Biomedical Engineering Reference
In-Depth Information
regime dependent on procedure and response of individual.
See main section “Analgesia” for more details.
advisable to place an intravenous cannula even if anes-
thesia with volatile agents is planned, as it will enable
fluid therapy to be administered and also allow emergency
drugs to be given rapidly if anesthetic complications
occur. The placement of a percutaneous saphenous vein
cannula may be problematical in females depending on
the stage of reproductive cycle, as the skin overlying the
vessel becomes thickened and rugous. The cephalic vein
may then be a preferable site. For marmosets the tail vein
is a useful site (
Figure 17.1
).
Nonrecovery Anesthesia
The same immobilization, induction, and maintenance
protocol can be used as above. No pre-emptive analgesia is
needed; however, since good tissue perfusion is often
a priority for nonrecovery procedures, the addition of
analgesia may still be beneficial, for instance in order to
avoid the hypotension associated with high doses of vola-
tile agents. For brief nonrecovery procedures (e.g.
perfusion-fixation) a barbiturate agent can be given as an
intravenous bolus following immobilization. Additional
incremental doses or a continuous infusion can be given
administered to extend anesthesia. The same standards of
intraoperative monitoring apply in order to ensure an
adequate depth of anesthesia.
(A)
ANESTHETIC MANAGEMENT AND
MONITORING
Management Before the Procedure Begins
Even during brief periods of anesthesia, it is important to
give attention to supporting the animal's vital body
functions. Onset of a surgical depth of anesthesia usually
results in the loss of all protective airway reflexes, and the
animal should be placed in a position with its head and
neck extended to help ensure the airway remains clear
and unobstructed. During longer periods of anesthesia,
even if inhalational agents are not used, it is often
advisable to provide oxygen to prevent the animal
becoming hypoxic. For most procedures it is preferable to
intubate the animal, as this helps to ensure an unob-
structed airway and ensures that assisted ventilation is
straightforward to perform if needed. For all but the most
brief procedures intravenous cannula placement is advised
in order to facilitate the administration of drugs and
fluids.
(B)
Intravenous Cannula Placement
To place a cannula in the saphenous vein, lie the animal
in ventral recumbency with the hind limbs extended.
After clipping and preparing the overlying skin an assis-
tant occludes the vessel proximal to the site of placement
and ensures that the vessel remains distended until the
entire length of the cannula is within the vessel. Push the
cannula through the overlying skin and vessel wall with
the bevel of the stylet facing upwards and the length of
the cannula at 15 degrees to the skin. The thumb of the
other hand can be placed alongside the vessel to stabilize
it. Once a flash of blood is seen in the hub of the cannula,
reduce the angle between the cannula and the skin and
advance the cannula proximally over the stylet. It
FIGURE 17.4
Intraoral views just prior to endotracheal intuba-
tion. (A) A rhesus macaque is positioned in ventral recumbency.
A Macintosh laryngoscope blade depresses the tongue to reveal the
entrance to the trachea bounded by the laryngeal folds and the epiglottis.
(B) A marmoset is positioned in dorsal recumbency. A Winsconsin
laryngoscope blade depresses the tongue to reveal the entrance to the
trachea bounded by the laryngeal folds and the epiglottis.
is
