Indications for implantation of a vascular prosthesis in hemodialysis. Vascular access for hemodialysis. Synthetic vascular grafts made of Dacron

Purpose of the work: to study the possibility of creating a native permanent vascular access on the upper limb in patients with end-stage chronic renal failure in type II diabetes mellitus. Materials and methods. The study included 108 patients with type II diabetes mellitus and end-stage chronic renal failure. 130 operations were performed to form arteriovenous fistulas in the lower third of the forearm, the middle third of the forearm, and the cubital fossa. When analyzing treatment results, we took into account the frequency of stenosis, thrombosis of native permanent vascular access, and the number of reoperations over three years. Results. When forming a native permanent vascular access in the lower third of the forearm in 86 patients, early complications developed in 17.4% of cases (thrombosis, low blood flow velocity), late complications - in 7% (stenosis, thrombosis of the fistula vein). When applying an arteriovenous fistula in the middle third of the forearm between v. cephalica and a. radialis (12 patients), 1 patient (8.3%) developed arterial thrombosis after 1.5 years. There were no complications when creating vascular access at the level of the cubital fossa (10 patients). The overall incidence of complications was 20.4%. After repeated operations, arteriovenous fistulas retained their functional viability. Conclusions. The results obtained indicate the possibility of forming a native arteriovenous fistula on the upper limb for program hemodialysis in patients with end-stage chronic renal failure in type II diabetes mellitus. The complications that developed were successfully eliminated as a result of repeated operations, after which the arteriovenous fistulas retained their functional viability.

diabetes.

terminal chronic renal failure

arteriovenous fistula

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Diabetes mellitus (DM) is one of the causes of end-stage chronic renal failure (ESRD) due to progression diabetic nephropathy. Programmed hemodialysis (PGD) remains the leading treatment method for patients with end-stage chronic renal failure (ESRD). The effectiveness of PGD is largely determined by the adequacy of the vascular access - arteriovenous fistula (AVF). Permanent vascular access (PVA) should ideally ensure that the blood flow velocity matches the prescribed dialysis dose and function for a long time without complications. Currently, there is no ideal version of PSD, but native AVF is considered optimal. The duration of operation of an AVF is about 3-5 years and decreases due to the development of complications that require repeated surgical interventions (thrombosis, stenosis, steal syndrome, etc.) and are the cause of re-hospitalization and increased costs of treating patients. The number of patients undergoing PGD is increasing every year, the proportion of elderly patients suffering from diabetes mellitus and cardiovascular diseases is growing, which explains the technical difficulties in the formation of PSD and the increase in the number of reoperations. Formation of PSD using synthetic vascular prostheses (SVP) is technically simpler compared to the formation of native AVF, but significantly reduces the time of operation of SVP as a vascular access due to complications, as indicated by publications of domestic and foreign authors. Numerous studies are devoted to planning issues, types of PSD, and tactics options for the development of complications. Despite the fact that in last years Although significant progress has been made in dialysis technology, the problems associated with providing PSD to patients with type II diabetes remain unresolved.

The purpose of this work was to study the possibility of creating a native permanent vascular access on the upper limb in patients with end-stage chronic renal failure in type II diabetes mellitus.

Materials and research methods

The work was carried out on the basis of the Municipal Clinical Hospital No. 1 in Orenburg, the Municipal Clinical Hospital No. 1 in Novotroitsk, the Municipal Clinical Hospital No. 1 in Orsk, the Municipal Clinical Hospital No. 1 in Buzuluka, Orenburg Region, and Emergency Hospital. Aktobe and CDEC "BIOS" Aktobe of the Republic of Kazakhstan in 2007 - 2013. The study included 108 patients with type II diabetes mellitus and end-stage chronic renal failure (47 men, 61 women; aged 18 to 72 years), who gave voluntary informed consent. 130 operations were performed to form an AVF in the lower third of the forearm, the middle third of the forearm, and the cubital fossa. According to the location of the primary AVF, the patients were divided into three groups: the 1st group included 86 patients with the AVF located in the lower third of the forearm; in the 2nd - 12 with AVF localization in the middle third of the forearm; in the 3rd - 10 with localization in the ulnar fossa. In all patients, the PSD was formed on the non-dominant upper limb.

Preoperative examination of patients included standard determination of indicators general analysis blood levels, urea levels, creatinine, total protein, fibrinogen, prothrombin index, clotting time, activated partial thromboplastin time, international normalized ratio, as well as visual examination of the upper limb, venous tourniquet test, Allen test, ultrasound examination of the vessels of the upper limb for choosing the optimal location for the formation of the AVF.

Surgical interventions were performed under local anesthesia, taking into account the data of the preoperative examination. A permanent vascular access was formed in the distal part of the forearm between the a.radialis and v.cephalica as an “end to side” artery. In the middle third of the forearm between a.radialis and v.cephalica there is an “end to side” artery. In the ulnar fossa between a.radialis or a.brahialis and v.cephalica or v.basilica, an “end to side” artery.

When analyzing the treatment results, we took into account the frequency of stenosis, AVF thrombosis, and the number of repeated operations to create vascular access for program hemodialysis for at least three years after the first surgical intervention.

Research results and discussion

An analysis of the results of the formation of vascular access for hemodialysis in 108 patients with end-stage chronic renal failure in type 2 diabetes mellitus for 2007 - 2012 was carried out.

For patients of the first group (86 patients), permanent vascular access was formed in the distal part of the forearm, between v. cephalica and a. radialis type “the end of the vein into the side of the artery.” In the early stages (2 - 7 days), 15 patients were operated on again. In 5 patients, due to low blood flow velocity in the fistula vein due to fibrosis of the latter, a low-effective AVF was eliminated within up to 7 days with the formation of a proximal arteriovenous fistula at the level of the cubital fossa between a. brahialis and one of the veins: v. cephalica, v. basilica, v. intermedia or v. perforans of the “end to side” type of artery. In another 10 patients, due to early thrombosis of the AVF, a repeat intervention was performed within 2-4 days after the first operation: in 6 patients - the formation of a new AVF between the same vessels 1-2 cm proximal to the previously performed anastomosis (the thrombosed anastomosis was not removed ), and in 4 patients, due to the development of phlebitis, a new AVF was formed at the level of the cubital fossa between a. brahialis and one of the veins: v. cephalica, v. basilica or v. intermedia as an “end to side” artery. In the latter case, the thrombosed anastomosis was also not removed.

At a later date, after 1.5-2 years of functioning of the distal AVF, in 6 patients, due to the development of stenosis of the fistula vein with thrombosis (without signs of phlebitis), an arteriovenous fistula was formed 1-2 cm proximal to the previous anastomosis between the same vessels . These patients had no previous operations for AVF dysfunction.

Thus, in the first group of patients, 15 (17.4%) patients were re-operated in the early stages and 6 patients (7%) - after 1.5 - 2 years of AVF operation. After repeated operations, the patients had no new complications, and the AVFs retained their functional capacity.

In patients of the second group (12 patients), the primary formation of the PSD was performed at the level of the middle third of the forearm between v. cephalica and a. radialis and “end to side” type arteries in the subcutaneous fat (with mandatory mobilization of a. radialis over 3 - 4 cm). There were no complications or reoperations in the early stages in this group. In one patient, after 1.5 years of AVF operation, due to the development of arterial thrombosis of the vascular access, arteriotomy, thrombectomy, and excision of the anastomotic zone were performed with the formation of an arteriovenous fistula in the same place. Thus, the rate of reoperations in the second group was 8.3% (1 patient), and the newly formed AVF retained its functional capacity for three years.

The primary formation of permanent vascular access in the cubital fossa (third group) was carried out in 10 patients with arterial hypotension, as well as scattered veins and severe calcification of the arterial wall on the forearm, identified during ultrasound examination. Vascular anastomosis was formed according to the “end to side” type between a. radialis (with a high division of a. brahialis into a. radialis and a. ulnaris) or a. brahialis and any suitable vein (v. cephalica, v. basilica, v. intermedia or v. perforans). To prevent retrograde arterial blood flow along the venous bed, the tributaries and anastomoses of the vein used were ligated distal to the formed fistula. If possible, form a vascular anastomosis with v. cephalica, this option was preferred as the most convenient in terms of operation. Anastomosis between a. brahialis and v. basilica is technically easier to form, but the length of the fistula vein suitable for puncture is very limited. In this case, we performed superficialization v. brahialis simultaneously or in the second stage, depending on anatomical structure vascular bed. There were no reoperations in patients in this group.

