Longitudinal Dialysis Adequacy and Clinical Performance of the VectorFlow Hemodialysis Catheter: A Prospective Study

Abstract

Purpose

To report clinical performance and longitudinal assessment of hemodialysis adequacy with the Arrow-Clark VectorFlow catheter, a symmetrical-tip device with a distal lumen configuration designed to reduce platelet shear stress and catheter thrombosis.

Methods and materials

We prospectively enrolled patients who required de novo placement of a chronic tunneled catheter for hemodialysis or exchange of a dysfunctional catheter as part of an Institutional Review Board (IRB)-approved protocol. Catheter patency, Kt/V, mean blood-flow (Q_b), and pump pressures were obtained at baseline and at monthly intervals to 90 days.

Results

Forty-six subjects were enrolled into the study. During the 90-day observation period, maximum blood-flow rate averaged 355-398 mL/minute; mean Q_b averaged 333-392 mL/minute. Mean Kt/V values were consistently ≥1.5. Dwell-time was 15-114 days, for a total of 2997 catheter days (mean 71.4 days). Excluding patients who died during the study and those receiving surgical access, overall intervention-free catheter patency rate was 94.9%, 92.2% and 88.8% at days 30, 60, 90, respectively. There were no acute complications. During the follow-up period, three patients developed complications (6.5%). Two catheter infections occurred (0.7/1000 catheter days) and one catheter malfunctioned; a rate of 1.0/ 1000 catheter days for all complications.

Conclusions

The VectorFlow catheter produced safe, effective hemodialysis with Kt/V ≥1.5. A single catheter occlusion occurred and a low rate of infection was seen. Results support the hypothesis that the VectorFlow design reduces thrombogenic risk during clinical performance.

Introduction

Vascular access is a necessity for hemodialysis patients. Percutaneously inserted catheters are often used for access until more permanent surgical access can mature (1). Unfortunately, many dialysis patients exhaust options for permanent access sites (arteriovenous fistula [AVF] or synthetic graft [AVG]) and a catheter is the only remaining vascular access. Essential for evaluation are complications and catheter function. Function commonly relates to the flow-rate, solute removal, and infection-free patency rates. The Arrow-Clark VectorFlow dialysis catheter (Teleflex Medical Inc., Morrisville, NC, USA; hereafter referred to as “VectorFlow”) purports to have easier placement and fewer complications in comparison to other catheters with less shear-induced platelet activation – resulting in reduced thrombogenic risk during clinical performance. The inventor and manufacturer contend the catheter also allows high blood-flow rates – highly beneficial in dialysis (2). However, neither solute clearance nor clinical performance has been assessed within a prospective study. The purpose of this single-center observational investigation was to evaluate the performance of the VectorFlow during hemodialysis to patients in chronic renal failure over a 90-day period.

Materials and methods

The study protocol and consent document were approved by IntegReview Institutional Review Board (Austin, TX, USA) and registered on ClinicalTrials.gov prior to study initiation.

Study device

The VectorFlow is a US Food and Drug Administration-cleared and CE-cleared Class II device indicated for use as long-term vascular access for hemodialysis and apheresis. The catheter is inserted percutaneously, preferably in the internal jugular (IJ) vein, in adult patients and has helically-contoured arterial and venous apertures (Fig. 1) designed to produce a spiral, three-dimensional transition in fluid vectors as blood enters and leaves the catheter, with less shear-induced platelet activation than other commercially available catheters.

Fig. 1

Tip design of the Arrow-Clark VectorFlow hemodialysis catheter. Helically contoured arterial and venous apertures are intended to produce a spiral, three-dimensional transition in fluid vectors as blood enters and leaves the catheter resulting in less shear-induced platelet activation.

Study design and hypothesis

The primary hypothesis of the study was using VectorFlow will result in adequate dialysis treatment, measured by Kt/V (defined below). Secondary hypotheses were that, compared to historical studies of other catheters, there will be fewer complications with VectorFlow resulting in the necessity for catheter exchange; and the catheter, designed to produce less shear-induced platelet activation during high flow conditions of hemodialysis, reduces thrombogenic risk during use and thereby produces higher intervention-free patency than historical controls.

