Fine work with reliable accuracy is made possible in microsurgery with the aid of an operating microscope or magnifying loupes, and the refined techniques and skills can be acquired only by many hours of practice. In this regard, training in the laboratory has proven a key factor before a surgeon can make a successful clinical contribution. Before participation in complex cases of complete or incomplete nonviable amputations, surgeons need to demonstrate adequate experience and skills acquired in the laboratory, where devotion of adequate time, practice and patience are prerequisite to performing small vessel anastomosis.
Microsurgical procedures are performed on small structures that require magnification. Magnification can be achieved with an operating microscope or ocular loupes. Although several types and models of operating microscopes are currently available, similar general principles apply to the use of most. In general, a magnification of 6x and 10x is used for dissection and exposure of small nerves and vessels, while microsurgical repair of vessels and nerves requires 16x and 25x magnification.
While magnification from 16x to 40x is provided by the microscope and is essential when working with structures less than 1 mm in diameter, many procedures may be performed using magnifying loupes of up to 5x. Ocular loupes are invaluable tools for anastomosis of large vessels (diameter 2-3 mm) or for the initial dissection.
Microvascular instruments are extraordinarily delicate so as to allow the surgeon to execute very precise procedures. Although a variety of specialized instrumentation exists, for the most part microvascular procedures require three or more straight and curved jeweller's forceps for manipulating fragile tissues:
• Fine suture, microscissors with blunt edges for fine dissection
• Microscissors with serrated blades for cutting without crushing the intima of the vessel
• Microvascular clamps with a closing pressure of less than 30 g per square millimetre to avoid damaging the vascular intima of small vessels and causing subsequent thrombosis.
The patency rate obtained in microvascular anastomosis is dependent upon the skills learned in the laboratory and
Fig. 14.3.1a,b End-to-end microvascular anastomosis. a Once the vessel ends are placed in a bar clamp, the two-stay sutures can be placed 120° apart. A suture is then placed in between the stay sutures in the anterior wall, followed by the even placement of subsequent sutures. The clamped vessel is then turned 180° to show the posterior wall. b A stitch is placed 120° from the initial stay sutures in the posterior wall, followed by evenly spaced sutures in between. Common technical errors during microvascular anastomosis include sutures catching on the back of the vessel, suturing the side wall of the vessel, sutures which are poorly placed and fail to fully penetrate the vessel wall, and uneven spacing of sutures with poor approximation of intima. The figure shows correctly placed sutures
Fig. 14.3.1a,b End-to-end microvascular anastomosis. a Once the vessel ends are placed in a bar clamp, the two-stay sutures can be placed 120° apart. A suture is then placed in between the stay sutures in the anterior wall, followed by the even placement of subsequent sutures. The clamped vessel is then turned 180° to show the posterior wall. b A stitch is placed 120° from the initial stay sutures in the posterior wall, followed by evenly spaced sutures in between. Common technical errors during microvascular anastomosis include sutures catching on the back of the vessel, suturing the side wall of the vessel, sutures which are poorly placed and fail to fully penetrate the vessel wall, and uneven spacing of sutures with poor approximation of intima. The figure shows correctly placed sutures upon careful attention and awareness of factors that influence the success of patency . Minimal, no more than 1-2 mm, advential stripping is recommended in order to visualize the lumen and avoid an excess of adventitia that can invert and occlude the lumen. On the other hand, extensive stripping of the adventitia can lead to necrosis of the advential wall at the anastomosis site (Fig. 14.3.2). Interrupted suturing is the technique of choice in contrast to a running suture that can cause unacceptable constric tion of the lumen. A few interrupted sutures are preferable to an excessive number, as the latter may produce increased areas of vessel wall necrosis that could subsequently lead to scar formation and intimal proliferation and necrosis. Furthermore, excessive suturing may cause added deformation of the ends of the vessel, causing exposure of more collagen of the tunica media to blood flow and, in turn, producing clot aggregation and thrombus formation .
Suturing of the vessels must be done on healthy tissue and under no tension. In general, correct tension can be indicated by a small loop of suture visible through the opposed vessel walls. In addition, the tension should be such that the suture does not break while knotting. The diameter of this loop should be equal to the thickness of the wall . Although perfusion of the lumen of the vessel is not always necessary since it may induce damage to the intima, irrigation of the edges of the vessel to remove any residual traces of blood is helpful.
Once anastomosis has been achieved, patency is evaluated. A simple patency test is to inspect the fullness and pulsation of the vessel or to gently palpate the site of anastomosis. However, the most reliable patency test is the "empty-and-refill" or "milking test" performed by clamping the artery proximal to the anastomosis site with forceps and then milking the vessel distal to the anastomosis site using different forceps, thus creating an empty vessel pocket. Once an empty segment has been obtained, then the proximal forceps are released. If the vessel is patent, then the empty space should show blood flow and rapid filling.
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