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The main method for diagnosing arteriovenous fistula for hemodialysis dysfunction is duplex ultrasound. Research objective – to study the structure of complications and changes in hemodynamics in the vascular access for hemodialysis and to determine the risk factors contributing to its development. Ultrasonography, clinical and laboratory examination was performed in 550 patients undergoing program hemodialysis, 517 (94.0%) of them had arteriovenous fistula, 33 (6.0%) patients had arteriovenous graft. Vascular access complications occurred in 26.7% (147 patients), there was no significant difference in the detection rate of thrombosis (26.5%), stenosis (23.8%), and aneurysm (21.1%), a combination of two complications was observed in 20.4%, the syndrome – in 8.2%. A correlation was established between the presence of significant stenosis, aneurysm of the outflow vein and the thrombosis development, between the presence of concomitant diseases of the peripheral arteries and the development of steal syndrome and the inflow artery stenosis and the anastomosis zone stenosis. Duplex ultrasound allows to diagnose complications of vascular access for hemodialysis and determine its causes.
vascular access, arteriovenous fistula, arteriovenous graft, ultrasound examination, stenosis, thrombosis, aneurysm, hand ischemia
Introduction. Carrying out hemodialysis is associated with the need for multiple punctures to ensure the collection and return of the patient's blood. The superficial veins of the upper extremities are suitable for repeated punctures, but they are not suitable for connecting the patient to the dialyzer due to the low volumetric blood flow velocity. In the arteries, the volumetric blood flow velocity is higher than in the veins, but it is also insufficient. The arteries are located deeper, so their puncture is technically difficult, and when the needle is removed, bleeding is often observed [1]. Central venous catheters are unsuitable due to frequent thrombotic complications. It is necessary to form such an access that would provide the possibility of multiple punctures, blood sampling, passing it through the dialyzer at the required speed and returning to the patient's bloodstream [1,2].
The maximum duration of operation of a surgically created permanent vascular access for hemodialysis rarely exceeds 4 years. In this case, the duration of a patient's stay on hemodialysis therapy can reach 20 years or more [3]. Effective long-term treatment is highly dependent on the successful maturation and functioning of the arteriovenous fistula (AVF). The main method for diagnosing AVF dysfunction is duplex scanning [4, 5, 6,7].
Purpose – to study the structure of complications and changes in hemodynamics in an arteriovenous fistula for hemodialysis, to determine the risk factors that contribute to their development.
Materials and methods. Ultrasound examination was performed in 550 patients on programmed hemodialysis, of which 52.4% (288 people) were men, 47.6% (262 patients) were women. Native arteriovenous fistula was observed in 517 (94.0%) patients, arteriovenous graft - in 33 (6.0%) patients. The age of the patients ranged from 20 to 88 years, the average age was 56.7±14.5 years. The duration of hemodialysis therapy ranged from 1 month to 20 years (on average, 74.5±20.1 months). The average duration of vascular access functioning was 41.3±15.7 months (from 1 month to 16 years).
All patients underwent an ultrasound examination of the vascular access for hemodialysis using a Vivid E9 ultrasound machine with a 7–10 MHz linear transducer. The research algorithm included the study of the adductor artery, anastomosis, outlet vein or prosthesis, main and head veins on the shoulder (with the formation of AVF on the forearm), subclavian vein. Determined the diameters of the adducting artery, anastomosis, vein or prosthesis; peak systolic blood flow velocity in the anastomotic zone; volumetric blood flow velocity in the outflow vein or in the prosthesis, in the adducting artery. During ultrasound examination, the state of the compensatory mechanisms of autoregulation of blood flow in the hand was assessed using a test with physical exertion (clenching and unclenching the hand into a fist for 2 min) and a test of postocclusive reactive hyperemia [3, 8].
We collected complaints, anamnesis of the disease, analyzed the surgical interventions performed to reconstruct the fistula, performed laboratory studies, echocardiography and consult a vascular surgeon if necessary.
To analyze the results of the study, we used the Statistica 10 statistical software package for the Windows XP operating system, developed by StatSoft. Statistical analysis included the calculation of extensive coefficients (%), arithmetic mean values (M) and mean error of arithmetic mean values (m) for the amplitude of the variation series. To check the significance of differences in frequencies and mean values, the Pearson Chi-square test and Student's t-test were used, the difference was considered significant at p <0.05.
Results and discussion. Complications of vascular access for hemodialysis occurred in 26.7% (147 patients), of whom thrombosis (26.5% - 39 patients), stenosis (23.8% - 35 patients) and aneurysm (21.1 % - 31 patients), there were no significant differences in the frequency of their detection. The combination of two complications of vascular access was noted in 20.4% (30 patients), less often the hand steal syndrome was observed - 8.2% (12 patients).
