Comparison of Symmetric Hemodialysis Catheters Using Computational Fluid Dynamics

Numerical Study on the Impact of Central Venous Catheter Placement on Blood Flow in the Cavo-Atrial Junction

An in silico study is performed to investigate fluid dynamic effects of central venous catheter (CVC) placement within patient-specific cavo-atrial junctions. Prior studies show the CVC infusing a liquid, but this study focuses on the placement without any liquid emerging from the CVC. A 7 or 15-French double-lumen CVC is placed virtually in two patient-specific models; the CVC tip location is altered to understand its effect on the venous flow field. Results show that the CVC impact is trivial on flow in the superior vena cava when the catheter-to-vein ratio ranges from 0.15 to 0.33. Results further demonstrate that when the CVC tip is directly in the right atrium, flow vortices in the right atrium result in elevated wall shear stress near the tip hole. A recirculation region characterizes a spatially variable flow field inside the CVC side hole. Furthermore, flow stagnation is present near the internal side hole corners but an elevated wall shear stress near the curvature of the side hole's exit. These results suggest that optimal CVC tip location is within the superior vena cava, so as to lower the potential for platelet activation due to elevated shear stresses and that CVC geometry and location depth in the central vein significantly influences the local CVC fluid dynamics. A thrombosis model also shows thrombus formation at the side hole and tip hole. After modifying the catheter design, the hemodynamics change, which alter thrombus formation. Future studies are warranted to study CVC design and placement location in an effort to minimize CVC-induced thrombosis incidence.

Tunneled Hemodialysis Catheter Tip Design and Risk of Catheter Dysfunction: An Australian Nationwide Cohort Study

RATIONALE & OBJECTIVE

Hemodialysis catheter dysfunction is an important problem for patients with kidney failure. The optimal design of the tunneled catheter tip is unknown. This study evaluated the association of catheter tip design with the duration of catheter function.

STUDY DESIGN

Observational cohort study using data from the nationwide REDUCCTION trial.

SETTING & PARTICIPANTS

4,722 adults who each received hemodialysis via 1 or more tunneled central venous catheters in 37 Australian nephrology services from December 2016 to March 2020.

EXPOSURE

Design of tunneled hemodialysis catheter tip, classified as symmetrical, step, or split.

OUTCOME

Time to catheter dysfunction requiring removal due to inadequate dialysis blood flow assessed by the treating clinician.

ANALYTICAL APPROACH

Mixed, 3-level accelerated failure time model, assuming a log-normal survival distribution. Secular trends, the intervention, and baseline differences in service, patient, and catheter factors were included in the adjusted model. In a sensitivity analysis, survival times and proportional hazards were compared among participants' first tunneled catheters.

RESULTS

Among the study group, 355 of 3,871 (9.2%), 262 of 1,888 (13.9%), and 38 of 455 (8.4%) tunneled catheters with symmetrical, step, and split tip designs, respectively, required removal due to dysfunction. Step tip catheters required removal for dysfunction at a rate 53% faster than symmetrical tip catheters (adjusted time ratio, 0.47 [95% CI, 0.33-0.67) and 76% faster than split tip catheters (adjusted time ratio, 0.24 [95% CI, 0.11-0.51) in the adjusted accelerated failure time models. Only symmetrical tip catheters had performance superior to step tip catheters in unadjusted and sensitivity analyses. Split tip catheters were infrequently used and had risks of dysfunction similar to symmetrical tip catheters. The cumulative incidence of other complications requiring catheter removal, routine removal, and death before removal were similar across the 3 tip designs.

LIMITATIONS

Tip design was not randomized.

CONCLUSIONS

Symmetrical and split tip catheters had a lower risk of catheter dysfunction requiring removal than step tip catheters.

FUNDING

Grants from government (Queensland Health, Safer Care Victoria, Medical Research Future Fund, National Health and Medical Research Council, Australia), academic (Monash University), and not-for-profit (ANZDATA Registry, Kidney Health Australia) sources.

TRIAL REGISTRATION

Registered at ANZCTR with study number ACTRN12616000830493.

PLAIN-LANGUAGE SUMMARY

Central venous catheters are widely used to facilitate vascular access for life-sustaining hemodialysis treatments but often fail due to blood clots or other mechanical problems that impede blood flow. A range of adaptations to the design of tunneled hemodialysis catheters have been developed, but it is unclear which designs have the greatest longevity. We analyzed data from an Australian nationwide cohort of patients who received hemodialysis via a tunneled catheter and found that catheters with a step tip design failed more quickly than those with a symmetrical tip. Split tip catheters performed well but were infrequently used and require further study. Use of symmetrical rather than step tip hemodialysis catheters may reduce mechanical failures and unnecessary procedures for patients.