Thus, the results obtained indicate that the formation of a native arteriovenous fistula (without the use of synthetic prostheses) for PGD in patients with ESRD can be performed against the background of diabetes mellitus. The use of vessels in the distal third of the forearm to create an AVF results in a certain percentage of reoperations due to the development of stenosis and thrombosis of the fistula (maximum - 24.4% when creating vascular access in the lower third of the forearm and in general - 20.4%). However, the number of such complications is comparable to the level indicated by foreign authors during similar operations in the general population.

The formation of an AVF at a higher level is accompanied by a sharp decrease in the frequency of reoperations due to a decrease in the number of complications. However, the imposition of proximal arteriovenous fistulas often leads to the development of the limb “steal” syndrome, its chronic ischemia, overload of the right heart with the development of heart failure or an increase in the severity of the latter. When choosing the level of AVF formation in patients of this category, a competent and complete assessment of the state of the vascular bed in each individual patient is necessary, which leads to a significant reduction in the number of thrombosis and repeated operations to create vascular access.

We did not use polytetrafluoroethylene prostheses in patients with diabetes mellitus undergoing program hemodialysis due to high risk thrombosis, infectious and ischemic complications associated with implantation of synthetic vascular prostheses.

conclusions

The results obtained indicate the possibility of forming a native arteriovenous fistula on the upper limb for program hemodialysis in patients with end-stage chronic renal failure in type 2 diabetes mellitus.

Developed complications (stenosis, thrombosis; 20.4% overall) were successfully eliminated as a result of repeated operations, after which the patients had no new complications, and the arteriovenous fistulas retained their functional viability.

Reviewers:

Abramzon O.M., Doctor of Medical Sciences, Professor of the Department general surgery, OrgMA, Orenburg.

Demin D.B., Doctor of Medical Sciences, Head of the Department of Faculty Surgery, OrgMA, MBUZ "Municipal City clinical Hospital them. N.I.Pirogov", Orenburg.

Bibliographic link

Hemodialysis is a procedure for purifying the blood in patients whose kidneys cannot cope with this function. A fistula is a natural or artificially created fistula, that is, a channel that connects any body cavities or a cavity with the external environment. An arteriovenous fistula for hemodialysis is an artificial fistula necessary for access to the blood system. The essence of the operation is that the artery is connected directly to the vein, due to which the vessel thickens, and it becomes easier to connect it to a blood purification device (“artificial kidney”).

Indications for surgery

The most common indication for hemodialysis is chronic renal failure. It is also necessary for poisoning by toxins or poisons. U healthy person The kidneys act as a kind of filter, control the amount of water in the body and cleanse the blood of toxins. In 5 minutes, absolutely all the blood passes through the kidneys and circulates through the vascular bed. In one day, the kidneys manage to filter more than 180 liters of blood, while toxins are excreted in the urine.

In case of chronic renal failure, the blood must be filtered artificially, since the patient’s body cannot cope with this task. For these purposes, special devices were developed. With chronic dialysis, that is, the patient is regularly connected to the device, it is necessary to have constant access to the vascular bed. To do this, simple operations are performed to create a fistula, which will allow obtaining the maximum amount of blood for purification.

Method of operation

Before surgical intervention the patient must undergo complete medical examination. Doctors pay attention not only to the condition of the kidneys and urinary system, but also take blood for analysis, examine the heart and blood vessels. The fistula for hemodialysis is located on the forearm, and the operation itself takes place in several stages.

1. The procedure is performed under local anesthesia. After this, the surgical access site is disinfected.
2. Next, a skin incision is made on the forearm, the artery is exposed, it is ligated and all its lateral branches are blocked.
3. Then the surgeon works with the vein at a distance of 4-5 cm from the artery. You need to do the same manipulations with it as with the artery.
4. Next, these two vessels need to be sewn together. To do this, a small longitudinal incision (2─2.5 cm) is made so that a suture can be placed on the edges of the vessels.
5. At the end of the operation, the wound is sutured layer by layer and covered with a bandage.

After the procedure, time must pass until the fistula forms. During the first week, the patient must be in the hospital so that doctors can constantly monitor him. Discharge usually occurs on days 7-10, but even after that the patient comes to the hospital for examination. Hemodialysis using a fistula can be performed no earlier than a month after surgery.

Postoperative care

A mature arteriovenous fistula looks like an abscess on the forearm. If treated properly, it can last for many years and even decades without complications. To do this, the patient needs to get used to it and follow some instructions:

• do not put pressure on the arm on which the fistula is located (do not sleep on it, do not wear jewelry or clothes with tight sleeves);
• exclude physical exercise(you can use your hand in everyday life, but sports will be contraindicated);
• do not measure pressure on this arm;
• listen to the noise ─ it should be the same all the time;
• if possible, do not provoke jumps blood pressure.

You need to understand that with any pathologies you need to consult a doctor. If the nature of the blood noise in the fistula has changed or bleeding does not stop for a long time after dialysis, the patient needs to be examined. An increase in local temperature should also be a cause for concern - this fact indicates the presence of inflammation. This situation can happen if hygiene is not maintained, especially after dialysis.

The patient must constantly raise his hand to his ear and listen to the noise. It should be drawn out, constant and rhythmic. This sound resembles the operation of mechanisms and is formed when blood moves through the veins. Any disturbance of this sound is a reason to consult a doctor. Decreased hearing or complete absence sounds indicate the formation of blood clots that must be removed surgically.

At first, many patients are afraid to touch the fistula and use their hand, but then they get used to the new way of life. You can and should touch it - this is the only way to feel the movement of blood through the connected vessels and control the local temperature.

There is no need to worry that light household loads will be harmful. On the contrary, moderate movements will prevent blood stagnation and keep the fistula in working condition for a long time.

Advantages of arteriovenous fistula over other methods

An arteriovenous fistula is not the only way to gain access to the vascular bed for hemodialysis. Artificial fistulas, subclavian or femoral catheters are also used. There is also a method of peritoneal dialysis, which does not require vascular access. Sterile liquid is poured through a special catheter tube directly into the abdominal cavity, and the filter in this case is the peritoneum. Then the solution is drained.

However, arteriovenous fistula is considered the best option for the patient and if there are several options, it is chosen. There are several reasons for this:

• To create a fistula, the patient’s own tissue is taken, which cannot cause rejection or allergies, unlike artificial materials.
• The fistula is located just under the skin and is easy to use to gain access to blood.
• The risk of infection, as well as the formation of blood clots, when this method minimal.
• The same fistula can last for many years if properly cared for.

The result of treatment depends not only on hemodialysis, but also on the responsibility of the patient himself. Arteriovenous fistula is one of the most gentle and affordable options for chronic renal failure. Compared to other methods of blood purification and kidney transplant surgery, this procedure is the safest.

Disadvantages and possible complications

Unfortunately, this method is not suitable for all patients. If the patient has low blood pressure or anemia, after suturing the vessels, a fistula may not form. In this case, it will be impossible to access the vessel through a non-working fistula. Among the disadvantages, one can also highlight the duration of fistula maturation. The first hemodialysis can be performed only a month after the operation.

Complications occur in rare cases. Among them are possible:

• formation of an aneurysm (expansion of the walls of blood vessels with the danger of their rupture);
• decreased or loss of sensitivity in the hand;
• insufficient oxygen supply to the myocardium;
• compression of the carpal (wrist) nerve, which can cause the hand to function less well.

Complications appear in isolated cases. You need to understand that chronic renal failure is a disease that the patient will have to fight all his life. In this case, a person needs to get used to a new lifestyle, constant procedures, prohibitions and diet. A hemodialysis fistula allows for regular blood purification without any particular danger to the body.

Carrying out a blood purification session using hemodialysis requires access to the patient’s circulatory system, the purpose of which is to obtain a sufficient volume of blood to pass through the dialyzer and return to the body. The more blood is purified in the dialyzer, the more effective hemodialysis is.

There are temporary and permanent vascular accesses to provide program hemodialysis. The first are used for emergency connection of a patient to equipment in case of threatening conditions or the inability to use permanent access, the second - for a long time ensure the purification of the patients’ blood and thereby the possibility of a full life.

The main temporary access is catheterization of the main veins with special single- or double-lumen catheters, which provide blood sampling and return after purification in the dialyzer. The most common technique for installing catheters in central veins is the Seldinger method. Catheterization of the femoral veins is used (not allowed when planning donor kidney transplantation) and internal jugular vein. The latter technique has significant advantages, since it less often leads to vascular stenosis and provides a high level of blood flow. Catheters for catheterization of great vessels are produced industrially in the form of special sterile kits, which include the catheters themselves and additional devices: a guide wire, puncture tunnel expanders, puncture needles, a scalpel, suture material etc., which allows manipulation to provide vascular access in the shortest possible time. The period of use of such catheters is 14-21 days.

