One- and Two-Step TBBAVF
Amid the growing methodological heterogeneity in TBBAVF, studies have been performed in an attempt to clarify the optimal procedure for TBBAVF construction. In a recent meta-analysis, Jun Yan Wee et al. [15] assessed 12 comparative studies between one- and two-stage TBBAVF (2 RCTs and 10 cohort studies involving 1,135 patients) and found that the two-stage procedure had significantly better 2-year primary patency rates; however, there were no statistically significant differences in the failure rates, 1-year primary and secondary patency rates, and 2-year secondary patency rates between the 2 groups. Their meta-analysis also showed no differences in the time to first fistula use or complication rates of steal syndrome, hematoma, infection, pseudoaneurysm, or stenosis between the 2 procedures. These results indicate the potential benefits of the two-stage versus one-stage procedure for construction of a TBBAVF [15] (Table 2). The superficialized basilic vein in the two-stage procedure could conceivably be associated with a reduced risk of kinking, twisting, or compression in the relocated subcutaneous space because of the sufficient interval for venous arterialization and wall thickening. An additional advantage of the two-stage technique is that the development of complications such as steal syndrome or venous hypertension after the arteriovenous anastomoses in the first stage could be managed before superficialization [16].
Table 2. Recent comparative studies of methodological differences in TBBAVF
TBBAVF Construction Using Tunnel Transposition or Elevation
The differences in the clinical outcomes between tunnel transposition and elevation for TBBAVF construction have been evaluated in a few retrospective observational studies. Hossny [9] reported no differences in cumulative primary patency and secondary patency between tunnel transposition and one- or two-stage elevation. The author found that the total complication rate was significantly higher in the elevated group. However, most complications involved postoperative arm edema or hematoma formation and could be treated conservatively without fistula failure [9]. In another recent study, Wang et al. [8] also found that for TBBAVF construction, both tunnel transposition and elevation achieved high cumulative patency rates of the whole fistula conduit, including the vasculature from the arteriovenous anastomosis to the right atrium, with an acceptable early postoperative complication profile despite the need for repeated endovascular interventions in a subset of patients. Interestingly, the authors found that compared with tunnel transposition, elevation was associated with better primary patency of the superficialized basilic vein segment and a lower requirement for interventions [8] (Table 2).
Tunnel Transposition of the Cephalic Vein
The clinical feasibility of AVF superficialization using tunnel transposition of the forearm and upper arm cephalic veins has been suggested by several groups. In a study evaluating the outcomes of 3 different types of one-stage AVF tunnel transposition (forearm cephalic vein transposition, upper arm cephalic vein transposition, and upper arm basilic vein transposition) by Korepta et al. [17], no statistically significant difference was found in the access maturation rate, primary 1-year patency, or primary assisted 1-year patency among the 3 groups. These results indicate that cephalic vein transposition in the forearm and upper arm could be a reliable alternative AVF procedure with patency equivalent to that of TBBAVF. In addition, a revisional tunnel transposition procedure using a minimal incision technique to ensure accessibility was introduced by Inkollu et al. [18].
Methodological Diversity of the Superficialization Procedure
Elevation
The elevation procedure of the arterialized vein was originally introduced as a surgical revision for the purpose of facilitating AVF cannulation. Adequate maturation of the fistula is required for the successful implementation of repeatable, safe cannulation in clinical practice. The updated NKF-K/DOQI guideline proposes the following parameters associated with maturity of a newly created AVF, famously known as “the rule of 6s:” flow of > 600 mL/min, diameter of ≥0.6 cm, depth of ≤0.6 cm, and discernible margins [2].
In general, the rate of initial or early non-maturation AVF failure ranges from 20 to 60% [19]. Moreover, according to a study by van Loon et al. [20], during the first 6 months of a newly placed VA, a substantial proportion of patients encounter cannulation-related complications resulting in the need for temporary VA methods such as single-needle dialysis (33%) and catheter dialysis (22%). Cannulation-related complications of VA, such as hematoma formation, infection, and aneurysms, might lead to morbidity, hospitalization, access revision, loss of the VA, and the consecutive occurrence of other serious adverse events potentially attributable to the temporary VA [20, 21]. Ultrasound-guided needling may facilitate successful cannulation of arterialized veins with inaccessibility. However, a fundamental resolution regarding the clinical value of this technique has not yet been reached, and a certain risk of mis-cannulation and patient burden inevitably remains. Additionally, ultrasound guidance requires advanced technical skill. Given these facts, adjunctive elevation should be used to improve the accessibility by decreasing the depth and lengthening the accessible segment of the arterialized vein, which will in turn minimize the incidental risk of mis-cannulation and its related complications.
The elevation technique was recently adapted to one- or two-stage TBBAVF construction as an alternative combined superficialization procedure of tunnel transposition, as mentioned earlier (Figs. 1, 2). Furthermore, several reports have suggested the practical feasibility of AVF creation combined with the elevation of deeply located forearm and upper arm cephalic veins in a one- or two-stage procedure [10, 22, 23].
The outcomes of various elevation procedures were evaluated in a retrospective study conducted by Bronder et al. [10]. The authors assessed 295 cases of vein elevation (172 brachiocephalic fistulas, 70 brachiobasilic fistulas, 46 radiocephalic fistulas, and 7 superficial femoral vein fistulas) performed in a one- or two-stage procedure. The two-stage procedure included revisional elevation implemented within certain terms after fistula construction. The authors demonstrated