Efficacy of Using a Vessel Dilator during Surgery to Evaluate Vein Diameter and Predict Radiocephalic Arteriovenous Fistula Maturation and Patency

Abstract

Background: We use vessel dilators to assess the diameter of the target vein during surgery for arteriovenous fistula (AVF) creation in hemodialysis patients. This study investigates the efficacy of using vein diameter as measured using dilators (surgical diameter; SD) versus that as measured by preoperative ultrasonography (ultrasonographic diameter; UD) to predict postoperative complications and patency. Methods: Sixty-three patients who underwent radiocephalic AVF creation and had measurements of UD and SD were retrospectively analyzed. Cutoff values for UD and SD regarding complications were used to dichotomize the patients into high and low groups for comparisons. Results: The 2-year primary and secondary patency rates overall were 66.5% and 88.9%, respectively. The optimal UD and SD cutoff values were 2.4 and 3.5 mm, respectively. The 2-year primary patency rate was higher in the high-SD group than the low-SD group (88.2% vs. 58.6%; p = 0.0426). The 2-year secondary patency rate was significantly higher in the high-UD/high-SD group than the low-UD/low-SD group (91.7% vs. 68.4%; p = 0.0067). Conclusions: Intraoperative measurement of vein diameter using dilators during AVF creation might be a useful method of predicting patency, particularly when SD is used in combination with UD.

1. Introduction

Creating arteriovenous fistulas (AVFs) for hemodialysis that are easy to access, provide adequate blood flow, and minimize postoperative complications is crucial. However, primary AVF failure is common and can be attributed to various factors, including inadequate vein size. Reported rates of AVF abandonment approach 21% [1], and some AVFs require percutaneous transluminal angioplasty (PTA) to salvage their function or surgical reconstruction.

AVF development is a complex vascular remodeling. Large amounts of blood flow through the access circuit increase blood pressure, velocity, and wall shear stress. Post operative dysfunction of AVFs can be caused by multiple factors. In the early postoperative period, potential causes of dysfunction include surgical anastomotic technical failure [2], pre-existing vascular injuries due to uremia, oxidative stress, and inflammation [3], vascular spasm [4], thrombus formation due to coagulation abnormalities [5] or endothelial damage, postoperative hypotension, physical compression, and reduced blood flow caused by hematoma formation. Preventive measures include employing precise anastomosis techniques, conducting detailed preoperative vascular assessments using ultrasound, administering anticoagulation or antiplatelet therapy postoperatively if needed, evaluating blood flow after surgery, managing blood pressure, and ensuring proper wound care as part of comprehensive postoperative management.

In the late postoperative period, AVF dysfunction may occur due to intimal hyperplasia and stenosis, which are induced by hemodynamic shear stress, turbulence, and compliance mismatch between noncompliant artery and compliant vein [6] caused by arterial blood flow into the vein. Additionally, vascular damage from repeated punctures during dialysis can contribute to AVF dysfunction [7]. Preventive measures include regular morphological evaluations using ultrasound scan and blood flow measurements, enabling appropriate therapeutic interventions for stenosis or occlusion when detected [8].

Arterial and venous diameters before AVF surgery play a pivotal role in predicting poor maturation and early postoperative obstruction [9]. However, ultrasound measurements can vary depending on the duplex scan device used, the examiner, and the position and intensity of the tourniquet, and it is often the case that the same ultrasound device and observer may measure different diameters on the same patient’s forearm cephalic vein on different days. The values may differ depending on the patient’s systemic conditions including hydration status, and daily variations of venous diameters in preoperative ultrasonographic assessment should not be ignored [10]. Even if the preoperative ultrasound diameter is small, when the vein is dissected and saline solution is passed through it during surgery, the diameter may appear large enough to create an autogenous arteriovenous fistula without any issues.

To address this discrepancy in target vein diameter between preoperative duplex ultrasonography and intraoperative observation, we have begun to use vessel dilators during AVF surgery to measure vein diameter. This study investigates the efficacy of using vein diameter as measured using vessel dilators versus that as measured by preoperative ultrasonography to predict postoperative complications and AVF patency.

2. Materials and Methods

2.1. Subjects and Procedures

This retrospective observational study examined 63 patients who underwent creation of a radiocephalic AVF (RCAVF) for hemodialysis between July 2020 and May 2022.