There are also so-called permanent catheters for long-term dialysis therapy. They are used in cases of recurrent thrombosis of arteriovenous fistulas, with low blood pressure (BP) in the patient, with small caliber peripheral vessels that prevent the formation of permanent accesses for hemodialysis. A distinctive feature of permanent catheters is the presence of Dacron cuffs on their surface, which are located in the subcutaneous tunnel, firmly fixing the catheter and preventing infection of its bed. Such catheters, when properly hygiene care and regular flushing of the lumen with heparin solution, can function for several years.

Arteriovenous fistulas for program hemodialysis - the main type of vascular access for connecting artificial kidney devices. The principle underlying the functioning of arteriovenous vascular anastomosis on the extremities is to create a constant discharge of blood from the artery to the vein, which prevents thrombus formation and makes it possible to regularly and high-volumely receive blood for purification in the “artificial kidney” apparatus. The most widespread are the Cimino and Breshia fistulas, in which, using microsurgical techniques, a vascular anastomosis is formed between the radial artery and the cephalic vein in the lower part of the forearm. The wound is sutured tightly and no artificial materials are used to drain blood. Within a short time (3-4 weeks), arterialization of the cephalic vein occurs with expansion of its lumen and thickening of the walls. The volume of blood passing through such an anastomosis reaches 150 ml/min and higher. The section of the arterialized vein is punctured with two fistula needles to obtain blood and return it after the cleansing process in the dialyzer. Other vascular accesses are also used using the principle of arterialization of veins various localizations. If there are no main veins suitable for puncture on the lower or upper limbs venous autografts are used, for example from the great saphenous vein of the thigh, placed in the form of a loop or a direct bridge between a large artery and vein. Special synthetic prostheses are also used as a vascular graft, which can be long time puncture and continue program hemodialysis. The formation of an AVF using any method is carried out in sterile operating room conditions using microvascular equipment (magnifying glass or microscope, microvascular atraumatic needles and instruments). Within 3-4 weeks, arterialization of the vein occurs, which becomes suitable for repeated punctures with fistula needles. Sometimes, due to the deterioration of the patient’s condition, it is necessary to start connecting the equipment at an earlier date, otherwise you may encounter an increase in the number dangerous complications- bleeding out and into subcutaneous tissue, anastomotic thrombosis, etc.

In this regard, emergency hemodialysis sessions must be performed through an external catheter in one of the main veins. In this case, the formation of AVFs is carried out in a planned manner and a period for their “maturation” is maintained. Only later can you switch to

use the puncture method to access the vessels, and then remove the catheter from the vein. Table 5 shows the indications for the use of various vascular accesses for hemodialysis in different categories of patients with acute and chronic renal failure.

A vascular graft is a human-made tube that replaces or bypasses a real blood vessel, most often an artery. The successful development of vascular prostheses is an outstanding event of our time. The first vascular graft was developed in 1960. Since that time, dramatic changes have taken place to improve the quality of the material used. Modern dentures are widely recognized as reliable and trustworthy. Vessel replacement surgeries have become traditional, and hundreds of thousands of people have been successfully treated.

To understand the need to replace a damaged vessel, you should consider the work of cardio-vascular system. All parts of the human body require blood to be delivered to them. Blood carries oxygen and nutrients to every cell of the body. Blood is distributed throughout the body through the vascular system, which consists of the heart, arteries and veins. The heart is a high-quality pump that works tirelessly throughout life to pump blood into the arteries. Arteries are tubes that distribute blood throughout the body. The arteries divide into branches, which become smaller and smaller until they become microscopic capillaries. In capillaries, oxygen and nutrients can easily leave the blood and enter tissues and organs. After the blood passes through the capillaries, it enters the veins, which carry the blood back to the heart to the right side. The right parts of the heart send blood to the lungs, where they are enriched with oxygen and flow to the left parts of the heart to be sent throughout the body again. This cycle keeps us alive. Normally, our heart beats more than 100,000 times a day (an average of 70 beats per minute), pumping about 7,000 liters over a total path of 19,000 kilometers across the world. vascular system.

With age, arteries become rigid (unyielding), and some people may develop atherosclerosis - the scourge of modern humanity. Atherosclerosis causes narrowing blood vessels and, ultimately, can lead to their complete blockage. The reasons for the development of atherosclerosis are not fully understood. Several factors are known to contribute to the development of this disease. Possible hereditary predisposition, hypercholesterolemia, increased low-density lipoproteins and decreased high-density lipoproteins, smoking, sedentary lifestyle, high blood pressure, diabetes mellitus. Disruption of blood flow to organs and tissues leads to disruption of their function. Damaged parts are unable to work as efficiently. At the same time, if there is a load, this provokes the appearance of symptoms, such as pain in the legs when walking (a symptom of intermittent claudication). Narrowed arteries lower limbs unable to provide a sufficient amount of oxygen and oxygen during muscle work, as a result of which pain appears in them. A similar process develops in the heart when the arteries supplying the heart muscle are damaged. If blood flow to the brain is disrupted, dizziness, short-term loss of vision, sensory disturbances in the extremities, and decreased memory and mnestic functions may occur. Another problem in the vascular system arises due to the thinning of the vessel wall, which results in an increase in the diameter of the vessel and the development of an aneurysm. When an aneurysm reaches a certain size, it may burst and the person will die from blood loss.

The problem of treating atherosclerosis is complex. It is extremely important to control those factors that are known to cause the development of the disease. Unfortunately, there is little we can do about our genetic predisposition. The most important thing is to quit smoking. Examination and treatment of high blood pressure, high level cholesterol, diabetes correction are also very important. If you follow all the above measures, atherosclerosis can stop its development and become even smaller, especially if you do not smoke. The condition of many patients improves with regular drug treatment aimed at treating high cholesterol, high blood pressure, improving the rheological properties of blood, relieving spasm in peripheral arteries, stimulating the development of collateral (roundabout) blood flow pathways, and improving nutrition of suffering tissues and organs. Physical exercise are also useful, but you should not work according to the principle: “the more, the better.” If pain occurs, you should stop exercising.

The above measures are practically all that a patient may need to treat atherosclerosis. However, for a certain group of patients these measures are not enough, and other forms of treatment are required - surgical. In case you need surgery, a very important stage of research is ultrasound duplex scanning and angiographic examination. An angiogram is an X-ray examination that is accompanied by the introduction of a contrast solution (dye) into the vascular system through a syringe in the groin or axillary area. An angiogram provides a map of the location of your arteries and shows the exact location of narrowings and blockages. Some of the narrowings can be widened using a balloon catheter inserted into the vessel through the groin or armpit. The balloon is placed against the narrowing and then inflated - this is the so-called angioplasty. Often, at the site of the former narrowing, a special frame is installed inside the vessel to prevent the narrowing from re-developing - this is stenting. Other vascular narrowings and blockages that are not amenable to angioplasty are treated with surgery– bypass (bypass), i.e. formation of a bypass of the blockage site.

A vascular bypass can be described as a bypass built around a crowded city. With this technique, the narrowed or blocked area is not removed, but a “bypass” is added in the area of ​​a healthy vessel above and below the narrowing area. An important feature of this technique is a good vascular bed before and after the blockage site (so that the road to the city and after it is good, paved, and not a country road). The choice of material for the shunt depends on the location of the damaged area of ​​the vessel.

Most often, an artificial vessel prosthesis is installed in the treatment of aneurysms and blockages of the abdominal aorta. With this localization, the prosthesis can work flawlessly for many years.

The photograph shows an artificial bifurcation prosthesis of the aorta and iliac arteries installed for a type 3 aortic aneurysm.

A shunt in the groin and lower extremities is often made from the patient’s own vein. Your own vein is the best material for bypassing in this area, but if such material is not available, you also have to use an artificial prosthesis.

Artificial vascular prostheses are, developed by scientists, substitutes for real vessels. human body. They work in a similar way to natural blood vessels. A vascular prosthesis is a complex material made in the form of a tube of various diameters and lengths. The vascular prosthesis has a large margin of strength and stability, significantly exceeding the strength and stability of natural arteries.

Is there some possibility that the shunt will not work forever? Yes it exists. This can be influenced by many factors. First of all, this is the further progression of atherosclerosis. How much atherosclerosis will progress after surgery depends on the patient’s compliance with the surgeon’s recommendations: quit smoking! drug treatment, Spa treatment. The reason for the cessation of the shunt operation may be the gradual formation of layers on the inner walls of the shunt, with its considerable length. Taking certain doses of “thinning” drugs can help prolong the work of the shunt and the functional state of the organ or limb.

