A prospective study of factors associated with successful maturation of arteriovenous fistulas for hemodialysis

The guidelines recommend performing arteriovenous fistula surgery preferably as the first vascular access⁽¹⁾. However, the failure rate of the maturation process of arteriovenous fistulas has reached 38.9% according to published studies^(2–4). An arteriovenous fistula is created by an anastomosis between the artery and vein, and successful maturation requires an increase in diameter and blood flow, and an adequate depth because enough pressure is needed⁽⁵⁾.

The factors associated with the failure of arteriovenous fistula maturation have been discussed across the world⁽⁶⁾. Many study results are different, and some are replicated; however, there is no consensus⁽⁷⁾. Planning includes early referral, selection of an ideal site for the arteriovenous fistula, adequate evaluation of comorbidities and timely follow-up, and artery and vein evaluation through physical examination, Doppler ultrasound, and angiography⁽⁸⁾. There is strong evidence of the need for preoperative ultrasound arterial and venous mapping for access planning and autologous arteriovenous fistulas as the first choice⁽⁹⁾. It is important to determine the size of the veins and arteries and compliance; age, sex and comorbidities; and the functioning of the vascular endothelium. Some research has shown that this factor is important for the maturation of arteriovenous fistulas^(6,10,11). Studies have found that several of these factors are implicated in the maturation of arteriovenous fistulas^(12,13). The aim of this study was to evaluate the factors associated with the successful maturation of arteriovenous fistulas.

The characteristics of all participants are shown in Tab. 1. There was a nonsignificant trend toward older age among the patients without maturation compared to those with maturation. All the other characteristics were similar between the groups. All the patients had residual diuresis, had been taking antihypertensive drugs, used erythropoietin, and had a similar number of sessions (Tab. 1). Body mass index (BMI), hypertension, diabetes mellitus, and biochemical parameters evaluated between the patients at maturation or without maturation are summarized in Tab. 1. Glucose, urea, creatinine, and hemoglobin were evaluated in all patients.

The presurgical characteristics of the vessels and of the surgeries are shown in Tab. 2. There were no significant differences in the flowmediated dilatation test, surgical time, bleeding or resistance index. However, a significant difference was observed in the diameter of the vein on which the surgery was performed. The vein diameter was 4.3 ± 1.0 mm (maturation group) vs 3.2 ± 0.9 mm (non-matu-ration group), p = 0.04. The artery diameter was similar: 4.5 ± 0.6 vs 4.5 ± 0.4, p = 0.88. Logistic regression analysis revealed that the diameter of the vein for which the surgery was performed was associated with successful maturation in our population, odds ratio = 4.77 (1.14–19.97), p-value = 0.032. Of the 37 patients with arteriovenous fistulas, 18 had brachycephalic fistulas (49%), nine had brachymedian fistulas (24%), five had brachycommunicating posterior fistulas (14%), three had brachibasil fistulas (8%), two had radiocephalic fistulas (8%), and two had radiocephalic fistulas (5%). In all the patients, autologous arteriovenous fistulas were performed without the use of native or synthetic grafts. This approach was preferred due to less complicated procedures and lower costs. Table 3 shows the changes in the postsurgical features of the mature fistulas.

In this study, we investigated the characteristics of the study population that could predict successful maturation of arteriovenous fistulas. Many patients have more than one risk factor for multiple comorbidities. Dialysis patients are among the most common patients⁽¹⁷⁾. Comorbidities may be problematic with respect to the maturation of arteriovenous fistulas. Diabetes mellitus has been linked to fistula maturation failure; it has been proposed that the number of comorbidities associated with diabetes influences fistula failure, and this seems to be true in our study⁽¹⁸⁾. In this study, we found no difference between the fistula maturing and nonmaturing groups regarding the presence of comorbidities⁽¹⁹⁾. Some other factors under discussion have included the female sex and older age. Many studies have shown that advanced age is a risk factor for decreasing life expectancy⁽²⁰⁾. Our population was young, with an average age of 49 years. However, the presence of comorbidities appears to have a stronger effect on survival than age itself⁽²¹⁾. Advanced age is often associated with comorbidities, but as an isolated variable it should not affect decisions regarding the creation of vascular access⁽²²⁾. However, in fistulas where the flow has been established in older patients, it can be seen that the survival rate of older patients in comparison with the groups of young patients shows no difference, while the success rates of fistulas in some other studies reveal that it does not interfere with the age. In investigations where an age of more than 65 years caused primary fistula failure, vascular mapping was not performed⁽²³⁾. In the study carried out by our team, we did not observe a significant difference in age between the failure or success groups either, but vascular mapping was performed for all the patients.

Most related research has shown differences between men and women. In one study, affected women had a greater risk of failure of arteriovenous fistula maturation compared to men⁽²⁴⁾. However, some other changes include women having a higher overall maturation rate than men, but the patency being shorter for women than for men at three and 12 months⁽²⁵⁾. Race was another important risk factor for failure at maturation. Hispanic individuals are half as likely to develop chronic kidney disease, however, this phenomenon is not a very clear risk factor for failure of arteriovenous fistula maturation⁽²⁶⁾. According to the 2016 Unites States Renal Data System (USRDS) data⁽²⁵⁾, the highest failure rate for successful arteriovenous fistula was in non-Hispanic patients at 29.2%, whereas the highest failure rate was observed in black patients. Success at 12 months was greater in Hispanics than in individuals of other races. This study was carried out in a low-income Mexican population; therefore, evaluating the success rate in this population is important for other groups with the same characteristics. Patients with kidney disease have certain limitations, and there is a greater risk of type 2 diabetes mellitus and other comorbidities, in addition to differences in the depth of the vessels, in patients with kidney disease. However, these patients have higher survival^(27,28). In the USRDS Dialysis Morbidity and Mortality Wave II study⁽²⁹⁾, an association was found between BMI ≥35 kg/m² and failure of arteriovenous fistula, and secondary dysfunction was also documented⁽³⁰⁾. Other surgical techniques are suggested to increase the success of fistulas in obese patients^(31,32). In our study, we cannot argue for or against this point since the patients in our population had a BMI less than 25 kg/m², both those with and without adequate maturation.