Effects of the tip structure of temporary indwelling catheters on blood recirculation at various blood flow rates and diameters of the mock blood vessel

AIMS

The aim of the present study was to determine the effects of the tip structure of the catheters used for hemodialysis on blood recirculation at varying blood flow rates and diameters of the mock blood vessel in a well-defined in vitro experimental system, focusing on reverse connection mode.

METHODS

A mock circulatory circuit was created with silicon tubing (15 or 20 mm), a circulatory pump, connected through the catheter to dialysis circuit and dialyzer attached to dialysis machine. The tip of the inserted catheter was fixed to the center of the silicone tube, and 3 L of pig blood was poured into the blood side of the dialyzer and the recirculation rates were measured at blood flow rates of 100, 150, and 200 mL/min. Five types of commercially available catheters were used: (A) Argyle™, (B) Gentle Cath™ (Hardness gradient type), (C) Gentle Cath™, (D) Niagara™, and (E) Power-Trialysis®.

RESULTS

In the case of reverse connection mode, (1) the recirculation rates were lower in the catheter with a relatively large side hole (catheter C, 17%), catheters with a greater distance between the end hole and side hole (catheters C and D, 25%), and catheter with a symmetrical tip structure (catheter E, 10%) as compared with those in catheters A and B (40% and 25%); (2) increase of the blood flow rate in the dialysis machine was associated with a reduced recirculation rate; and (3) a wider inner diameter of the mock blood vessel and faster flow rate in the vessel were associated with a reduced recirculation rate.

CONCLUSION

The lowest recirculation was observed with the catheter with symmetrical holes, which produces a helical blood flow line that does not intersect with the blood streamline flowing out to the blood supply hole.

Safety and durable patency of tunneled hemodialysis catheter inserted without fluoroscopy

BACKGROUND

A tunneled hemodialysis (HD) catheter is preferred due to its lower incidence of infection and malfunction than non-tunneled ones. For safer insertion, fluoroscopic guidance is desirable. However, if the patient is unstable, transfer to the fluoroscopy may be impossible or inappropriate.

METHODS

From June 2019 to September 2022, 81 tunneled HD catheter insertion cases performed under ultrasound guidance without fluoroscopy and 474 cases with fluoroscopy in our institutional HD catheter cohort were retrospectively compared.

RESULTS

Immediate complications, later catheter-associated problems, including infections and catheter dysfunction, were comparable between the two groups (p = 0.20 and p = 0.37, respectively). The patency of tunneled catheters inserted without fluoroscopy was comparable to the patency of tunneled catheters inserted with fluoroscopic guidance (p = 0.90).

CONCLUSION

Tunneled HD catheter insertion without fluoroscopy can be performed safely and has durable patency compared to the insertion with fluoroscopy. Therefore, this method can be considered for the selected unstable patients (e.g., ventilator care) in the intensive care unit.

Comparison of Clinical Performance Between Two Types of Symmetric-Tip Hemodialysis Catheters: A Single-Centre, Randomized Trial

PURPOSE

To compare the clinical performance of a newly designed, symmetric-tip Arrow-Clark™ VectorFlow® tunnelled haemodialysis catheter, with a Glidepath™, symmetric-tip tunnelled haemodialysis catheter.

MATERIAL AND METHODS

From November 2018 to October 2020, patients with End-Stage Renal Disease requiring a de novo tunnelled catheter for hemodialysis, were randomized to Vectorflow® (n = 50) or to Glidepath™ catheter (n = 48). The primary outcome was catheter patency at one year following catheter insertion. Catheter failure was defined as the removal of the catheter due to infectious complications, or low blood flow rate by intraluminal thrombosis or fibrin sheath occlusion. Secondary outcomes were blood flow rate, fractional urea clearance and urea reduction ratio during dialysis.

RESULTS

Demographic characteristics were not different between the two groups. At three months and on the one-year endpoint the patency rates with the Vectorflow® catheter were 95.83% and 83.33% respectively, compared to 93.02% at both endpoints with the Glidepath™ catheter (P = 0.27). Catheter failure to infectious complications or low blood flow rate was similar in both groups. Catheter blood flow rate reached the threshold of 300 ml/min at all time points for both catheters. All patients had a high mean fractional urea clearance (1.6-1.7).

