The problem of organizing the formation of vascular access. Hemodialysis

The preparation and establishment of vascular access should be an essential part of predialysis care and education for patients with CKD. Preparation includes the preservation of veins for future vascular access and the timing of adequate time to plan, create, and mature the vascular access.

1. Vascular access planning

An arteriovenous fistula usually requires at least 6 weeks to mature before it can be used for hemodialysis. Additional time may be required for conservative or surgical interventions in cases of delayed maturation of the fistula. For this reason, it is advisable to create an arterio-venous fistula at least 2-3 months before the earliest likely start of dialysis. The vascular prosthesis does not take time to mature and can be used 2-3 weeks after implantation. But the prosthesis cannot be considered optimal as the first vascular access. Moreover, the initiation of hemodialysis on central catheters should be avoided due to the risk of infection and the need for prolonged hospitalization.

Since the rate of progression of CKD often accelerates immediately before the onset of stage V CKD, the ideal time to decide on the preparation of a vascular access is the onset of stage IV CKD (reduced glomerular filtration rate).< 30 мл/мин) или даже ранее при документированном быстром прогрессировании ХБП или при других особых клинических условиях, затрудняющих создание сосудистого доступа (сахарный диабет, serious disease peripheral vessels).

1. Preoperative preparation

Successful creation and long-term functioning of the access is largely determined by preoperative examination and preparation. An objective examination of the chosen limb includes an assessment of the pulse in the distal part of the artery and the presence, diameter, and course of veins in the forearm and shoulder. Objective examination is difficult in obese patients. Preoperative ultrasound improves the chances of successful creation and long-term functioning of an arteriovenous fistula: in a randomized trial, the use of ultrasound reduced the risk of fistula failure from 25% to 6%. Although data from several studies are conflicting, a radial artery diameter of less than 1.6 mm was generally associated with a disproportionately worse prognosis for fistula function, and arterial blood flow velocity was less certain. Vein diameter less than 1.6 mm was also associated with worse prognosis. Among patients with well-functioning fistulas, there was an increase in vein diameter after tourniquet application by 48%, while poor fistula function was preceded by only a 12% increase in vein diameter after tourniquet application. A vein preservation policy to create vascular access throughout the course of CKD and exercise of the forearm muscles can increase the diameter and condition of the veins and arteries to create a fistula.

Routine venography with iodinated contrast prior to establishing a vascular access may cause an irreversible reduction in residual renal function. A reasonable alternative would be gadolinium or CO2 contrast. MRI angiography (TOF or gadolinium contrast) is rarely used for planning vascular access, but gives excellent results in agreement with conventional venography. NMR angiography can provide particularly accurate information about the central veins.

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

To understand the need to replace a damaged vessel, one should consider the work of the cardiovascular system. All parts of the human body require blood to be delivered to them. Blood carries oxygen and nutrients to every cell in 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 and pumps blood into the arteries. Arteries are tubes that distribute blood throughout the body. Arteries divide into branches that get smaller and smaller until they become microscopic capillaries. In the capillaries, oxygen and nutrients can easily leave the blood and enter the tissues and organs. After the blood passes through the capillaries, it enters the veins, which carry the blood back to the right side of the heart. The right side of the heart sends blood to the lungs, where it is enriched with oxygen and sent to the left side of the heart to be recycled throughout the body. This cycle keeps us alive. Normally, our heart beats more than 100,000 times a day (70 beats per minute on average), pumping about 7,000 liters on a total journey of 19,000 kilometers across the entire vascular system.

With age, the arteries become rigid (stubborn), some people may develop atherosclerosis - the scourge of modern humanity. Atherosclerosis causes narrowing of the blood vessels and can eventually lead to complete blockage. The reasons for the development of atherosclerosis are not fully understood. Several factors are known to contribute to the development this disease. Possible hereditary predisposition, hypercholesterolemia, increased low-density lipoproteins and lowered high-density lipoproteins, smoking, inactive lifestyle, high blood pressure, diabetes mellitus. Violation of blood supply to organs and tissues leads to a violation of their function. Damaged parts are not able to work with the same efficiency. However, if there is a load, it provokes the appearance of symptoms, such as pain in the legs when walking (a symptom of intermittent claudication). Narrowed arteries lower extremities unable to provide enough blood and oxygen during the work of the muscles, as a result, pain appears in them. A similar process develops in the heart, with damage to the arteries that feed the heart muscle. If the blood supply to the brain is disturbed, dizziness, short-term loss of vision, impaired sensitivity in the limbs, decreased memory and mnestic functions may appear. Another problem in the vascular system arises due to the thinning of the vessel wall, with an increase in the diameter of the vessel and the development of an aneurysm. When the aneurysm reaches a certain size, the latter can burst and the person will die from blood loss.

The problem of atherosclerosis treatment is complex. It is extremely important to control those factors that are known as the causes of the development of the disease. Unfortunately, there is little we can do about our genetic predisposition. Most important is smoking cessation. Examination and treatment of high blood pressure, high cholesterol, correction of diabetes are also very important. If all of the above measures are followed, 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 from peripheral arteries, stimulating the development of collateral (roundabout) blood flow paths, and improving the nutrition of suffering tissues and organs. Physical exercise are also useful, but you should not work on the principle: "the more the better." If pain occurs, you should stop exercising.

The above measures are almost 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. If you need surgical treatment, duplex ultrasound and angiography are a very important stage of the study. An angiogram is an x-ray examination, which is accompanied by the introduction of a contrast solution (dye) into the vascular system through a syringe in the groin or armpit area. An angiogram maps the location of your arteries and shows the exact location of narrowing and blockages. Some of the constrictions can be widened with a balloon catheter inserted into the vessel through the groin or axilla. 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 re-development of the narrowing, this is stenting. Other vascular narrowings and blockages that are not amenable to angioplasty are treated with a surgical operation - bypass, i.e. forming a bypass of the blockage.

A vascular shunt can be described as a bypass road built around an overcrowded city. With this technique, the narrowed or blocked area is not removed, but a "bypass" is attached in the area of ​​the healthy vessel above and below the narrowed 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 country). 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 photo shows an artificial bifurcation prosthesis of the aorta and iliac arteries, installed for a type 3 aortic aneurysm.

The shunt in the groin and lower extremities is very often made from the patient's own vein. Own vein is the best material for shunting in this area, however, if such material is not available, an artificial prosthesis must also be used.

Artificial vascular prostheses are, developed by scientists, substitutes for real vessels. human body. They work in a similar way to natural 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 chance that the shunt won't last forever? Yes, there is. Many factors can influence this. 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 termination of the shunt may be the gradually forming layers on the inner walls of the shunt, with its considerable length. Taking certain doses of "thinning" drugs can help prolong the operation 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 are the only method of prolonging a full life.

Synthetic arteriovenous prostheses.

1. What is an arteriovenous access for hemodialysis? To conduct an effective hemodialysis session with a sufficiently high degree of purification, it is necessary to provide 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 from an artery. It is impossible to obtain blood at such a rate from a peripheral vein. The idea of ​​launching arterial blood flow into the saphenous vein was realized in 1966. Then the first arteriovenous fistulas (AVF) were formed on the forearm and good practical results of their application were obtained. The formation of an anastomosis between the artery and the saphenous vein leads to a multiple increase in blood flow in this vein. As a result of the constant discharge of blood, the vein dilates. For passing through an artificial kidney, blood is diverted into the extracorporeal circuit using two dialysis needles inserted into the lumen of the "fistula" vein at a certain distance from each other, for blood sampling and return, 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 AVF ligation.