The creation of artificial artery prostheses is one of the greatest medical achievements of the 20th century. The next step is the creation of a full-fledged venous prosthesis. It is possible in the future to learn how to grow artificial prostheses from stem cells, but for now prosthetics with artificial vessels is the only method of prolonging a full life.

Synthetic arteriovenous prostheses.

1. What is arteriovenous access for hemodialysis? To conduct an effective hemodialysis session with enough high degree cleaning, it is necessary to ensure a blood flow rate through the dialysis machine of 300 ml/min. Blood in this volume can only be obtained from a central vein or artery. It is impossible to obtain blood from a peripheral vein at such a speed. The idea of ​​launching arterial blood flow into the saphenous vein was implemented in 1966. Then the first arteriovenous fistulas (AVFs) were formed on the forearm and good practical results of their use were obtained. The formation of an anastomosis between the artery and the saphenous vein leads to a manifold increase in blood flow in this vein. As a result of the constant discharge of blood, the vein dilates. To pass through the artificial kidney, blood is diverted into the extracorporeal circuit using two dialysis needles inserted into the lumen of the “fistula” vein at some distance from each other to collect and return blood, respectively. Such unnatural shunting of blood past the peripheral bloodstream certainly changes regional hemodynamics, but these changes are usually compensated by collaterals, and clinical manifestations Ischemia or venous hypertension of peripheral tissues rarely develop. Severe hemodynamic disturbances completely regress after ligation of the AVF.

2. When does the need for a synthetic prosthesis arise? The service life of the AVF is limited. Loss of vascular access occurs as a result of thrombosis or infection. Following the old one, a new AVF is formed, then another and another. In the life of many dialysis patients, there comes a time when years of hemodialysis treatment, several operations to form an arteriovenous fistula (AVF), and the possibilities of forming a new native (i.e., from one’s own vessels) vascular access are exhausted. In some cases, already at the very beginning of dialysis therapy, the surgeon faces significant difficulties in forming an AVF from his own vessels, for example in obese patients. In such situations, the formation of permanent vascular access (PVA) is possible using a prosthesis. Arteriovenous prostheses (AVP) can be biological: autogenous (prosthesis from an autovenous vein), allogeneic (cadaveric vein, umbilical cord vein), xenogenous (bovine carotid artery, bovine ureter, bovine mesenteric vein). Arteriovenous prostheses can also be synthetic: polyurethane, Teflon, Dacron, polytetrafluoroethylene. The most widespread at the present stage of development of vascular access surgery are synthetic prostheses made of microporous polytetrafluoroethylene (PTFE). Available on the market are options of different lengths, thicknesses and diameters, reinforced with removable and built-in rings, prostheses with a narrowed arterial or widened venous end. The following describes the specifics of installing and maintaining a WUA.

3. How are synthetic prostheses used in the arteriovenous position? The arteriovenous graft is sutured at one end into the artery and the other end into the vein, functioning as a subcutaneous arteriovenous shunt. The implanted prosthesis plays the role of a fistula vein and is punctured to provide access to blood for hemodialysis. Accordingly, it should be located superficially and straight under the skin on the side of the limb convenient for puncture. In this case, the prosthesis must be of sufficient length (minimum 15-20cm). This is necessary for puncture rotation (changing puncture sites between sessions to scar wall defects) and to ensure the minimum acceptable distance between dialysis needles (5 cm), preventing recirculation between needles. During recirculation, already purified blood from the “return” needle is re-sucked into the “sampling” needle. This leads to a decrease in the effectiveness of hemodialysis. In addition, a necessary condition for the normal operation of the AV prosthesis is a sufficient level of blood flow (according to the literature, 600 ml or more). The fact is that a high blood flow rate is necessary not only for effective hemodialysis. The high blood flow rate in the prosthesis is a natural obstacle to thrombosis. The linear speed of blood in the prosthesis is many times higher than the speed in the artery under natural conditions. This condition (one of three according to Virchow) provides a certain “margin of safety” against the other two possible thrombogenic factors: a) hypercoagulation and b) damaged (in our case, foreign) vascular wall. Eager to get high speed blood flow in the prosthesis, for implantation it is necessary to select vessels that can provide such blood flow. Artery – high blood flow, vein – low resistance.

4. Vascular access planning stage. The location of the prosthesis on the limb depends on the location of the vessels that can provide the necessary blood flow to the prosthesis. The anatomy of the vessels can be changed by previous operations to form the PSD. The consequences of phlebitis of the superficial veins, atherosclerosis or diabetic calcification of the distal arteries can make adjustments to the surgical plan. When choosing the future location of the prosthesis, it is necessary to observe the principle of vascular economy, that is, other things being equal, the choice should be made in favor of a more distal location, so as to preserve vascular vacancies for future operations. The patient should be examined in a warm, well-lit room. Veins are palpable below the tonometer cuff, inflated to 50 mmHg. Palpation must be supplemented with ultrasound examination of the diameter and patency of blood vessels. The diameter of the artery and vein for implantation of the prosthesis must be at least 3 mm. Determination of pulsation on the brachial artery is a sufficient condition for a prosthesis. Distal arteries cannot always be involved in access formation with certainty. Limiting factors for the use of distal arteries are the common widespread calcification and small diameter. The vein can be used either saphenous or deep (one of two accompanying the brachial artery). The larger the diameter of the vein, the better the short- and long-term prognosis for the prosthesis. It has been noted that stenosis as a result of pseudointimal hyperplasia develops less often in large veins.

The prosthesis can be placed on the limb in two versions: straight and loop. The most common is the loop. This form is used in cases where the vein and artery suitable for surgery are located close to each other on the limb. The advantage of the loop is that the maximum length of the prosthesis fits in a limited area, leaving ample opportunity for rotation of punctures on both halves of the prosthesis. The prosthesis is placed in a loop, for example, when the access involves the brachial artery in the ulnar fossa and the ulnar venous fork, or the brachial artery and basilar vein, or the brachial artery and deep vein. In all these cases, the distance between the vessels is no more than 3 cm; they can be isolated from one incision. The loop is also used for the brachial artery and cephalic vein in the upper arm. In this case, the large distance between the vessels requires two separate incisions to isolate each of them. Non-standard loop options with branches of different sizes are also possible. It all depends on the specific anatomical situation and the location of the vessels suitable for the formation of AVP. The main condition remains a sufficient total length of the prosthesis segments intended for puncture - more than 15-20 cm. It is necessary to understand and take into account that hemodialysis doctors, who are responsible for the safety of the prosthesis, will not take risks by puncturing near anastomoses and near the top of the loop. The 3-5 cm of the prosthesis closest to the subcutaneous scars will not be used for punctures. Also, the bending zones of the prosthesis will not be used for punctures, if such are allowed during implantation. Therefore, the total length of the prosthesis used in the form of a loop must be at least 25-30 cm.

The prosthesis can also be placed on the limb and in a straight form. This is possible when the artery and vein are far removed from each other. For example, when the distal segment of the radial artery is used (a very rare option) and one of the veins at the level of the elbow or the lower third of the shoulder. The second option for a direct prosthesis: the brachial artery in the ulnar fossa - the axillary vein. In both cases, the puncture segment of the prosthesis must also be of sufficient length. In addition to the listed options, a direct prosthesis can be located in the form of a “bridge” between an artery and a fistula vein that are distant from each other, remaining after the loss of an AVF. This is possible when the already served fistula vein is dilated and suitable for dialysis, but the nearest artery is obliterated, and without the mediation of a prosthesis, the connection of the vein with the nearest suitable artery is impossible. For example: a direct prosthetic bridge between the brachial artery in the cubital fossa and the dilated cephalic vein in the lower half of the forearm. Such a prosthesis can be used for punctures, but can also remain intact, performing solely the role of a “bridge”. In this case, only the vein will be punctured with both needles.

The planning stage should be completed with a clear plan that answers the questions: which vessels and at what level will be used for implantation of the prosthesis? If a loop is planned, will these vessels be accessible from the same incision or from different ones? Can the incision be extended proximally (toward increasing the diameter of the vessels) if necessary? Where will the prosthesis be placed and how long should it be?

Surgery involving a synthetic prosthesis cannot be planned in case of systemic manifestations bacterial infection. Possible hematogenous contamination of the prosthesis conservative treatment does not give in. The infected prosthesis will have to be removed.

