Proper microsurgical dissection is as important for success as the anastomosis itself. Take your time to learn it. Do not forget to keep the tissues moist. Soaked tissues are easier to dissect. Start the microsurgical dissection with the microscope set at a low magnification. Using cotton swabs, move aside the para-aortic fat to visualize the abdominal aorta.
You may need to move the microscope or work field to be able to work at the desired magnification.
Starting just below the renal vessels, pick up the tissue overlying the aorta with one forceps and tear it away with another. Make sure to point both forceps exclusively at the aorta. The walls of the inferior vena cava are very fragile and easily ruptured. Keep a relatively small distance between your instrument tips in order to tear only those tissues you want to tear. Tearing over long distances is likely to cause an aneurism of the inferior vena cava or one of its branches.
Excessive stretch on the aorta itself can rip off collateral vessels or lead to spasm.
Once you have freed a segment of vessel on its superficial aspect, continue on its sides. Momentarily leaving some tissue attached on the superficial aspect of the vessel may not look elegant, but allows very atraumatic vessel handling.
Free the vessel on its underside as well. Whenever you place an instrument under the vessel, make sure its tips are closed and not pointing at the inferior vena cava.
Dissecting one Segment after another increases safety
Dissecting one segment of vessel after another provides the advantage of being able to interrupt bleeding by placing vascular clamps on the vessel, if a mistake should occur.
Collateral vessels need to be accurately dissected from the intersection with the main vessel to quite some distance from it. Perform spreading movements slowly and in a controlled fashion to safely avoid ripping off the collateral. Once you have dissected a segment of vessel, move the operating field to keep working in its middle. Continue dissecting the aorta down to the aortic bifurcation. Before proceeding, assure yourself that the aorta is free all along its underside.
Here you can see the abdominal aorta lying next to the inferior vena cava, dissected from immediately distal to the renal vessels, down to its bifurcation into the common illiac arteries. To finish the dissection, the illiolumbar vessels and all other small collateral vessels must be ligated and cut.
Each collateral needs to be ligated directly on its emergence from the main vessel in order to avoid stasis and thrombus formation inside its stump. Assure yourself that the intersection of each collateral with the main vessel is accurately dissected, as any excess of tissue could cause the ligatures to be insufficiently tight.
For a simple ligature, pass a short length of suture (or the rear end of the entire suture) under the collateral, make a double loop and tie a knot, pulling only on the long end of suture while holding the loop as close as possible to the main vessel. Tie two more single loops to finish the knot. Then place another ligature at some distance to the first. Cut the collateral vessel at a safe distance to the main vessel to prevent the ligature from slipping off.
As demonstrated in the chicken leg model, collateral vessel stumps can be used for atraumatic vessel handling, as long as the ligature itself is not grasped.
To ligate a collateral on the underside of the vessel, you can pass the suture around the collateral indirectly. First pass the suture under the main vessel distal to the collateral, then pass it back around proximal to the collateral. Tie a knot in the closest possible proximity to the main vessel.
Here you can see the loop being placed on the emergence of the collateral again at a higher magnification.
Instead of the distal ligatures, you could also use a low-powered bipolar coagulator at a safe distance to the main vessel to economize use of time and suture.
Microsurgical dissection – pitfalls, tips and tricks
If a collateral is ligated too far from the main vessel, stasis and thrombus formation can result, potentially leading to anastomotic failure. Grasping a ligature can make it slip off, making the placement of another ligature or a repair stitch necessary. Grasping the collateral itself, on the other hand, is very atraumatic.
Keep calm and take time for damage control
If you should inadvertently loosen a ligature, tear or cut off a collateral vessel, gently press a cotton swab on it. As long as you know what you are doing, see what you are doing and do not panic at any time, most mishaps can be repaired. Since even small amounts of blood lost may be enough to compromise the animal’s circulation, resist the urge to check more than once whether the bleeding has stopped on its own. Keeping the cotton swab in place, clamp the vessel, clean the operating field. If there still is a vessel stump, place a repair stitch through it and tie knots on either side of it. If just a hole in the vessel remains, place a simple repair stitch in the direction of blood flow.