2. When is the need for a synthetic prosthesis? The service life of the AVF is limited. Loss of vascular access occurs as a result of thrombosis or infection. Following the old, a new AVF is formed, then another and another. In the life of many dialysis patients, there comes a point when years of hemodialysis treatment are behind us, several operations to form an arteriovenous fistula (AVF), and the possibilities of forming a new native (i.e. from own vessels) vascular access have been exhausted. In some cases, already at the very beginning of dialysis therapy, the surgeon encounters significant difficulties in the formation of AVF from their own vessels, for example, in obese patients. In such situations, the formation of a permanent vascular access (PSA) is possible with the help of a prosthesis. Arteriovenous prostheses (AVP) can be biological: autogenous (prosthesis from an autovein), allogeneic (cadaveric vein, vein of the umbilical cord), xenogenic (bovine carotid artery, bovine ureter, bovine mesenteric vein). Arteriovenous prostheses can also be synthetic: polyurethane, teflon, dacron, polytetrafluoroethylene. At the present stage of development of vascular access surgery, synthetic prostheses made of microporous polytetrafluoroethylene (PTFE) are most widely used. Variants of different lengths, thicknesses and diameters are available on the market, reinforced with removable and built-in rings, prostheses with a narrowed arterial or dilated venous end. The following are the features of the installation and maintenance of WUAs.

3. How are synthetic prostheses used in the arteriovenous position? An arteriovenous prosthesis is sutured with one end into an artery and the other end into a vein, functioning as a subcutaneous arteriovenous shunt. The implanted prosthesis plays the role of a fistula vein, punctured for access to blood for hemodialysis. Accordingly, it should be located superficially and rectilinearly under the skin on the side of the limb convenient for puncture. In this case, the prosthesis must be of sufficient length (at least 15-20cm). This is necessary to rotate the punctures (changing puncture sites between sessions to scar wall defects) and to ensure the minimum allowable distance between dialysis needles (5 cm), preventing recirculation between the needles. During recirculation, the already purified blood from the “return” needle is re-sucked into the “intake” 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. High blood flow velocity in the prosthesis is a natural barrier to thrombosis. The linear velocity of blood in the prosthesis many times exceeds the velocity in the artery under natural conditions. This condition (one of the three according to Virchow) gives a certain “margin of safety” against the other two possible thrombogenic factors: a) hypercoagulability and b) damaged (in our case, alien) vascular wall. In an effort to obtain a high blood flow velocity in the prosthesis, it is necessary to select such vessels for implantation that can provide such blood flow. Artery - high blood flow, vein - low resistance.

4. Stage of vascular access planning. 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. Vascular anatomy may have been altered by prior surgeries to form the PSD. The consequences of phlebitis of the superficial veins, atherosclerosis or diabetic calcification of the distal arteries can make their own adjustments to the operation plan. When choosing the future location of the prosthesis, it is necessary to observe the principle of vascular economy, that is, all other things being equal, the choice should be made in favor of a more distal location, so as to save vascular vacancies for future operations. Examination of the patient should be performed in a warm, well-lit room. The veins are palpated below the cuff of the tonometer, swollen to 50 mm Hg. Palpation should be supplemented with an ultrasound examination of the diameter and patency of the vessels. The diameter of the artery and vein for the implantation of the prosthesis must be at least 3 mm. The definition of pulsation on the brachial artery is a sufficient condition for the prosthesis. Distal arteries may not always be involved with certainty in access formation. Constraining factors for the use of distal arteries are common widespread calcification and small diameter. The vein can be used both subcutaneous and deep (one of the two accompanying the brachial artery). The larger the vein diameter, 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 frequently in large veins.

The prosthesis can be located on the limb in two versions: straight and loop. The most common 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 a wide opportunity for rotation of punctures on both halves of the prosthesis. The prosthesis is placed with a loop, for example, when the brachial artery in the cubital fossa and the ulnar venous fork, or the brachial artery and the basilar vein, or the brachial artery and the deep vein are involved in the access. 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 variants of the loop with branches of different sizes are also possible. It all depends on the specific anatomical situation and the location of vessels suitable for the formation of AVP. The main condition remains a sufficient total length of the segments of the prosthesis intended for puncture - more than 15-20 cm. It must be understood and taken into account that hemodialysis doctors, who are responsible for the safety of the prosthesis, will not risk puncturing near the anastomoses and near the top of the loop. The 3-5 cm prosthesis closest to the p / o scars will not be used for punctures. Also, they will not be used for punctures of the prosthesis bending zone, if such are allowed during implantation. Therefore, the total length of the prosthesis used in the form of a loop should be at least 25-30 cm.

The prosthesis can also be placed on limbs and in direct form. This is possible with a large distance between the artery and vein. For example, when using the distal segment of the radial artery (a very rare option) and one of the veins at the level of the elbow or lower third of the shoulder. The second option for a direct prosthesis: the brachial artery in the cubital fossa is the axillary vein. In both cases, the puncture segment of the prosthesis must also be of sufficient length. In addition to the above options, a direct prosthesis can be located in the form of a "bridge" between an artery remote from each other and a fistula vein left after the loss of an AVF. This is possible when the fistula vein that has already served 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 bridge prosthesis 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 it can also remain intact, performing only the role of a "bridge". In this case, only the vein will be punctured with both needles.

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

An operation involving a synthetic prosthesis cannot be planned in case of systemic manifestations bacterial infection. Probable hematogenous contamination of the prosthesis conservative treatment does not lend itself. The infected prosthesis will have to be removed.

5. Technique of implantation of arteriovenous prosthesis.

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

Operational planning after a thorough examination should be completed with an operative access plan. Adequate access to the vessels is half the success of the operation. Adequate access is an 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 according to the surrounding landmarks (moles, p / o scars), since after infiltration anesthesia appearance limbs may change, skin folds and venous pattern will disappear. In all cases, longitudinal incisions are recommended. Firstly, a longitudinal incision on the limb is less traumatic (the longitudinally located nerves and lymphatic vessels are less likely to be damaged). Secondly, such an incision can, if necessary, be extended along the selected vessels.

Consider the most common version of the arteriovenous prosthesis on the forearm - a loop with anastomoses in the cubital fossa. After a longitudinal incision, usually 5 cm is sufficient, an ulnar venous fork is exposed in the subcutaneous fat layer. The location of the venous anastomosis is advantageous here, since from here the 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 communicating vein, which is constantly present here, in the direction of the system of deep veins accompanying the artery. Venous hemodynamic conditions in this zone are most favorable for the prosthesis, providing maximum outflow and low resistance. The brachial artery stands out here after dissection of Pirogov's fascia. In this place, its trifurcation is usually located (division into the radial, ulnar and common interosseous branches). For an anastomosis with a prosthesis, a section of the brachial artery is allocated immediately above its division. The standard prosthesis suitable for use in this location is 6 mm in diameter and 40 cm long. To minimize contact of the prosthesis with external environment, it must 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 carried out under the skin after the allocation of vessels and before the imposition of anastomoses. For this, a curved forceps or a special tunneler is used. To lay the prosthesis in the form of a loop, one or two additional incisions of 1-2 cm in the bend area will be required. The prosthesis should be carried directly under the dermis in a straight path, without bending and diving deep. There should be no twists and kinks of the prosthesis in the canal. If a stretch prosthesis (stretch) is used, it should be submaximally stretched before trying on 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 in wave-like bends under the skin. These curves 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, nevertheless, a small margin of elasticity should be left. The fact is that the elasticity of the prosthesis determines its ability to soften the systolic wave to some extent, which probably plays a role in the development of pseudointimal hypertension and vein stenosis. After passing the prosthesis under the skin, additional incisions must be sutured. So we reduce the duration of contact of the prosthesis with environment to the 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 total outflow path. All venous outflow tracts accessible through the venotomy are filled with heparinized saline using a pressurized syringe to prevent thrombosis and to assess resistance, to finally verify the suitability of the vein. The 20 ml syringe must empty into the vein in less than 4 seconds. If the diameter of the veins is borderline small, it is recommended to destroy the proximal distal venous valve with a bellied probe in order to ensure additional outflow of blood in a retrograde direction to the nearest collaterals. The first superimposed venous anastomosis, then arterial. Both anastomoses are superimposed according to the type of the end of the prosthesis in the side of the vessel. If a large diameter vein (greater than 5 mm) is present, end-to-end anastomosis may be performed. The cut of the ends of the prosthesis should be made oblique, so that the prosthesis leaves the artery and approaches the vein at an angle - this is a necessary condition for a 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 into the vein more physiological. From this point of view, the ideal configuration of the anastomosis, provided that the diameter of the vein 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 narrowing of the vessel when applying stitches of a continuous suture 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 achieve an increase in blood flow, since the diameter of the prosthesis still remains constant - 6 mm. But to reduce the blood flow through the prosthesis (for example, in order to prevent the steal syndrome) it is possible by reducing the diameter of the arterial anastomosis (by suturing the prosthesis itself or using a prosthesis with an arterial end narrowed to 4 mm).