CONCLUSIONS

The catheter patency rate was not significantly different in patients with a VectorFlow® or a Glidepath™ catheter. Both catheters presented satisfactory dialysis adequacy over one year.

Staphylococcus aureus accumulation at the tip of hemodialysis catheters with or without tip side holes in catheter related bloodstream infection in a large animal

BACKGROUND

Eighty percent of hemodialysis patients start their dialysis with a tunneled hemodialysis catheter. Catheter related bacteremia is the second most common cause of death in these patients. Side holes near the tips of the tunneled cuffed central venous catheters are associated with accumulation of thrombus, which can lead to catheter dysfunction and, possibly, also to catheter-related infection. To assess the hypothesis that a catheter without side holes would be associated with less bacterial growth, this study compared the susceptibility of a side-hole-free catheter to accumulation of pathogenic bacteria at the catheter tip with that of two catheters which have side holes.

METHODS

Eight tunneled cuffed double-lumen central venous catheters were inserted into both jugular veins of four sheep; one side-hole-free and one control catheter with side holes at the tip in each animal. Staphylococcus aureus bacteria were then infused intravenously to cause bacteremia. Six hours later, the catheters were removed, the clots that accumulated in their tips were collected and cultured, and the bacterial colonies were counted after additional 12 h of incubation.

RESULTS

Bacteria grew on culture plates seeded with the clot homogenate obtained from the tips of all catheters. The colony counts from the catheters with side holes at the tip exceeded the colony counts of bacteria accumulated in the tips of the side-hole-free hemodialysis catheters by one or more orders of magnitude, with a difference of at least two orders of magnitude observed in three of the four intra-animal comparisons.

CONCLUSIONS

In paired intra-animal post-inoculation comparison made in this limited study, fewer colony forming units of pathogenic bacteria accumulated at the tip of the side-hole-free catheters than at the tips of the catheters which have side holes. This may translate to a decreased rate of catheter-related blood stream infections in the side-hole-free catheters.

Hemodynamic Analysis of the Geometric Features of Side Holes Based on GDK Catheter

Hemodialysis is an important means to maintain life in patients with end-stage renal disease (ESRD). Approximately 76.8% of patients who begin hemodialysis do so through catheters, which play vital roles in the delivery of hemodialysis to patients. During the past decade, the materials, structures, and surface-coating technologies of catheters have constantly been evolving to ameliorate catheter-related problems, such as recirculation, thrombosis, catheter-related infections, and malfunction. In this study, based on the commercial GDK catheter, six catheter models (GDK, GDK1, GDK2, GDK3, GDK4, and GDK5) with different lumen diameters and different geometric features of side holes were established, and computational flow dynamics (CFD) were used to measure flow rate, shear stress, residence time (RT), and platelet lysis index (PLI). These six catheters were then printed with polycarbonate PC using 3D printing technology to verify recirculation rates. The results indicated that: (1) the catheter with a 5.5 mm outer diameter had the smallest average shear stress in the arterial lumen and the smallest proportion of areas with shear stress > 10 pa. With increasing catheter diameter, the shear stress in the tip volume became lower, the average RT increased, and the PLI decreased due to larger changes in shear stress; (2) the catheters with oval-shaped side holes had smaller shear stress levels than those with circular-shaped holes, indicating that the oval design was more effective; (3) the catheter with parallel dual side holes had uniformly distributed flow around side holes and exhibited lower recirculation rates in both forward and reverse connections, while linear multi-side holes had higher shear stress levels due to the large differences in flow around side holes. The selection of the material and the optimization of the side holes of catheters have significant impacts on hemodynamic performances and reduce the probability of thrombosis, thus improving the efficiency of dialysis. This study would provide some guidance for optimizing catheter structures and help toward the commercialization of more efficient HD catheters.

Relationship between resistance index and recirculation rate in vascular access

Background

The state of vascular access affects the efficiency of hemodialysis. Poor blood flow of vascular access causes recirculation, which reduces treatment efficiency. In the clinical setting, the resistance index (RI) is a commonly used parameter to evaluate the state of vascular access. However, there are few reports investigating the direct relationship between RI and the recirculation rate. In this study, the relationship between RI and the recirculation rate was investigated using computational fluid dynamics analysis.

Methods

We created a three-dimensional model that mimics vascular access in hemodialysis patients. Next, we input various blood flow waveforms (RI 0.00, 0.50, 0.60, 0.80, and 0.94) into the vascular model. Then, two needles were punctured into the blood vessel model. Blood was removed from the vessel by one needle at a rate of 200 ml/min and returned by the other needle at the same speed. The recirculation rate was calculated using the backflow from the blood return needle.