Vascular access stenosis was detected in 48 (8.7%) patients, of which 26 (54.2%) were diagnosed with hemodynamically significant stenosis. Stenosis of the outlet vein was more common (72.9% - 35 people), less often - stenosis of the adducting artery (14.6% - 7 patients) and the anastomotic zone (10.4% - 5 patients), stenosis of the ipsilateral subclavian vein was detected in 1 (2.1%) patient. Stenosis was significantly more frequent in patients with arteriovenous graft (18.2% - 6 out of 33 people) than in patients with native fistula (6.2% - 32 out of 517 people). In 2 (6.1%) patients with a prosthesis, stenosis of the distal anastomosis of the prosthesis and the outlet vein was noted, in 4 (12.1%) patients - stenosis of the outlet vein. Hemodynamically significant stenosis developed more often in patients with distal approach than with proximal one (p = 0.01), which is probably due to the larger diameter of the vessels on the shoulder. Hemodynamically significant stenosis of the adductor artery was diagnosed only in patients with radiocephalic AVF.
Stenosis developed at different times from the moment the vascular access was formed: from 3 months to 12 years (on average, 45.9±19.3 months). Its development did not depend on gender (p = 0.54) and age of the patient (p = 0.06), the underlying disease that caused end-stage renal failure (p>0.05). In all patients with stenosis of the adductor artery and the proximal anastomosis zone (arteries and veins or arteries and grafts), concomitant peripheral arterial diseases (diabetes mellitus and generalized atherosclerosis) were noted, which is consistent with the literature data on the causes of AVF stenosis for hemodialysis [2]. No correlation with the presence of concomitant peripheral vascular diseases (p>0.05) was found in those examined with stenosis of the outlet vein and the area of the distal anastomosis of the arteriovenous graft (between the prosthesis and the vein). The causes of stenosis of the outlet vein and the anastomotic zone in most patients were high blood flow velocity, multiple punctures in the local zone, turbulent blood flow, constantly traumatizing the vein wall and causing intimal hyperplasia, which is also noted by other authors [1, 2, 9]. Subclavian vein stenosis in 1 patient was associated with previous vein thrombosis after its catheterization [2, 3].
As a result of the study, the criteria for hemodynamically significant stenosis of the adducting artery and outlet vein were determined (fig. 1): the diameter of the vessel in the stenosis zone is less than 2 mm, the ratio of peak systolic velocities in the pathology zone and in the proximal section is more than 2 for stenosis of the adducting artery and more for stenosis of the outflow vein, the volumetric blood flow velocity in the outflow vein is less than 300 ml/min [10].
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Fig. 1. Echograms of significant stenosis of the outflow vein: stenotic area in B-mode is 1,7 mm (a), peak systolic velocity in the stenotic area is 464 cm/s (b), peak systolic velocity in proximal to the narrowing area is 81.3 cm/s (c), access flow in the outflow vein distal to the stenotic zone is 134 ml/min (d) |
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Thrombosis of the vascular access for hemodialysis was detected in 66 (12.0%) patients, of whom non-occlusive thrombosis was observed in 60.6% (40 patients), occlusive thrombosis - in 39.4% (26 patients). Thrombosis significantly more often developed in women (15.7% - 40 out of 262 people) than in men (9.0% - 26 out of 288 people), p = 0.025. In patients with proximal access, thrombosis was more common (22.1% - 27 people out of 122) than in distal AVFs (9.0% - 38 out of 424 people), p = 0.025. Of 4 patients with a hip prosthesis, 1 (25.0%) had non-occlusive access thrombosis. In patients with prostheses, thrombosis was observed more often (24.2% - 8 out of 33 people) than in those examined with a native fistula (11.2% - 58 out of 517 people), which corresponds to the literature data [3].
There was no significant relationship between the development of thrombosis and the patient's age, the underlying disease that caused chronic renal failure (p>0.05). Thrombosis developed on average after 20.6±11.2 months. after access formation (from 1 month to 12 years). There were no significant differences between the diameter of the adductor artery (p = 0.72) and the diameter of the anastomosis (p = 0.36) in patients with and without thrombosis.
The reasons for the development of thrombosis were: a decrease in the blood flow velocity in the access due to stenosis or low systemic arterial pressure, disturbances in the homeostasis system, damage to the vessel wall, especially during punctures in the local zone [3, 11]. The volumetric blood flow rate in patients with thrombosis ranged from 100 ml/min to 2400 ml/min (average 860.6±575.1 ml/min).