For the imposition of anastomoses, polypropylene or polytetrafluoroethylene 6-0 suture material is used. At the proximal angles of the anastomoses, the distance between the stitches of the continuous suture should be kept to a minimum to reduce the tightening "purse-string" effect that any continuous suture has. Rough and rare seams in this place can lead to narrowing of the already small lumen of the vessel. Depending on the specific situation and the preferences of the surgeon, the anastomoses are superimposed with a continuous suture on two or one holder, from the outside or from the inside, with one or two needles towards each other. But it is not recommended to sew the proximal, most important angle of the anastomosis (arterial and venous) blindly, that is, the last one, when it is impossible to control the quality of the seam from the inside. Thus, it is desirable to start a continuous suture from the distal angle of the anastomosis or from the middle of the lateral wall and finish it there. After being released into the bloodstream, bleeding from the needle punctures of the prosthesis along the suture line is observed for several minutes. Such bleeding is stopped by patient, tight, 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, systolic-diastolic tremor should be felt over the entire prosthesis. The absence of trembling in diastole indicates high resistance, low blood flow velocity in the prosthesis, and a high probability of thrombosis in the early stages. If the trembling is not felt even in systole, and only a high pulsation on the prosthesis is determined, there is high resistance, and the blood flow is very low or absent altogether. If a weak pulsation and low turgor of the prosthesis is determined, a weak blood flow from the artery is likely. The most common causes of low blood flow through the prosthesis are: gross defect in the anastomosis, bending of the prosthesis at the top of the loop, torsion of the prosthesis in the canal, unaccounted for defect of the vein above the anastomosis (stenosis or occlusion), overestimation of the capacity of the artery. Many of the identified defects leave room for immediate correction and retention of access.

Before suturing, it is necessary to treat the wound with hydrogen peroxide for the purpose of antisepsis and mechanical cleaning of the wound from detritus, dust and random microbial bodies. Wound closure should be layered.

6. Early postoperative period. In the early postoperative period, various negative phenomena can 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 thrombectomy, shift the anastomoses. An early thrombosed prosthesis should be removed. 2) If thrombosis of the prosthesis develops several days after the operation, the probability of successful thrombectomy is quite high. If thrombectomy is not effective, the prosthesis must be removed. 3) Shortly after the operation, edema of the limb usually develops, within a few days it can progress. 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-term edema is stenosis of the central venous outflow tracts (at the level of the subclavian, brachiocephalic, or even superior vena cava). These are the consequences of standing central venous catheters. Pronounced edema of the limb can become an obstacle to the safe puncture of the prosthesis. In severe cases, the prosthesis must be removed or ligated. After the cessation of the arteriovenous discharge, the edema quickly regresses. 4) Lymphorrhea from the p / o wound increases the risk of infection of the prosthesis, it is more common with transverse skin incisions. Therefore, longitudinal incisions are recommended as less traumatic. 5) Infection of the wound and prosthesis in the early p / o period is a consequence of intraoperative violations of asepsis. The infected prosthesis must be removed.

2-3 weeks after the operation, the prosthesis can be used for hemodialysis. By this time, the edema has already completely regressed, the superficially located prosthesis is easily determined by palpation along its entire length, the soft tissues around the prosthesis are somewhat compacted. But a more reliable fixation of the prosthesis in the canal (fouling with connective tissue) occurs after a few months. The patient should be taught how to clean the skin of the puncture site with soap and water a few minutes before dialysis. Before the puncture, the dialysis staff treats this 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 that the lateral and posterior walls of the prosthesis are not injured. This can lead to the formation of a hematoma and a false aneurysm. Usually, 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) - for the arterial (fetching) needle, the venous half - for the return needle. It is necessary to alternate the puncture sites from dialysis to dialysis, splitting “paths” with a step of 5 mm, the maximum possible length of the prosthesis. Punctures near the anastomoses and the top of the loop are not recommended, since when puncturing any non-linear segment of the prosthesis, the risk of damage to the lateral or posterior wall is higher. At the end of the hemodialysis session after the removal of the needles, hemostasis is carried out by moderate pressing 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 anastomosis zone and for some extent of the vein above it. In this case, the wall of the vein 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 systolic wave, which are unusual for a 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 it depends on the initial diameter of the vein, the configuration of the anastomosis. As the stenosis progresses, the pressure in the prosthesis increases and blood flow decreases. A decrease in linear and volumetric blood flow can be recorded using ultrasound. Problems can be suspected by indirect signs: in recent months, the prosthesis has become harder, the pulsation is high; pressure in the venous line gradually increases from dialysis to dialysis; the dose of dialysis is reduced, hyperkalemia is observed after dialysis. The effectiveness of dialysis in stenosis is reduced as a result of an increase in blood recirculation between the needles as the blood flow velocity decreases. The 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 inactivation of the injected heparin, against the background of hypovolemia and blood clotting - 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 vein stenosis.

V rare cases, the cause of low blood flow in the access, predisposing to thrombosis, may be stenosing atherosclerosis of the artery. Also, in some cases, it is not possible to establish the presence of stenosis, and after a 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. Restoration of the patency of the arteriovenous prosthesis. In case of thrombosis of the prosthesis, an attempt should always be made to disintegrate it. Access to the prosthesis is carried out in one of the non-punctured areas: either the top of the loop, or near the venous anastomosis. The latter localization is more profitable, since if venous stenosis is detected during thrombectomy, this access will be used for subsequent reconstruction - bypass reanastomosis. So, the prosthesis is allocated in the non-punctured zone, it is incised transversely along the upper wall by 4-5 mm. Thrombectomy is performed using a 6 French Fogarty balloon catheter. The filling of the balloon is about 1 ml. Thrombectomy is performed in stages and repeatedly to ensure complete cleaning of the prosthesis from thrombus fragments. In addition to fresh soft blood clots, sometimes there are old dense overlays in the form of a cast of the prosthesis. Such an old parietal thrombosis is a confirmation of vein stenosis. By the way, they are usually located in the venous half of the prosthesis. In such cases, a bellied probe should come to the aid of the Fogarty catheter. With the help of a probe or a long jaw of tweezers inserted into the lumen of the prosthesis, the prosthesis is mechanically processed from the inside, lumps are easily removed with a balloon. First, thrombectomy is performed from the venous part of the prosthesis with an entry into the vein by 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 the release of the venous part, thrombectomy is performed from the arterial part of the prosthesis, going beyond the arterial anastomosis. The artery with prosthesis thrombosis usually remains passable, and prosthesis thrombosis has its origin from the anastomosis line. In this place, a dense red thrombus is formed with a white or gray concave surface corresponding to the lumen of the artery. This "arterial plug" has a length of 1-2 cm and the longer the thrombosis, the denser it is. The thrombus behind the cork along the entire length of the prosthesis is soft and easily fragmented during thrombectomy, while the cork 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 removal of the balloon catheter from the lumen of the prosthesis, the cork is knocked out by a fountain of blood unnoticed by the operator. In this case, upon careful examination, it can be found on linen around the surgical area. After receiving the plug, it is necessary to evaluate the blood flow from the side of the arterial anastomosis by releasing the lumen from the clamp for a fraction of a second: the blood flow should be “gushing”, “foaming”. If the blood flow is weak, it is likely that an arterial plug has 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 in late thrombectomy, when the arterial plug is already tightly 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 with a probe from the nearest access. This approach to thrombosis allows restoring the patency of the prosthesis several weeks after thrombosis.

After cleaning each half, the prosthesis is filled under pressure with heparinized saline. solution. At the same time, according to the speed of emptying the syringe towards the venous anastomosis, one can approximately estimate the resistance. If a 20 ml syringe empties faster than 4 seconds, the resistance is considered low. But the syringe must be untouched. First you need to check the syringe in the glass, so as not to confuse the property of a vein with the property of a tight syringe plunger.