5. Technique for implanting an arteriovenous prosthesis.

It is very important to provide anti-infective protection. It may include pre- and postoperative systemic administration of antibiotics, local administration of an antibiotic along with an anesthetic solution. It is necessary to carefully observe asepsis, treat the surgical field repeatedly during the operation, or use a barrier. The role of a barrier can be played by a self-adhesive film or surgical linen hemmed around the perimeter of the surgical wound. It is important to prevent contact of skin bacterial flora with the prosthesis material.

Surgical planning after a thorough examination should be completed with a plan for the surgical approach. Adequate access to blood vessels is half the success of the operation. Adequate access is such access from which it will be easy to isolate the vessels of the required length selected for the prosthesis, after which reliable anastomoses with the prosthesis will be applied. It is necessary to outline the incision in advance with a marker, or remember its course and length based on surrounding landmarks (moles, subcutaneous scars), since after infiltration anesthesia appearance limbs may change, skin folds and venous patterns will disappear. In all cases, longitudinal incisions are recommended. Firstly, a longitudinal incision on a limb is less traumatic (longitudinally located nerves and lymphatic vessels). Secondly, such an incision can, if necessary, be extended along the identified vessels.

Let's consider the most common version of an arteriovenous prosthesis on the forearm - a loop with anastomoses in the cubital fossa. After a longitudinal incision, usually 5 cm, the ulnar venous fork is identified in the subcutaneous fat layer. The location of the venous anastomosis here is advantageous, since from here blood is discharged in three directions at once: in the direction of the cephalic vein, in the direction of the basilar vein, and, through the communicant vein that is always present here, in the direction of the system of deep veins accompanying the artery. Venous hemodynamic conditions in this area are most favorable for the graft, providing maximum outflow and low resistance. The brachial artery is isolated here after dissection of Pirogov's fascia. Its trifurcation (division into radial, ulnar and common interosseous branches) is usually located in this place. For anastomosis with the prosthesis, a section of the brachial artery is isolated immediately above its division. A standard prosthesis suitable for use in this location has a diameter of 6 mm and a length of 40 cm. To minimize contact of the prosthesis with the external environment, it should be removed from the packaging immediately before implantation. It is recommended to impregnate the porous material of the prosthesis under pressure (using a syringe) with an antibiotic solution. The prosthesis is placed under the skin after isolating the vessels and before performing anastomoses. For this, a curved forceps or a special tunnel is used. To install the prosthesis in the form of a loop, one or two additional cuts of 1-2 cm each will be required in the bend area. The prosthesis should be placed directly under the dermis along a straight path, without bending or diving deeper. There should be no twists or kinks of the prosthesis in the canal. If a stretch prosthesis is used, it should be stretched submaximally before fitting to the vessels and cutting off the excess at the ends. If the prosthesis is not stretched in advance, then after inclusion in the bloodstream the prosthesis will be stretched under the influence of blood pressure, and the excess length of the prosthesis will fit into wavy curves under the skin. These bends will complicate dialysis punctures in the future. Such a prosthesis will not be accessible to the dialysis needle along its entire length, as it should be. But still a small margin of elasticity should be left. The fact is that the elasticity of the prosthesis determines its ability to somewhat soften the systolic wave, which probably plays a role in the development of pseudointimal hypertension and vein stenosis. After placing the prosthesis under the skin, additional incisions must be sutured. This way we reduce the duration of contact between the prosthesis and environment to a minimum. Venotomy is performed in such a way that the anastomosis is located above the mouths of the existing venous branches, so that the blood flow from the prosthesis has the widest possible total outflow path. All venous outflow pathways accessible through venotomy are filled with a heparinized saline solution using a syringe under pressure to finally ensure the suitability of the vein in order to prevent thrombosis and to evaluate resistance. The 20 ml syringe should empty into the vein within 4 seconds. If the diameter of the veins is borderline small, it is recommended to destroy the near distal venous valve with a button probe in order to ensure additional blood outflow in the retrograde direction to the nearest collaterals. The venous anastomosis is performed first, then the arterial one. Both anastomoses are applied like the end of the prosthesis to the side of the vessel. If there is a vein of large diameter (more than 5 mm), an end-to-end anastomosis with the vein can be performed. The cut of the ends of the prosthesis should be made obliquely, so that the prosthesis departs from the artery and approaches the vein at an angle - this is necessary condition for successful thrombectomy in the future. In addition, the convergence of the axes of the prosthesis and the vein makes the flow of blood from the prosthesis to the vein more physiological. The ideal anastomosis configuration from this point of view, provided that the vein diameter is sufficient, is an end-to-end anastomosis. The venous end of the prosthesis should also be cut obliquely in the shape of the letter S, so that when stitching, transverse sections of the prosthesis wall are inserted into the corners of the venotomy. This reduces the risk of vessel narrowing when applying continuous suture stitches at the corners of the anastomosis. The size of the venous anastomosis is from 1 to 2 cm. The size of the arterial anastomosis is about 1 cm. By increasing the size of the arterial anastomosis, it is impossible to increase blood flow, since the diameter of the prosthesis still remains constant - 6 mm. But you can reduce blood flow through the prosthesis (for example, in order to prevent steal syndrome) by reducing the diameter of the arterial anastomosis (by placing a suture on the prosthesis itself or using a prosthesis with the arterial end narrowed to 4 mm).

For anastomosis, 6-0 polypropylene or polytetrafluoroethylene suture material is used. At the proximal corners of anastomoses, the distance between continuous suture stitches should be kept to a minimum to reduce the tightening “purse string” effect that any continuous suture has. Rough and sparse sutures in this place can lead to a narrowing of the already small lumen of the vessel. Depending on the specific situation and the surgeon’s preferences, anastomoses are performed with a continuous suture on two or one holder, from the outside or from the inside, with one or two needles facing each other. But it is not recommended to sew the proximal, most important angle of the anastomosis (arterial and venous) blindly, that is, last, when it is impossible to control the quality of the seam from the inside. Thus, it is advisable to start a continuous suture from the distal corner of the anastomosis or from the middle of the side wall and end it there. After release into the bloodstream, bleeding is observed for several minutes from the needle punctures of the prosthesis along the suture line. Such bleeding is stopped by patient, firm, but not strong pressure with a napkin along the entire length of the vascular sutures for several minutes. Against the background of hypocoagulation, bleeding may be longer. Normally, a systole-diastolic tremor should be felt over the entire prosthesis. The absence of trembling in diastole indicates high resistance, low blood flow in the prosthesis and a high probability of thrombosis in the early stages. If trembling is not felt even in systole, and only high pulsation on the prosthesis is detected, there is high resistance, and the blood flow is very low or absent altogether. If weak pulsation and low turgor of the prosthesis are detected, weak blood flow from the artery is likely. The most common causes of low blood flow through the prosthesis: a gross defect in the anastomosis, a bend in the prosthesis at the top of the loop, torsion of the prosthesis in the canal, an unaccounted defect in the vein above the anastomosis (stenosis or occlusion), and an overestimation of the capabilities of the artery. Many of the identified defects leave room for immediate correction and maintenance of access.

Before suturing, it is necessary to treat the wound with hydrogen peroxide for the purpose of antiseptics and mechanical cleaning of the wound from detritus, dust and random microbial bodies. Suturing the wound should be layer-by-layer.

6. Early postoperative period. In the early postoperative period, various negative phenomena may be observed. 1) Thrombosis of the prosthesis within a few minutes or hours after surgery indicates unacceptable anatomical and functional conditions for the prosthesis on these vessels (do not provide sufficient blood flow). You can perform a thrombectomy and perform anastomoses. A prosthesis that is thrombosed in the early stages must be removed. 2) If thrombosis of the prosthesis develops several days after surgery, the probability of successful thrombectomy is quite high. If thrombectomy is not effective, the prosthesis must be removed. 3) Soon after surgery, swelling of the limb usually develops; it can progress over several days. Compensation of venous hypertension associated with arteriovenous shunting occurs within 1-2 weeks due to collaterals and, probably, due to adaptation mechanisms at the tissue level. The cause of long-lasting edema is stenosis of the central venous outflow pathways (at the level of the subclavian, brachiocephalic or even superior vena cava). These are the consequences of standing central venous catheters. Severe swelling of the limb can become an obstacle to safe puncture of the prosthesis. In severe cases, the prosthesis must be removed or ligated. After the cessation of arteriovenous discharge, the edema quickly regresses. 4) Lymphorrhea from a subcutaneous wound increases the risk of infection of the prosthesis, and is more common with transverse skin incisions. Therefore, longitudinal incisions are recommended as they are less traumatic. 5) Infection of the wound and prosthesis in the early postoperative period is a consequence of intraoperative violations of asepsis. The infected prosthesis must be removed.

