Biology Reference
In-Depth Information
transferred onto a heating pad and secured with tapes.
The nose and mouth are placed into a plastic mask (cut conical
end of a 15 ml polypropylene tube) and connected to
miniventilator. Small sterile drapes are placed around the
mouse. A midline skin incision is made over the anterior neck
below the jaw and the fat is dissected to visualize the muscles
covering the trachea. With blunt iris forceps the pre-tracheal
muscles are separated in the midline to visualize the trachea.
Using a 5-0 silk the muscles and the skin on either side are
retracted. Then under microscope or using magnifying loops,
endotracheal tube is placed under direct vision into the tra-
chea. This usually requires removal of plastic mask, gentle pull
on the tongue with an iris forceps and then placing the ET
tube into the mouth towards the trachea. Next step includes
gentle manipulation of the tip into trachea under direct vision.
An opaque ET tube or marking of the ET tube tip with a
marker is helpful in visualizing the tip. The ET tube for mice is
prepared as follows (Fig.
2b
): cut the cannula part of 21 G
catheter, place its proximal end into a polythene tube (ID
0.9 mm) which is further fit into a polythene tube (ID
14-16 mm) which should fit into the “Y” connector of the
tubings from the mini ventilator. The tip of the metal stylet
that comes with the cannula can be cut to adequate length
(2-2.5 cm) and used as a stylet for intubation purpose. Under
magnification small grooves are made on the outer surface
proximal polythene tube which would later help to lodge a
knot to secure it. After the ET tube is placed into the trachea,
using a 5-0 silk, it is secured to the skin over lower jaw (the free
end of the tie is first tied into the groove on the tube, then a
stitch is taken through the skin over the lower jaw). The inci-
sion is suture closed with monofilament (4-0 or 5-0 prolene
nylon). Surgical anesthesia is maintained with 2% isoflurane in
100% oxygen (see Note 2).
3. After the ET tube is secured it is connected to the ventilator.
The ventilators are adjusted so that the pCO
2
is between 35 and
40 mm of Hg and pO
2
is above 100 mm of Hg. ETCO
2
moni-
tor can also be used to maintain an ETCO2 of 35-40 mm of
Hg. For mouse the mini-ventilator rate is usually adjusted in
the range of 150-200/min with a stroke volume of 150-175
l
(0.15-0.175 ml). For rats the ventilator is set at a rate of
70-80/min, flow rate of 700-800 ml/min, and inspiratory
time of 0.4 s (tidal volume of 4-5 ml). Arterial blood gases
should be analyzed to check for pO
2
and pCO
2
values and cor-
relation between pCO
2
and ETCO
2
(see Note 3).
4. Arterial and venous catheterization: In rats the tail artery is
catheterized. A 2-4 mm incision is made in the proximal sec-
tion of tail and the artery is catheterized using a 22 G arterial
μ
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