Results

The recirculation rates for the blood flow waveforms of RI 0.00, 0.50, 0.60, 0.80, and 0.94 were 0.00%, 0.29%, 0.44%, 11.6%, and 28.1%, respectively. The recirculation rate was higher for blood flow with higher RI. In addition, more recirculation occurred during the diastolic phase, when blood flow was slow.

Conclusions

When the minimum blood flow was slower than the hemodialysis blood removal speed, both backflow and the recirculation rate increased. Sufficient diastolic blood flow needs to be maintained to suppress recirculation.

Pathology of catheter-related complications: what we need to know and what should be discovered

Despite the considerable efforts made to increase the prevalence of autogenous fistula in patients on hemodialysis, tunneled cuffed catheters are still an important access modality and used in a high percentage of the hemodialysis population. However, because of the conundrum posed by tunneled cuffed catheters, patients can develop a multitude of complications, including thrombosis, infections, formation of a fibrin sheath, and central vein stenosis, resulting in increased morbidity and mortality as well as placing a heavy burden on the healthcare system. However, with an increasing number of studies now focusing on how to manage these catheter-related complications, there has been less translational research on the pathology of these complications. This review of the most recent literature provides an update on the pathological aspects of catheter-related complications, highlighting what we need to know and what is yet to be discovered. The future research strategies and innovations needed to prevent these complications are also addressed.

Computational investigation of the haemodynamics shows criticalities of central venous lines used for chronic haemodialysis in children

BACKGROUND

Haemodialysis is a life-saving treatment for children with kidney failure. The majority of children have haemodialysis through central venous lines (CVLs). The use of CVLs in pediatric patients is often associated to complications which can lead to their replacement. The aim of this study is to investigate haemodynamics of pediatric CVLs to highlight the criticalities of different line designs.

METHODS

Four models of CVLs for pediatric use were included in this study. The selected devices varied in terms of design and sizes (from 6.5 Fr to 14 Fr). Accurate 3D models of CVLs were reconstructed from high-resolution images including venous and arterial lumens, tips and side holes. Computational fluid dynamics (CFD) analyses were carried out to simulate pediatric working conditions of CVLs in ideal and anatomically relevant conditions.

RESULTS

The arterial lumens of all tested CVLs showed the most critical conditions with the majority of blood flowing through the side-holes. A zone of low flow was identified at the lines' tip. The highest shear stresses distribution (>10 Pa) was found in the 8 Fr line while the highest platelet lysis index in the 10 Fr model. The analysis on the anatomical geometry showed an increase in wall shear stress measured in the 10 F model compared to the idealised configuration. Similarly, in anatomical models an increased disturbance and velocity of the flow was found inside the vein after line placement.

CONCLUSION

This study provided a numerical characterization of fluid dynamics in pediatric CVLs highlighting performance criticalities (i.e. high shear stresses and areas of stagnation) associated to specific sizes (8 Fr and 10 Fr) and conditions (i.e. anatomical test).

Development of New Hemodialysis Catheter Using Numerical Analysis and Experiments

A hemodialysis (HD) catheter, especially one with a symmetric tip design, plays an important role in the long-term treatment of patients with renal failure. It is well known that the design of the HD catheter has a considerable effect on blood recirculation and thrombus formation around it, which may cause inefficiencies or malfunctions during HD. However, hemodynamic analyses through parametric studies of its designs have been rarely performed; moreover, only comparisons between the existing models have been reported. In this study, we numerically analyzed the design of the HD catheter's side hole and distal tip for evaluating their effects on hemodynamic factors such as recirculation rate (RR), shear stress, and blood damage index (BDI). The results indicated that a larger side hole and a nozzle-shaped distal tip can significantly reduce the RR and shear stress around the HD catheter. Furthermore, based on these hemodynamic insights, we proposed three new HD catheter designs and compared their performances with existing catheters using numerical and in vitro methods. These new designs exhibited lower RRs and BDI values, thus providing better performance than the existing models. These results can help toward commercialization of more efficient HD catheters.