2-3 weeks after surgery, the prosthesis can be used for hemodialysis. By this time, the swelling has already completely regressed, the superficially located prosthesis is easily determined by palpation along its entire length, soft fabrics around the prosthesis become somewhat denser. But more reliable fixation of the prosthesis in the canal (overgrowth with connective tissue) occurs after a few months. The patient should be taught to thoroughly clean the puncture area with soap and water a few minutes before dialysis. Before the puncture, dialysis staff treats the area with an antiseptic. During puncture, the direction of the needle must coincide with the axis of the prosthesis and the direction of blood flow. The puncture site, depth and direction of the needle must ensure against injury to the lateral and posterior walls of the prosthesis. This can lead to the formation of a hematoma and false aneurysm. Typically, when using a loop prosthesis, each half of it is intended for the corresponding needle: the arterial half (which is closer to the arterial anastomosis) is for the arterial (sampling) needle, the venous half is for the return needle. It is necessary to alternate puncture sites from dialysis to dialysis, splitting the maximum possible length of the prosthesis in “paths” in 5 mm increments. Punctures near anastomoses and the top of the loop are not recommended, since when puncturing any non-linear segment of the prosthesis, there is a higher risk of damage to the lateral or posterior wall. At the end of the hemodialysis session after removal of the needles, hemostasis is carried out by moderate pressure for 5-15 minutes.

7. Without stenosis there is no thrombosis? The first disease of arteriovenous accesses for hemodialysis is the so-called pseudointimal hyperplasia, which develops in the wall of the vein in the area of ​​the anastomosis and in some part of the vein above it. In this case, the vein wall thickens significantly, the lumen gradually narrows, which leads to a decrease in blood flow through the access and, sooner or later, to thrombosis. It is believed that the cause of hyperplasia and stenosis of the vein is high pressure and a systolic wave unusual for the vein, as a result of which the vein wall produces a (compensatory?) reaction in this form. Hyperplasia develops in most, but not all cases, and does not always lead to significant stenoses. Perhaps this depends on the initial diameter of the vein and the configuration of the anastomosis. As stenosis progresses, pressure in the prosthesis increases and blood flow decreases. A decrease in linear and volumetric blood flow can be recorded using ultrasound. You can suspect problems based on indirect signs: in recent months the prosthesis has become harder, the pulsation is high; the pressure in the venous line gradually increases from dialysis to dialysis; The dialysis dose is reduced, and hyperkalemia is observed after dialysis. The effectiveness of dialysis with stenosis decreases as a result of an increase in blood recirculation between the needles as the blood flow rate decreases. A progressive decrease in blood flow in the prosthesis leads to its thrombosis sooner or later. This usually happens a few hours after the next dialysis as the injected heparin is inactivated, against the background of hypovolemia and blood thickening - the consequences of ultrafiltration.

It is believed that thrombosis of the arteriovenous access, including the arteriovenous prosthesis, in the vast majority of cases is caused by venous stenosis.

In rare cases, the cause of low access blood flow, predisposing to thrombosis, may be stenotic atherosclerosis of the artery. Also, in some cases, it is not possible to establish the presence of stenosis, and after successful thrombectomy, the vascular access functions for a long time and effectively. The cause of access thrombosis without any anatomical prerequisites may be severe arterial hypotension after hemodialysis.

8. Restoring the patency of the arteriovenous prosthesis. In case of thrombosis of the prosthesis, an attempt should always be made to dissolve it. Access to the prosthesis is carried out in one of the non-punctured zones: either the top of the loop, or near the venous anastomosis. The latter localization is more advantageous, since if venous stenosis is detected during thrombectomy, this access will be used for subsequent reconstruction - bypass reanastomosis. So, the prosthesis is isolated in the non-punctured area and incised transversely along the upper wall by 4-5 mm. Thrombectomy is performed using a Fogarty balloon catheter with a diameter of 6 French. The filling of the balloon is about 1 ml. Thrombectomy is performed in stages and multiple times to ensure complete clearance of the prosthesis from thrombus fragments. In addition to fresh soft blood clots, sometimes old dense overlays in the form of a cast of the prosthesis are encountered. Such old parietal thrombosis is confirmation of vein stenosis. By the way, they are usually located in the venous half of the prosthesis. In such cases, a button probe should come to the aid of the Fogarty catheter. Using a probe or a long branch of tweezers inserted into the lumen of the prosthesis, the prosthesis is mechanically processed from the inside; the debris is easily removed with a balloon. First, thrombectomy is performed from the venous part of the prosthesis, entering the vein 10-20 cm. During the procedure, the presence, degree and extent of vein stenosis is assessed by the volume of the maximum filling of the balloon. After releasing the venous part, thrombectomy is performed from the arterial part of the prosthesis, entering the arterial anastomosis. In case of thrombosis of the prosthesis, the artery usually remains patent, and thrombosis of the prosthesis originates from the line of the anastomosis. A dense red thrombus with a white or gray concave surface corresponding to the lumen of the artery forms at this location. This “arterial plug” is 1-2 cm long and the longer the thrombosis, the denser it is. The thrombus behind the plug along the entire length of the prosthesis is soft and easily fragments during thrombectomy, but the plug retains its shape. Obtaining an arterial plug during thrombectomy is the main and mandatory criterion for cleaning the arterial part of the prosthesis. Sometimes, after removing the balloon catheter from the lumen of the prosthesis, the plug is knocked out with a fountain of blood unnoticed by the operator. In this case, upon careful examination, it can be found on the linen around the operation area. After receiving the plug, you should evaluate the blood flow from the side of the arterial anastomosis by releasing the lumen from the clamp for a split second: the blood flow should be “gushing”, “foaming”. If the blood flow is weak, the arterial plug has probably not been obtained, fragments of blood clots remain in the lumen of the prosthesis, or there is a narrowing of the artery.

In some cases, especially with late thrombectomy, when the arterial plug is already firmly fixed in the prosthesis, additional access is required near the arterial anastomosis: when the plug cannot be removed remotely with a catheter, it may be possible to pick it out using a probe from the nearest access. This approach to thrombosis makes it possible to restore the patency of the prosthesis several weeks after thrombosis.

After cleaning each half, the prosthesis is filled under pressure with heparinized saline. solution. In this case, by the rate of emptying of the syringe towards the venous anastomosis, one can approximately estimate the resistance. If a 20ml syringe empties in less than 4 seconds, the resistance is considered low. But the syringe must not be rubbed in. First you need to check the syringe in the glass so as not to confuse the property of the vein with the property of the tight syringe piston.

If good blood flow is obtained from the artery and no venous stenosis is detected, the prosthesis defect is sutured, blood flow in the prosthesis is restored, and access can be immediately used for hemodialysis. Venous stenosis is most often detected. If technically possible, stenosis can be confirmed intraoperatively using angiography.

The surgeon’s task is to maintain vascular access. If vein stenosis is detected in the area of ​​the venous anastomosis, in most cases reconstruction of the venous anastomosis can be performed. There are 3 reconstruction options:

1) Plastic surgery of venous anastomosis. The entire area of ​​the prosthetic-venous anastomosis is isolated from the scars, the stenotic area is dissected along the stenotic area (with the incision continuing along the prosthesis if necessary) and a patch made of a similar material (PTFE) is sewn in.

2) Venous reanastomosis. The prosthesis can be cut off from the vein and a new anastomosis can be applied to another vein of suitable diameter, if, of course, one is available nearby.

3) Proximal venous reanastomosis (bypass reanastomosis) is the most common and simplest option. It is necessary to isolate the prosthesis and cut it off near the venous anastomosis; then, from a separate incision, isolate the “fistula” vein draining it above its identified stenosis; extend the prosthesis end to end with a piece of a similar prosthesis of the required length; The prosthesis lengthened in this way is passed under the skin to the vein identified above and sewn into it end to side or end to end.

The benefits of immediate venous reconstruction are difficult to overestimate: firstly, the cause of thrombosis – stenosis – is removed; secondly, the prosthesis can be used immediately after surgery; thirdly, there is no need for central vein catheterization; fourthly, the principle of saving vascular resources is observed, because the same vein above the stenosis is used. If, if stenosis is detected, reconstruction of the anastomosis is not performed, recurrence of thrombosis will likely occur within several days or weeks.

It is possible to identify and correct stenoses in advance, without waiting for thrombosis. With regular monitoring of vascular access, signs of decreased blood flow may be recorded. Stenosis is confirmed by routine angiography. Correction of stenosis is performed by endovascular angioplasty or by the above-described reconstruction of the anastomosis in a planned manner.

