Midazolam is better absorbed after IM injection, is a better anxiolytic, and
has a shorter half-life. It has been used in conjunction with ketamine in
macaques and Chlorocebus aethiops for PET scans. Some age-related dose
sensitivity was noted, with older animals requiring lower dosages.
Tiletamine-Zolazepam
Occurrence
of seizures nearly eliminated in comparison to ketamine. In juvenile rhesus,
Telazol induces sufficient restraint for minor surgical procedures, rapid onset
and smooth recovery. There are minimal cardiovascular side effects at a dose of
1.5-3.0mg/kg, with depressed myocardial contractility. The combination has been
anecdotally used successfully for surgical anesthesia of macaques, squirrel
monkeys, patas monkeys, marmosets and chimps.
2. Alphaxalone-Alphadolone (Saffan)
This steroid combination has been used in New World species at dosages of
11.5-15.5 mg/kg IM for surgical procedures. Squirrel monkeys demonstrate
respiratory depression and hypothermia. Old World monkeys need higher dosages
for anesthesia, in the range of 120mg/kg as an IM bolus or 18mg/kg followed by
intermittent boosts of 6-12 mg/kg IV. Infusion has been used in Erythrocebus
and Papio.
3. Propofol
| Used for procedures of short
duration or for induction |
| Apnea following induction dosages
can be avoided by slow administration |
| Need strict asepsis to guard
against infection |
4. Barbiturates
| Pentobarbital - induces minimal
changes in cerebrospinal fluid pressure and decreases cerebral blood flow
and metabolic rate, therefore is useful in some neurosurgical procedures |
| Thiopental can be used as an
induction agent to facilitate intubation. Blood pressure is only minimally
affected. |
5. Opioids
| Advantage of opioid anesthesia is lack of impaired cardiovascular
function, but in humans there is concern over awareness during high-dose
opioid anesthesia. |
| Morphine
and oxymorphone commonly used for postoperative analgesia; fentanyl most
often used in balanced anesthesia |
| Naloxone used as a reversal prior to extubation, to reverse hypercapnia |
6. Neuroleptanalgesics
Fentanyl-droperidol (Innovar-Vet) and fluanisone (Hypnorm) useful for minor
procedures. Nonhuman primates do not become transiently aroused by auditory stimuli
after the administration of Innovar-Vet.
7. Muscle
Relaxants
(Pancuronium, vecuronium)
| Pancuronium produces moderate
elevation in heart rate and blood pressure |
| Vecuronium has no hemodynamic
effects and is a viable alternative to pancuronium in cardiovascular
procedures |
| Increase in heart rate and blood pressure of 20% over baseline indicates
that anesthesia is inadequate. Lacrimation and attempts to buck the
ventilator are also indicators.
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1. Nitrous
Oxide
| High minimum alveolar
concentration (MAC) – 200% in macaques
versus 105% in humans |
| Produces second gas effect thus
accelerates induction. Principal effect is a less pronounced circulatory
depression. |
| Diffusion hypoxia may occur if an
animal is allowed to breathe air at the conclusion of anesthesia |
2. Halothane
| Decline in systemic blood
pressure and heart rate proportional to the depth of anesthesia |
| Sensitizes the heart to the
dysrhythmogenic effects of epinephrine, regardless of the halothane dose |
| Causes a dose-dependent increase
in cerebral blood flow and cerebral vasodilation, therefore should be used
with caution for neurosurgical procedures |
| Causes reduced uterine blood flow in pregnant NHPs, with fetal acidosis
and hypoxia. Monitor BP when using halothane in pregnant NHPs, position them
carefully and use good fluid management. |
3. Isoflurane
| Minimally
metabolized due to its chemical stability and low solubility, and accordingly,
it is exhaled essentially unchanged. |
| Does not sensitize myocardium to arrhythmias caused by epinephrine |
4. Methoxyflurane (no longer
available in US)
| Low vapor pressure and high
solubility, therefore not used much in NHPs |
| Potential nephrotoxicity |
5. Enflurane
| Less likely than halothane to sensitize the myocardium to
the effects of epinephrine. |
| Like halothane, produces dose-dependent decrease in myocardial
contractility, thus decreased blood pressure and cardiac output and
increased central venous pressure. |
6. Sevoflurane {4539}
| Cardiopulmonary effects similar to isoflurane |
| Faster induction than isoflurane |
| Less airway irritation than isoflurane |
| Induction time in bush babies 75 seconds; recovery time 25 seconds |
| MAC in other species is around 2% (dog, human, pig) |
| Stable respiratory rate, PCO2, ETCO2= lack of respiratory depression |
| Temperature decreases in small NHPs (bush babies) |
| Initial increase in HR, then slow decrease, but not significant; MAP
stable around 40 mm Hg |
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Tongue seems to
be less influenced by intraoperative conditions such as hypothermia or
hypotension; better than ear for pulse oximetry |
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Core body
temperature can be monitored by inserting esophageal probe into the lower
third of the esophagus |
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Urinary output
can serve as a useful guide of intravascular volume status |
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Minor to moderate
blood loss can be replaced with crystalloid solutions given in the amounts
equal to about three times the amount of blood loss |
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Phenylephrine is
drug of choice in treating isoflurane-induced hypotension. If there is
cardiovascular collapse, use dopamine (which preserves renal blood flow) or
norepinephrine.
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Seldinger
technique used for femoral artery catheterization, to prevent the catheter
from accidental dislodgment: first, catheterize with standard short IV
catheter. Put guide wire through catheter into artery, withdraw short
catheter, and replace with longer catheter threaded further into vessel. |
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Swan-Ganz
catheter can be used to monitor cardiac function, preload, and response to
intervention during cardiac surgery [Note: these authors have a real bias
towards cardiac surgery; they spent a page and a half on anesthesia for
cardiac bypass surgery.] |
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Special
Anesthetic Considerations
Obstetric Anesthesia – maternal
hypotension is the most common complication encountered during anesthesia.
Ephedrine at 1.25-2.5mg increments is the safest vasopressor.
Pediatric Anesthesia
| Cardiac output is heart rate
dependent in pediatric animals, so avoid heart rate reduction by using
ketamine and atropine |
| Suckling reflex can be used as
one of the indicators for depth of anesthesia |
| Isoflurane is the anesthetic of
choice for pediatric animals
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Circulatory complications –
Protamine is usually administered over a period of time to reverse heparin
anticoagulation
Pain management
| Aspirin used empirically for mild pain |
| Ketorolac for moderate pain, but may incite bleeding |
| Morphine, oxymorphone and meperidine have all been used. Oxymorphone is
used most often because it doesn't cause respiratory depression in NHPs. |
| Oral codeine plus acetaminophen used in apes |
| Buprenorphine lasts 6-8 hours or longer; butorphanol also used |
| Potential disadvantage of
agonist-antagonist opioids is the “ceiling effect” when repeated doses
do not induce further analgesia but instead produce marked respiratory
depression. Use naloxone to reverse. |
| Absorption from IM injection can be slow, but IV injection can exacerbate
respiratory depression. Morphine is used via the epidural
route; it has low lipid solubility which makes systemic absorption less
likely to occur from the epidural site. More of the drug
is available at the receptor sites in the spinal cord, resulting in
prolonged analgesia. Placement of an epidural catheter at either L5-6 or
L6-7 is relatively easy in macaques and baboons. |
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