Biology Reference
In-Depth Information
3. The tip of the ETCO
2
probe is placed into the metal cannula
provided at the “Y” junction (for rats) or into a small hole
drilled into the “Y” junction (in mice). During the pilot phase
of the study it is important to check the arterial blood gases
and adjust the tidal volumes and respiratory rates to keep pCO
2
between 30 and 35 mmHg and pO
2
above 100%. It is impor-
tant to check the correlation between the ETCO
2
from the
capnometer with the pCO
2
from the arterial blood gases. In
rats 0.5 ml of blood can be safely withdrawn 2-3 times during
a 6-8 h monitoring period. In mice only 50
l can be safely
withdrawn for arterial blood gas analysis. In a mouse that
weighs 20 g the total blood volume is only 1-2.4 ml and the
safe bleeding volume is only 0.1-0.2 ml (as removal of >10% of
blood volume will result in hypotension and this can affect the
results of the study).
4. Double secure the arterial and venous catheters as they can
dislodge while turning the animal to prone position on the
stereotactic frame.
5. It is important to maintain the temperature of the animal as
it can affect the body metabolism, blood flow and contusion
volumes.
6. The craniectomy size should be optimal (around 8-10 mm for
a 8 mm impactor tip and 4 mm for a 3 mm impactor tip). If the
craniectomy is too wide it can result in excessive bleeding,
dural tear, or brain herniation and if it is too small (than the tip
of impactor) then the bone at the edges can fracture and result
in more severe injuries. The drilling is usually done under
magnification (loops for rats and microscope for rats). Drilling
should be away from the inter-parietal suture in the midline (as
shown in Fig.
2
), otherwise it can result in fatal venous sinus
bleed. During drilling sterile saline is used to irrigate the bone
to decrease the amount of heat that is generated during the
drilling. If there is bleeding a piece of gel foam of the size of
the craniectomy defect is placed over the bleeding site and irri-
gated with for few minutes. Dura should be kept wet till the
impaction because the desiccated dura is more prone for tears.
The tip of the impactor is also kept wet before the impact to
prevent the dural tear. It is important to apply artificial tears to
the eyes especially in chronic (survival) experiments as corneal
ulcers can influence the postoperative behavioral studies.
7. It is important to check the cylinder pressure and the impac-
tion parameters during the trial impact. The impactor should
be advanced precisely. It is useful to keep a mark (with a per-
manent marker) on the impactor tip in the pneumatic impactor
and calculate the number of rotations advanced (one rotation
is equal to 1 mm). This should be calibrated regularly.
μ
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