9. Hemodynamic complications. The unnatural discharge of blood from an artery into a vein, bypassing the peripheral bed, leads to disruption of both regional and systemic hemodynamics. Volumetric blood flow through a 6-mm prosthesis rarely exceeds 1 l/min, so hemodynamic complications with AV prostheses are less common. These complications are more typical for native proximal (on the brachial artery) or, less commonly, distal (on the radial artery) AVF. During the “life” of some AVFs, the anastomosis gradually stretches, the artery and vein dilate, which leads to an increase in volumetric blood flow, sometimes up to 2-3 l/min. The diameter of the synthetic AV prosthesis is constant - 6 mm, and the blood flow increases over time to a small extent.

There are 3 types of disorders: steal syndrome, venous hypertension syndrome, heart failure.

Steal syndrome develops in cases where the degree of blood shunting past the periphery exceeds the compensatory capabilities of the limb. The fact is that AVF and AVP often “take away” not only the entire main blood flow from the proximal part of the artery, but also part of the retrograde blood flow from the distal part of the artery, which is provided by collaterals. The severity depends on the degree of theft of collateral blood flow and the capabilities of this collateral blood flow. clinical picture steal syndrome. In mild cases, patients are bothered by paleness and chilliness of the hand, and they constantly wear gloves. Depending on the severity, numbness, constant pain in the fingers and hands, muscle weakness, and dry gangrene of the fingers may occur. Treatment of severe cases is urgent ligation of the access. After stopping blood shunting, improvement occurs within the first minute, symptoms regress completely. In some cases, a good effect can be achieved by partial ligation (narrowing) of the vein (prosthesis).

Steal syndrome should not be confused with ischemic neuropathy. In the latter case, intense pain along the nerve (usually the median) increases significantly during dialysis. During the interdialysis period, they may be completely absent or of an unexpressed nature.

There is also another complication accompanied by pain in the arm - carpal tunnel syndrome. This problem is not related to the functioning of the AVF, occurs in long-term dialysis patients, and is caused by amyloidosis and compression of the median nerve in the canal under the flexor tendon retinaculum. Patients complain of constant pain in the hand in the area of ​​responsibility of the median nerve and the inability to fully straighten the fingers.

Venous hypertension syndrome develops against the background of stenosis or occlusion of the central vein. It manifests itself as swelling of the limb, cyanosis and trophic disorders, including ulcers (usually on the back of the hand). The severity of the syndrome depends on the amount of discharge along the AVP, the degree of stenosis of the subclavian (and/or brachiocephalic) vein, the development of venous outflow collaterals on chest. Correction of venous hypertension syndrome in case of stenosis can be successfully performed by endovascular angioplasty of central vein stenosis. With occlusion this is not possible. However, the likelihood of recurrence of stenosis after angioplasty is high. Severe cases of venous hypertension require ligation of the AVF.

Heart failure after the application of an AVF and AVP can be aggravated due to the additional load on the heart, the minute volume of which is increased by the “idle” volume of blood circulation through the AVP. The severity of this complication and the need for access ligation is determined individually.

10. Infection of the prosthesis. Infection of a surgical wound in the early postoperative period is usually associated with infection of the prosthesis. Antibacterial therapy in case of infection of the prosthesis it is ineffective. This prosthesis must be removed. The prosthesis is completely removed with ligation or plastic surgery of the artery. The arterial defect can be closed with a continuous suture; Arterial grafting with an autologous vein can be performed. If this is not possible, the artery can be ligated.

At a later date, infection of the prosthesis is often local in nature, associated with puncture and violation of the rules of asepsis during dialysis. In such cases of infection limited in extent, reconstruction of the prosthesis is performed: half of the loop carrying the fistula is excised and replaced with a new prosthesis. From two incisions, half of the loop is isolated within healthy (non-infected) tissues outside the puncture zones. Then, from the third incision bordering the fistula, a segment of the prosthesis containing the infected area is excised. The prosthesis loop is restored by two end-to-end anastomoses using a section of a similar prosthesis passed under the skin away from the infected area. Dialysis continues using the other half of the loop.

11. Aneurysms of the prosthesis. Each puncture of the prosthesis with a dialysis needle leaves a defect in its wall. All punctures are performed along the front surface of the prosthesis, along one line. 1 dialysis - 2 punctures, per week - 6 punctures, within a month - more than 24, per year - approximately 300 punctures. Each defect in the prosthesis is replaced by scar tissue. After years of operation, the front wall of the prosthesis is cut along its entire length, the edges of the prosthesis diverge, and punctures are performed into the wall of the so-called true aneurysm, which is a single layer connective tissue, which includes a prosthetic capsule and scarred skin. It can be conditionally called a true aneurysm of the prosthesis, since the prosthesis itself does not stretch. Such aneurysms, with the correct alternation of puncture sites, replace the entire length of the prosthesis. If punctures were performed in selected areas, local sac-like degeneration develops faster, does not look aesthetically pleasing, and limits the puncture areas. Vein stenosis and high blood pressure in the prosthesis probably contribute to the more rapid development of aneurysms. Usually, the deepest places of protrusions are lined with old parietal thrombi. Such prostheses are more difficult to thrombose; a balloon catheter of a larger diameter than usual is needed. True AV graft aneurysms themselves are not an indication for any intervention. Sometimes, as a result of local infection of scar tissue at the puncture site, the aneurysm wall becomes so thin that there is a risk of rupture. In this case, the prosthesis must be ligated upstream of the bloodstream. In rare cases of widespread infection of such prostheses, removing them may present technical difficulties. As a result of a long-term latent infection, the capsule around the prosthesis thickens significantly and takes on a cartilaginous density, thus acting as a protective shaft that localizes the source of infection. The prosthesis can be removed from long incisions, often in fragments, along with the surrounding tissue.

Sometimes during dialysis the needle injures the side or back wall prosthesis. It is more difficult to perform hemostasis here with a finger than on the anterior wall. In this case, a hematoma forms near the prosthesis. If the defect in the prosthesis wall is large (longitudinal needle wound), a false aneurysm may form. A false aneurysm is a rounded hematoma with a cavity inside, in which turbulent blood flow is recorded. Palpation reveals a distinct pulsation of the hematoma and systolic and diastolic rhythm. Pulsating hematomas are always tense and can lead to compression and thrombosis of the prosthesis. The operation is performed: suturing the prosthesis defect; or replacement of a segment of a prosthesis bearing a defect with a segment of a new similar prosthesis. If the aneurysm has formed in early after surgery in the anastomosis area, it is necessary to perform an inspection and suture the anastomotic defect. If an aneurysm appears late in the anastomotic area, infection and arosion should be suspected. In this case, it is recommended that before the revision, the brachial artery is isolated from a separate incision above and placed on a holder. Such a prosthesis must be removed, and the artery in the anastomosis area must be repaired or ligated.

12. Are dentures the future? Probably not for synthetic ones. The craze for polytetrafluoroethylene prostheses is already a thing of the past. In the United States in the 1980s, up to 80% of primary vascular accesses were performed using commercial prostheses. Today, most surgeons in the world support the priority of relocated veins (transposition of veins in the arms, use of the great saphenous vein as a prosthesis) over synthetic prostheses. But practice shows: it is impossible to do without synthetic prostheses. They firmly occupy their considerable niche in the structure of vascular access surgery for hemodialysis. The search and development of new synthetic and biological materials for the production of more reliable and durable Arterio-Venous Prostheses is actively underway.

Vascular prostheses interact with the blood and surrounding tissues, therefore, due to their inherent thrombogenicity, soon after implantation, synthetic prostheses become covered with fibrin and platelet clots. This lining remains thrombogenic and stabilizes a year or more after surgery. Healing of a synthetic prosthesis occurs through two mechanisms - migration of endothelial cells along the implant and capillary ingrowth.

The amount of endothelialization varies significantly as endothelial cells migrate from the artery to the surface of the graft. Although this process can result in complete endothelialization in animal models, in humans a monolayer of endothelial cells never forms in synthetic vascular grafts. Capillaries grow from surrounding tissues. The degree of incorporation varies depending on the porosity of the prosthesis; the higher the porosity, the more vessels are embedded into it.

Synthetic vascular grafts made of Dacron

Synthetic Dacron prostheses are made from polyfilament polyester threads, which are woven or braided on special machines. Woven Dacron vessel substitutes consist of threads woven together at right angles. Such prosthetic materials have a rigid structure, and their cut edges easily unravel. They are poorly permeable to blood (minimal bleeding during implantation), but have poor handling characteristics and very low elasticity.

