Evaluation of hemodialysis arteriovenous fistula maturation by color-flow Doppler ultrasound

Abstracts

CONTEXTO: Quando se confecciona uma fístula arteriovenosa para hemodiálise (FAVH) autógena, é necessário que se aguarde a dilatação da veia em questão e o desenvolvimento de volume de fluxo mínimo, fenômeno chamado de maturação. Ainda hoje se discute qual o tempo necessário para ocorrer essa maturação. OBJETIVO: Avaliar a maturação de FAVH utilizando-se critérios ecográficos. MÉTODO: Entre maio de 2004 e 2005, 40 pacientes foram selecionados prospectivamente, sendo 23 homens (57,5%), com média de idade de 17,5±51,3 anos, com indicação de confecção de uma FAVH. Utilizou-se o aparelho Logic III® com transdutor de 10 MHz para a avaliação no pré-operatório e nos 7º, 14º, 21º e 28º dias de pós-operatório. Os critérios para a maturação após a cirurgia foram: veia com diâmetro médio maior que 4 mm e volume de fluxo maior que 400 mL/min. RESULTADOS: O diâmetro médio pré-operatório foi de 3,24±1,43 e 3,71±1,37 mm para fístulas de punho e de cotovelo, respectivamente. O diâmetro final foi de 5,01±0,87 mm para as FAVH de punho (p = 0,006) e de 6,15±1,16 mm para as FAVH de cotovelo (p = 0,95). O volume de fluxo no 7º dia pós-operatório foi de 493,63±257,49 mL/min e 976,33±332,90 mL/min para as FAVH de punho e cotovelo, respectivamente. Ao final do estudo, foi calculado o valor de 556,81±288,42 mL/min nas FAVH de punho (p < 0,05) e de 1031,62±614,812 mL/min nas FAVH de cotovelo. Baseados nos dois critérios, a maturação ocorreu em 57,1% das fístulas de punho e em 100% das fístulas de cotovelo após a 1ª semana. Após 4 semanas, 67,9% das fístulas de punho e 100% das fístulas de cotovelo apresentaram maturação. CONCLUSÃO: A maioria das FAVH de cotovelo apresentou diâmetro e fluxo adequados para punção logo após a 1ª semana de pós-operatório. Para as FAVH de punho, houve melhora progressiva dos padrões de maturação com o passar das semanas, sugerindo que essas FAVH devem ser puncionadas preferencialmente após a 4ª semana de pós-operatório.

Fístula; arteriovenosa; hemodiálise; eco-Doppler colorido

ORIGINAL ARTICLE

Evaluation of hemodialysis arteriovenous fistula maturation by color-flow Doppler ultrasound

Jeferson Freitas Toregeani^I; Claudio Jundi Kimura^II; Antonio S. Trigo Rocha^III; Giuliano Giova Volpiani^IV; Ângela Bortoncello^V; Keity Shirasu^V; Luiz A. Peres^VI

^IVascular surgeon, Hospital Universitário do Oeste do Paraná, Cascavel, PR, Brazil. Assistant professor, Vascular Surgery, Universidade Estadual do Oeste do Paraná (UNIOESTE), Cascavel, PR, Brazil. Specialist in Vascular Surgery, SBACV. Certificate in Vascular Ultrasound with Doppler, SBACV and Colégio Brasileiro de Radiologia (CBR)

^IIVascular surgeon, Hospital Universitário do Oeste do Paraná, Cascavel, PR, Brazil. Certificate in Vascular Ultrasound with Doppler, SBACV and CBR

^IIIVascular surgeon, Hospital Universitário do Oeste do Paraná, Cascavel, PR, Brazil. Assistant professor, Vascular Surgery, UNIOESTE, Cascavel, PR, Brazil. Specialist in Vascular Surgery, SBACV. Certificate in Vascular Ultrasound with Doppler, SBACV and CBR

