Changes in the Profile of Endovascular Procedures Performed in Freestanding Dialysis Access Centers over 15 Years

Discussion

The profile of procedures performed for dialysis access salvage and maintenance in freestanding dialysis access centers changed markedly during the years of 2001 through 2015 (Figure 1). To make comparisons using comparable data, these data were compared with the percentage of dialysis access types in prevalent patients receiving dialysis using an arteriovenous access from 2001 to 2014, according to the USRDS (1,7). Although exact identity cannot be assured, a reasonably close approximation can be assumed in view of the corresponding demographics of the patients, the numbers of patients treated, and the number and distribution of the centers involved. An explanation of the changes observed in intervention frequency can best be understood by placing them in context with changes in access prevalence.

The arteriovenous procedure profile from 2001 to 2015 changed from one characterized by approximately equal numbers of angioplasties and thrombectomies performed on AVGs to one characterized primarily by angioplasties performed on AVFs. The yearly increase in AVF procedures was roughly parallel and proportional to the increase in AVF utilization in the prevalent dialysis patient population (Figure 2). Angioplasty was the predominant procedure performed in AVFs, representing >50% of all arteriovenous procedures (Table 3). The percentage of AVF thrombectomies performed was consistently <6%, with a mean of 4.7% of arteriovenous procedures. A mean of 41.1% (88.6% of AVF procedures) were angioplasties (Table 3) with a range of 13.3%–58.6% of arteriovenous procedures.

Procedures performed on AVFs with increasing prevalence did not decrease as was anticipated. There are several issues that have grown out of the push to increase AVF utilization that might explain this. A clinically functional AVF (15) has a lower incidence of stenosis, thrombosis, and infection than an AVG. However, if all AVFs that are created are considered, the primary patency of AVFs and AVGs is comparable for the first year after creation because of AVF FTM (16–18). Most FTM cases can be salvaged, but it is procedure-intensive (19–21). In this study, FTM as an indication for angioplasty had a mean incidence of 12.6%. However, this number is deceptive as to its contribution to the overall number of resulting angioplasties. Many FTM-AVFs require more than one procedure to become clinically usable. Frequently, repeat procedures are not recorded as FTM. In addition, multiple studies (22–24) have shown that a salvaged FTM-AVF requires additional interventions to maintain its patency. FTM as an indication for treatment is not listed for these cases. Unfortunately, 70%–80% of patients starting dialysis do so with a catheter (7,25–27). If these patients then have an AVF created, time is required for it to become clinically usable resulting in prolonged catheter usage (18,28). This increases the risk of central vein stenosis. Once it has occurred, these cases often require repetitive intervention.

As was expected, a decreasing percentage of AVG utilization resulted in a progressive decrease in the percentage of AVG procedures. This decrease was roughly parallel to the changes in AVG use, but as anticipated was disproportionately higher (Figure 3). AVGs have a higher incidence of procedures performed for maintenance and salvage than AVFs (29). In addition, an AVG is less tolerant of low blood flow and thromboses relatively early. Reports have indicated that the numbers of thrombectomies and angioplasties performed on AVGs are approximately equal (29), as was seen in this series (Figure 3).

Procedural success for AVF and AVG angioplasty on the basis of NKF-K/DOQI definitions (9) started at a high level and improved over the 15-year period (Table 3). Although more complications were seen in association with AVF interventions, the total complication rate (major and minor combined) for both AVFs and AVGs was below the recommended 5% threshold for the SIR complication classification system (11). Complications occurred more often in AVFs and were more frequently observed in association with a thrombectomy than an angioplasty. As was the case in this series, angioplasty-induced venous rupture has been the most commonly reported complication associated with both angioplasty and thrombectomy (30). Only a small number of accesses experiencing venous rupture could not be salvaged. The second most common complication, seen primarily in association with thrombectomy, was arterial embolization. It is important to note that these were symptomatic emboli and as such undoubtedly represent under-reporting. Most emboli that occur are small and asymptomatic (31). As a result, they are frequently unrecognized and not reported (32). Emboli were reported three times as often with an AVG versus an AVF thrombectomy.

Endovascular stents were first used in this cohort of cases in 2005. During the 11 years in which they were used, their utilization increased ten-fold. In the beginning, virtually all stents were bare metal; however, covered stent utilization increased progressively as did stent placements in general. Stents were used more often in AVFs and utilization was higher in thrombectomy than in angioplasty cases for both AVFs and AVGs.

Previous studies have shown that AVF-PTAs require significantly more time and supplies to accomplish, and are more cognitively, physically, and psychologically demanding (8,33).These observations, along with the statistically significant lower success rate for AVF thrombectomy, longer procedure times, and a higher complication rate for all AVF procedures demonstrated in this study, attest to the fact that evolving from predominantly AVG to AVF utilization has introduced an increased level of complexity to the procedures being performed.

TDC cases in this cohort of patients decreased over the 15 years of the study by 20%. This change was due primarily to falling numbers of TDC-P. In recent years, most of these procedures have been performed in the hospital setting. According to Centers for Medicare and Medicaid Services claims data for 2015, the site of service for TDC-P was Inpatient Hospital 62.2%, Outpatient Hospital 30.2%, Physician’s Office (freestanding dialysis access center) 5.1%, and Ambulatory Surgical Center 0.5%. Exchanges and removals increased slightly but not enough to offset the decrease in primary TDC placements.

Catheter dysfunction was the major indication for TDC exchange, with a mean incidence of 67.4% versus 18% for catheter-related bloodstream infection. This latter indication decreased significantly during the study, resulting in an increase in the ratio between the indications from 2.2 to 11.5. Cases were routinely checked for a fibrin sheath at the time of catheter exchange. This was found to be present in a mean of 30.6% of cases. The most frequent complication observed with TDC cases was bleeding. Most of the bleeding that occurred in this series was related to skin bleeding occurring at the dialysis facility after the administration of heparin, when the patient dialyzed immediately after having a TDC procedure.

It is important that all dialysis access procedures be accomplished in a timely manner. Patients are sedated using a short-acting sedative, many patients have missed one or more dialysis treatments and returning the patient to the dialysis facility is a high priority, and operational efficiency of the treatment facility is important in the management of daily caseloads. Analysis of this data demonstrated that procedure times for all categories of access cases decreased progressively.

The profile of problems presenting for treatment in freestanding dialysis access centers has been materially affected by changes in the overall vascular access profile of the United States dialysis patient population. With the change from primarily AVGs to AVFs has come increasing numbers of angioplasties and decreasing numbers of thrombectomies. With this, the overall complexity of arteriovenous access maintenance and salvage cases has increased. The catheter procedure profile has been altered by the fact that the majority of these devices are being placed in the hospital setting. Judging by changes in success rates, procedure times, and complication rates, the effectiveness, efficiency, and safety of these procedures has improved over the past 15 years.