We measured ultrasonographic diameter (UD) preoperatively, while the surgical diameter (SD) was measured intraoperatively using a vessel dilator. Preoperative ultrasonographic measurements of the cephalic vein diameter at the wrist were taken in the sedentary position with a rubber tourniquet placed on the upper arm; this size was recorded as UD. Cephalic vein continuity throughout the upper arm was confirmed. The preoperative ultrasound evaluation was performed by the vascular surgeon. Ultrasonographic examination was performed using B-mode measurement (probe of 7 to 15 MHz, Affiniti 70, Philips Ultrasound LLC, Bothell, WA, USA). Preoperative evaluation also included palpation of the radial pulse and administration of the Allen test.

Regarding the patients’ condition before the surgery, patients were fasted for 2 h prior to surgery, and intravenous infusion of starting fluids was initiated 1 h prior to surgery at a rate of 20 mL/h. Two vascular surgeons, three nephrologists, and one radiologist performed the procedure, with the vascular surgeon serving as the teaching assistant when the nephrologist or radiologist performed the surgery.

Stainless steel vessel dilators (diameters 2.0, 2.5, 3.0, 3.5, and 4.0 mm; BOSS Surgical Instruments, Gordonsville, VA, USA) (Figure 1A) were used during surgery to measure vein diameter in each patient. The length of the dilator was around 13 cm. After peripheral vein disconnection, the vein was dilated using injection of saline solution. The dilators were then sequentially inserted (starting at 2.0 mm) (Figure 1B) until the maximum diameter was reached; this size was recorded as SD. Subsequently, the vein was dilated again with saline while compressing the outflow vein to facilitate vein distension. After the end of the dilated vein was trimmed with a Potts sharp knife, a 6 mm incision was made in the radial artery with bulldog forceps to cut off blood flow, and end-to-side anastomosis was performed with a 7-0 polypropylene thread.

2.2. Outcomes

Postoperative follow-up was performed the day after surgery and 1 week, 3 months, 6 months, and every 6 months thereafter in the outpatient clinic if there were no complications. PTA was indicated for problems such as poor blood flow or elevated venous pressure on the return site during dialysis and flow volume less than 200/min on ultrasonographic examination. Postoperative complications, 2-year primary and secondary patency rates, and adverse events associated with dilator use were recorded as study outcomes. Complications were defined as AVF stenosis or occlusion requiring therapeutic intervention or causing AVF failure.

Patency rate was defined according to the recommended standards [11] approved by the Committee on Reporting Standards of the Society for Vascular Surgery and the American Association for Vascular Surgery. The primary patency interval was defined as the time from surgery to any intervention intended to maintain patency. The secondary patency interval was defined as the time from surgery to access abandonment or attempt to re-establish AVF functionality. The primary and secondary patency rates were calculated using Kaplan–Meier estimates. Optimal cutoff values for UD and SD regarding complications were determined using receiver operating characteristic curve analysis and used to dichotomize the patients into high and low groups for comparisons.

2.3. Statistical Analysis

Probability ellipses (0.95) were used to determine associations between UD and SD. Patency rates were calculated using the Kaplan–Meier method and compared using the log-rank test. p < 0.05 was considered significant. Statistical analyses were performed using JMP software version 14.3.0 (SAS Institute, Cary, NC, USA).

3. Results

3.1. Patient Characteristics

The mean age was 70.4 ± 15.0 years. Forty-five patients were men (71.4%). The underlying cause of renal failure was diabetes mellitus in 34 patients (54.0%), nephrosclerosis in 21 (33.3%), autosomal dominant polycystic kidney disease in 2, chronic glomerulonephritis in 1, IgA nephropathy in 1, renal cancer in 1, and unknown in 3. Fifty-two patients (82.5%) had hypertension, 37 (58.7%) had diabetes, and 30 (47.6%) had dyslipidemia. Seventeen patients (27.0%) were taking antiplatelet agents and four (6.3%) were on anticoagulants. Fifty-five AVFs (87.3%) were placed on the non-dominant arm. The mean UD was 2.6 mm. SD was 2.0 mm in 4 patients, 2.5 mm in 13 patients, 3.0 mm in 29 patients, 3.5 mm in 12 patients, and 4.0 mm in 5 patients. A 2 mm dilator could be inserted in all cases. The mean SD was 3.0 mm. In all cases, bruit and thrills were good during, immediately after, and the day after surgery. Hemodialysis was introduced in all patients—the mean time from surgery to AVF use was 55 days. The median follow-up after surgery was 806 days.