If a good blood flow is obtained from the artery and no venous stenosis is detected, the prosthesis defect is sutured, the blood flow in the prosthesis is restored, and access can be immediately used for hemodialysis. Venous stenosis is more common. If technically feasible, stenosis can be confirmed intraoperatively by angiography.

The task of the surgeon 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) Venous anastomosis plasty. The entire area of ​​the prosthetic-venous anastomosis is isolated from the scars, the stenotic area is dissected along (with the continuation of the incision, if necessary, along the prosthesis) and a patch 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 made with another vein of a suitable diameter, if one is available nearby.

3) Proximal venous reanastomosis (bypass reanastomosis) is the most common and simplest option. It is necessary to highlight the prosthesis and cut 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 segment of a similar prosthesis of the required length; the prosthesis elongated in this way is carried under the skin to the vein highlighted above and sewn into it end to side or end to end.

It is difficult to overestimate the benefits of immediate venous reconstruction: first, the cause of thrombosis, stenosis, is removed; secondly, the prosthesis can be used immediately after the operation; thirdly, there is no need for catheterization of the central vein; fourthly, the principle of saving vascular resources is observed, because the same vein is used above the stenosis. If the anastomosis reconstruction is not performed with the detected stenosis, the recurrence of thrombosis is likely to occur within a few days or weeks.

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

9. hemodynamic complications. Unnatural discharge of blood from an artery into a vein, bypassing the peripheral channel, 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 characteristic of 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 with time to a small extent.

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

The steal syndrome develops when 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 artery, but also part of the retrograde blood flow from the distal artery, which is provided by collaterals. The severity of the clinical picture of the steal syndrome depends on the degree of stealing of the collateral blood flow and the possibilities of this collateral blood flow. In mild cases, patients are concerned about the pallor and chilliness of the hand, they constantly wear a glove. Depending on the severity, numbness, constant pain in the fingers and hands, muscle weakness, dry gangrene of the fingers join. Treatment of severe cases is urgent ligation of access. After the cessation of blood shunting, improvement occurs already in the first minute, the symptoms regress completely. In some cases, a good effect can be achieved by partial ligation (narrowing) of the vein (prosthesis).

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

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

The syndrome of venous hypertension develops against the background of stenosis or occlusion of the central vein. It is manifested by edema of the limb, cyanosis and trophic disorders up to ulcers (usually on the back of the hand). The severity of the syndrome depends on the magnitude of the discharge along the AVP, the degree of stenosis of the subclavian (or / and 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 AVF ligation.

Heart failure after the imposition of AVF and AVP may 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 postoperative wound in the early postoperative period is usually associated with infection of the prosthesis. Antibacterial therapy for prosthesis infection is ineffective. Such a prosthesis must be removed. The prosthesis is removed completely with ligation or plasty of the artery. The defect in the artery can be sutured with a continuous suture; plasty of the artery with an autovein can be performed. If this is not possible, the artery may be ligated.

In later periods, infection of the prosthesis is more often local in nature, associated with puncture and violation of the rules of asepsis on dialysis. In such cases of limited infection, the 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, the segment of the prosthesis carrying the infected area is excised. The prosthesis loop is restored by two end-to-end anastomoses using a segment of a similar prosthesis, held under the skin away from the infected area. While 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 anterior surface of the prosthesis, in one line. 1 dialysis - 2 punctures, a week - 6 punctures, within a month - more than 24, a year - about 300 punctures. Each defect of the prosthesis is replaced by scar tissue. After years of operation, the front wall of the prosthesis is dissected 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 of connective tissue that includes the capsule of the prosthesis 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 prosthesis along the entire length. If punctures were performed in selected areas, local saccular degeneration develops faster, does not look aesthetically pleasing, and limits the puncture zones. vein stenosis and high blood pressure in the prosthesis are likely to contribute to the more rapid development of aneurysms. Usually, the deepest places of protrusions are lined with old parietal blood clots. Such prostheses are more difficult to thrombose; a balloon catheter of a larger diameter than usual is needed. By themselves, true aneurysms of AV prostheses are not an indication for any intervention. Sometimes, as a result of a local infection of the scar tissue at the puncture site, the aneurysm wall becomes so thin that there is a threat of rupture. In this case, the prosthesis must be ligated upstream. In rare cases of widespread infection of such prostheses, their removal can be technically difficult. As a result of a long-term latent infection, the capsule around the prosthesis thickens significantly, takes on a cartilaginous density, thus acting as a protective shaft that localizes the focus of infection. The prosthesis can be removed from long incisions, often in fragments, along with the surrounding tissues.

Sometimes during dialysis, the side or back wall of the prosthesis is injured with a needle. It is more difficult to perform hemostasis with a finger here than on the anterior wall. In this case, a hematoma forms near the prosthesis. If the defect in the wall of the prosthesis 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. On palpation, a distinct pulsation of the hematoma and systole-diastolic friendship are determined. Pulsating hematomas are always tense and can lead to compression and thrombosis of the prosthesis. The operation is performed: suturing the defect of the prosthesis; or replacement of the segment of the prosthesis bearing the defect with a segment of a new similar prosthesis. If an aneurysm formed early after surgery in the anastomotic area, it is necessary to perform a revision and suture the anastomotic defect. If the aneurysm appeared late in the area of ​​the anastomoses, infection and erosion should be suspected. In this case, it is recommended beforehand, before the revision, to isolate the brachial artery from a separate incision above and take it on a holder. Such a prosthesis is subject to removal, the artery in the anastomosis zone - plastic or ligation.

12. The future of prostheses? Probably not for synthetic. The craze for polytetrafluoroethylene prostheses is already in 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 displaced veins (transposition of veins in the arms, use of the great saphenous vein as a prosthesis) over synthetic prostheses. But practice shows that it is absolutely impossible to do without synthetic prostheses. They firmly occupy their considerable niche in the structure of vascular access surgery for hemodialysis. There is an active search and development of new synthetic and biological materials for the production of more reliable and durable Arterio-Venous Prostheses.

Vascular prostheses interact with blood and surrounding tissues, therefore, due to their inherent thrombogenicity, shortly after implantation, synthetic prostheses are covered with fibrin and platelet thrombi. This lining retains thrombogenicity and stabilizes a year or more after surgery. The healing of a synthetic prosthesis occurs through two mechanisms - migration of endothelial cells along the implant and ingrowth of capillaries.

The extent of endothelialization varies significantly as endothelial cells migrate from the artery to the surface of the prosthesis. Although this process may result in complete endothelialization in animal models, in humans synthetic vascular prostheses never form a monolayer of endothelial cells. Capillaries grow from surrounding tissues. The degree of incorporation varies from the porosity of the prosthesis, the higher the porosity, the stronger the vessels penetrate into it.

Synthetic vascular prostheses made of Dacron

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

In braided prostheses, 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. Braided prostheses are characterized by a relatively high porosity, therefore, to prevent bleeding, it is necessary to carry out their preliminary thrombosis. They tend to dilate over time, but they promote ingrowth of surrounding tissues and have excellent handling characteristics. In recent years, most braided vascular prostheses have been impregnated with collagen, albumin, or gelatin, which eliminates the need for pre-thrombosing. There is evidence that such coatings can reduce early thrombogenicity of the vascular prosthesis surface, with an expected improvement in patency. However, in a randomized trial, a reduction in blood loss or an improvement in patency has not been proven.

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

Stretched polytetrafluoroethylene prostheses

Expanded polytetrafluoroethylene (rPTFE) vascular prostheses are produced by pressing a PTFE polymer, which results 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 a high porosity and low permeability. PTFE is an inert substance with a negative charge, which makes the prosthesis hydrophobic. Some vascular prostheses are covered with a thin outer sheath to increase wall strength and further reduce permeability. Currently, PTFE prostheses are produced with a thin wall, which improves their manipulation properties and increases the longitudinal elasticity. External support helps to prevent their bending in the area of ​​​​the joints and, thereby, to increase patency in the long term. However, in a prospective randomized trial, the use of external support did not show improvement in patency.

Some surgeons prefer PTFE prostheses over Dacron prostheses because of their higher resistance to infection and low thrombogenicity in subgroin grafts.

Only one randomized comparative study of Dacron and PTFE vascular prostheses in aortic surgery has shown their equivalent properties.