^IVVascular surgeon, Hospital Universitário do Oeste do Paraná, Cascavel, PR, Brazil

^VStudent, UNIOESTE, Cascavel, PR, Brazil. Study Center, Instituto de Cirurgia Vascular e Angiologia (ICV), Cascavel, PR, Brazil

^VINephrologist, Hospital Universitário do Oeste do Paraná, Cascavel, PR, Brazil. Assistant professor, Nephrology, UNIOESTE, Cascavel, PR, Brazil. Member of Sociedade Brasileira de Nefrologia

Correspondence

ABSTRACT

BACKGROUND: When a hemodialysis arteriovenous fistula (HAVF) is created, it is important to wait for venous dilatation and volume flow increase through the HAVF, a phenomenon called maturation. There is still some controversy as to the exact time required for this maturation to occur.

OBJECTIVE: To evaluate the time required for HAVF maturation using ultrasound criteria.

METHOD: From May 2004 through May 2005, 40 patients were prospectively selected. The sample was comprised of 23 men (57.5 %), mean age of 51.3±17.5 years, with indication of HAVF creation. Logic III^® ultrasound with 10 MHz transducer probe was used for pre- and postoperative evaluation 7, 14, 21 and 28 days after the procedure. Criteria for maturation after the procedure were vein diameter larger than 4 mm and volume flow larger than 400 mL/min.

RESULTS: Preoperative mean diameter was 3.24±1.43 and 3.71±1.37 mm for fist and elbow fistula, respectively. Final diameter of the fist HAVF was 5.01±0.87 mm (p = 0.006) and 6.15±1.16 mm for the elbow HAVF (p = 0.95). Flow volume in the 7th postoperative day was 493.63±257.49 and 976.33±332.90 mL/min, respectively, for the fist and elbow HAVF. At the end of the study, the value of 556.81±288.42 mL/min was calculated for the fist HAVF (p < 0.05) and 1,031.62±614.812 mL/min for the elbow HAVF. Based on both cut-off values, maturation occurred in 57.1% of the fist fistula and in 100% of the elbow fistula after the first week. After 4 weeks, 67.9% of the fist HAVF and 100% of the elbow HAVF presented maturation.

CONCLUSION: Most elbow HAVF showed adequate diameter and flow volume for puncture 1 week after the procedure. For the fist fistula, gradual maturation occurred throughout the weeks, suggesting that these HAVF should be punctured 4 weeks after the surgery.

Keywords: Fistula, arteriovenous, hemodialysis, color-flow Doppler ultrasound.

Introduction

Surgeries to create accesses for hemodialysis are the most common vascular surgeries in the USA. The importance of obtaining long-lasting accesses is due to the increased incidence of renal diseases, life expectancy of the general population and especially of the population with chronic renal disease.^1,2 A good hemodialysis arteriovenous fistula (HAVF) has to obey two basic rules to allow proper treatment to the patient: have proper diameter and have proper flow volume.³ The diameter of the HAVF superficial vein normally increases some weeks after the surgery; the same is observed as to flow volume. Such increase is variable and dependent on factors such as quality of vessels before the surgery, patient age, tributaries, comorbidities, among others.

Autogenous HAVF, located in the wrist, has been the first choice for most surgeons, and radiocephalic HAVF originally described by Brescia & Cimino in 1966 still has the lowest risk of complications, besides having good durability.^4-6

Despite being a relatively simple procedure, proper planning of anastomosis site, pre- and postoperative cares, and definition of time to start punctures are essential for a successful surgery. Problems regarding treatment planning of patients with renal failure are already present in a predialytic stage. Some authors⁷ indicate late creation of the HAVF, i.e., after the patient has effectively entered terminal renal failure (stage 5), forcing the patient to implant central venous catheters for hemodialysis or peritoneal dialysis catheters for some months until an HAVF is ready for use. According to Bonucchi et al.,⁷ initial stage of chosen hemodialysis is performed by central venous catheters, removing them as soon as the fistula reaches maturation, which is the name given to all HAVF able to be cannulated and to provide minimal flow for the hemodialysis machine. It was possible to remove the central venous catheter in about 40% of these patients, considering the presence of an HAVF in conditions of receiving a puncture.