Table 1. The details of 7 cases that required reconstruction or catheter insertion in the early postoperative period or at a remote period are shown.

No.	Age (years)	Sex	UD (mm)	SD (mm)	Causes for AVF Abandonment	Procedures	Days Until Intervention (days)
1	78	Female	2.0	2.5	Poor maturation	AVF creation at the elbow	71
2	58	Male	2.0	2.0	Occlusion	AVF creation at the elbow	127
3	69	Female	1.9	3.0	Poor maturation	AVF creation at the elbow	15
4	83	Male	1.9	3.0	Occlusion	AVF creation at the forearm	42
5	70	Male	2.0	2.5	Occlusion	Tunneled cuffed central venous catheter insertion	249
6	88	Male	3.5	3.5	Occlusion	AVF creation at the forearm	15
7	55	Male	2.2	3.0	Occlusion	AVF creation at the forearm	27

shows UD and SD, the reason for AVF abandonment, and the number of days until intervention for the seven cases that required reconstruction surgery or catheter insertion. In two of the seven cases, poor maturation of the vein and in five cases, AVF occlusion was observed. In six of the seven cases, AVF reconstruction was required, and in one case, insertion of a tunneled cuffed central venous catheter was performed.

Five patients out of 63 patients died in the follow-up period for reasons unrelated to AVF creation (renal failure, respiratory failure, bowel obstruction, coronavirus infectious disease, and unknown, respectively).

3.2. UD, SD, and Complications

Receiver operating characteristics curves for UD and SD in relation to complications are shown in Figure 2A,B. The optimal UD cutoff value was 2.4 mm (area under the curve, 0.55) (Figure 2A). The optimal SD cutoff value was 3.5 mm (area under the curve, 0.66) (Figure 2B).

3.3. UD, SD, and Patency Rates

The 2-year primary and secondary patency rates overall were 66.5% and 88.9%, respectively. The Kaplan–Meier curves of primary and secondary patency in patients dichotomized according to optimal UD cutoff value (≥2.4 mm and <2.4 mm) are shown in Figure 3. The 2-year primary patency rates did not significantly differ between the high- and low-UD groups (74.8% and 55.6%, respectively; p = 0.0872). However, the 2-year secondary patency rate was significantly higher in the high-UD group (97.2% vs. 77.8%; p = 0.0169).

The Kaplan–Meier curves of primary and secondary patency in patients dichotomized according to optimal SD value (≥3.5 mm and <3.5 mm) are shown in Figure 4. The 2-year primary patency rate was significantly higher in the high-SD group (88.2% vs. 58.6%; p = 0.0426). However, the 2-year secondary patency rates in the high-SD group (94.1%) and low-SD group (87.0%) did not significantly differ (p = 0.4504).

The Kaplan–Meier curves of primary patency in patients grouped according to both UD and SD cutoffs (high UD/high SD, high UD/low SD, low UD/high SD, and low UD/low SD) are shown in Figure 5. The high-UD/high-SD group exhibited a higher secondary patency rate compared to the low-UD/low-SD group (91.7% vs. 68.4%; p = 0.0067).

3.4. Adverse Events

No adverse events such as vascular injury due to the insertion of dilators or anomalies immediately after anastomosis that could be attributed to vascular spasm occurred in any of the cases.

4. Discussion

The National Kidney Foundation guidelines [12] suggest the following to define AVF suitability for use in hemodialysis vascular access: vein diameter > 6 mm, vein depth < 6 mm, and blood flow > 600 mL/min on ultrasonography. Among the various factors associated with AVF maturation [13], preoperative vein diameter is an independent predictor [14].

Preoperative measurement of UD and physical examination findings are important in determining the appropriate site of AVF creation [15,16,17,18]. Mihmanli showed that the incidence of initial failure after AVF creation was up to 25% when only physical findings were checked in the preoperative examination, but was 5.6% when ultrasonographic assessment was performed before surgery [19], and it is now generally agreed that UD measurement should be performed as a preoperative examination. However, consensus regarding the optimal cutoff UD value has not been reached [20]. The Japanese Society for Dialysis Therapy guidelines recommend UD ≥ 2.0 mm when measured in conjunction with torniquet application [21]. Bashar suggested that in the older patients, AVF creation at the wrist should be avoided if the vein diameter is less than 2.5 mm [14]. Although UD ≥ 2.0 mm is a rough indicator, sometimes the vein diameter encountered during surgery differs from the preoperative ultrasonographic assessment. This may be due to various factors such as patient general condition, hydration status, room temperature, intensity and time of tourniquet placement, and the effect of local anesthetics, although it has been reported that forearm superficial venous diameter is not influenced neither by the observer performing the measurement nor the method of congestion [10]. Therefore, we hypothesized that quantitative evaluation of vein diameter using vessel dilators during surgery might be more accurate.