The benefit of PTFE vascular prostheses in lower limb revascularization was recently evaluated in a randomized trial that showed comparable results with PTFE and Dacron vascular substitutes.

Mechanism of insufficiency of vascular prostheses

The failure mechanism of synthetic vascular prostheses differs from that of venous grafts. The main causes of prosthesis insufficiency include thrombogenicity of their lumen, elasticity mismatch and intimal hyperplasia in the anastomotic area.

Lumen thrombogenicity, endothelial cell seeding, and antithrombotic coatings of vascular prostheses

In humans, a monolayer of endothelial cells is not formed in synthetic vessels. Thus, the surface of the prosthesis retains thrombogenic properties with permanent platelet activation 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 the coating of its inner surface with endothelial cells makes it possible to create a functioning biological prosthesis. This process is called "seeding of endothelial cells".

When sowing, 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 endotheliocytes are then incubated on the inner surface of the plastic, whereby a stable endothelial monolayer is formed. Seeding of endothelial cells is performed in 1 or 2 stages. Two-stage seeding consists in obtaining a small amount of endotheliocytes from a peripheral vein, cell propagation in culture, and their subsequent fixation. The entire process usually takes up to 8 weeks. With one-stage seeding, a large number of endotheliocytes are obtained from the omentum and immediately fixed on the inner surface of the new vessel.

In animal experiments, the use of plastic vessels coated with endothelial cells resulted in a significant increase in the patency rate and a decrease in the thrombogenicity of vascular prostheses. However, in clinical settings, mainly due to methodological difficulties, disappointing initial results were obtained. Recent studies indicate the feasibility of two-stage seeding of endothelial cells in the clinical setting. They revealed an increase in the frequency of prosthesis patency when bypassing vessels below the inguinal ligament and coronary arteries. At present, seeding of endothelial cells seems to be too expensive a procedure to be recommended for widespread use. 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 prosthesis thrombogenicity, as well as hyperplasia of smooth muscle cells and intima, both in plastic vessels and autovenous grafts.

In an attempt to reduce thrombogenicity of the inner surface of the lumen, modification of prostheses is also used. So, the carbon coating creates a negative charge, which reduces thrombogenicity. Animal studies have shown that the use of carbon-coated PTFE vessels reduces platelet fixation, although no significant increase in permeability has been observed in randomized trials.

Small-diameter heparin-coated and 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 in 209 patients with femoropopliteal bypass showed a significant increase in the patency rate of such vascular substitutes compared to PTFE (55% vs. 42% at 3-4 years), but, more importantly, a significant increase in limb sparing .

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

Elasticity mismatch and intimal hyperplasia in the anastomotic area

Elasticity mismatch occurs due to different properties of the prosthesis and the artery. The elastic artery serves as a reservoir, storing 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 in a few millimeters on both sides of the anastomosis - a zone of paraanastomotic hyperelasticity. Intimal hyperplasia predominantly develops in these areas.

The elasticity mismatch results in a zone of excessive mechanical stress, which can initiate the proliferation of smooth muscle cells with subsequent production of extracellular matrix. Elasticity changes also affect flow and shear stress. The turbulent flow causes shear stress, which in turn can initiate cellular changes leading to intimal hyperplasia. The experiment revealed a relationship between the elasticity of the prosthesis and patency.

Polyurethane prostheses

Polyurethanes are segmented polymers with hard (urethane group) and soft (macromonomer) sites. Polyurethanes have superior viscoelastic properties compared to PTFE and Dacron, as well as superior blood and tissue compatibility. In view of these characteristics, active attempts are being made to obtain polyurethane vascular prostheses for clinical use. Unfortunately, early clinical trials have shown a low patency rate and a tendency to degrade with aneurysm formation.

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

Vascular access is the way of life for hemodialysis patients. Vascular access enables life-saving hemodialysis treatment. Hemodialysis is a treatment for kidney failure in which a machine sends the patient's blood through a filter called a dialyzer outside the body. Access is a vein operation done to remove and restore blood during hemodialysis.

Blood flows through the needles, several ounces at a time. The blood then moves through a tube that delivers it to the dialyzer. Inside the dialyzer, blood flows through fine fibers that filter out waste and excess fluid. The machine returns the blood filtered to the body through another tube. Vascular access allows a large amount of continuous blood flow during a hemodialysis procedure to filter out as much blood as possible for each procedure. About 500 ml of blood passes through the machine every minute. Vascular access should be made several weeks or months before the first hemodialysis session.

Two types of vascular access designed for long-term use include arteriovenous (AV) fistula and AV graft. The third type of vascular access is a catheter vein for short-term use.

What is an arteriovenous fistula?

An AV fistula is a connection made by a vascular surgeon from an artery to a vein. Arteries carry blood from the heart to the body, while veins carry blood from the body back to the heart. Vascular surgeons specialize in vascular surgery. The surgeon usually places an AV fistula in the arm or forearm. An AV fistula causes extra pressure and extra blood to flow into the vein so it gets bigger and stronger. Large veins provide easy and reliable access to blood vessels. Without such access, regular hemodialysis sessions will not be possible. Unregulated veins cannot withstand multiple needle insertions. The veins will be damaged like broken straw due to the strong suction force.

• provide good blood flow for dialysis
• last longer than other types of access
• less chance of infection or blood clots than other types of access

Before an AV fistula operation, the surgeon may do a blood smear test. Vascular mapping uses Doppler ultrasound to evaluate blood vessels, which surgeons can use to create AV fistulas. An ultrasound uses a device called a transducer that reflects sound waves into an organ to create an image of the organ's structure. A trained technician specifically performs procedures in the supplier's office medical services, in an outpatient center or in a hospital. A radiologist who specializes in interpreting medical images. The patient is not anesthetized. Doppler ultrasound shows how much and how fast blood is flowing through arteries and veins so surgeons can select the best blood vessels to use.

A surgeon performs an operation on a fistula in an outpatient center or hospital. Vascular access procedures may require an overnight stay in the hospital; However, many patients go home afterwards. Medical professionals use local anesthesia to numb the area where the surgeon is creating the fistula.

AV fistulas often take 2 to 3 months to form or can be used before a patient can use them for hemodialysis. If the AV fistula fails after surgery, the surgeon must repeat the procedure.

What is an arteriovenous graft?

An AV graft is a looped plastic tube that connects arteries to veins. A vascular surgeon performs an AV transplant operation, such as fistula surgery, in an outpatient center or hospital. As with AV fistula surgery, patients may need to stay in the hospital, although many patients may return home after the procedure. medical worker uses local anesthesia to numb the area where the surgeon creates the AV graft.

The patient can usually use the AV graft 2 to 3 weeks after surgery. AV grafts are more likely than AV fistulas to have problems with infection and clotting. Blood clots can block blood flow through damaged sperm. However, a good transplant can take several years.

What is a venous catheter?

A venous catheter is a tube that is inserted into a vein in the neck, chest, or leg near the groin, usually only for short-term hemodialysis. The tube is divided into two tubes from the body. The two tubes have a top designed to connect to a channel that brings blood into the dialyzer and a channel that brings blood from the dialyzer back into the body. The person must close the clamp each time the catheter is connected and removed from the tube.

If kidney disease has developed rapidly, patients may not have time to place an AV fistula or AV graft before starting hemodialysis treatment.

A nephrologist, kidney doctor, or radiologist uses medical imaging equipment to perform a venous catheter surgery in a hospital or outpatient center. The patient receives local anesthesia and sedation to remain calm and relaxed during the procedure.

Venous catheters are not ideal for long-term use. With a venous catheter, patients may experience blood clots, infections, or injury to the veins, causing narrowing of the blood vessels. However, if the patient needs to start hemodialysis directly, the venous catheter will work for several weeks or months until the surgeon can perform long-term access surgery and the AV fistula or AV graft can be used.

If fistula or graft surgery fails, the patient will need access to a long-term venous catheter. When a patient needs a venous catheter for more than 3 weeks, the surgeon will "tunnel" the catheter under the skin instead of inserting it directly into a vein. The catheter tunnel is more convenient and has fewer problems. But the tunneled catheter can also become infected.

What problems can be caused by vascular access?