Influence of hemodialysis blood flow rate on the thrombogenic potential in patients with central venous catheters

In this study we apply methods to determine the tendency for thrombus formation in different central venous catheters (CVC) models associated with flow rate variation. To calculate the thrombogenic potential, we proposed a new numerical model of the platelet lysis index (PLI) equation. To compare the results of PLI and flow rate in different models of catheters, numerical calculations were performed on three different tips of CVC. The results showed that the PLI increases as a power function of the flow rate independent of the type of CVC. This study evidenced that the higher the blood flow rate used in the catheter, the greater the potential for thrombus formation. The PLI computed at the catheter outlet presented higher values when compared to the values computed at the vein outlet indicating that the blood flow through the CVC arterial lumen presents a proportionally larger thrombogenic potential when compared to the blood flow that leaves the vein towards the atrium. This finding may have consequences for clinical practice, since there is no specific flow value recommended in the catheter when the hemodialysis machine is turned on, and with this equation it was possible to demonstrate the thrombogenic potential that the flow rate can possibly offer.

Computational fluid dynamics of the right atrium: Assessment of modelling criteria for the evaluation of dialysis catheters

Central venous catheters are widely used in haemodialysis therapy, having to respect design requirements for appropriate performance. These are placed within the right atrium (RA); however, there is no prior computational study assessing different catheter designs while mimicking their native environment. Here, a computational fluid dynamics model of the RA, based on realistic geometry and transient physiological boundary conditions, was developed and validated. Symmetric, split and step catheter designs were virtually placed in the RA and their performance was evaluated by: assessing their interaction with the RA haemodynamic environment through prediction of flow vorticity and wall shear stress (WSS) magnitudes (1); and quantifying recirculation and tip shear stress (2). Haemodynamic predictions from our RA model showed good agreement with the literature. Catheter placement in the RA increased average vorticity, which could indicate alterations of normal blood flow, and altered WSS magnitudes and distribution, which could indicate changes in tissue mechanical properties. All designs had recirculation and elevated shear stress values, which can induce platelet activation and subsequently thrombosis. The symmetric design, however, had the lowest associated values (best performance), while step design catheters working in reverse mode were associated with worsened performance. Different tip placements also impacted on catheter performance. Our findings suggest that using a realistically anatomical RA model to study catheter performance and interaction with the haemodynamic environment is crucial, and that care needs to be given to correct tip placement within the RA for improved recirculation percentages and diminished shear stress values.

Technology Innovations in Continuous Kidney Replacement Therapy: The Clinician's Perspective

Continuous kidney replacement therapy (CKRT) has improved remarkably since its first implementation as continuous arteriovenous hemofiltration in the 1970s. However, when looking at the latest generation of CKRT machines, one could argue that clinical deployment of breakthrough innovations by device manufacturers has slowed in the last decade. Simultaneously, there has been a steady accumulation of clinical knowledge using CKRT as well as a multitude of therapeutic and diagnostic innovations in the dialysis and broader intensive care unit technology fields adaptable to CKRT. These include multiple different anticlotting measures; cloud-computing for optimized treatment prescribing and delivered therapy data collection and analysis; novel blood purification techniques aimed at improving the severe multiorgan dysfunction syndrome; and real-time sensing of blood and/or filter effluent composition. The authors present a view of how CKRT devices and programs could be reimagined incorporating these innovations to achieve specific measurable clinical outcomes with personalized care and improved simplicity, safety, and efficacy of CKRT therapy.

Clot accumulation at the tip of hemodialysis catheters in a large animal model

Background:

The issue of side holes in the tips of the tunneled cuffed central venous catheters is complex and has been subject to longstanding debate. This study sought to compare the clotting potential of the side-hole-free Pristine hemodialysis catheter with that of a symmetric catheter with side holes.

Methods:

Both jugular veins of five goats were catheterized with the two different catheters. The catheters were left in place for 4 weeks and were flushed and locked with heparin thrice weekly. The aspirated intraluminal clot length was assessed visually prior to each flushing. In addition, the size and weight of the clot were recorded upon catheter extraction at the end of the 4-week follow-up

Results:

The mean intraluminal clot length observed during the entire study follow-up measured up to a mean of 0.66 cm in the GlidePath (95% CI, 0.14–1.18) and 0.19 cm in the Pristine hemodialysis catheter (95% CI, −0.33 to 0.71), the difference being statistically significant (p = 0.026). On average, 0.01 g and 0.07 g of intraluminal clot were retrieved from the Pristine and GlidePath catheters, respectively (p = 0.052).

Conclusion:

The Pristine hemodialysis catheter was largely superior to a standard side hole catheter in impeding clot formation, and, contrary to the side hole catheter, allowed for complete aspiration of the intraluminal clot.