Other services have increasingly recommended early indication of HAVF creation, even when the patient still has some residual renal function (stages 3 and 4), but is evolving to the terminal phase (stage 5).⁷ In addition, presence of a central venous catheter as temporary access may interfere with HAVF maturation, as shown in the study by Rayner & Pisoni.⁸ According to the same authors, HAVF creation in earlier stages of the disease reduces the need of unprogrammed puncture, which may lead to early failure of the fistula.^8,9

It is important to have a standardization of conducts and creation of accreditation services in hemodialysis in order to achieve success in fistula creation, where the ideal is failure rates below 10%. To do so, it is extremely important to have preoperative planning.⁷ Many studies have shown methods of identifying arteries and veins with minimal proper criteria for the creation of a good HAVF.^10,11

The advent of the color-flow Doppler ultrasound (CD) has recently facilitated preoperative assessment of possible donor and receptor vessels, with the possibility of identifying precisely the quality of superficial veins (cephalic and basilic) and the status of superficial and deep venous flow, which is often difficult on clinical examination. At the same time, the CD provides an analysis of the characteristics of arterial flow and wall, detecting presence of changes, which may put a good functioning of HAVF at risk. Important characteristics of this method include the fact of having a relatively low cost and not being invasive. The association of the CD to the development of HAVF in vascular surgery services has caused improvement in technical results of this procedure.¹¹²

There are controversies regarding the ultrasound criteria to define a fistula as mature. Fistulas larger than 4 mm and that allow a blood flow greater than 250-500 mL/min can be considered mature according to some authors.¹³ On the other hand, the exact time required for maturation is still unknown.¹⁴ Some studies showed that early puncture (in less than 2 weeks) should be avoided. Between 2 and 4 weeks, puncture should only be performed in emergency situations. Some authors recommend minimal maturation time of 1 month and, under some circumstances, over 2 months.^4,15,16

The current need to be a low-cost method, easy to perform and that provides reliable information on the maturation stage of HAVF have motivated this study.

Methods

Forty patients were evaluated throughout 12 months, from May 2004 to May 2005; 23 were male and 17 were female, mean age was 51.3±17.5 (ranging between 23-78 years), and all had indication of hemodialysis. Initially 76 patients were allocated, and 36 were excluded for not meeting the inclusion criteria throughout the study period. Inclusion criteria are presented in Table 1.

The fistulas were created in the nondominant limb where there was presence of patent veins, and preference was given to distal anastomoses in the wrist (70%). All the patients were submitted to the CD examination before and after the surgery. At the end of the study, the patients were released for hemodialysis or for reexploration of the fistula in case it was not mature.

Patients with hyperuricemia or hyperpotassemia were maintained under catheter hemodialysis until maturation of the HAVF. Patients who had borderline creatinine clearance values waited to perform hemodialysis using the HAVF itself.

The data were expressed as mean and standard deviation and compared by variance analysis or F test (ANOVA), and were considered statistically significant when p < 0.05.

Ultrasound technique

The Logic III^® (General Electric) device with 10 MHz transducer was used. All patients were sitting during the examination, with their arm standing on the examination table (Figure 1). The environment was maintained at a constant temperature of 25 ºC.

Scanning of superficial venous system veins was performed using a large amount of coupling agent (gel), with the aim of avoiding vein compression by the transducer. Cephalic vein compressibility and diameter were registered in many points. Continuity of the deep venous system until the axillary and subclavian veins was assessed. Next, the diameter of the radial artery was investigated. Patency of the palmar arch was assessed using Allen maneuver. Evaluation of the dominant arm was only performed when the nondominant arm had dissatisfactory evaluation.

