 Pressure Measurements in Mice
Arterial Catheter Construction: TN#82 3-97 |
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Introduction
This is a technique for making catheters to measure arterial pressure in
mice. The catheters are comprised of two separate portions, each of which is constructed out of polyethylene tubing. The smaller tubing, which is used to cannulate the
femoral or carotid artery is made of PE10 that has an inside diameter of .28mm and an outside diameter of .61mm. The PE10 catheter is then glued inside a 15-20 cm long
segment of PE50 polyethylene tubing, approximately .58mm inside diameter and .965mm outside diameter.
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Catheter Construction
A length of PE10 catheter of about 3 1/2-4 inches is heated using either a
heat gun or a candle chimney and the catheter material is drawn down to a very thin length of tubing. The rate of taper should be such that the catheter goes from an
outside diameter of .61mm to an outside diameter of .25mm over a distance of approximately 14mm. When working with the polyethylene catheters use a scalpel blade or razor
blade to cut the material so that it is not distorted (as it would be with a pair of scissors). The PE10 catheter is then shortened to a length of approximately 7mm from
the end of the catheter, where it is at its widest part, to the beginning at the taper which will be introduced into the artery. This length of the PE10 catheter is then
glued inside a longer segment of PE50 polyethylene tubing which is approximately 15-20cm long. PE50 polyethylene tubing is approximately .58mm inside diameter and
.965mm outside diameter. The adhesive used to glue these two pieces of catheter materials together is made by the Loc Tight Corporation and is sold under the trade name of
Plastix. This is a two component adhesive system consisting of an activator and a bonding agent which is applied to the outside of the PE10 segment which is then
introduced into the PE50 catheter material. Once joined, these segments become bonded. An alternative method of joining these two pieces of material would be
heat welding.
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Scale: each division equals 1 mm
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Welded catheter
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 Catheter Bending
After the PE10 and PE50 catheter is
constructed, the PE10 catheter tubing is formed into a sharp 360 bend just beyond the point at which is welded into the PE50 material.
The catheter can be bent by creating a mandril about which the catheter material can be formed. The mandril should be approximately 2
-2.5mm in diameter. The easiest way to bend the catheter material is to form it around the mandril and dip it into boiling water for
approximately 1 1/2-2 seconds. Immediate immersion into cold water after boiling water will set the plastic catheter in the new shape.
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Catheter Tip
Once formed into a 360 bend, the tip of the catheter is cut on an angle
with a razor blade so that it can be introduced into the femoral artery or the carotid artery. The tip of the catheter, from the point at which the taper has begun to the
end of the catheter which is first introduced into the artery should be 13-14 mm long. These catheters can be sterilized using ethylene oxide cold gas sterilization
procedure or a bacteriocidal soaking solution such as Cidex may be employed, although we have not tried Cidex with this adhesive to make sure that it is compatible.
The portion of the catheter which exits through the animal's skin should
be long enough to provide manipulation by the investigator (4-5 cm in length). Sealing of the catheter after it is flushed with heparinized saline and supplied with a
heparin lock should be done using heat sealing. The catheter
is clamped after being flushed using covered hemostats to prevent
destruction of the plastic catheter.
The open end of the catheter is heated until it flares and is then quickly
collapsed upon itself (or crushed) to form a heat seal while it is still plastic and hot.
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Catheter Protection
The easiest way to contain the catheter once it is outside the mouse (so
that the mouse does not destroy the catheter or bite it) is to contain the catheter within some sort of protective device. The easiest and least expensive device available
is found in fabric stores and consists of a two component cloth-covered button kit. These are made of nickel plated brass and consist of a 14mm base and a 16-17mm cover
which fits upon the base. The two halves snap together providing an excellent protective device for the mouse catheter. They weigh only 750 milligrams. This button is sewn
to the mid-scapular region on the mouse's back. The base is attached to the mouse and the catheter comes through the middle of the base. Excess catheter which is outside
the mouse is coiled inside the snap-on cap. The cap is snapped onto the base and the catheter is protected.
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Covered Button Kit: to store coiled infusion or pressure catheter.
"Cloth" covered metal button - open Top cover has small teeth and snaps onto bottom rim;
Catheter is brought out exit slot, coiled inside button and protected by top cover until measurements are made.
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Pressure Measurements Continued
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Chronic ->
Acute ->
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