Characterizing Complications of Intracranial Responsive Neurostimulation Devices for Epilepsy Through a Retrospective Analysis of the Federal MAUDE Database

OBJECTIVES

Responsive neurostimulation is an innovative modality in the treatment of medication-refractory epilepsy for patients who are not suitable candidates for surgical intervention. While being a potentially life-changing treatment option for many individuals with epilepsy, little is known about the system's complications aside from its performance in initial clinical trials. Therefore, the goal of this study was to characterize all reported complications of the RNS system made to the Food & Drug Administration since its approval.

MATERIALS AND METHODS

The Manufacturer and User Facility Device Experience (MAUDE) database was queried for entries reported under "implanted brain stimulator for epilepsy" through the dates of November 1, 2013 to March 1, 2020. After correction of duplicate entries, each was sorted into complication types based on the entries' narrative descriptions.

RESULTS

The searched yielded 241 unique complication events. The most common complications were attributed to infections (40%) and lead breaks (12%). Other reported complications included poor wound healing (10%) and intrinsic device failure (7%). Focal neurological deficits were found in 2%. Over half (67%) of the reported complications required return to the operating room for revision or explant. The remainder of the adverse events were self-resolved or treated with either medication or software adjustment.

CONCLUSIONS

Future research endeavors should attempt to optimize the implantable device for preventing infections. The data of complications provided by this review will also aid physicians in providing the most accurate informed consent for patients when deciding to undergo implantation with the responsive neurostimulation system.

Impact of side-hole geometry on the performance of hemodialysis catheter tips: A computational fluid dynamics assessment

Hemodialysis catheters are used to support blood filtration, yet there are multiple fundamentally different approaches to catheter tip design with no clear optimal solution. Side-holes have been shown to increase flow rates and decrease recirculation but have been associated with clotting/increased infection rates. This study investigates the impact of changing the shape, size and number of side-holes on a simple symmetric tip catheter by evaluating the velocity, shear stress and shear rate of inflowing blood. A platelet model is used to examine the residence time and shear history of inflowing platelets. The results show that side-holes improve the theoretical performance of the catheters, reducing the maximum velocity and shear stress occurring at the tip compared to non-side-hole catheters. Increasing the side-hole area improved performance up to a point, past which not all inflow through the hole was captured, and instead a small fraction slowly 'washed-out' through the remainder of the tip resulting in greater residence times and increasing the likelihood of platelet adhesion. An oval shaped hole presents a lower chance of external fibrin formation compared to a circular hole, although this would also be influenced by the catheter material surface topology which is dependent on the manufacturing process. Overall, whilst side-holes may be associated with increased clotting and infection, this can be reduced when side-hole geometry is correctly implemented though; a sufficient area for body diameter (minimising residence time) and utilising angle-cut, oval shaped holes (reducing shear stress and chances of fibrin formation partially occluding holes).

Comparison of Clinical Performance of VectorFlow and Palindrome Symmetric-Tip Dialysis Catheters: A Multicenter, Randomized Trial

PURPOSE

To compare clinical performance of 2 widely used symmetric-tip hemodialysis catheters.

MATERIALS AND METHODS

Patients with end-stage renal disease initiating or resuming hemodialysis were randomized to receive an Arrow-Clark VectorFlow (n = 50) or Palindrome catheter (n = 50). Primary outcome was 90-d primary unassisted catheter patency. Secondary outcomes were Kt/V ([dialyzer urea clearance × total treatment time]/total volume of urea distribution), urea reduction ratio (URR), and effective blood flow (Q_B).

RESULTS

Primary unassisted patency rates with the VectorFlow catheter at 30, 60, and 90 d were 95.5% ± 3.3, 87.2% ± 7.3, and 80.6% ± 9.8, respectively, compared with 89.1% ± 6.2, 79.4% ± 10.0, and 71.5% ± 12.6 with the Palindrome catheter (P = .20). Patients with VectorFlow catheters had a mean Kt/V of 1.5 at 30-, 60-, and 90-day time points, significantly higher than the mean Kt/V of 1.3 among those with Palindrome catheters (P = .0003). URRs were not significantly different between catheters. Catheter Q_B rates exceeded National Kidney Foundation-recommended thresholds of 300 mL/min at all time points for both catheters and were similar for both catheters (median, 373 mL/min). Catheter failure, ie, poor flow rate requiring guide-wire exchange or removal, within the 90-day primary outcome occurred in 3 VectorFlow subjects and 5 Palindrome subjects (P = .72). Infection rates were similar, with 0.98 infections per 1,000 catheter days for VectorFlow catheters compared with 2.62 per 1,000 catheter days for Palindrome catheters (P = .44).