The patients were reassessed 7, 14, 21 and 28 days after the surgery, measuring the diameter of the cephalic vein responsible for HAVF flow in at least three points. Measurement of flow volume was performed at a site far enough from the anastomosis to avoid natural turbulence of that area. Three measurements were performed, placing the sample-volume in the vessel center. Standard angle was 60º, corrected whenever possible with changes in transducer position. Next, vessel diameter value was measured after image freezing, and flow volume measure was then calculated using the device software. Final value used in the study was the arithmetic mean of three measurements, both of diameter and flow. Each examination lasted 10 minutes in average (Figure 2). Ultrasound criteria for fistula maturation were mean vein diameter larger than 4 mm and flow higher than 400 mL/min.

Surgical technique

The patients were submitted to outpatient surgery to create the AVF using local anesthesia with 2% xylocaine, with no vasoconstrictor. A longitudinal incision was performed in the wrist between the radial artery and the cephalic vein, and the vessels were repaired with silicon loops. Before clamping, diluted solution of heparin (5,000 U diluted in 250 mL of 0.9% saline solution) was administered by an adequate probe, performing dilatation of the cephalic vein by pressure. The clamping was then performed, and longitudinal arteriotomy measuring about 0.50-0.75 cm and terminolateral anastomosis were performed using 6-0 or 7-0 polypropylene. At the end of the procedure, the vein was dilated by external massages and compression in the proximal course. When there was no thrill after dilatation, 3,000 U systemic heparin was administered, in addition to vasodilators such as papaverine, as described by Moreira.¹⁷ Incision was closed with simple suture. In case of elbow fistulas, the difference was the incision site, normally oblique, in the elbow crease, where the cephalic vein and the brachial artery were dissected, following the same standard of terminolateral with 6-0 polypropylene.

Results

Mean preoperative caliber was 3.24±1.43 and 3.71±1.37 mm for wrist and elbow HAVF, respectively. There was increase to 4.73±0.87 mm in the 7th postoperative day in wrist HAVF (p = 0.0011) and to 5.84±1.23 mm in elbow HAVF (p = 0.23) over the same period, resulting in a percentage increase in diameter of 45.8 and 57.4%, respectively. These data are shown in Figures 3 and 4.

Around the 14th postoperative day, wrist HAVF had mean diameter of 4.86±1.05 mm, and 6,02±1,38 mm for elbow HAVF. As to preoperative assessment, there was statistical significance only for wrist HAVF (p = 0.027). On the 21st postoperative day, measurement of mean wrist HAVF diameter was 4.84±0.98 mm, and 6.10±1.30 mm for elbow HAVF, both with no statistical significance (p = 0.14 and 0.85, respectively). At the end of the study (28th postoperative day), mean value for wrist HAVF was 5.01±0.87 mm, and 6.15±1.16 mm for elbow HAVF. Again there was importance from the statistical perspective for variations in diameter found in wrist HAVF (p = 0.006).

Maturation, considering the parameter of diameter larger than 4.0 mm obtained by CD, occurred in 85.7% of wrist fistulas and in 100% of elbow fistulas after the first week. On the 14th postoperative day, 78.6% of wrist HAVF and 91.7% of elbow HAVF reached the minimal criterion, and on the 21st postoperative day, 75% of wrist HAVF and 100% of elbow HAVF had diameters larger than 4.0 mm. By the end of the study, 100% of wrist and elbow fistulas had maturation from the diameter perspective.