Patient population

Patients in chronic renal failure needing tunneled catheter access for hemodialysis were included in the study. Those with known central venous stenosis or occlusion, occluded IJ vein, expected survival <90 days, positive blood cultures within 14 days before catheter placement (if undergoing de novo VectorFlow catheter placement; bacteremia was permissible if an indication for catheter exchange to a VectorFlow catheter), or history of uncorrectable coagulopathy were excluded.

Catheter placements

Placements were performed in the interventional suite. For de novo catheter placement, access to the target vein was achieved using ultrasound and fluoroscopy. Insertion of the VectorFlow was performed in accordance with the device's instructions for use by retrograde radiologic technique. For exchange of a dysfunctional/infected catheter, the existing catheter was removed over a guidewire and exchanged for a VectorFlow. Catheter tips were positioned within the mid-right atrium.

Hemodialysis

Patients underwent hemodialysis three times a week using high efficiency, high flux dialyzers. Dialyzers used were Fresenius Optiflux F160NR (n = 9 patients) or Optiflux F180NR (n = 29 patients) (Fresenius, Waltham, MA), Baxter Revaclear (n = 2 patients), Polyflux 21R (n = 3 patients) or Polyflux 24R (n = 1 patient) (Baxter International, Deerfield, IL) or Asahi Kasei Rexeed18R (n = 1 patient) (Asahi Kasei Medical, Toyko, Japan). Median membrane surface area was 1.8 m² (range 1.4-2.4 m²). In one patient, the specific dialyzer used could not be obtained.

Data recording

Insertion procedure data were collected prospectively in the interventional suite and recorded on the case report form. Follow-up data were retrospectively collected from dialysis records.

Study end-points

Patients were followed until the VectorFlow was removed or 90 days had elapsed. Indications for catheter removal included poor function, infection, maturation of AVF/AVG, and patient death.

Following catheter placement, dialysis parameters were collected at weeks 1, 2, and 3 and months 1, 2, and 3, including mean and maximum blood-flow, dialysis duration, arterial and venous pressure, and fluid removal. Means were calculated for each parameter on each designated day. Additionally, at months 1, 2, and 3, dialysis adequacy was determined by urea clearance rate calculation – Kt/V, as defined by the National Kidney Foundation (NKF): K_urea is effective (delivered) dialyzer urea clearance in milliliters per minute integrated over the entire dialysis, T_d is time in minutes measured from beginning to end of dialysis, and V_urea is patient's volume of urea distribution in milliliters; all abbreviated as Kt/V (3).

Rates of complication occurrence were calculated by dividing the number of catheters removed for complications by the total dwell-time of all placed catheters, and expressed as events per 1000 catheter days. Catheter patency was estimated using the Kaplan-Meier technique. Patients were censored from analysis for catheter removal for a working surgical access, conversion to peritoneal dialysis, or death from unrelated causes.

Results

Between August 2015 and March 2016, 46 patients were enrolled into the study. The mean age was 58.1 years and the mean weight was 88.6 kg; 57% were female and 66% were African-American. Ninety-eight percent of the patients were outpatients and all catheters, except one, were inserted due to the patient being in end-stage renal disease (ESRD). Patient demographics are provided in Table I.

Table I

Patient demographics

Mean age; years (SD)	58.1 (13.7)
Mean weight; kg (SD)	88.6 (21.0)
Female/male (n)	26/20
Race (n)	African American	37
	Caucasian	8
	Other	1
Indication (n) for catheter placement	First access	3
	Failed AV access	10
	Infected catheter	2
	Malfunction (mechanical)	19
	Malfunction (thrombosis)	1
	No details provided	10
	Other	1
Previous dialysis access type (n)	AVF	23
	Catheter (right IJ)	12
	None	6
	Catheter (left IJ)	4
	Graft	1
Patient status (%)	Outpatient	45
	Inpatient	1

SD = standard deviation; AV = arteriovenous; AVF = arteriovenous fistula; IJ = internal jugular.