CONCLUSIONS

The 90-day primary patency rates of Palindrome and VectorFlow catheters were not significantly different, and both achieved sustained high Q_B through 90 day follow-up. However, dialysis adequacy based on Kt/V was consistently better with the VectorFlow catheter versus the Palindrome.

Computational optimization of a novel atraumatic catheter for local drug delivery in coronary atherosclerotic plaques

Early identification and treatment of high-risk plaques before they rupture, and precipitate adverse events constitute a major challenge in cardiology today. Computational simulations are a time- and cost-effective way to study the performance, and to optimize a system. The main objective of this work is to optimize the flow of a novel atraumatic local drug delivery catheter for the treatment of coronary atherosclerosis. The mixing and spreading effectiveness of a drug fluid was analyzed utilizing computational fluid dynamics (CFD) in a coronary artery model. The optimum infusion flow of the nanoparticle-carrying drug fluid was found by maximizing the drug volume fraction and minimizing drug velocity at the artery wall, while maintaining acceptable wall shear stress (WSS). Drug velocities between 15 m/s and 20 m/s are optimum for local drug delivery. The resulting parameters from this study will be used to fabricate customized prototypes for future in-vivo experiments.

Hemodialysis arterio-venous graft design reducing the hemodynamic risk of vascular access dysfunction

Although arterio-venous grafts (AVGs) represent the second choice as permanent vascular access for hemodialysis, this solution is still affected by a relevant failure rate due to graft thrombosis, and development of neointimal hyperplasia (IH) at the distal vein. As a key role in these processes has been attributed to the abnormal hemodynamics establishing in the distal vein, the optimization of AVGs design aimed at minimizing flow disturbances would reduce AVG hemodynamic-related risks. In this study we used computational fluid dynamics to investigate the impact of alternative AVG designs on the reduction of IH and thrombosis risk at the distal venous anastomosis. The performance of the newly designed AVGs was compared to that of commercially available devices. In detail, a total of eight AVG models in closed-loop configuration were constructed: two models resemble the commercially available straight conventional and helical-shaped AVGs; six models are characterized by the insertion of a flow divider (FD), straight or helical shaped, differently positioned inside the graft. Unfavorable hemodynamic conditions were analyzed by assessing the exposure to disturbed shear at the distal vein. Bulk flow was investigated in terms of helical blood flow features, potential thrombosis risk, and pressure drop over the graft. Findings from this study clearly show that using a helically-shaped FD located at the venous side of the graft could induce beneficial helical flow patterns that, minimizing flow disturbances, reduce the IH-related risk of failure at the distal vein, with a clinically irrelevant increase in thrombosis risk and pressure drop over the graft.

Ambulatory Hemodialysis-Technology Landscape and Potential for Patient-Centered Treatment

CKD is a worldwide health problem and the number of patients requiring kidney replacement therapy is rising. In the United States, most patients with ESKD rely on in-center hemodialysis, which is burdensome and does not provide the same long-term benefits as kidney transplantation. Intensive hemodialysis treatments have demonstrated improved clinical outcomes, but its wider adoption is limited by equipment complexity and patient apprehension. Ambulatory devices for hemodialysis offer the potential for self-care treatment outside the clinical setting as well as frequent and prolonged sessions. This article explains the motivation for ambulatory hemodialysis and provides an overview of the necessary features of key technologies that will be the basis for new wearable and implantable devices. Early work by pioneers of hemodialysis is described followed by recent experience using a wearable unit on patients. Finally, ongoing efforts to develop an implantable device for kidney replacement and its potential for implantable hemodialysis are presented.

Clinical and Regulatory Considerations for Central Venous Catheters for Hemodialysis

Central venous catheters remain a vital option for access for patients receiving maintenance hemodialysis. There are many important and evolving clinical and regulatory considerations for all stakeholders for these devices. Innovation and transparent and comprehensive regulatory review of these devices is essential to stimulate innovation to help promote better outcomes for patients receiving maintenance hemodialysis. A workgroup that included representatives from academia, industry, and the US Food and Drug Administration was convened to identify the major design considerations and clinical and regulatory challenges of central venous catheters for hemodialysis. Our intent is to foster improved understanding of these devices and provide the foundation for strategies to foster innovation of these devices.

