1、 Operation skills and precautions of microvascular anastomosis

Microvascular anastomosis is a decisive step in microsurgical repair. In operation, because of incomplete debridement of vascular injury, surgical trauma, poor vascular anastomosis, poor blood supply of vascular bed, postoperative local hematoma formation, vasospasm, improper immobilization, infection and other factors, anastomotic vascular stenosis or thrombosis can be caused, leading to failure of operation. A well-trained physician should try to avoid the occurrence of the above adverse factors and ensure the success of the operation.

（1） The difference between laboratory ability and clinical ability

The doctors who have acquired the skill of anastomosing blood vessels in the laboratory have laid a solid foundation for their clinical microsurgical work. However, there is a significant difference between the laboratory work ability and clinical work ability, which should be paid attention to by beginners. The clinical conditions of donor site and recipient site are changeable, and the conditions of vascular anastomosis in laboratory are relatively simple. In clinical practice, two anastomotic vessels may have different caliber, different direction, different wall thickness, different vascular bed and different position, which may cause difficulties in vascular anastomosis. A new microsurgery doctor should be prepared for these factors and take corresponding measures for various changes.

In the laboratory operation, doctors can have a comfortable seat for vascular anastomosis. But in clinic, especially in the microsurgical tissue transplantation of head and neck, the doctor can only stand for vascular anastomosis, and the elbow and wrist have no good support, which brings great difficulties to the operation.

（2） Identify whether the anastomotic vessels are normal or not

The choice of normal blood vessels for anastomosis is the premise of successful operation. The normal arterioles or venules are in the state of filling, lying in the soft tissue, with loose connective tissue around them. The wall of the tube is soft. After cutting off, the inner wall of the lumen is milky white, clear, and the intima and media of the vessels are closely connected. It is difficult to distinguish the boundary under the 8-10 times operating microscope. After trauma, such as avulsion injury, crush injury, electric injury, radiation injury or inflammation, the blood vessels lose their normal shape. During operation, the diseased blood vessels should be removed until they are completely normal to ensure successful anastomosis. Based on the experience of thousands of emergency or selective microsurgery cases in our hospital, the authors feel that the following vascular conditions are not suitable for vascular anastomosis, which can only be performed after the diseased vessels are completely removed.

1. Purpura sign: there are purplish plaques on the wall of blood vessels. One is scattered or dense purplish plaques. It is common in crush avulsion injury, causing bleeding in the wall of blood vessels. Only when the blood vessels with purpura are removed to the normal part, can vascular anastomosis be carried out. The other is that the blood vessels are long strips of blue and purple, which often appear in the small arteries. This is often because the branches of the small arteries are broken, there is no knot, and hematoma is formed under or around the small arteries. This kind of blood vessels do not need to be resected in the whole section. It is only necessary to cut the adventitia, remove the lingering hematoma, find the bleeding place of the small artery branches, and ligate them for anastomosis.

2. Segmental sign: common in small artery injury. When the adventitia of small arteries is removed, the blood vessels alternately present a thick and thick section, and a thin and empty section. This is often due to the avulsion injury of blood vessels, resulting in the rupture of the inferior part of the adventitia, or the rupture of the media and intima. This kind of blood vessels can also be seen in the tissue transplantation with blood vessels after a long period of hypoxia. Only by removing the damaged blood vessels can the anastomosis be achieved.

3. Pump sign: common avulsion injury of small artery. The results showed that the intima was swollen and separated from the media, the gap between the two was obviously enlarged, the milky white intima extended out of the vascular orifice, while the media and adventitia contracted back, like a telescope tube. This kind of situation is often seen in long-term traction of blood vessels during free flap transplantation, or because of long-term spasm of blood vessels and long-term hypoxia. In the author's impression, this manifestation is more common in elderly patients and may be related to arteriosclerosis. This segment of blood vessel should be completely removed until the normal lumen, intima and media are closely attached, and there is no obvious separation of intima and media under 8-10 times microscope.

4. Reticular sign: it is a symptom before vascular embolism. There are more or less silver filaments in the vascular lumen, attached to the vascular intima. It is often caused by the injury of vascular intima or the involvement of adventitia in anastomotic stoma, so it is named because of the network of cellulose deposition in the lumen. For this kind of vessels, the damaged part of intima should be removed, the cellulose in the lumen should be removed, and the lumen should be washed thoroughly until the inner wall is smooth and free of foreign bodies.

5. Thrombosis: there is thrombosis in the vascular cavity. It can be seen in arterioles and venules, white thrombus and red thrombus, the latter is common in blocked venules. Where there is white thrombus, often caused by vascular injury, must remove the thrombus, cut off the damaged blood vessels, until the normal place. Red thrombus can be seen in the distal end of the blocked vein, and its vascular intima is not necessarily accompanied by damage. Therefore, the blood vessels with red emboli can be removed effectively, and they can still be anastomosed if the intima is not damaged.

6. Vascular compaction sign: it is the manifestation of pathological changes in blood vessels and vascular bed. The stiff blood vessels are embedded in extensive scars. The blood vessels are thin, hard and pale, and there is no obvious boundary with the surrounding scar tissue. The sclerotic tissue is like a plate. If the blood vessels were separated, the wall of the blood vessels was thickened, the pulsation of the arteries was not obvious, and the veins lost their softness and deformability. Cut off the artery, it can be seen that the lumen is seriously narrow, the diameter of the artery is more than 1 mm, its lumen is like the tip of a needle, only slow bleeding, no active bleeding. These manifestations of blood vessels can be seen after electric injury, Volkmann contracture after avulsion injury, tumor tissue infiltration, and chronic inflammation, especially after radiotherapy. These vessels should be resected until they are normal; Or another healthy blood vessel was taken for anastomosis.