5.1 Vascular Suturing

The walls of small arteries consist of three layers: the intima, which faces the lumen; the media; and the adventitia, which is the outermost layer. The intima consists of a monolayer of endothelial cells and internal elastic lamina. Smooth muscle cell proliferation and atheromatous plaques are usually observed in intima of aged patients. The media occupies up to 80% of the thickness of the vascular wall and, depending on the order of segments of arteries, includes varied layers of smooth muscle cells, a small amount of elastic fibers, and a collagen framework. In small terminal branches of cerebral vessels, the elastic fibers of the media are usually absent, and the media consists mostly of reticulin fibers and smooth muscle cells. Of the three layers, the media provides the most strength for the vascular suture because of its pronounced collagen network. ¹ The adventitia has the highest thrombogenic properties.

There are several basic requirements for microvascular sutures. Correctly placed sutures will:

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  Permit no major leakage from the vessel

  
  
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  Allow precise coaptation of the intima

  
  
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  Be durable

  
  
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  Cause no narrowing of the lumen

  
  
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  Leave no sutures or adventitia in the lumen

The main requirement for a vascular suture is that it is tight enough to prevent leaks. The choice of appropriate needles and sutures is one of the most important factors for successful vascular suturing. Most microsurgical needles are curved, although straight needles are sometimes used for end-to-end microanastomosis. Inexpensive, nonsterile sutures can be chosen for training; however, only special vascular needles should be used for surgery. The following sizes of sutures are usually used: 11–0 for a vessel diameter of less than 1 mm, 10–0 for a vessel diameter of 1 mm, 9–0 for a vessel diameter of 2 mm, and 8–0 and larger for a vessel diameter of more than 2 mm. The carotid artery is sutured with 6–0 sutures.

In anastomosis of two vessels of unequal sizes, approximation of the vessel walls should be performed only within their natural elasticity by slight stretching. Overstretching of the vessel wall can damage the intima or the entire wall and can result in bleeding or thrombosis during or after the surgery. Weakness of the vascular wall at the anastomosis may also result in aneurysm formation.

The suturing must be precise, and the connection of intimal layers is very important in vascular suturing. The muscular membrane or the adventitial cover must not get into the lumen of sutured vessels; otherwise, they may cause thrombosis and failure of the anastomosis.

When all the knots on one side have been formed, the vessels should be turned to check the quality of the sutures from inside. The common mistakes are shown in Fig. 5.1.

5.2 Exercise: End-to-End Anastomosis on Rat Carotid Arteries

This exercise simulates rare neurosurgical situations where end-to-end anastomosis is needed, primarily for in situ intracranial reconstructions. Performing end-to-end anastomosis is a relatively straightforward task (Fig. 5.2, Video 5.1). However, there are several critical nuances that can make suturing either easy and successful or difficult and unsuccessful.

To begin, you should prepare and dissect a clean and wide operative field with sufficient length of vessel available. Next, apply the clip approximator in either of the two ways. The first and most common method is to place it horizontally for the front wall exposure and then to rotate it 180 degrees for the back wall exposure. This procedure can be used if the vessel length allows for this degree of axial rotation. The second method is to apply the clip approximator vertically, then rotate it 90 degrees in one direction for front wall exposure, and then 90 degrees in the other direction for back wall exposure. This method can be used for short vessels that do not allow much axial rotation. If no rotation is possible, which is relatively common, then the back wall can be sutured from the inside, like in a side-to-side anastomosis, or you can use a single stay suture technique.

Adventitia should be cleaned from the vessel ends for a distance that allows for safe and convenient vessel end approximation and for choice of the needle puncture site, usually about half the diameter of the vessel. Arteries will be in a contracted state at this step, so you may want to dilate them with a dilator or forceps, which will help you to make even spaces between the sutures later. Stay sutures are commonly used in microsurgical practice for end-to-end anastomosis because they help to hold the vessel lumen open. When used, stay sutures are placed in the free ends of the arteries and are secured in slits of a silicon dam or on an approximator. However, in neurosurgery, arteries are usually not as small, so this step can be omitted. In addition, an approximator does not always fit in the space available in operative approaches within the brain, so they are less likely to be used in actual surgery.

There are three common strategies for beginning interrupted vascular suturing with stay sutures: two stay sutures may be placed 180 degrees apart ² ; two stay sutures may be placed 120 degrees apart ³ ; or one stay suture may be placed in the back wall and suturing continued from both sides. ⁴

While suturing, gently grab the vessel wall by the remaining adventitia with forceps and avoid applying pressure to the media and intima. Use the counter-press technique for passing the needle. For end-to-end anastomosis on a rat carotid artery, eight sutures are usually enough, but additional stitches should be applied if needed. Do not hesitate to check the lumen from inside, as it is better to know whether the back wall is captured before all sutures are tightened. Usually in small vessels, walls are semitransparent, so if the needle can be seen through the wall, it means the needle is usually under only one layer, but if it is not seen, it is usually under two layers, meaning that the opposite wall of the vessel has been inadvertently captured by the needle and trapped into the knot, which should be avoided. When the anastomosis is finished, check for bleeding, achieve hemostasis as necessary, and check the blood flow through anastomosis.

You can perform multiple end-to-end anastomoses on different vessels from the same animal and combine these anastomoses with other types of anastomoses. We advise trying three different techniques for placing the stay sutures and different vessel orientations to bring variety and interest to your training sessions.

5.3 Exercise: End-to-Side Anastomosis on Rat Carotid Arteries—Continuous Suture

This exercise simulates the technique needed to create a superficial temporal artery-to-middle cerebral artery anastomosis in the end-to-side fashion. The carotid arteries are preferred over the femoral arteries for this simulation because femoral vessels are considerably smaller than the middle cerebral arteries. This exercise can be completed twice on one animal. Because rats usually have a well-developed circle of Willis, they can easily tolerate occlusion in one carotid artery, when a survival experiment is planned.

The approach to the carotid arteries is described in Chapter 4. After the arteries are dissected free from the periadventitial tissues, one artery is chosen as a donor and another as a recipient (Fig. 5.3). A stepwise description of the end-to-side anastomosis technique on rat carotid arteries is presented in Fig. 5.4. The donor artery is clipped proximally and distally, then cut at the distal end and rotated across the midline to the contralateral side. The path depends on the available length of the transferring carotid artery. A long artery can be moved across the midline in front of the trachea, while a shorter vascular pedicle can be passed behind the trachea. The distal end of the donor artery is ligated.

Linear arteriotomy on the recipient vessel is begun using an unused 27-gauge needle and continued with microscissors. The techniques for tailoring the donor vessel optimally and end-to-side anastomosis are described in Chapter 3 (Figs. 3.31, Fig. 3.32). Trainees can practice classic fish-mouth tailoring first to understand how much of a toe is required to achieve an optimal angle for enlargement of the anastomosis. Heparinized saline should be used to keep the tissues moist. Fig. 5.4 and Video 5.2 show the creation of an anastomosis with continuous suture. After placing the toe and heel stay sutures, suture the back wall first and proceed with the easier front wall last. Before tying the last knot, temporarily release the distal clip to wash out possible thrombus and air.