An AVF was the previous mode of dialysis access for 50% of the patients. Patients were in the interventional suite for a mean 58 minutes and the mean insertion procedure time was 29 minutes. The right internal jugular vein was the insertion site for 78% of patients. No placements were made in subclavian or femoral veins. Fluoroscopy was used for 98% of the catheter insertions and there were no catheter insertion failures. Procedural parameters are provided in Table II.

Table II

Dialysis catheter placement

Mean insertion time, minutes (SD)		29.2 (21.6)
Mean room time, minutes (SD)		58.2 (36.3)
Catheter IJ side (n)	Left	10
	Right	36
Mean ease of use, 0-10 (SD)		9.98 (0.1)
Insertion success		100%
Fluoroscopy used		97.8%

SD = standard deviation; IJ = internal jugular.

During the 90-day observation period, the maximum Q_b during dialysis averaged between 355 mL/min (Week 1) and 398 mL/min (Month 2); mean Q_b averaged between 333 mL/min(Week 1) and 392 mL/min (Month 2). Mean dialysis time averaged between 3.3 hours (Day 7 and Month 2) and 3.5 hours (Day 21, Month 1 and Month 3). The mean fluid volume removed averaged between 2195 mL (Day 14) and 2766 mL (Month 3). Mean Kt/V values were consistently at 1.5 or higher at all time-points (Tab. III).

Table III

Intra-dialysis data

	Week 1	Week 2	Week 3	Month 1	Month 2	Month 3
Maximum Q_b (mL/minute)	355 (61)	377 (42)	379 (49)	384 (39)	398 (46)	396 (50)
Mean Q_b (mL/minute)	333 (65)	366 (43)	370 (64)	368 (56)	392 (45)	374 (61)
Dialysis time (h)	3.3 (0.7)	3.4 (0.6)	3.5 (0.5)	3.5 (0.5)	3.3 (0.6)	3.5 (0.6)
Arterial pressure (mmHg)	184 (39)	187 (38)	193 (34)	189 (35)	197 (38)	180 (44)
Venous pressure (mmHg)	171 (48)	143 (21)	150 (35)	154 (30)	156 (36)	148 (43)
Volume removed (mL)	2273 (1235)	2195 (1199)	2583 (1385)	2355 (1067)	2560 (1198)	2766 (1309)
Mean Kt/V				1.52 (0.3)	1.49 (0.3)	1.55 (0.5)

Data are presented as mean (SD).

SD = standard deviation; Q_b = blood-flow; Kt/V = catheter patency.

Dwell-time ranged from 15 to 114 days for a total of 2997 catheter days (median 86 days, mean 71.4 days). Excluding patients who died during the study and those receiving AVF/AVG, the overall intervention-free patency rate of the VectorFlow was 94.9%, 92.2%, and 88.8% at days 30, 60 and 90, respectively (90 days being the extent of the scheduled observation period). Due to 11 patients returning for follow-up after their scheduled 90-day visit, primary unassisted catheter patency for the study cohort remained at 88.8% until 114 days (Fig. 2).

Fig. 2

Kaplan-Meier curve of primary unassisted (intervention-free) patency of the VectorFlow hemodialysis catheter. Overall intervention-free catheter patency rate was 94.9% at 30 days, 92.2% at 60 days, and 88.8% at 90 days. Error bars represent standard error.

There were no acute complications. Specifically, there were no instances of arrhythmia, pneumothorax, or air embolism during or following the catheter insertion procedures. During the follow-up period, three patients suffered late complications (6.5%). Two acquired infected catheters; one of whom had undergone guidewire exchange to VectorFlow for an infected catheter. One catheter malfunctioned, rendering a complication rate of 0.7 per 1000 catheter days for infected catheters; 1.0 per 1000 catheter days for all complications.