Our study indicates that SD ≥ 3.5 mm may be more effective in avoiding AVF complications that require intervention. After AVF establishment, PTA is the primary option for addressing inadequate blood flow and access difficulty. Surgical reconstruction is reserved for cases of AVF failure or when PTA has failed. When we perform AVF, the vein is anastomosed after saline pressure dilatation. SD denotes the vein diameter just before anastomosis and represents dilation capacity, which is challenging to predict solely through preoperative measurement of UD. This observation suggests that SD serves as a more robust predictor of postoperative vascular maturation than UD. Even when the preoperative UD is consistent, a larger SD presumably indicates an increased vasodilatory capacity, thus increasing the likelihood of substantial vascular development. Conversely, in cases where both UD and SD are diminutive, the surgeon should anticipate challenges in salvaging the AVF using PTA; in such cases, surgical reconstruction in the future is likely.

Regarding whether UD alone is sufficient to predict the avoidance of reconstruction if differences are observed in 2-year secondary patency rates for UD ≥ 2.4 mm and <2.4 mm, the following reasons may justify the use of SD in combination with UD. Among the 27 patients with UD < 2.4 mm, 6 underwent reconstruction, whereas none of the eight patients with UD < 2.4 mm and SD ≥ 3.5 mm required reconstruction, suggesting the possibility that reconstruction can be avoided if the vein has the ability to dilate. With ultrasonography measurement being important, intraoperative measurement may also be significant.

Potential complications associated with dilator insertion include vascular injury and retrograde blood flow owing to destruction of venous valves. Although the stainless steel composition of the dilators and their blunt tip minimize the risk of vascular injury, the risk is further minimized with a gentle operative technique. Moreover, the likelihood of venous valve destruction is mitigated when adequate blood flow is maintained. However, as with the use of balloons in PTA, invasion of the vessel wall may induce intimal thickening resulting from vessel inflammation. Although measuring vein diameter without a saline flush is ideal, dilator insertion before pressurized dilation with saline is technically difficult.

Another method to measure the diameter of the vein, including its dilatation capacity, is to measure the vein diameter by ultrasonography even during surgery, after saline drainage. Ultrasound measurement is less invasive and carries no risk of vascular injury or loss of vascular endothelial cells. High levels of mechanical stimulation has been shown to impair vascular endothelial function in veins and lead to thrombus formation [22], and the venous endothelial cell damage can occur when dilators are inserted. However, ultrasonographic measurements are also dependent on how the operator applies pressure with the probe and the subcutaneous distance of the vein. Therefore, we decided that a quantitative, surgeon-independent method of intraoperative evaluation would be the insertion of a dilator. Additionally, insertion of a dilator is a simple and time-saving procedure, and since it is performed after saline solution is passed through, it can be inserted without resistance, which is considered highly reproducible.

In addition to measuring vessel diameter, another method of quantitative assessment during surgery is to measure blood flow using a flow meter after anastomosis, as is carried out during coronary artery bypass grafting or peripheral artery bypass surgery. Quantitative assessment and prediction of postoperative venous development and patency by some method may be useful in adjusting postoperative follow-up intervals and in explaining to patients what to expect after surgery.

This study is limited by its retrospective design and small sample size. In addition, only patients who underwent RCAVF surgery were analyzed; therefore, our findings may not be generalizable to AVFs created in other locations. Although no short-term adverse events were observed due to the insertion of the dilator, the possibility of long-term adverse events due to intravascular insertion cannot be ruled out. In this regard, there is a need to conduct a prospective comparative study by randomly assigning patients to either the dilator insertion group or the non-insertion group.

5. Conclusions

In conclusion, intraoperative dilator measurements of the cephalic vein, which can also reflect the dilatation capacity of the vein, can more accurately predict the avoidance of future reconstruction when used in combination with preoperative ultrasonographic diameter, although UD alone is useful for predicting secondary patency.