As to flow volume, preoperative values were suppressed, considering the extremely low velocities obtained in superficial veins, as well as the large variations that they have in terms of flow, such as those occurring in respiration stages. In this case, comparisons were performed using only postoperative data, and the initial value was didactically considered as close to zero for graphic analysis. Regarding wrist HAVF: on the 7th postoperative day, calculated flow volume was 493.63±257.49 mL/min; on the 14th postoperative day, flow volume was 521.34±264.44 mL/min; on the 21st postoperative day, mean HAVF value was 458.84±210.58 mL/min; and on the 28th day, it was 556.81±288.42 mL/min. Statistical analysis was significant only for variations around the 3rd postoperative week (p = 0.00048). Regarding elbow HAVF: on the 7th postoperative day, calculated flow volume was 976.33±332.90 mL/min; on the 14th postoperative day, flow volume was 1137.75±430.00 mL/min; on the 21st postoperative day, mean HAVF value was 1151.56±498.45 mL/min; and on the 28th day, it was 1031.62±614.812 mL/min. There was no statistical significance when the data from several stages of the study were compared (p > 0.05).

According to the parameter of minimal flow volume of 400 mL/min, 57.1% of wrist fistulas and 100% of elbow fistulas had maturation after the 1st postoperative week. On the 14th postoperative day, 60.7% of wrist HAVF and 91.7% of elbow HAVF reached the minimal criterion, and on the 21st postoperative day, 57.1% of wrist HAVF and 91.7% of elbow HAVF had flow volumes larger than 400 mL/min. By the end of the study, 67.9% of wrist HAVF and 100% of elbow HAVF had maturation from the flow volume perspective.

Table 2 shows the percentage of maturated HAVF when diameter and flow volume were analyzed in combination.

Four patients with wrist HAVF that did not reach the minimal maturation parameters were submitted to a new HAVF exploration. After identification of flow leakage through some large tributaries, ligation of these tributaries was performed, with improvement in maturation parameters in the postoperative period.

As to postoperative problems, there were no infections or any other surgical complication.

Discussion

The HAVF created with autogenous material have been the most widely used, as they have better primary and secondary patency than the HAVF created with synthetic graft.^18,19 Grafts or catheters have shorter survival due to ischemic complications, higher incidence of thrombosis and occlusion due to intimal hyperplasia, in addition to higher susceptibility to infections, providing higher morbidity and mortality rates for the patients when compared with an autogenous HAVF.²⁰ Native HAVF are the best vascular access for hemodialysis, according to the National Kidney Foundation²¹.

Some services have recommended a more frequent use of proximal fistulas (elbow), considering the long-term better patency rates in relation to wrist HAVF.⁷ However, distal HAVF usually generate hemodynamic changes for the circulatory system, therefore bringing more safety for the patient.

Because they have lower diameters, distal vessels (mainly the radial artery and cephalic vein) require an assessment prior to the surgery, so that only quality vessels are used, thus avoiding unnecessary surgeries, which usually result in technical failure. In the literature, it is hard to find a consistent study showing the minimal diameter value a vein should have to be used for HAVF creation. Some authors recommend a minimal value of 1.8 mm; others prefer 2.0 mm.^4,1022 The same occurs with the donor artery, and a minimal diameter of 2.0 mm has been used. According to Malovrh,¹⁶ there is increased risk of early HAVF failure when the internal diameter of the donor artery is lower than 1.6 mm. Minimal systolic peak of 50 cm/s can be used as cut-off point, and the calculation of the radial artery resistance index (RI) before and after a test of reactive hyperemia can be performed using color-flow Doppler ultrasound. Presence of an RI > 0.7 in the radial artery indicates an artery with probability of being dilated.⁴

Many groups have registered the value of using noninvasive imaging methods before and after creating vascular accesses. According to the Dialysis Outcomes Quality Initiative (DOQI), assessment using CD is important. In addition to being a noninvasive examination, it allows easy assessment of superficial veins, provides spectral analysis of arterial flow and allows following the development of HAVF diameter and flow volume (maturation), improving their technical outcome.^19,23 The HAVF assessed by CD have lower incidence of early failure and better long-term patency.¹ Use of color-flow Doppler ultrasound can identify some type of abnormality in approximately 40% of cases.²³ Surratt et al.²⁴ emphasized the importance of deeper examinations in suspect cases, such as preoperative venography. In a recent study conducted by these authors, 40% of all patients with history of central venous catheter had significant stenoses in the origin of subclavian and/or jugular veins.