Discussion

As of December 2013, there were nearly 662,000 cases of ESRD in the USA with 64% receiving hemodialysis (4). In North America, hemodialysis catheters enable vascular access for up to 70% of patients initiating hemodialysis and up to 38% within subsets of ESRD-prevalent patients (5 –7). In the USA, more than 50% of patients sustained on chronic dialysis depend on catheters and synthetic vascular access (8). Tunneled hemodialysis catheters are a vital mode of temporary vascular access for patients in whom arteriovenous access has not matured or become non-functional, and those awaiting renal transplantation (9). While these catheters are generally considered to be a bridge to permanent access, they may become permanent access for patients without other options (10). In response to the continued utilization of these catheters, more studies have been conducted to investigate outcomes of long-term use of catheters in dialysis patients.

In the USA, hemodialysis providers are increasingly under pressure to improve parameters of clinical quality as defined by the Centers of Medicare and Medicaid Services. Treatment centers are required to submit monthly reporting of three parameters relevant to dialysis catheters: the proportion of in-center patients with catheters in place >90 days, Kt/V (with a target ≥1.2), and infection rates. Moreover, as an incentive to align their performance within CMS expectations, financial penalties are imposed to centers failing to reach national benchmarks. Therefore, it is in the best interest of providers to ensure that catheter patients are transitioned into a permanent working access within 90 days and to ensure they have the highest Kt/V and lowest infection rates possible (11).

In a 2014 article by Li et al, 43 chronic dialysis patients with Permcath catheters (Tyco International, Boca Raton, FL, USA), 49 with Palindrome catheters (Covidien, Mansfield, MA, USA), and 56 with AVFs were studied to compare catheter-function, dialysis-adequacy, and dialysis-related complications (11). Dialysis adequacy was measured by Kt/V and urea reduction rate. Investigators reported maximum blood-flow rates of 306, 391 and 355 mL/min for the Permcath, Palindrome, and AFV groups, respectively. In our 90-day study, blood-flow rates were recorded at weeks 1, 2, and 3, and days 30, 60, and 90 following catheter insertion. The maximum blood-flow rate averaged 355-398 mL/min (at 60 days). Mean blood-flow rate averaged 333-392 mL/min (at 60 days) – comparable to the maximum blood-flow rate reported by Li for the Palindrome group. Regarding dialysis adequacy, the Li team reported Kt/V values of 1.28, 1.39 and 1.43 for the Permcath, Palindrome and AVF groups, respectively. In our study, mean Kt/V values were 1.52, 1.49 and 1.55 at days 30, 60, and 90, respectively; all substantially superior to values reported by Li, regardless of access device or mode. Moreover, our mean Kt/V values exceeded the NKF's recommended target of 1.4 (12).

Li reported access dysfunction rates of 25.6% (Permcath), 8.2% (Palindrome), and 7.15% (AVF). Moreover, they reported access infection rates of 14.0% (Permcath), 12.2% (Palindrome), and 1.8% (AVF). In our study, VectorFlow failure-rate was 6.5%; 4.3% and 2.2% due to failure and malfunction, respectively. The 4.3% infection rate is higher than that reported by Li for AVF access; but substantially lower than they reported for Permcath and Palindrome catheters. Finally, Li reported thrombosis rates of 48.8%, 30.6%, and 5.4% for Permcath, Palindrome and AVF, respectively (11). The thrombosis rates reported by Li for the Permcath and Palindrome catheters align with those generally reported for dialysis catheters, 30%-40% (13). In contrast, during our observational study, there was a single catheter malfunction (from presumed thrombosis) with the VectorFlow (2.2%).

Fibrin sheath is among the most commonly reported cause of tunneled hemodialysis catheter failure (14). In 2008, Spector et al reported a Palindrome catheter (n = 126) study in which 17.4% of catheters were removed due to poor function, and 8.7% of catheters were removed due to fibrin-sheath formation (15). VectorFlow failure rate in our study was 6.5%; 4.3% due to infection and 2.2% due to malfunction – none due to fibrin-sheath. The mean and median dwell times in the Spector study were 105 and 73 days, respectively. In our study of 90 days dwell, mean and median dwell times were 71 and 83 days, respectively.