All three types of vascular access (AV fistula, AV graft, and catheter vein) can cause problems that require further treatment or surgery. The most common problems include access infection and low blood flow due to access to blood clots.

Infection and poor blood flow are less common in AV fistulas, which are well formed than in AV graft and venous catheter. However, the presence of an AV fistula does not guarantee access will be problem-free.

The AV graft is more likely to experience poor blood flow, signs of clotting, or access narrowing. A damaged AV may require angioplasty, a procedure to widen a narrow area. Another option involves surgery on the AV graft to replace the narrow part.

A venous catheter most commonly causes infections and clotting problems. If this problem develops, the use of medications may help. Antibiotics are medicines that fight bacteria that can cause an infection. Blood thinners such as warfarin help prevent blood from clotting. If this treatment fails, the catheter should be replaced by a nephrologist or radiological intervention specialist.

Vascular access for hemodialysis

1

Purpose of work: to study the possibility of forming 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 diabetes Type II with terminal 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 the results of treatment, the frequency of stenosis, thrombosis of the native permanent vascular access, the number of repeated operations within three years were taken into account. Results. In the formation of 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 during the formation of 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 terminal chronic renal failure with type II diabetes mellitus. The developed complications 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

1. Bikbov B. T., Tomilina N. A. Status of renal replacement therapy in patients with chronic renal failure in Russian Federation in 1998-2007 (report according to the Russian Register of Renal Replacement Therapy) // Nephrology and dialysis. - 2009. - T. 11, No. 3. – S. 144-243.

2. Conner K. Vascular access for hemodialysis // Nephrology. - 2009. - T. 13, No. 4. - P. 9-17.

3. Moysyuk Ya.G., Belyaev A.Yu. permanent vascular access. - Tver: "Triad", 2004. - 152 p.

4. Berardinelli L., Vegeto A. Lessons from 494 permanent accesses in 348 haemodialysis patients older than 65 years of age: 29 years of experience// Nephrol. Dial. transplant. - 1998. - Vol.13, Suppl. 7.– P. 73-77.

5. Clinical practice guidelines for hemodialysis adequacy, update 2006// Am. J. Kidney. Dis. 2006. - Supplement 1. - P. 2-90.

6. Dhingra R.K., Young E.W., Hulbert-Shearon T.E. et al. Type of vascular access and mortality in U.S. hemodialysis patients // Kidney Int.- 2001. - V. 60(4). - P. 1443-1451.

7. Mortaz S.S., Davati A., Ahmadloo M.K. et al. Evaluation of patency of arteriovenous fistula and its relative complications in diabetic patients// Urol. J. - 2013. - Vol. 10(2). - P. 894-897.

8. Murphy G.J., Nicholson M.L. Autogeneous elbow fistulas: the effect of diabetes mellitus on maturation, patency, and complication rates// Eur. J. Vasc. Endovasc. Surg. - 2002. - Vol.23(5). - P. 452-457.

9. Ott U., Sperschneider H. Demands on dialysis access from the nephrologists point of view // Chirurg. - 2012. - Vol. 83(9). - P. 775-778.

10. Tordoir J.H., Dammers R., van der Sande F.M. Upper extremity ischemia and hemodialysis vascular access // Eur. J. Vasc. Endovasc. Surg. - 2004. - Vol. 27(1). – P. 1-5.

Diabetes mellitus (DM) is one of the reasons for the development of end-stage chronic renal failure (ESRD) due to the progression of diabetic nephropathy. Programmed hemodialysis (PGD) remains the leading treatment for patients with terminal chronic renal failure (ESRD). The effectiveness of PGD is largely determined by the adequacy of vascular access - arteriovenous fistula (AVF). Permanent vascular access (CVA) ideally should ensure that the blood flow rate corresponds to the prescribed proportion of dialysis, and function for a long time without complications. Currently, there is no ideal variant of PSD, but native AVF is recognized as optimal. The duration of AVF functioning is about 3-5 years and decreases due to the development of complications that require repeated surgical interventions (thrombosis, stenosis, the “steal” syndrome, etc.) and are the cause of repeated hospitalization, the increase in the cost of treating patients. The number of patients on 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 PDS and an increase in the number of reoperations. The formation of SVP using synthetic vascular prostheses (SVP) is technically simpler compared to the formation of native AVF, but significantly reduces the time of SSP functioning as a vascular access due to complications, as indicated by the publications of domestic and foreign authors. Numerous studies are devoted to planning issues, types of PDS, options for tactics in the development of complications. Despite the fact that significant progress has been made in dialysis technology in recent years, the problems associated with providing PDS for patients with type II diabetes remain unresolved.

The aim of this work was to study the possibility of forming a native permanent vascular access on the upper limb in patients with terminal chronic renal failure with type II diabetes mellitus.

Materials and methods of research

The work was carried out on the basis of the MUZ "MGKB SMP No. 1" in Orenburg, the MUZ "GKB No. 1" in Novotroitsk, the MUZ "GKB No. 1" in Orsk, the MUZ "GKB No. 1" in Buzuluk, the Orenburg Region, "BSMP" Aktobe and CDIK "BIOS" Aktobe of the Republic of Kazakhstan in 2007 - 2013 The study included 108 patients with type II diabetes mellitus with 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 AVF in the lower third of the forearm, the middle third of the forearm, and the cubital fossa. According to the localization of the primary AVF, the patients were divided into three groups: group 1 included 86 patients with AVF localization 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 cubital fossa. In all patients, PSD was formed on the non-dominant upper limb.

Preoperative examination of patients included a standard determination of CBC parameters, levels of urea, creatinine, total protein, fibrinogen, prothrombin index, blood clotting time, activated partial thromboplastin time, international normalized ratio, as well as a visual examination of the upper limb, a test with a venous tourniquet, Allen test, ultrasound examination of the vessels of the upper limb to select the optimal site for the formation of AVF.

Surgical interventions were performed under local anesthesia, taking into account the data of the preoperative examination. Permanent vascular access was formed in the distal part of the forearm between a.radialis and v.cephalica in the "end-to-side" artery type. In the middle third of the forearm between a.radialis and v.cephalica in an end-to-side artery type. In the cubital fossa between a.radialis or a.brahialis and v.cephalica or v.basilica in an end-to-side artery type.

When analyzing the results of treatment, the frequency of stenosis, AVF thrombosis, the number of repeated operations to form a vascular access for program hemodialysis for at least three years after the first surgical intervention were taken into account.

Research results and discussion

The 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), a permanent vascular access was formed in the distal part of the forearm, between v. cephalica and a. radialis according to the "end of the vein to the side of the artery" type. In the early stages (2 - 7 days), 15 patients were operated on again. In 5 patients, due to the low blood flow velocity in the fistula vein due to fibrosis of the latter, the elimination of low-efficiency AVF was performed within 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 end-to-side of the artery. In the other 10 patients, due to early AVF thrombosis, a repeated 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 according to the "end to side" type of the artery. In the latter case, the thrombosed anastomosis was also not removed.

Later, 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 . Previously, these patients had no operations for AVF dysfunctions.

Thus, in the first group of patients, 15 (17.4%) patients were operated on again at an early stage and 6 patients (7%) after 1.5–2 years of AVF operation. After repeated operations, there were no new complications in patients, and AVFs retained their functional viability.

In the 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 according to the "end-to-side" type of the artery in the subcutaneous fat (with mandatory mobilization of a. radialis for 3-4 cm). There were no complications and reoperations in the early stages in this group. In one patient, after 1.5 years of AVF functioning, due to the development of arterial thrombosis of the vascular access, an arteriotomy, thrombectomy, excision of the anastomotic zone with the formation of an arteriovenous fistula in the same place was performed. Thus, the frequency of reoperations in the second group was 8.3% (1 patient), and the newly formed AVF retained its functional viability for three years.

The primary formation of a permanent vascular access in the cubital fossa (group 3) was performed in 10 patients with arterial hypotension, as well as loose type of veins and severe calcification of the arterial wall on the forearm, detected by ultrasound. 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 in the venous bed, the inflows and anastomoses of the used vein were ligated distally 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 punctures is very limited. In this case, we superficialized v. brahialis at once or in the second stage, depending on the anatomical structure of the vascular bed. There were no reoperations in this group of patients.