Maturation of arteriovenous fistulas usually occur in a variable period from 4 to 12 weeks. There are several phenomena over that period, such as increase in the afferent artery and in arterial blood flow. In veins, there is also dilatation, arterialization and increase in overall flow by HAVF. Venous arterialization consists of venous parietal thickening by proliferation of smooth muscle cells of the vascular wall, making the vein less susceptible to extrinsic compression. Such series of changes accounts for the so-called fistula maturation, allowing repeated punctures and use of compressive bandages after removing the collecting needle, without, however, obstructing the vein.²⁵ Although much has been published on maturation, the number of analyses that provide more precise conclusions is small.^7,21

To understand what maturation is, it is necessary to know the hemodynamics, anatomy, molecular and functional structure of involved vessels. One of the most important hemodynamic changes is increase in shearing forces occurring both in the afferent artery and in the vein responsible for HAVF flow.²¹

To calculate shearing force (τ), the mathematical formula τ = 6 µQ/wh² is used, where µ = blood viscosity, Q = blood flow, w = width and h = height.²⁶

Vessels with high laminar flow have high shearing forces. Vessels with slow, multidirectional flow have low shearing forces. Therefore, the human body always tries to maintain shearing force within normal levels. If there is an increase in blood velocity and, consequently, shearing force, the vessel responds by dilating, since viscosity is not changed, resulting in reduced shearing forces.²¹

A study by Corpataux et al.,³ using ultrasound techniques, measured flow volume, vascular wall diameter and thickness, and calculated shearing forces. Mean value of 539 mL/min was found in the 1st week after HAVF creation (325-990 mL/min), resulting in an increase in shearing force to 24.5 dyn/cm² - in a normal forearm vein, this parameter does not exceed 5-10 dyn/cm², i.e., a nearly threefold increase. Such result was followed by an increase in internal diameter of the cephalic vein vessel from 2.37 to 4.43 mm in 1 week of functioning. By the end of the 4th week of study, vein diameter increased to 5.04 mm and, after the 3rd month, it reached a maximal diameter of 6.62 mm. Since shearing forces are inversely proportional to vessel diameter, there is a gradual reduction to levels close to normal (18.1 dyn/cm² in the 4th week and 10.4 dyn/cm² in the 12th week). A progressive increase was observed in the cephalic vein cross-sectional area, from 4.4 mm² in 1 week to 5.3 mm² in 4 weeks and 6.9 mm² in 12 weeks (p = 0.028), indicating an increase in vascular mass. Results were similar in this study, indicating that the main changes in volume and flow already occur 1 week after the surgery.

At a biological level, vascular dilatation occurs due to an increase in shearing forces, which cause alignment of endothelial cells and stimulation to release of relaxation factors, such as nitric oxide and prostacyclines, which also promote inhibition of platelet aggregation.³ In contrast, low shearing forces activate the endothelium, stimulating release of prothrombotic and vasoconstrictive factors, such as thromboxanes.³

There is also a relationship with the function of metalloproteases that digest components of the extracellular matrix and growth factors, such as platelet derived growth factor (PDGF) in this process. Some authors showed that removal of the vascular endothelium causes suppression of these responses.³

Vessel attempt to reduce shearing forces is sometimes blocked by medial hyperplasia that occurs in the HAVF vein, leading to reduced lumen and to a consequent increase in shearing force. Therefore, after creation of the HAVF, these two forces interact, resulting in shearing forces variations that will lead to maturation or not of the HAVF.³

About 30% of fistulas will never achieve maturation, either due to low flow in the afferent artery or due to lack of flow vein. These values can improve in case there is a system of preoperative evaluation in which small-caliber vessels or those with natural stenoses can be detected.⁶ The failure rate for primary HAVF can be significantly reduced, as seen by Silva et al.,¹ who observed a reduction in failure rate from 36 to 8% after implantation of a protocol for preoperative assessment, a fact that increased use of primary HAVF to 64%. According to Tordoir et al.,²⁷ 10 to 24% of surgeries for creation of HAVF fail, due to thrombosis or failure in maturation.