In a five-month study, Clark et al compared characteristics of the VectorFlow (n = 33) and Ash Split Cath (n = 46, Medcomp, Harleysville, PA, USA) catheters (16). Catheter patency was defined using Society of Interventional Radiology standards (17). The overall intervention-free patency rate at one month was 88.6% for the VectorFlow and 75.6% for the Ash Split Cath. In our study of VectorFlow, the overall patency rate at 30 days, excluding patients who died during the study and those who received definitive access, was 94.9% – similar to that reported by the Clark team.

Regarding infections caused by dialysis catheters, in 2004 O'Dwyer et al compared performance of the PermCath (n = 33) and Ash Split Cath (n = 36) catheters (18). The infection rate for the PermCath was 0.07 per 100 catheter days and 0.1 per 100 catheter days for the Ash Split. The 2015 Clark study reported an infection rate of 0.22 per 100 catheter days for the Ash Split Cath and 0.06 per 100 catheter days for the VectorFlow (17). In our study, the infection rate was 0.07 per 100 catheter days, similar to that for PermCath described by O'Dwyer and VectorFlow described by Clark. This relatively low infection rate has favorable implications for patients and treating clinicians in an environment in which the mean cost of treating catheter-related infections ranges from $4000 to $80,235 per occurrence (19).

O'Dwyer also reported mean catheter insertion times of 30.7 minutes for PermCath and 29.9 minutes for Ash Split Cath (18). Similarly, we found the mean catheter insertion time was 29.2 minutes. We also measured ease-of-use during the insertion procedure using a scale of 0-10, with 0 indicating extremely difficult; 10 indicating extremely easy. The mean score was 9.98, indicating relative ease in placing the device. We found little in the clinical literature with which to compare our findings. The O'Dwyer group reported no significant difference between the PermCath and Ash Split Cath in the ease-of-insertion, but failed to indicate a score assessing whether insertions were relatively easy or difficult.

Historically, dialysis catheters have been commonly associated with complications including thrombosis, infection, and fibrin-sheath formation (14). However, improvements to catheter designs in recent years show modest but continued improvement in the complication rates previously reported. The VectorFlow was specifically designed to produce less shear-induced platelet activation in order to reduce thrombogenic risk during clinical performance (20). This advantage may prove to be true if subsequent studies corroborate our findings and those by Clark et al (16). While AVF remains the preferred vascular access for chronic dialysis patients, improved performance and safety characteristics of newer-generation catheters, such as the VectorFlow, can potentially improve clinical outcomes, quality of life, and even survival of ESRD patients. Moreover, catheters have little effect on patient hemodynamics and may be especially suitable for vulnerable patients such as the elderly and those with multiple comorbidities in whom continuous cardiovascular demands of arteriovenous shunts may be detrimental, as well as those for whom AVF/AVG surgery or peritoneal dialysis is not possible (21 –23).

Limitations to the study included the single-center, non-randomized study design. Comparison to results from other patient cohorts and devices were limited to historical controls. Consistent patient follow-up was difficult, resulting in incomplete data-sets, and outpatient records were not consistently available. Patients underwent dialysis using high efficiency dialyzers, which could have contributed to the high observed values of Kt/V. Adherence to strict sterile technique and patient compliance could also have influenced the low rate of infections observed in this study.

Conclusions

In conclusion, we found the VectorFlow to be a safe and effective vascular access device for patients requiring hemodialysis. The catheter produced high blood-flow rates and efficient solute clearance with Kt/V at or above 1.5 at all time-points. The results closely mirror a previous study of the same device and were generally superior to results reported for other dialysis catheters. Results also support the hypothesis that the catheter, designed to produce less shear-induced platelet activation, reduces thrombogenic risk during its clinical performance. Randomized, controlled trials are needed to further validate these findings.

Footnotes

Financial support: This study has been supported by Teleflex Incorporated.

Conflict of interest: John R. Ross is a paid consultant to the manufacturer of the study device, Teleflex Incorporated, and his organization received a grant from the device manufacturer to conduct the study. Tatiana A. Puga and Thomas E. Philbeck are employees of the manufacturer of the study device, Teleflex Incorporated.

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