Development of New Hemodialysis Catheter Using Numerical Analysis and Experiments

A randomized controlled trial of catheters with different tips and lengths for patients requiring continuous renal replacement therapy in intensive care unit

BACKGROUND

The tip design and length of catheter impact catheter function. Two types of catheters with different tips, side-hole catheters and step-tip catheters, are commonly used during continuous renal replacement therapy (CRRT). However, there is insufficient evidence comparing their efficacy and safety in CRRT. In addition, whether the insertion of a longer catheter could enhance catheter function remains poorly studied and controversial.

METHODS

In this open-label, three-arm, randomized trial, critically ill patients receiving CRRT were randomized to three groups. Group A received 20 cm side-hole catheters (GDHK-1120), group B received 20 cm step-tip catheters (GDHK-1320) and group C received 25 cm step-tip catheters (GDHK-1325). The primary outcomes were the incidence of catheter dysfunction and catheter survival time.

RESULTS

A total of 351 patients were enrolled, with 116 in group A, 117 in group B, and 118 in group C. The incidence of catheter dysfunction in group A (35.7%, 51/143) was significantly higher than that in group B (17.7%, 22/124) (P = 0.001). However, there was no difference between group B and group C (15.6%, 23/147) (P = 0.744). The catheter survival time was comparable between group A (5.5 days, IQR 2.5-9.3) and group B (5.0 days, IQR 3.0-10.0) (P = 0.626). In contrast, group C (6.4 days, IQR 3.9-12.0) demonstrated a significantly longer catheter survival time compared to group B (P = 0.019). Cox regression analysis identified BMI (HR 1.052, 95% CI 1.003-1.103, P = 0.036) as an independent risk factor for catheter dysfunction. Results were not consistent across BMI tertiles, with similar results observed only in patients with a lower BMI (BMI < 24.2) (chi-square 13.65, P = 0.001). There was also a trend that patients in group C have a longer filter lifespan (36.5 h, IQR 16.9-68.1, P = 0.001) and a lower incidence of catheter-related thrombosis (10.40 per 1000 catheter-days, 95% CI 5.93, 17.83, P = 0.019). Other secondary outcomes were not significantly different among groups.

CONCLUSIONS

Step-tip catheters may be preferable for CRRT, particularly for patients in the lower BMI tercile. Longer femoral vein catheterization demonstrated enhanced benefits in CRRT, especially among obese patients. Further high-quality, multicenter RCTs are essential to strengthen the evidence guiding catheter selection during CRRT.

TRIAL REGISTRATION

ChiCTR2300075107. Registered 25 August 2023.

Niagara@ catheter equipped with a novel helical flow inducer to improve hemodynamic performance

Hemodialysis is an important means to sustain life in patients with end-stage renal disease In China, more than 100,000 hemodialysis patients need to have a catheter fitted at least once (temporary or long term) for dialysis. Despite the widespread use and low cost of HD catheters, they remain prone to critical issues such as high thrombosis rates, infections, and dysfunction. This study addresses the persistent challenge of thrombosis formation in dialysis catheters by investigating the incorporation of helical flow inducers, a strategy inspired by the naturally occurring helical blood flow in arterial systems. In this research, helical flow inducers with varying pitch and diameter were integrated into the widely used Niagara@ catheter. Computational fluid dynamics simulations were conducted to evaluate the impact on key parameters such as local normalized helicity (LNH), residence time (RT), shear stress, and flow velocity. The results demonstrated that 1) small-diameter inducers produce helical flow. Among inducers with identical diameter, those with a smaller thread pitch are more likely to induce increased LNH; 2) a small thread pitch helical flow inducer reduced the percentage of blood volume, with RT exceeding 0.015 s from 40.8% in the control to 12.7%, suggesting a substantial reduction in thrombosis risk; 3) the study also found that the introduction of small thread pitch helical flow inducers led to increased shear stress, with Model A showing an average shear stress of 49.2 Pa, compared to 32.0 Pa in the control. This highlights the need for careful optimization to balance the benefits of reduced thrombosis risk with the potential for shear-induced hemolysis. In conclusion, the integration of helical flow inducers into dialysis catheters offers a promising strategy for improving intraluminal flow dynamics and reducing the risk of thrombosis.

Comparative effectiveness and safety among different tip-design hemodialysis long-term catheters: A meta-analysis

PURPOSE

The aim of this meta-analysis is to compare effectiveness and safety among different tip-design long-term hemodialysis (HD) catheters.