Failure in HAVF maturation may occur due to absence of dilatation of the afferent artery. This is evident in diabetic and/or uremic individuals, where exaggerated calcification prevents secretion of mediators that cause vasodilation. Failure may also occur as a result of problems in the venous portion of the HAVF, which due to previous punctures or inflammatory process, or even constitutional changes, make the vein fibrotic and cancel its dilatation ability. Finally, inability of reaching maturation can occur weeks or months after HAVF creation, due to changes in shearing forces at the anastomosis site, resulting in stitches where these forces are very low, leading to intimal hyperplasia and HAVF obstruction.³ According to Brunori et al.,²⁸ maturation should not follow a single criterion, as suggested by some authors, who set the period of time of 14 days as the limit date. Brunori et al. prefer to analyze each case individually and let the fistula maturate for at least 30 days. Other authors suggested a minimal period of 1 month, and preferentially 2 to 3 months before cannulating a recently formed HAVF.¹⁹

Some services perform postoperative assessment of fistulas using a simple physical examination, trying to cannulate the HAVF after 4-6 weeks. In these cases, the fistulas in which the examination showed easily visible and/or palpable veins and easy cannulization are considered mature. The HAVF that have a different presentation are referred to assessment using invasive methods. Clinical success, in addition to easy cannulization, should have minimal flow volume of 500 mL/min.⁶

In a recent analysis, Saran et al.²⁹ analyzed questionnaires completed by nurses working at hemodialysis units. According to their data, in Japanese hospitals, 74% of HAVF had been cannulated before the 30th postoperative day; 50% in European hospitals; and only 2% of HAVF were cannulated before 30 days in American hospitals.

According to Basile et al.,³⁰ mature fistulas but that have flow volume lower than 700 mL/min should be closely followed, considering the significantly higher incidence of medium-term failure.

Changes in flow volume in the HAVF occur in the first minutes after anastomosis. Several authors showed these changes through analysis using Doppler ultrasound. In a study of 50 HAVF, Won et al.³¹ identified an increased flow volume from 20.9 mL/min to 174 mL/min 10 minutes after HAVF creation. In another study, Yerdel et al.³² showed that changes still occur throughout the weeks, with increase in flow volume to 754, 799 and 946 mL/min 1, 7 and 42 days after the surgery.

Robin et al.³³ published data relative to changes in flow volume and diameter occurring in vessels after creation of an HAVF. The main changes occur early, during the first weeks. After 4 weeks, there was mean diameter of 4.5 mm and flow volume of 700 mL/min. After 12 weeks, the values were a little different: 4.7 mm in diameter and 675 mL/min in flow volume. The study by Robin et al.³³ determined an important factor: minimal venous diameter of 4.0 mm and minimal flow volume of 500 mL/min were associated with mature fistulas in 70% of cases. When the patient had these two minimal requirements, in an association of these two variables, 95% of the fistulas were proper for use. These values remained with little variation 2, 3 and 4 months after the surgery.

Many studies showed that a good part of fistulas that do not reach one of the minimal parameters of diameter (4.0 mm) and flow volume (500 mL/min) close within 6-8 weeks.^27,33,34 Other authors believe that lower flow volumes may allow hemodialysis, depending on how the hemodialysis machine is adjusted. One example was the study by Tordoir et al.,²⁷ in which a flow volume of 250 mL/min was considered proper for maturation. For some authors, minimal flow volume in HAVF should be 300 mL/min, thus avoiding collapsing during hemodialysis.⁴ In the study by Sivanesan et al.,³⁵ a minimal diameter of 3 mm and a minimal flow volume of 150 mL/min was considered sufficient for maturation. In our sample, the cut-off value was set in 400 mL/min, on the basis that minimal flow to have the hemodialysis machine working properly is 350 mL/min. HAVF with values equal or lower than 400 mL/min usually progress with vein collapse and process interruption.

