|
ANESTHESIA AND ANALGESIA IN LABORATORY
ANIMALS AT UCSF
II. SPECIES-SPECIFIC CONSIDERATIONS
In general, smaller animals have higher metabolic rates
and frequently require higher doses at more frequent
intervals to achieve the desired effect. Species,
strain and age differences often overshadow this general principle however.
It is always best to start with a drug regimen developed
in the species, age and
strain with which the Principal Investigator is working, rather than extrapolate
from one species to another.
Mice
Isoflurane is encouraged as the first choice anesthetic
in mice. It should be delivered as a known percentage (1-3%
for maintenance; up to 5% for induction) in oxygen from a
precision vaporizer. See: Inhalant
Anesthetics
Anesthetic monitoring
of small rodents includes testing of rear foot reflexes
before any incision is made, and continual observation of respiratory
pattern,
mucous membrane color and responsiveness to manipulations throughout the procedure.
Rectal temperature and heart rate are monitored electronically during long
or involved procedures.
Injectable anesthetics are typically administered by intraperitoneal
route. Injectable analgesics and reversal agents are often administered by
the subcutaneous
or
the intraperitoneal route. Intramuscular injections must generally be avoided
because of the small muscle mass. Diluting drugs in sterile saline solution
will make it easier to accurately measure volume for injection. It may also
make some
drugs less irritating when injected. Dilution may decrease shelf-life; the
LARC standard is to discard drugs within one month of dilution. Vials containing
sterle,
diluted drugs must be labeled with the contents and the expiration date.
Ketamine-xylazine
and ketamine-medetomidine combinations produce short-duration surgical anesthesia
in larger species, but are frequently insufficient for
major surgical procedures in many strains of mice. An excellent approach
is to use
a ketamine combination, but then titrate to effect with isoflurane from
a precision vaporizer. Safety and efficacy should be demonstrated in a pilot
group of animals
before a large-scale study is initiated. Partial reversal of the xylazine
or medetomidine using yohimbine or atipamezole is possible, and will restore
cardiovascular
staus more quickly. See: Dissociative
Anesthetics
Mice are nocturnal animals, and are frequently housed in
groups of nearly identical animals. These two factors make diagnosis of mild
to moderate
pain challenging.
Weight loss is frequently monitored in animals at risk for ongoing pain.
Pre-emptive treatment of pain before signs of pain are obvious is recommended.
Isoflurane provides no post-operative pain relief. If used
for surgery, concurrent and follow-up use of ketamine and/or buprenorphine
and/or
a non-steroidal
anti-inflammatory will be necessary. LARC veterinary staff recommend
injecting the analgesic 30
minutes prior to the start of surgery.
See: Mouse Formulary
Rats
Rat anesthesia and analgesia considerations are similar
to mouse anesthesia considerations, though some doses vary.
In rats, ketamine combinations are more likely to provide
adequate surgical anesthesia than in mice, and so may not
require supplemental isoflurane.
See: Dissociative
Anesthetics, Inhalant
Anesthetics, and, Rat
Formulary
Hamsters
Hamster anesthesia is similar to rat and mouse anesthesia,
though some anesthetic doses differ. Peripheral veins
are extremely difficult to access in hamsters, limiting some
of the anesthetic options.
Rabbits
UCSF works only with Pasteurella-negative rabbits,
greatly reducing the risk of respiratory disease under anesthesia. Long
procedures are best performed
using inhalant anesthesia with an endotracheal tube in place. IACUC staff
are available to train researchers in this technique. See: Rabbit
Formulary
Guinea Pigs
Guinea pigs can be difficult to anesthetize, especially
on a survival basis. Intravenous injection is difficult. Intramuscular injection
is acceptable
for non-survival procedures, though animals may self-mutilate at injection
sites if they have recovered from anesthesia. Intraperitoneal (IP) administration
works well, if the large cecum can be avoided. Guinea pigs may be anesthetized
by face mask with volatile anesthetics; endotracheal intubation requires
specialized training.
Cats
Cats are readily anesthetized using a variety of injectable or inhalant methods.
Initial restraint of a fractious or frightened cat can
be a challenge for the researcher’s safety and for the animal’s
welfare; choice of technique will depend on the skill level of the researchers
as well as the individual cat’s temperament. Intravenous injection of a fractious cat requires
a very high level of skill. Chamber induction with isoflurane can be stressful
to the cat, and poses occupational exposure risk to the workers. Intramuscular
or subcutaneous injection of sedatives requires a moderate level of skill,
and carries some risk of cat bites and scratches. Training is available through
the IACUC staff, and LARC veterinarians
and veterinary technicians can provide direct assistance when necessary.
Non-steroidal anti-inflammatory drugs are useful, but must
be used with caution in cats. Do not exceed recommended doses or frequencies
of administration.
Acetaminophen is never used with cats. See: Cat
Formulary
Dogs
Dogs are easily anesthetized with a variety of techniques.
Intramuscular injection of ketamine or ketamine combinations are to be avoided,
because of the incidence
of behavioral disturbances. See: Dog Formulary
Nonhuman Primates
Nonhuman primates require specialized handling and restraint
to deliver anesthetics without compromising human safety. Ketamine or ketamine-midazolam
are typically
used by intramuscular injection for initial sedation. Once sedated, primates
are easily anesthetized with a variety of techniques. Use of palatable
oral medications decreases the need for restraint for medication. See: Nonhuman
Primates
Formulary
Swine
Swine are easily anesthetized with a variety of techniques.
Ketamine-xylazine is a common intramuscular sedative, but requires a large
volume of injection.
Use of Telazol® or Telazol® combinations can significantly reduce
the volume of injection for larger animals. See: Swine Formulary
Frogs
Immersion anesthetic (tricaine methanesulfonate, or MS-222)
is common, especially for fully aquatic species like Xenopus. Once a surgical
plane
of anesthesia
has been reached, anesthesia may be supplemented, but not eliminated, by
maintaining the animal at 4o C. Post-operative pain management can include
local infiltration
of bupivicaine or with systemic xylazine. See: Local anesthetics
Sheep
Sheep anesthesia is challenging because of the animals’ large size and
the unusual ruminant digestive physiology and anatomy. Adult sheep should have
food withheld for 24-48 hours prior to general anesthesia, though they should
be allowed access to water. Assessing anesthetic depth during constant-infusion
ketamine anesthesia requires specialized training and, at UCSF, specialized
certification by LARC veterinarians.
Fish
Immersion anesthetic (Tricaine methanesulfonate, or MS-222) is the most
common anesthetic in use with fish
Birds
Small birds may be anesthetized by inhalation anesthetics
(such as isoflurane) or injectable. Fasting is not generally required in
advance. It is vital
to maintain adequate warmth during the anesthetic period.
|