In woven dentures, the threads are arranged in the form of loops, covering each other. The loops can be oriented in the longitudinal or transverse direction. Longitudinal weave dentures are more stable and most dentures currently available have a similar configuration. Woven prostheses are characterized by relatively high porosity, therefore, to prevent bleeding, it is necessary to pre-thrombose them. They tend to dilate over time, but they promote ingrowth of surrounding tissue and have excellent handling characteristics. In recent years, most braided vascular grafts have been impregnated with collagen, albumin, or gelatin, eliminating the need for prethrombosis. There is evidence that such coatings can reduce early thrombogenicity of the surface of a vascular graft with an expected improvement in patency. However, a randomized trial has not demonstrated a reduction in blood loss or an improvement in patency.

Braided vascular prostheses can be made softer by adding a thread to the weave at a right angle to the surface. The velor surface promotes the formation of stable neointima. As a rule, corrugated Dacron prostheses are made, which gives them flexibility, elasticity and shape stability.

Stretched polytetrafluoroethylene dentures

Expanded polytetrafluoroethylene (ePTFE) vascular grafts are produced by pressing PTFE polymer, resulting in a material consisting of dense knots intertwined with thin fibrils. The distance between individual fibrils in them is less than between the fibers in Dacron prostheses, due to which it has high porosity and low permeability. PTFE is an inert substance with a negative charge, which makes the prosthesis hydrophobic. Some vascular grafts are coated with a thin outer lining to increase wall strength and further reduce permeability. Currently, PTFE prostheses with a thin wall are produced, which improves their handling properties and increases longitudinal elasticity. External support allows you to prevent bending in the joint area and, thereby, increase patency in the long term. However, in a prospective randomized trial, external support did not improve patency.

Some surgeons prefer PTFE grafts to Dacron grafts due to higher resistance to infection and low thrombogenicity when bypassing below the inguinal ligament.

Only one randomized comparison study of Dacron and PTFE vascular grafts in aortic surgery showed their equivalent properties.

The benefit of PTFE vascular grafts in lower extremity revascularization was recently assessed in a randomized trial that showed comparable results between PTFE and Dacron vascular grafts.

Mechanism of vascular graft failure

The mechanism of failure of synthetic vascular grafts differs from that of vein grafts. The main reasons for the failure of prostheses include thrombogenicity of their lumen, discrepancy in elasticity and intimal hyperplasia in the area of ​​the anastomosis.

Luminal thrombogenicity, endothelial cell seeding, and antithrombotic coatings of vascular grafts

In humans, a monolayer of endothelial cells does not form in synthetic vessels. Thus, the surface of the prosthesis retains thrombogenic properties with constant activation of platelets and the risk of thrombosis. It is believed that the absence of a monolayer of endothelial cells is a key factor in the occlusion of the prosthesis, and therefore covering its inner surface with endothelial cells makes it possible to create a functioning biological prosthesis. This process is called “endothelial cell seeding.”

When seeding, it is necessary to fix endothelial cells on the surface of the prosthesis. They can be obtained from a vein, subcutaneous fat, or omentum and stabilized in tissue culture. The endothelial cells are then incubated on the inner surface of the plastic, resulting in the formation of a stable endothelial monolayer. Seeding of endothelial cells is performed in 1 or 2 stages. Two-stage seeding involves obtaining a small number of endothelial cells from a peripheral vein, multiplying the cells in culture, and then fixing them. The entire process usually takes up to 8 weeks. With one-stage sowing from the omentum one gets a large number of endothelial cells and are immediately fixed on the inner surface of the new vessel.

In animal experiments, the use of endothelial cell-coated plastic vessels resulted in significantly increased patency rates and decreased thrombogenicity of vascular grafts. However, in clinical settings, largely due to methodological difficulties, initial results have been disappointing. Recent studies suggest the feasibility of two-step endothelial cell seeding in a clinical setting. They revealed an increase in the frequency of prosthetic patency when shunting vessels below the inguinal ligament and coronary arteries. At present, endothelial cell seeding appears to be too costly a procedure to be recommended for wide application. However, in the future, advances in cellular and recombinant DNA technology will make it possible to use endothelial cells as a transport for targeted gene therapy that reduces the thrombogenicity of the prosthesis, as well as hyperplasia of smooth muscle cells and intima, both in plastic vessels and autovenous grafts.

In an attempt to reduce the thrombogenicity of the inner luminal surface, modification of the prostheses is also used. Thus, the carbon coating creates a negative charge, which reduces thrombogenicity. Animal studies have shown that the use of carbon-coated PTFE vessels reduces platelet retention, although randomized studies have not shown a significant increase in patency.

Small-diameter heparin-coated, collagen-sealed Dacron vessels have been developed. They are characterized by reduced platelet aggregation in the early period. However, there is a small risk of increased aggregation in sensitized patients. A randomized trial of 209 patients with femoropopliteal bypass surgery showed a significant increase in the patency rate of such vessel substitutes compared with PTFE (55% vs. 42% at 3-4 years), but more importantly, a significantly increased rate of limb salvage .

Experimental studies have shown that the use of fluoropolymer prostheses causes a less pronounced tissue reaction and reduces thrombogenicity. In the near future, such artificial vessels will become available commercially. Meanwhile, there is no clinical data confirming the advantage of these prostheses.

Elasticity discrepancy and intimal hyperplasia in the anastomotic area

The discrepancy in elasticity occurs due to different properties of the prosthesis and the artery. The elastic artery serves as a reservoir that stores energy during systole, which is released during diastole. Using a hard channel reduces this pulsating energy by 60%. IN artificial prostheses the discrepancy in elasticity is especially pronounced in the area of ​​the anastomosis. A paradoxical increase in elasticity is observed a few millimeters on both sides of the anastomosis - a zone of para-anastomotic hyperelasticity. Intimal hyperplasia predominantly develops in these areas.

The discrepancy in elasticity results in an area of ​​excessive mechanical stress that can initiate the proliferation of smooth muscle cells with subsequent production of extracellular matrix. Changes in elasticity also affect flow and shear stress. Turbulent flow causes shear stress, which can in turn initiate cellular changes leading to intimal hyperplasia. The experiment revealed a connection between the elasticity of the prosthesis and patency.

Polyurethane dentures

Polyurethanes are segmented polymers with hard (urethane group) and soft (macromonomer) sections. Polyurethanes have superior viscoelastic properties compared to PTFE and Dacron, and also have excellent blood and tissue compatibility. Taking into account these characteristics, active attempts are being made to obtain polyurethane vascular prostheses for clinical application. Unfortunately, early clinical trials showed low patency rates and a tendency to degrade to form aneurysms.

Recently, a chemical modification has been developed that makes it possible to obtain biologically stable polyurethane vascular grafts that do not undergo degeneration. Some of them are currently used in clinical practice, but are not routinely used in peripheral vascular surgery.

The August 2018 issue of the Journal of Vascular Surgery published an article: “A prospective randomized trial of stent after balloon angioplasty versus balloon angioplasty alone for the treatment of vascular graft stenosis in hemodialysis patients.”

The presented study, which took place in Taiwan, involved 98 adult patients ( average age 64 years old, 72% female) with clinically significant vascular graft stenosis (polytetrafluoroethylene: ePTFE) for hemodialysis. The ePTFE graft was required to show >50% stenosis on baseline angiography, where the degree of stenosis was defined as the narrowest portion of the venous outflow compared with the diameter of the nearest normal vein.

All patients were divided into 2 groups:

A study group of 49 patients received stent placement after a balloon angioplasty procedure.

A control group of 49 patients received balloon angioplasty only.

Vascular access was performed using an angioplasty catheter in the graft (6 F for the control group and 8 F for the test group) without systemic heparinization. Diagnostic angiography was then performed to determine the site of the lesion.

In the control group, an angioplasty balloon of the appropriate size was used to dilate the lesion within 1 minute. Then dilatation was repeated at intervals of 1 minute (but not more than 3 times) if further stenosis was observed.

In the test group, the lesion site was initially dilated with an angioplasty balloon (according to the same scheme as in the control group). A covered stent was then placed at the lesion site according to the size of the adjacent normal drainage vein. One dilation was then performed with the balloon just used.

The access catheter was removed after angiography and a hemostatic suture was placed. After the procedure, no additional antibiotics, antiplatelet drugs, or anticoagulants were used in either group.

According to the research results:

Restenosis developed after 3 months in 9% of patients in the study group, compared with 69% of the control group.

Restenosis developed after 6 months in 29% of patients in the study group, compared with 72% in the control group.

The authors conclude that the use of a stent after balloon angioplasty in patients on hemodialysis and with outflow stenosis of the prosthesis provides better results compared with the isolated use of balloon angioplasty.

See attached file for more details..