In 10 (15.2%) patients with thrombosis, hemodynamically significant stenosis of the outlet vein and a decrease in volumetric blood flow to 300 ml/min or less were noted. A correlation was established between the presence of hemodynamically significant stenosis of the vascular access and the development of thrombosis (p = 0.02), which corresponds to the literature data on the main cause of AVF thrombosis [5, 11, 12]. A number of authors claim that the risk of thrombosis is significantly reduced with a minimum volumetric blood flow rate of more than 500–600 ml/min in a native fistula and more than 800 ml/min in a prosthesis [2, 4, 12].
In patients with thrombosis, aneurysm of the discharge vein was detected in 14 (21.2%) people (fig. 2) and aneurysmal dilatation of the prosthesis - in 3 (37.5%). A correlation was found between the presence of an aneurysm of the discharge vein or prosthesis and the development of thrombosis (p <0.01).
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Fig. 2. Echograms of outflow vein aneurism, B-flow mode: non-occlusive (a) and occlusive (b) thrombosis
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A discharge vein aneurysm was detected in 45 (8.7%) patients with AVF, aneurysmal dilatation of the prosthesis - in 3 (9.1%) patients. In our study, the development of aneurysm did not depend on the diameter of the afferent artery and the anastomosis (p>0.05). The formation of aneurysms was facilitated by numerous punctures of a vein in a small area, localization was noted in the area of confluence with the tributary veins, in the area of the valve apparatus, as well as in rigid areas formed as a result of previous surgical interventions or catheterizations. The turbulent nature of the blood flow in the aneurysm leads to the deposition of platelets on the endothelium in places with a low blood flow rate, their subsequent agglutination and activation of the fibrin coagulation process [2, 9].
Ischemic hand steal syndrome was detected in 2.7% (15 patients). Steel syndrome appeared at different times from the moment of vascular access formation: from several weeks to 8 months (on average 3.5±1.3 months) in patients with a prosthesis and from 1 month to 15 years (on average 32.7±10.7 months) with AVF. Among patients with a proximal approach, it occurred significantly more often (4.4%) than in patients with radio-cephalic fistulas (2.3%).
In ultrasound examination, the diameter of the anastomosis in patients with the steal syndrome was significantly greater (5.9±0.9 mm) than in the group of patients without hand ischemia (4.1±1.5 mm). In the case of hand steal syndrome, the volumetric blood flow velocity in the adductor artery in the case of the formation of the brachial AVF was on average 1802.6±147.5 ml/min, with a radio-cephalic fistula - 753.3±117.6 ml/min; in the outflow vein with brachial AVF - 1607.5±126.2 ml/min and with distal fistula - 1008±115 ml/min. There were no significant differences in mean values of volumetric blood flow in patients with and without hand steal syndrome (p = 0.06).
Ultrasound examination revealed the main reasons for the development of steal syndrome: stenosis of the adducting artery in patients with atherosclerosis and diabetes mellitus, which do not allow increasing the volumetric blood flow in the artery (20.0% - 3 patients); large diameter of the anastomosis, leading to significant shunting of blood, dilatation of the vein and an increase in the volumetric blood flow rate (13.3% - 2 people); insufficient blood flow through the ulnar, anterior interosseous arteries and the absence of collateral branches, which did not compensate for the retrograde blood flow from the radial artery distal to the anastomosis into the fistula (40.0% - 6 patients); violation of the mechanisms of regulation of the tone of resistive vessels and pathological changes in the microvasculature of the hand (26.7% - 4 patients).
Conclusion. Complications of vascular access for hemodialysis were found in 26.7% (147 patients), there were no significant differences in the frequency of detection of thrombosis (26.5%), stenosis (23.8%) and aneurysm (21.1%), the syndrome of stealing of the hand (8.2%) was less common. The combination of two complications was found in 20.4%. The presence of concomitant diseases of the peripheral arteries was a risk factor for the development of stenosis of the adductor artery (p = 0.024) and the anastomotic zone (p = 0.037). A significant relationship was established between the presence of hemodynamically significant stenosis of the vascular access (p = 0.02), aneurysm of the outlet vein or prosthesis (p <0.01) and the development of PVA thrombosis. Thrombosis was more common in patients with a proximal approach than with a distal one (p = 0.025), as well as with an arteriovenous prosthesis than with a native AVF (p = 0.026). Pathological changes in the arteries of the forearm, which do not compensate for the deficit of blood flow in the hand, and the state of the microvasculature of the hand, are of major importance in the development of the steal syndrome. Dynamic ultrasound examination of the vascular access allows timely identification of complications and their correction.
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