An Accessible and Humane Approach to Mouse Intubation

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An Accessible And Humane Approach To Mouse
Intubation E Tonsfeldt, DL Hickman, DM Van Winkle
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Fig. 1
Introduction
Abstract
Fig. 3
An Accessible and Humane Approach to Mouse
Intubation E Tonsfeldt1, DL Hickman1, DM Van
Winkle2,3 1Veterinary Medical Unit,
2Anesthesiology Research, Portland VA Medical
Center, Portland, OR 3Physiology and
Pharmacology, Oregon Health and Sciences
University, Portland, OR With several surgeons
operating a complicated model of coronary
occlusion/reperfusion requiring mechanical
ventilation and using inhalant anesthesia, we
required a novel approach to rapid, accurate
mouse intubation that did not require specialized
peripheral equipment. The method that we
developed incorporates common laboratory
implements and greatly reduces anesthesia time,
user error, and tracheal damage. Mice
anesthetized with Isoflurane are placed supine on
the crook side of the vertical leg of an L-shaped
plexiglass support (fabricated in-house, each leg
2 x 5). The animal is restrained with a rubber
band placed beneath the animals incisors and
around the support. Trans-illumination is
accomplished by aiming a horizontal microscope
light at the mid-tracheal level. The animals
tongue is held aside with a pair of forceps
shielded with PE tubing and the tongue is
flattened against the lower jaw with the bent end
of a small weighing spatula. The backlit larynx
is easily visualized and a 20-gauge, 1.25-in.
Teflon i.v. catheter is inserted into the
trachea. The animal is placed supine by rotating
the plexiglass support 90 degrees about the
vertex and endotracheal tube placement verified
by presence of condensation on the tube and
actuation of the lungs with a small disposable
pipette. The animal is removed from the
apparatus, and the endotracheal tube attached to
a ventilator. With this technique, the animals
move from induction chamber to supplemental
ventilation and anesthesia very rapidly and with
minimal equipment. Thus, the window for hypoxia
and laryngeal trauma is reduced, addressing
Refinement (3 Rs). As of May 2007, this
technique has been employed by the surgical team
for nearly 4 years, and has increased
survivability by approximately 50. The nature of
this technique requires both mouse handling and
anesthesia familiarity, and thus is ideally
taught to an experienced technician.
Additionally, this technique may be more easily
taught with the use of injectable anesthesia,
reducing the input required to maintain a
surgical plane as the surgeon develops mechanical
proficiency.
Survival animal models requiring thoracotomy, by
definition, depend on a reversible route of
mechanical ventilation. Most animal subjects lend
themselves easily to intubation visualization of
the larynx is easily accomplished in animals even
as small as rats, and larger airways facilitate
blind techniques. Mice, however, prove more
difficult to intubate. Not only is visualization
of the larynx difficult even when backlit, but a
long airway, large, thick tongue, and light
weight of the animal (confounding handling and
airway management efforts) further complicate
matters. In a model using strictly inhalant
anesthesia (for scientific reasons, in our case),
the difficulty of the task is compounded by the
brief window of residual unconsciousness between
induction and assisted ventilation. With several
surgeons operating a complicated model of
coronary occlusion/reperfusion, we required a
novel approach to rapid, accurate mouse
intubation that did not require specialized
peripheral equipment.
Materials and Methods
All procedures were approved by the Institutional
Animal Care and Use Committee of the Portland
Veterans Affairs Medical Center prior to
development. Male and female C57BL/6J and DBA/2J
mice 4-52 weeks old are anesthetized with
Isoflurane and placed supine on the crook side of
the vertical leg of an L-shaped plexiglass
support (fabricated in-house, each leg 2 x 5)
(fig.1). The animal is restrained with a rubber
band placed beneath the animals incisors and
around the support (fig. 2). Because the animals
are ventilated immediately following intubation,
this procedure is performed at the surgery
station. The ventilator (Inspira, Harvard
Apparatus Inc., South Natick, MA) is primed prior
to induction. Our intubation tubes are slightly
modified 20-gauge, 1.25-in. Teflon i.v.
catheters the catheters are slightly bent in a
slow arc to maintain the view when inserted, and
the stylets dulled with a mechanical grinder to
prevent laryngeal trauma. Adequate lighting is
essential for this procedure, and both surgical
lights and microscope lights are employed to
provide thorough illumination. Trans-illumination
is accomplished by aiming a horizontal microscope
light at the mid-tracheal level (fig. 2). The
animals tongue is held aside with a pair of
forceps shielded with PE tubing and the tongue is
flattened against the lower jaw with the bent end
of a small weighing spatula. The backlit larynx
is easily visualized and intubation tube inserted
into the trachea. When further magnification is
needed for adequate visualization, a dissecting
scope (already at the station) or ophthalmic loop
is used to obtain an effective view (fig. 3).
Once the tube has been placed, the animal is
placed supine by rotating the plexiglass support
90 degrees about the vertex. Endotracheal tube
placement is verified by presence of condensation
on the tube and actuation of the lungs with a
small disposable pipette. When placement has been
verified, the endotracheal tube is attached to
the ventilator. When appropriate ventilation and
an adequate plane of anesthesia have been
attained stable, the rubber band beneath the
animals incisors is cut and the apparatus gently
removed from beneath the animal.
Fig. 2
Discussion
This streamlined technique has several benefits.
The animals move from induction chamber to
supplemental ventilation and anesthesia very
rapidly. Thus, the window for hypoxia and
laryngeal trauma is reduced, addressing
Refinement (3 Rs). As of May 2007, this
technique has been employed by the surgical team
for nearly 4 years, and has increased
survivability by approximately 50. The procedure
also requires minimal equipment, making it
cost-effective and seamless to integrated into
the surgical station. The biggest challenges with
this technique revolve around the dexterity and
experience required to perform it with
predictable accuracy. The nature of this
technique requires both mouse handling and
anesthesia familiarity, and thus is ideally
taught to an experienced technician. This
technique is more easily taught with the use of
injectable anesthesia, reducing the input
required to maintain a surgical plane as the
surgeon develops mechanical proficiency.