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 AVF for creation using the vessels of the distal third of the forearm gives a certain percentage of reoperations due to the development of stenosis and thrombosis of the fistula (maximum - 24.4% in the formation of 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 in similar operations in the general population.

The formation of 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 “steal” syndrome of the limb, its chronic ischemia, overload of the right parts of the 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 decrease in the number of thrombosis and repeated operations to form a vascular access.

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

conclusions

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

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

Reviewers:

Abramzon O.M., Doctor of Medical Sciences, Professor of the Department of General Surgery, Orenburg State Medical Academy, 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

Fadeev S.B., Grigoriev E.N., Fadeev S.B., Tarasenko V.S. FORMATION OF VASCULAR ACCESS FOR HEMODIALYSIS IN PATIENTS WITH TERMINAL CHRONIC RENAL INSUFFICIENCY WITH TYPE II DIABETES MELLITUS // Modern Problems of Science and Education. - 2013. - No. 6.;
URL: http://science-education.ru/ru/article/view?id=10769 (date of access: 01.02.2020). We bring to your attention the journals published by the publishing house "Academy of Natural History"

Chronic renal failure (CRF) is an inevitable outcome of a number of kidney diseases. The number of patients with chronic renal failure is constantly growing. In 2014, 2 million people in the world had the last (terminal) stage of CKD, i.e. were on hemodialysis, peritoneal dialysis or needed a donor kidney.

Over the past 20 years, the number of such patients has quadrupled. Number of patients with initial stage CRF exceeds the number of patients with the last stage of CRF by more than 50 times. Currently, the number of patients increases annually by 10-12%.

Adequate hemodialysis therapy requires a permanent vascular access (PSA) and regular monitoring of its condition. An ideal vascular access is recognized as one that ensures that the blood flow rate corresponds to the prescribed dose of dialysis, functions for a long time (many years) and has no complications. Currently, none of the known variants of PSD is ideal, however, the native arteriovenous fistula (AVF) satisfies the requirements to a greater extent.

Complications associated with PSD are a major cause of morbidity, hospitalization, and increased cost of treatment in patients on permanent hemodialysis (PGD). Vascular access procedures require hospitalization of 14 to 45% of hemodialysis patients, and the costs represent 10% of the budget allocated for the treatment of patients with CKD: for example, such costs in the United States are estimated at more than 1 billion dollars annually.

Improvement in the quality of PGD and an increase in patient survival lead, along with a shortage of kidney transplants, to a lengthening of the time spent by patients on PGD. As a result, the requirements for a longer functioning of vascular accesses increase. On the other hand, among patients in need of the formation of primary PDS, the proportion of elderly people suffering from diabetes mellitus and cardiovascular diseases is growing, which leads to an increase in both the intensity of vascular interventions and technical difficulties in the formation of PDS.

Although significant progress has been made in dialysis technology in recent years, certain problems associated with providing permanent vascular access remain unresolved. Numerous studies are devoted to the issues of planning, priority of the type of PDS, options for treatment tactics in the development of complications.

With regard to the period of creation of the DED, there is a single point of view. The optimal situation is recognized when it is possible to form a design estimate at least a few months before the expected start of PGD. Most authors believe that such a moment occurs with plasma creatinine levels of 4-5 mg / dl and glomerular filtration rate of 15-25 ml / min.

The advantages of this approach are obvious: a margin of time for the “ripening” of the AVF and healing of the postoperative wound, the achievement of adequate blood flow through the AVF, the absence of the need for temporary vascular access with its attendant complications (infection, stenosis of the main vein, artery damage). Nevertheless, the problem remains relevant due to the fact that the proportion of patients in whom PDS is formed in advance remains insufficient and, according to various authors, ranges from 32 to 50%.

Over the four decades of its existence, hemodialysis has become a completely independent and full-fledged discipline that has contributed to the development of an entire branch of the medical industry. During this period, a lot of experience has been accumulated and analyzed in the long-term replacement of lost kidney function in hundreds of thousands of patients.

The problem of hemodialysis reached a qualitatively new level at the beginning of the 19th century, when, with the development of biochemistry, many processes became clear, which subsequently formed the basis of renal replacement therapy. The physical foundations of hemodialysis were laid in 1854 by the Scottish scientist Thomas Graham, who published his work “Osmotic Force”, in which he first described a method for manufacturing semi-permeable membranes from specially treated parchment for separating colloidal and crystalloid solutions.

The first human hemodialysis (a patient suffering from uremia) was carried out in Germany by the doctor Georg Haas in October 1924. Purified hirudin was used as an anticoagulant. In 1927, heparin was used as an anticoagulant for the first time in hemodialysis. Thus, Haas was the first to bring together all the ingredients needed for successful hemodialysis.

For the first time, the successful removal of a person from a uremic coma using hemodialysis was carried out on September 3, 1945 by the Dutch physician Willem Kolf. Thus, in practice, the clinical effectiveness of the method has been unequivocally proven. In 1946, Willem Kolff published the first guidelines for the treatment of uremia patients with hemodialysis.

The beginning of the era of chronic hemodialysis is considered to be 1960, when Belding Scribner and Wayne Quinton managed to solve the problem of long-term vascular access, which was provided by implanting two thin-walled Teflon tubes into the radial artery and saphenous vein. This technique in the vast majority of cases required ligation of vessels at the end of the procedure and led to a rapid depletion of the vascular resource.

Vessel catheterization according to the method of S. I. Seldinger, first used by S. Shaldon in 1961, was associated with a high risk of infectious, hemorrhagic and thromboembolic complications. With the improvement of the materials used and the introduction of the so-called permanent catheters, the duration of their stay in vivo has increased significantly, and recently they can be considered as a permanent vascular access.

This technique, however, has many disadvantages, and therefore it is used in somatically severe patients with an exhausted vascular resource, and also as an intermediate access during the formation of a permanent one. Priority at the puncture site today is as follows: jugular vein; femoral vein; subclavian vein.

The introduction of long-term hemodialysis in a wide clinical practice began after VN Scribner's (1960) proposal to use an external arteriovenous shunt in the forearm area for repeated procedures. The proposed shunt was originally made of Teflon. Subsequent use of shunts with Dacron and Teflon cuffs made it possible to avoid the development of infections, damage to the intima and, as a result, its hyperplasia. However, the high level of complications and the limited duration of operation of such shunts (maximum 1–2 years for the arterial segment, 10–12 months for the venous segment) do not allow their use as a permanent vascular access.

A breakthrough in the field of providing permanent vascular access was achieved after the development of M. J. Brescia and J. E. Cimino in 1996, the operation to create a subcutaneous arteriovenous fistula. It was proposed to form a vascular anastomosis between a. radialis and v. cephalica in the region of the lower third of the forearm according to the "side of the vein to the side of the artery" type. Currently, the priority is the method of applying an anastomosis according to the principle of the end of the vein to the side of the artery, less often the end of the vein to the end of the artery.

In 20% of patients, at a certain stage of hemodialysis, one has to resort to the implantation of vascular prostheses as an alternative to arteriovenous fistula, since the possibilities of using one's own vessels are completely exhausted. The main indications for the use of vascular prostheses are the features of the anatomical structure of peripheral vessels (insufficient diameter, loose type of structure), their pathological changes (thrombosis, stenosis, phlebitis, aneurysm), as well as previous surgical interventions.

Numerous varieties of vascular prostheses make up three main groups: biological (autovein, allovein, alloartery, xenografts), semi-biological (prosthesis from a human umbilical cord vein), synthetic (dacron, polytetrafluoroethylene).

The high frequency of thrombosis and occlusion in the late postoperative period due to the rapidly progressive biodegradation of the venous graft, the trauma and duration of surgery prevented the widespread use of autografts.

The best results were achieved when using synthetic materials for the manufacture of vascular prostheses (dacron, lavsan, velor, mandrill, polytetrafluoroethylene, polyurethane). Clinical studies have shown the absolute advantages of synthetic vascular prostheses (SSP) made of polytetrafluoroethylene (PTFE), produced under various commercial names (Goretex, DIASTAT, Impra, Vectra, etc.).