Implantable Device-Related Infection

Over half of the nearly two million healthcare-associated infections can be attributed to indwelling medical devices. In this review, we highlight the difficulty in diagnosing implantable device-related infection and how this leads to a likely underestimate of the prevalence. We then provide a length-scale conceptualization of device-related infection pathogenesis. Within this conceptualization we focus specifically on biofilm formation and the role of host immune and coagulation systems. Using this framework, we describe how current and developing preventative strategies target specific processes along the entire length-scale. In light of the significant time horizon for the development and translation of new preventative technologies, we also emphasize the need for parallel development of in situ treatment strategies. Specific examples of both preventative and treatment strategies and how they align with the length-scale conceptualization are described.

Longitudinal dialysis adequacy and clinical performance of the VectorFlow hemodialysis catheter: a prospective study

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 (Qb), 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 Qb 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.

Urea-based recirculation validation of the symmetrical palindrome catheter

BACKGROUND

High blood flow and low recirculation rates are central for adequate haemodialysis. A new symmetrical tip has been invented promising efficient haemodialysis even if the ports are reversed.

OBJECTIVE

To evaluate access recirculation of the 'palindrome' catheter and to report initial experiences in a clinical setting.

MATERIAL AND METHODS

After implantation of the new catheter in 20 patients (male: 14; female: 6; mean age 72 ± 12.2), access recirculation was evaluated using the urea-based recirculation test. After 30 minutes of haemodialysis, ultrafiltration was stopped and arterial and venous samples were taken. Afterwards, the blood flow rate was reduced to 120 ml/min. Another systemic arterial blood sample was taken 10 seconds after the blood pump was switched off.

RESULTS

All 20 interventions were performed successfully without complications. The average recirculation rate was 8.1% with a median of 2.5% ranging from 0 to 85.8%. Recirculation rates under 5% were measured in 13 patients and more than 10% recirculation were found in two patients. The median of days between catheter implantation and recirculation assessment was the day following implantation.

CONCLUSION

The new symmetrical catheter presented low recirculation rates in a clinical setting. Since there is just a single tip, fluoroscopic placement in the right atrium is facilitated.

Device thrombosis and pre-clinical blood flow models for assessing antithrombogenic efficacy of drug-device combinations

Thrombosis associated with blood-contacting devices is a complex process involving several component interactions that have eluded precise definition. Extensive investigations of individual biological modules such as protein adsorption, coagulation cascade activation and platelet activation/adhesion/aggregation have provided an initial foundation for developing biomaterials for blood-contacting devices, but a material that is intrinsically non-thrombogenic is yet to be developed. The well-recognized association between fluid dynamics parameters such as shear stress, vortices, stagnation and thrombotic processes such as platelet aggregation and coagulation aggravate thrombosis on most device geometries that elicit these flow disturbances. Thus, antithrombotic drugs that were developed to treat thrombosis associated with vascular diseases such as atherosclerosis have also been adapted to mitigate the risk of device thrombosis. However, balancing the risk of bleeding with the antithrombotic efficacy of these drugs continues to be a challenge, and surface modification of devices with these drug molecules to mitigate device thrombosis locally has been explored. Pre-clinical blood flow models to test the effectiveness of these drug-device combinations have also evolved and several in-vitro, ex-vivo, and in-vivo test configurations are available with their attendant merits and limitations. Despite considerable efforts toward iterative design and testing of blood contacting devices and antithrombogenic surface modifications, device thrombosis remains an unsolved problem.

Influence of catheter insertion on the hemodynamic environment in coronary arteries

Intravascular stenting is one of the most commonly used treatments to restore the vascular lumen and flow conditions, while perioperative complications such as thrombosis and restenosis are still nagging for patients. As the catheter with crimped stent and folded balloon is directly advanced through coronary artery during surgery, it is destined to cause interference as well as obstructive effect on blood flow. We wonder how the hemodynamic environment would be disturbed and weather these disturbances cause susceptible factors for those complications. Therefore, a realistic three-dimensional model of left coronary artery was reconstructed and blood flow patterns were numerically simulated at seven different stages in the catheter insertion process. The results revealed that the wall shear stress (WSS) and velocity in left anterior descending (LAD) were both significantly increased after catheter inserted into LAD. Besides, the WSS on the catheter, especially at the ending of the catheter, was also at high level. Compared with the condition before catheter inserted, the endothelial cells of LAD was exposed to high-WSS condition and the risk of platelet aggregation in blood flow was increased. These influences may make coronary arteries more vulnerable for perioperative complications.