MATERIALS AND METHODS

PubMed, Embase, and Cochrane Library databases were searched until 8 December 2021 to identify randomized controlled trials (RCTs) and cohort studies comparing step-tip, split-tip, or symmetrical-tip design catheters in patients undergoing HD will be included. The Cochrane Risk of Bias tool and the Newcastle-Ottawa Scale were used to evaluate the quality of RCTs and cohort studies. Data extracted from the articles were integrated to determine mean effective blood pump velocity (Qb), blood recirculation rates, secondary patency, catheter-related infection, catheter-related blood stream infection (CRBSI), thrombosis rates, and all-cause mortality for the three tip-designs. We performed meta-analysis on dichotomous outcomes using a random-effects model to evaluate risk ratios (RRs) and 95% confidence intervals (Cls). The effect sizes of continuous outcomes were reported as the mean difference (MD). Sensitivity and subgroup analyses were also performed. The study was registered in the PROSPERO (CRD42021297069).

RESULTS

Six RCTs and 11 cohort studies of 2617 individuals were included in our meta-analysis, of which 1088 individuals inserted split-tip catheters, 897 individuals inserted step-tip catheters and 650 received symmetrical-tip design catheters. Sym-tip performed better in mean Qb (MD = 43.85, 95% Cl = 18.13-69.56, p = 0.0008) than step-tip. Split-tip had better outcomes vs step-tip in blood recirculation (RR = 3.44, 95% Cl = 2.49-4.39, p < 0.00001). Sym-tip had significantly better outcomes compared with step-tip (RR = 0.28, 95%Cl = 0.09-0.81, Z = 2.34, p = 0.02) and split-tip (RR = 0.19, 95% Cl = 0.09-0.43, p < 0.0001) in thrombotic events. No significant difference was found in secondary patency, infection rates, CRBSI, and all-cause mortality among the three tip-designs.

CONCLUSION

The sym-tip of tunneled cuffed catheters performed better mean Qb, lower thrombotic events, and lower blood recirculation when blood line reversed, which may have an advantage over other two catheter-tips.

Development of in-vitro pulsatile flow generator for evaluating the performance of hemodialysis catheters

Hemodialysis (HD) using an HD catheter is performed widely on renal failure patients. The catheter was evaluated using the recirculation ratio in pre-clinical status, which is a crucial index indicating its performance. However, pre-clinical in-vivo experiments have limitations: high cost, and ethical issues. Hence, computational and in-vitro methods have been developed as alternatives. However, computational methods require fluid dynamic knowledge, whereas in-vitro experiments are complicated and expensive. In this study, we developed a pulsatile flow generator to mimic blood flow achieving cost effectiveness and user convenience. The device used iterative learning control, achieving blood flow in the superior and inferior vena cava within a 3.3% error. Furthermore, the recirculation ratios were measured based on two insertion directions and two different external pipe materials to evaluate the catheter regarding patients' posture and blood vessel stiffness. The results provide a better understanding of cardiovascular device performance without complicated and costly pre-clinical tests.

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.

Enhancing Mixing Performance in a Rotating Disk Mixing Chamber: A Quantitative Investigation of the Effect of Euler and Coriolis Forces

Lab-on-a-CD (LOCD) is gaining importance as a diagnostic platform due to being low-cost, easy-to-use, and portable. During LOCD usage, mixing and reaction are two processes that play an essential role in biochemical applications such as point-of-care diagnosis. In this paper, we numerically and experimentally investigate the effects of the Coriolis and Euler forces in the mixing chamber during the acceleration and deceleration of a rotating disk. The mixing performance is investigated under various conditions that have not been reported, such as rotational condition, chamber aspect ratio at a constant volume, and obstacle arrangement in the chamber. During disk acceleration and deceleration, the Euler force difference in the radial direction causes rotating flows, while the Coriolis force induces perpendicular vortices. Increasing the maximum rotational velocity improves the maximum rotational displacement, resulting in better mixing performance. A longer rotational period increases the interfacial area between solutions and enhances mixing. Mixing performance also improves when there is a substantial difference between Euler forces at the inner and outer radii. Furthermore, adding obstacles in the angular direction also passively promotes or inhibits mixing by configuration. This quantitative investigation provides valuable information for designing and developing high throughput and multiplexed point-of-care LOCDs.