The flow needs to be increased in the artery that supplies the arteriovenous fistula to irrigate correctly⁽³³⁾. Flow-mediated dilation measures the ability of the arteries to dilate, and patients with higher flow-mediated dilation are expected to be more likely to have successful fistula completion. After release of the brachial cuff, blood flow increases in response to local vasodilators, nitric oxide is released from the endothelium, and there is subsequent dilation of healthy arteries^(7,34). Flow-mediated dilation is considered a marker of endothelial function because it measures the endothelium-dependent arterial response^(35,36).

These tests are likely to be unfavorable for arteriovenous fistula failure⁽³⁷⁾. We evaluated flow-mediated dilatation to observe its relationship with arteriovenous fistula flow or diameter at six weeks; however, this study could not determine such a relationship.

Vascular evaluation was performed in our study. It involved studying the vessels in patients in preparation for vascular access. Vascular mapping is considered the standard of practice for vascular evaluation prior to the creation of an arteriovenous fistula⁽³⁸⁾. The number of failures is lower in the groups where vascular mapping is used, which is more beneficial as a routine⁽³⁹⁾. Each patient was evaluated three times before the skin incision was made for surgery: first in the outpatient department when referred, then one day prior to the arteriovenous fistula, and finally in the operating room prior to the start of the procedure. These careful reviews are performed and greatly improve upon any errors that may arise; similarly, the best anatomy is chosen in each patient, and vascular mapping is of utmost importance for successful surgery. Physical examination of the veins without accompanying vascular mapping has been adequate in only one-third of cases in some studies⁽⁴⁰⁾. With the initial evaluation and subsequent use of vascular mapping, the surgical plan for arteriovenous fistulas can be modified in up to one-third of cases⁽⁴¹⁾. In other studies, physical examination, ultrasound and venography were performed. In 9% of the patients, the surgical plan based on the physical examination was modified by the ultrasound results by 22.6% according to the results of venography. In our study, all patients underwent physical and ultrasound examinations, and only 13% of the patients failed this way⁽⁴²⁾.

The anatomy of the vessels is very important for creating vascular access and for successful surgery, with a minimum threshold of 2 mm established for arterial diameter⁽⁴³⁾. Several authors have suggested using a different arterial diameter than this value, with good results^(44,45). The size of the artery is important, as is its quality; with the increasing age of the dialysis population and the growing prevalence of diabetes and hypertension as comorbidities, arterial occlusive disease is becoming more common. Patients with diabetes mellitus exhibit calcifications that can complicate the technical aspects of anastomosis creation and can hinder the maturation process by preventing compensatory artery hypertrophy⁽⁴⁶⁾. Another problem is related to the veins, which are frequently an issue in renal patients due to abnormalities that may occur and iatrogenic multiple punctures. The diameter and depth of the vein and the dilation capacity of the vein should also be evaluated⁽⁴⁷⁾. As with the artery, there is no established standard for the size of the vein, although the most commonly approved size is 2.5 mm⁽⁴⁸⁾. In our study, the diameters of the veins were demonstrated to be an important predictive factor. In an observational study of 122 patients, only the diameter of the vessels and the compliance of the veins had a significant predictive value, reaching a maturation success rate of up to 89%⁽⁴⁸⁾.

In our study, we observed a larger vein size than in the aforementioned studies, and the vein dimension was almost double of that suggested in the guidelines. This is why we believe that when evaluating a patient, vascular mapping and the correct measurement of glasses will result in the correct choice of surgery for each patient. In Mexico, prolonged waiting times and saturation of interconsulting services often mean that a patient must be subjected to the insertion of a catheter, which leads to increased mortality, morbidity, and costs and supersaturation during hospitalization and emergency department admission. The creation of an interventional nephrology service would decrease waiting times, as the same nephrologist would identify and treat the problem, reducing the need to place a catheter and therefore, decreasing the risk of infection related to it, limiting hospitalizations, and increasing the opportunity for research and innovation in this area⁽⁴²⁾.

After evaluating the demographic factors, we found no differences in sex, age, or comorbidities. Of the total of 37 patients with fistulas, most had a brachiocephalic fistula, which had the best anatomical characteristics, vein compliance, and best approach. We found no difference from the flow-mediated dilation test in our study. We observed an important and significant difference in the diameter of the vein used to make the fistula. We think that, in our study population, the diameter of the vessels, as well as vascular mapping, were of utmost importance and represented the factor with the most significant impact. It is important that nephrologists have an opportunity to plan vascular access early, that they evaluate patients for substitution treatments, that they have the knowledge and ability to decide on the vessel to be approached with the support of the vascular surgeon, and that this approach is not a unilateral decision. Collaboration with angiologists is necessary to improve the quality of care for these patients.

One limitation of our study was the number of patients enrolled. Another limitation was the age of the study patients.

It is highly important to plan vascular access in patients to perform vascular mapping and measure veins and arteries. Vein measurement is a key factor in the successful maturation of arteriovenous fistulas.