Laboratory Exercises

The most commonly used means of end-to-end models for arterial anastomosis are that of the abdominal aorta, carotid and femoral arteries. The ideal animals for microsurgery exercises are rats weighting 250-350 g. After the anesthesia, the abdomen, the ventral side of the neck, and the internal sides of the inferior limbs should be shaved. After placing the animal on its back we immobilize the limbs with bandage stripes.

Features: diameter approx. 1.5 mm, length approx. 3 cm, its preparation requires ligaton and cutting of vessels.

Anatomy
The abdominal aorta lies between the diaphragm and the aortic bifurcation into the 2 iliac arteries, stretching over a length of approximately 3 cm. It is positioned along the spine, slightly posterior to the inferior vena cava. The left renal vein crosses it. Among the aortic branches, the left and right iliolumbar arteries must also be mentioned because they need to be dissected and ligated during the preparation of the vessel.

Macrodissection
Incise the skin with scissors, starting at the pubis and ending at the xiphoid process. We open the peritoneal cavity in order to avoid unnecessary bleeding from the muscular wall. Identify the linea alba and use it as a landmark to in order to avoid unnecessary bleeding from the muscular wall. Retract the wound using 2 paper clips and exteriorize the intestinal mass to the right of the rat, folding it in moisturized gauze. Tear the posterior peritoneum with 2 moisturized cotton swabs by gentle transverse movements, thus exposing the aorta (between the renal and iliac arteries) and the inferior vena cava.

Microdissection
Set your microscope over the operating field and adjust it to a medium magnification. Using 2 microvascular forceps, free the aorta completely from the fatty tissue surrounding it and dissect the lateral iliolumbar branches. If we want to achieve a longer section, we can ligate the renal vessels. Then we separate the aorta from the vena cava carefully, because the wall of the vena cava is extremely thin and fragile. We pick up the adventitia of the aorta with one of your forceps while creating a space between the 2 vessels with the other forceps and using gentle movements with the other forceps tip, we remove the surrounding connective tissue.

Attention
When picking up the vessel, hold it only by its adventitia, because picking up the vessel in its complete thickness produces traumatic lesions of the intima and create the potential for thrombosis or perforation. The most delicate dissection part is at the level of the arterial iliolumbar branches, which are strongly bound to the wall of the vena cava. Keep your operating field clean at all time. The unavoidable bleeding that occurs during dissection can be controlled by gentle compression with cotton swabs, lasting about 3 minutes.

Features: diameter approx. 1.0 mm, length approx. 2 cm, no branches to be ligated.

Anatomy
Leaving the thorax, each carotid artery lies parallel to the trachea until reaching the thyroid gland where it divides into the external and the internal branches.

Macrodissection
After making a skin incision between the mandible and the sternum, we find the vessel medially sternomastoid muscle and place a retractor on each side of the neck.

Microdissection
Identify and separate the vagus with forceps under the microscope, and free the artery from the surrounding connective tissue in about 2 cm of its length. Care should be taken to injure neither the vagus nor the internal jugular vein.

This graphic (sec. Yonekawa 1999) shows the rigth carotid artery (A), the neighboring vagus (yellow), which can be visualized be exposing the sternocleidomastoid (B) and omohyoid muscles (C). The external jugular vein (D) can be found at the lateral side of the sternocleidomastoid muscle.

Anatomy
The femoral artery continues the iliac artery and extends from the inguinal ligament to its final ramifications (descending genicular, saphenous, and popliteal arteries). A unique vein accompanies the artery, and both of the vessel are sheltered inside a common perivascular sheath.

Macrodissection
After making a 3 cm-long oblique skin incision, we expose the field by using a retractor side-wise.

Microdissection
Using a higher magnification, we remove the fine layer of connective tissue that covers the tissues with 2 cotton swabs until the femoral bundle appears wrapped in the vascular sheath. We create an opening in the sheath with 2 forceps using blunt preparation and gently (the vein wall is extremely thin) separate the femoral artery from the vein by handling only the adventitia of the artery. Then we isolate the muscular branch over a length of 1-2 mm and cut it after ligation. We make sure that the femoral artery is completely free on its course between the inguinal ligament and the origin of the superficial epigastric branch.
During the dissection of the femoral artery spasm often occur (because of the trauma caused by the dissection, the contact with fresh blood, and dropping of wound temperature) which can be relieved by irrigating the wound with a warm solution of lidocaine 1 % for a minimum of 3 minutes (Beekman 1988).

Anatomy
The vein has a bigger diameter than the artery but its walls are thinner and more fragile. In addition, the blood flow is lower, and as a result, even minor trauma can easily produce thrombosis. When we empty the vein of blood, its walls collapse and adhere to each other, making it difficult to localize the lumen of the vein.

Microdissection
Under high magnification, we separate the vein from the femoral artery carefully prepare the muscular branch over a length of 1-2 mm, and section it after ligation or bipolar cauterization. At this moment in time you should make sure that the femoral vein is completely freed from its surrounding tissues, between the inguinal ligament and the emerging site of the superficial epigastric branch, and that the vein does not contain any thrombi. When checking for thrombi you should slide the instrument along the length of the walls of the vein (thrombi will appear as brown spots). If there are thrombi in the vein, you should abandon the versel and restart the exercise in the contralateral area.


The graphics show the infrarenal section of the abdominal aorta and the inguinal region with the femoral vessels and the epigastric branch (left) and the prepared femoral vessels (left) (Yonekawa 1999, Acland 1989)

• Work in a clean field with as little blood present as possible.
• Keep your microscopic image clear and focused at all times.
• Dissect, retract, and pick up only in those areas where you have perfect visual control over the active parts of your instruments.
• Stop if a problem occurs, be it bleeding or spasm. You should continue the dissection only after the problem has been solved.

Place a piece of background material underneath the prepared vessel. This will ensure a clear view of the fine details and prevent you from confusing the surrounding tissues during suturing. Before placing the microapproximator you should check to be sure that (1) the vessel is clean and free of any coagulated blood or tissues, (2) both clamps can be opened easily, and their jaws overlap perfectly, (3) both clamps move easily on the bar that holds them together.
We pick up the caudal portion of the artery by its adventitia, lift it and place it within the open clamp of the approximator. We open the second clamp (the cranial one), pick up the artery again, and place it between the jaws of the clamp. This was we produce a supplementary vasodilatation. Make sure that the vessel is not twisted.