When the anastomosis is finished, inspect it to see if the stitches look evenly spaced, if all suture ends are pointing away from the suture line and if all knots are still tied firmly. If you find a knot that has become loose, like this one, tighten it once more.
Cut the sutures of the second and first knot shorter, to mark the front wall. Then cut out the anastomosis, open it up with the vasodilator to check for backstitches, cut it open between two knots and role it open.
Looking at the inside of the anastomosis with increased magnification can reveal numerous potential causes of anastomotic failure. Having marked the first, second and sixth stitch, it may be possible to remember why a certain mistake happened. In any case, one can observe symmetry and size of bite, parallelism of stitches with blood flow and evenly distanced spacing of stitches. In our case, there may be some exposure of the vascular media and maybe even some overlap caused by asymmetric bite, or by not penetrating all vascular wall layers of this thick vessel at the same distance to the cut. The last stitch may be a little small, as well.
Here are some further examples of common mistakes.
These two stitches are too loose and do not properly approximate the cut edges, mpossibly causing leakage. Oblique stitches like this one potentially create turbulence and aid thrombus formation.
This one is too close to the edge on both sides of the cut, carrying a high risk of tearing the vessel and creating a fuzzy edge that is difficult to repair.
This one here is placed too superficially, not penetrating the intimal layer, potentially causing exposure of the vascular media leading to thrombosis.
Here a stitch is missing, causing leakage.
These stitches have an asymmetric bite, leading to overlapping vascular edges with exposure of the vascular media, again causing thrombosis.
Evaluate each anastomosis
All of these mistakes carry a risk of anastomotic failure and should be learned from.
Since many of them are not apparent when looking at the outside of the vessel, we recommend cutting open every single anastomosis in preclinical learning to become aware of imprecisions and even serious mistakes, that would otherwise remain undetected.
Dye injection testing is another option for anastomotic patency assessment.
However most dyes have a different viscosity than blood, so incorrect results are to be expected. Patency testing is most accurate in living models and will hence be presented in the rat model.