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Preparation
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Mouse pressure measured via a PE10PEE50 tapered catheter in the femoral artery.
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The mouse is prepared for surgery by anesthetizing it with ketamine and xylazine as described earlier. After anesthesia
is attained, the groin area of the left rear leg and the mid scapular region behind the neck are shaved using animal
clippers. The area is disinfected using Betadine scrub and Betadine solution.
Mid-Scapular Incision
A small incision is made in the mid-scapular region to allow
later exteriorization of the catheter from the body. The mouse is then placed on its back with the legs extended.
Surgery
A 15 mm skin incision is made over the femoral artery and vein region. The fat pad
which overlies the femoral artery and vein is then reflected from the artery and vein; clamped, and transected after clamping. Minimal bleeding occurs following this
procedure.
The femoral artery is then very carefully dissected away from the vein; the surgeon
should use a great deal of care to avoid damaging either the femoral vein or the femoral nerves which lie adjacent to the femoral artery. The use of Dumont vessel
dilators, either D-5a or D-5az, is recommended for this procedure because of the delicate structure of the femoral artery and vein.
A 4-5 mm section of femoral artery is dissected free from the surrounding tissue
between the area where the artery and vein send branches to the overlying fat pad and the peritoneal wall. Once isolated, 3-4 drops of a 2% lidocaine solution is
applied to the surface of the femoral artery and vein to prevent vasospasm. This greatly facilitates cannulation of this vessel which is approximately 400 micrometers
in diameter.
Three 7-0 silk ligatures are placed around the femoral artery.
1) The first ligature is placed most distally, close to where the artery branches to
the fat pad overlying the femoral area. This most distal 7-0 silk ligature is tied completely, occluding the blood vessel.
2) A second 7-0 silk ligature is placed proximally on the femoral artery and should go
around the femoral artery and have a half of a surgical knot tied in it. This ligature should be loose and it should be close to the abdominal wall.
3) A third ligature is placed between the first two, again half of a surgical knot should be loosely tied.
Cannulation
To cannulate the femoral artery, traction is applied to the most distal ligature which
is then taped into position with masking tape, putting tension on the artery. The most proximal ligature is then elevated using a pair of forceps clamped to the end of
the ligature and used as a weight to apply traction. This will occlude blood flow into
the remaining middle portion of the femoral artery which is then isolated so that the blood vessel can be cut or incised and the catheter introduced.
At this point ensure that the proximal ligature completely occludes the blood vessel
by pushing the blood back proximal to the ligature and verifying that no reflow occurs. A small incision should be made approximately half-way across the femoral
artery within two millimeters of the most distal ligature. A pair of Dewecker iris scissors works very well.
Using the tip of a pair of 5/45 sharp-pointed Dumont forceps, gently open the vessel
and elevate the proximal edge of the incised artery and introduce the tip of the catheter into the artery at this point. Gently advance the catheter tip until it is
against the most proximal ligature and tighten the middle ligature loosely around both the blood vessel and catheter. Release the most proximal ligature and advance
the catheter as far into the femoral artery as it will go. It should advance until the taper begins which is 13-14mm in length from the tip.
At this point, both the proximal and middle ligature should be securely tied around
the artery and catheter combination and the remaining ligature left on the most distal tie on the femoral artery should be brought around the catheter itself and tied
again so that three separate ligatures hold the catheter within the blood vessel. A fourth ligature, consisting of either 5-0 or 7-0 silk, should be placed into the heavy
thigh muscle on the inner aspect of the mouse thigh and tied around the catheter body, and helping to hold the catheter body away from the femoral vein.
Occlusion of the femoral vein probably results in increased morbidity of the ipsilateral
foot and limb. The remainder of the catheter should be brought subcutaneously from the femoral region to the mid-scapular region. This is done using a 15 gauge needle
which has been threaded below the skin from the mid-scapular area to the femoral area. The catheter end is brought through the 15 gauge needle to the exit at the
mid-scapula region. The needle is then withdrawn from the femoral area, over the edge of the catheter, and away from the animal. This leaves the catheter in
position under the skin with a bend at the femoral region.
Completion
Completion of the femoral site requires reapproximation of the femoral fat pad over
the underlying femoral artery and vein and reapproximation of the skin. Both procedures utilize 7-0 silk suture. Interrupted skin sutures are recommended at the
femoral site so that if the animal chews through one of the sutures as healing progresses, the entire suture line will not become unraveled.
Place the animal on its sternum and complete the operative procedure by placing a
piece of Mersilene® mesh over the catheter, sliding it down to the mid-scapular area and suturing it under the skin using 4-0 Vetafil® suture. The suture goes in
through the skin, through the Mersilene mesh and then back out through the skin again as it exits. The piece of Mersilene mesh should be approximately 1cm x 1cm.
The skin is reapproximated over the Mersilene mesh and the catheter itself exists through the mid-scapular incision along the central midline at the middle of the
incision. The mid-scapular incision is approximately 1 cm in length.
The procedure is completed by sliding the bottom half of the cloth covered button
catheter holder over the catheter, suturing it in place with the Vetafil sutures, and then coiling the end of the catheter within the top half of the cloth covered button.
The catheter may require shortening to allow a length of catheter outside the mouse of approximately 4 cm.
Catheter Patency
Prior to final heat sealing and closure, the catheter should be filled with pure heparin
, 1000 units per ml. This will not provide any long lasting antihemostasis to the mouse and will help ensure catheter patency.
Properly performed these catheters should require little or no maintenance for a
period of seven days. Arterial pressure measurements are made using materials which have been sterilized and aseptic techniques should be used in handling of all
catheters and catheter materials. Sterile saline should be used for filling up the transducers and catheters and the exterior portion of the catheters should be
cleaned with isopropyl alcohol prior to opening the catheter for arterial pressure measurements.
Acknowledgement
Thomas L. Smith, Ph.D., Department of Orthopedic Surgery, Wake Forest Medical
Health Science Center, Winston-Salem, NC.Acute Pressure Measurement.
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Chronic Pressure Measurements