Data from the literature show that changes in diameter and flow volume occur early, between 1 and 4 weeks. Therefore, it is believed that in 6 weeks the fistula should be evaluated for puncture, since during this period, the HAVF that have maturation problems can already be identified.^3,36

In this study, ultrasound maturation occurred in more than 50% of patients in the first week. However, it is known that this is not a sufficient criterion, as many patients that needed early puncture of HAVF lost it. In this example, there are two patients that unfortunately had HAVF loss due to a break in the protocol. Both developed hyperpotassemia associated with infection of the temporary catheter. This required removal of the catheter and frustrated attempt of early HAVF puncture, resulting in hematoma and HAVF occlusion, even if these had the minimal criteria.

In cases where the HAVF did not have appropriate development due to factors that could be corrected, color-flow Doppler ultrasound proved to be efficacious in the early identification of these factors. As an example, there was one case of leak through the tributaries, with mean blood flow of 250 mL/min. After ligation of the tributaries, there was improvement in HAVF flow, which reached 824 mL/min.

A trained team that does not have many additional resources can determine whether a fistula reached or not maturation. Robins et al.³³ published a study comparing clinical assessment of HAVF maturation using criteria such as easily palpable thrill of at least 10 cm of vein proper for puncture. The data were crossed with data obtained from ultrasound evaluation of HAVF maturation. Thirty patients were examined. Of 21 clinically mature HAVF, 17 (81%) were really mature in the ultrasound. On the other hand, seven out of nine HAVF (78%) were evaluated by nurses as inadequate, which they in fact were. Thus, the accuracy of an experienced examiner is around 80%.

In a study published by Tordoir et al.²⁷ failure in maturation occurred in 33% of HAVF, and in 64% of the fistulas that did not maturate it was possible to identify an anatomical cause that could be corrected by recent techniques of endovascular treatment. These techniques, when used, allowed salvage of 47% of the HAVF with maturation problems due to localized anatomical changes.

Physical examination can determine the causes of failure in maturation. A weak arterial pulse can presuppose stenosis above the HAVF level. Leak through tributaries is a frequent situation, avoiding proper flow volume through the main vein. One form of identifying it is compressing the vein causing the supposed flow leak and noting the changes in thrill (physical examination) or in flow volume (ultrasound), which indicate whether the leak is significant or not and if that vessel can be ligated.³

A fact perceived in our sample is that ligation of tributaries that supposedly drain part of the blood coming from the HAVF should be avoided before performing the tributary compression test. This test allows determining whether or not the leak is significant, and ligation is indicated in positive cases. In cases when the leak is not significant, the tributary should be maintained, as these vessels may maintain the cephalic vein patent when there is fistula occlusion, allowing creation of new accesses for hemodialysis with remaining courses.

Conclusion

Based on the ultrasound criteria defined for the cut-off point between mature HAVF or not, it can be concluded that most elbow HAVF had proper diameter and flow for puncture soon after the first week of postoperative period. For wrist HAVF, there was progressive improvement in maturation standards throughout the weeks, and these should be preferentially punctured 4 weeks after the surgery.

Acknowledgements

We would like to thank the nephrology team at da Renalclin, in Cascavel, Dr Hi Yung, Dr. Noris Rhode, Dr. Mauricio Carvalho and Dr. Vanessa Uoscocowich, as well as nurse Solange Santos and Claudinete Balbino Alvarez.

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Publication Dates

• Publication in this collection
  08 Dec 2008
• Date of issue
  Sept 2008

History

• Accepted
  15 May 2008
• Received
  10 Oct 2007