PTFE SSP is inert, mechanically and chemically stable, resistant to biological degradation, highly thrombo-resistant, elastic, does not deform when bent, simple and easy to use. The microporous structure of PTFE allows connective tissue and blood vessels to grow inside the prosthesis, promotes the formation of neointima and connective tissue capsule, giving it the properties of a semi-biological substitute.

The initial attempts at total application of SSP showed that this method has no significant advantages over native AVF, and is significantly inferior to it in a number of indicators.

In recent years, there has been a tendency both to limit the indications for the use of SSP as a primary vascular access, and to increase the proportion of operations with the use of vascular prostheses when performing repeated accesses and reconstructive interventions.

This is due, on the one hand, to the shorter duration of the SSP functioning and the large number of necessary corrective procedures (thrombectomy and angioplasty) in the immediate and late postoperative periods compared to native AVFs. In addition, CVDs are a serious risk factor for the development of infectious complications.

On the other hand, improving the quality of hemodialysis leads to an increase in both life expectancy and the proportion of elderly patients and those with comorbidities. This requires an increase in the duration of the functioning of the DPM. In such a situation, vascular prostheses are an indispensable element when performing multiple repeated surgical interventions for the formation of new and reconstruction of existing vascular accesses.

The use of cuffed silicone intravenous catheters, which has become widespread in recent years, is justified, and in many cases the only one acceptable for chronic hemodialysis when it is impossible or inappropriate to form PDS in a certain category of patients (with an exhausted resource of native vessels, the impossibility of hemodialysis, young children, patients with diabetes, etc.).

However, only about 30% of cuffed catheters remain functional after 1 year, even with thrombectomy performed, and the incidence of infectious complications and mortality significantly exceed those with AVF formation and SSP implantation. All this does not allow us to fully attribute this type of vascular access to the category of permanent access.

Candidates for placement of cuffed intravenous catheters should only be considered for patients in whom PDS cannot be formed or performed. replacement therapy by peritoneal dialysis.

In recent years, a fundamentally new variant of vascular access has been proposed for clinical use, combining the advantages of an intravenous catheter (sufficient blood flow in the main vein, minimal effect on cardiac output, ease of installation) and subcutaneous punctures (prevention of infectious complications) - the device "Dialock hemodialysis system" (" Biolink Corp.") and "LifeSite hemodialysis access system" ("Vasca Inc.").

The system consists of a multiple puncture port implanted subcutaneously in the subclavian region and connected to two silicone catheters placed through the jugular vein into the right atrium or superior vena cava. It is assumed that such systems should become an alternative to intravenous catheters (including cuffed ones) and provide safe temporary vascular access for the period of formation and “maturation” of a permanent one. Taking into account the small to date world experience in the application of this method, it is not possible to fully evaluate its effectiveness.

Most hemodialysis centers suggest that the strategic direction for improving the safety of the function of PSD is not the formation of a new vascular access, but the provision of the longest possible function of the existing one through the timely diagnosis of complications, percutaneous intervention and angioplasty, stenting, and surgical reconstruction.

After summarizing all available data, the vascular access working group concluded that the quality of life of hemodialysis patients and overall treatment outcomes can be markedly improved if the number of formed native AVFs increases and access dysfunction is recognized before its thrombosis develops.

For this purpose, considerable attention has been paid to the characteristics of the blood flow of the PDS using angiography methods, ultrasound, thermodilution, determination of venous resistance and recirculation. It has been proven that prospective monitoring and correction of hemodynamically significant stenosis improves the function of vascular access and reduces the number of complications, primarily thrombosis.

Despite the availability of a wide range of methods for the formation of permanent vascular access, which surgeons own, there are many unresolved problems. The main, perhaps, is stenosis and, as a result, thrombosis of the anastomosis due to the formation of neointima. Constant punctures of dialysis veins and vascular prostheses with thick needles cause protective processes of inflammation, local parietal thrombus formation. In the case of the end of the hemodialysis procedure, this process has beneficial effects, contributing to the closure of the puncture holes and preventing bleeding. In general, it leads to endothelial dysfunction and neointimal hyperplasia.

The endothelium is involved in both the initiation and completion of the inflammation process due to protein receptors (intercellular adhesion molecule-1 - ICAM-1, vascular adhesion molecule-1 - VCAM-1, endothelial leukocyte adhesion molecule-1 - ELAM-1) and cytokines secreted into the lumen of blood vessels (modified lipoproteins, inflammatory cytokines, vasoactive peptides, neuropeptides P- and E-selectins). Leukocyte adhesion molecule activators such as E-selectin, P-selectin, ICAM-1 and VCAM-1 allow leukocytes to attach to the endothelium and then move into tissues, increasing the local inflammatory response. Inflammation is one of several factors that can alter endothelial cell function and cause damage to the endothelial layer.

To date, data have been accumulated on the versatility of the influence of the endothelium on the occurrence and development of various pathological conditions. This is due not only to the participation of endotheliocytes in the regulation of inflammation, but also to their direct effect on vascular tone, hemorheology and thrombus formation, protection of the integrity of the vascular wall, regulation of atherogenesis and other processes. Hemodialysis itself causes oxidative stress and the development of endothelial dysfunction (nitric oxide, endothelin 1, von Willebrand factor, etc.). Markers of endothelial dysfunction are currently well studied.

It was established that hemodialysis causes an increase in the concentration of monocytic chemoattractant protein 1, hepatocyte growth factor and pentaxin-3, a decrease in the level of asymmetric dimethylarginine and nitrate/nitrite was recorded. The serum obtained after hemodialysis stimulates the proliferation of endothelial cells. Hemodialysis-induced intravascular inflammation alters endothelial function, which can lead to the formation of neointima, obstruction of 60% of AVF and vascular prostheses within 2 years.

Endothelial cells of arteriovenous fistulas from uremia mice or hemodialysis patients are capable of expressing mesenchymal markers (FSP-1 and/or a-SMA), they are also characterized by increased expression and nuclear localization of the Notch intracellular domain. In addition, endotheliocytes derived from AVF from uremic mice showed a decrease in the level of VE-cadherin and an increase in the expression of Notch-1 and -4, Notch ligands, Notch transcription factor, RBP-JK, and target Notch genes.

Ectopic expression of Notch ligands or exposure of TGF-]31 in cultured endotheliocytes were trigger mechanisms for the expression of mesenchymal markers and caused endothelial dysfunction. Both mechanisms can be blocked by Notch inhibition or RBP-JK knockout. These results suggest that an increase in TGF-pi levels as a complication of uremia activates the Notch domain in endothelial cells, which leads to the progressive formation of neointima and obstruction of arteriovenous fistulas. Suppression of Notch activation may be a novel strategy to improve AVF patency in uremic patients.

Interesting data are presented on the content of nitric oxide in patients with chronic renal failure receiving hemodialysis treatment. Nitric oxide levels in CKD patients on hemodialysis were markedly elevated, which is associated both with the hemodialysis procedure itself (stimulation of cytokine-induced NO synthase) and with stimulation of nitric oxide production by platelets against the background of uremia. High concentrations of nitric oxide act as cytotoxic molecules leading to dialysis complications due to nitrosative stress.

Since nitric oxide production correlates with creatinine and urea concentrations, high levels of nitric oxide may indicate insufficient blood purification. Therefore, changes in kidney function, which are reflected in fluctuations in creatinine concentration, will be accompanied by changes in the level of nitric oxide, the determination of which in peripheral blood can be useful in assessing the effectiveness of hemodialysis and used to determine the prognosis in patients with chronic renal failure. The study of the mechanisms of development of endothelial dysfunction and intimal hyperplasia can improve understanding of the processes leading to stenosis and thrombosis of permanent vascular access.

Thus, extensive knowledge has been accumulated in the field of surgical and endovascular methods for creating, correcting and maintaining the patency of a permanent vascular access in dialysis patients. Developments are underway to improve materials for the creation of vascular prostheses, the search for a new, ideal vascular access.

Currently, this is a native arteriovenous fistula. Search medical methods correction and prevention possible complications will contribute to the "life extension" of the ideal vascular access already available today.

R. E. Kalinin, I. A. Suchkov, A. S. Pshennikov, N. D. Mzhavanadze, A. A. Egorov