Blood flow in hemodialysis catheters: a numerical simulation and microscopic analysis of in vivo-formed fibrin

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.

Comparative Clinical Performances of Tunneled Central Venous Catheters versus Arterio-Venous Accesses in Patients Receiving High-Volume Hemodiafiltration: The Case for High-Flow DualCath, a Tunneled Two-Single-Lumen Silicone Catheter

Tunneled central venous catheters (CVC) are mainly considered as a rescue vascular access option in dialysis but are still used on approximately one quarter of prevalent patients worldwide even though they are associated with poor performances and higher risks.

STUDY DESIGN

in this retrospective single-center study, we aimed to report on the clinical performances achieved with high-flow tunneled CVCs (DualCath or DCath) and compared them with arteriovenous accesses (AVAs, e.g., AV fistula, AV graft, and Thomas Shunt) in a hospital-based dialysis unit.

METHODS

Sixty-eight stage 5 chronic kidney disease dialysis-dependent patients (CKD5D) receiving high volume hemodiafiltration were followed-up with for 30 months. The study consisted of two phases: baseline cross-sectional and longitudinal follow-ups of key performance indicators. Clinical performances consisting of effective blood flow and blood volume, recirculation, urea and ionic Kt/V, total Kt, ultrafiltration volume, and percent reduction in β2-M were measured monthly as part of quality control in our unit.

RESULTS

At baseline, the effective blood flow using a DCath was close to 400 mL/min, similar to an AVA. Recirculation with a DCath (7%, 6-13%) was higher than with an AVA. The diffusive dialysis dose delivered with a DCath (spKt and eKt/V) and convective dialysis dose achieved with a DCath were slightly lower than those achieved with AVAs, but they were still much higher than is recommended by guidelines. The percent reduction in β2-M achieved with a DCath was also 4 to 10% lower than that achieved with an AVA. On longitudinal follow-up, the main clinical performance indicators of DCaths (total Kt and total ultrafiltration volume, L/session) were maintained as very stable over time and close to those achieved with AVAs.

CONCLUSIONS

As shown in this study, high-flow DualCath tunneled two-single-lumen silicone catheters may be used to deliver high volume hemodiafiltration in a reliable and consistent manner without compromising clinical performance. These results relied on the specific design of the two silicone cannulas and the strict adherence to best catheter practices.

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.

Hemostatic changes in patients undergoing hemodialysis: differences between central venous catheters and arterio-venous fistulas

BACKGROUND

Failure to mature the fistula in patients undergoing hemodialysis leads to prolonged use of the central venous catheter (CVC) and can compromise the patency of the catheter and the arteriovenous fistula (AVF) due to thrombus development.

OBJECTIVE

to evaluate hemostatic changes in patients undergoing hemodialysis with prolonged use of CVC or AVF.

METHOD

cross-sectional study with a total of 200 adult participants who were divided into the following groups: I:control; II: patients who had 5 to 8 months of CVC insertion; III: patients who had 9 to 36 months of insertion; IV patients who had 5 to 8 months of AVF and V: patients who had 9 to 36 months of AVF. Platelet activation was investigated by expressions of GPIIb/IIIa and p-selectin using flow cytometry. The Elisa-thrombomodulin test was used to compare groups III and V.

RESULTS

the p-selectin percentage expression of group I was 15.30 (12.30-16.80), II 23.25 (20.75-30.55) and III 54.00 (44.75 -59.29) were significant (p<0.001). Groups I, IV and V were also significant (p<0.001). The median fluorescence for GPIIb/IIIa for groups I, II and III were significant (p<0.0001). As for the Elisa test, an increased absorbance of thrombomodulin was verified in patients who used the CVC 4372 (3951-4733) when compared to those patients who used the AVF 2162 (1932-2485) (p<0.0001).

CONCLUSION

It can be concluded that CVC patients had a larger platelet expression of GPIIb/IIIa and p-selectin than AVF patients. The high concentration of thrombomodulin in CVC patients may suggest a greater stimulation of the intrinsic than extrinsic coagulation pathways.

Hemodynamic analysis for stenosis microfluidic model of thrombosis with refined computational fluid dynamics simulation

Disturbed blood flow has been increasingly recognized for its critical role in platelet aggregation and thrombosis. Microfluidics with hump shaped contractions have been developed to mimic microvascular stenosis and recapitulate the prothrombotic effect of flow disturbance. However the physical determinants of microfluidic hemodynamics are not completely defined. Here, we report a refined computational fluid dynamics (CFD) simulation approach to map the shear rate (γ) and wall shear stress (τ) distribution in the stenotic region at high accuracy. Using ultra-fine meshing with sensitivity verification, our CFD results show that the stenosis level (S) is dominant over the bulk shear rate (γ₀) and contraction angle (α) in determining γ and τ distribution at stenosis. In contrast, α plays a significant role in governing the shear rate gradient (γ^′) distribution while it exhibits subtle effects on the peak γ. To investigate the viscosity effect, we employ a Generalized Power-Law model to simulate blood flow as a non-Newtonian fluid, showing negligible difference in the γ distribution when compared with Newtonian simulation with water medium. Together, our refined CFD method represents a comprehensive approach to examine microfluidic hemodynamics in three dimensions and guide microfabrication designs. Combining this with hematological experiments promises to advance understandings of the rheological effect in thrombosis and platelet mechanobiology.

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.

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).

Assessment of surface roughness and blood rheology on local coronary haemodynamics: a multi-scale computational fluid dynamics study

The surface roughness of the coronary artery is associated with the onset of atherosclerosis. The study applies, for the first time, the micro-scale variation of the artery surface to a 3D coronary model, investigating the impact on haemodynamic parameters which are indicators for atherosclerosis. The surface roughness of porcine coronary arteries have been detailed based on optical microscopy and implemented into a cylindrical section of coronary artery. Several approaches to rheology are compared to determine the benefits/limitations of both single and multiphase models for multi-scale geometry. Haemodynamic parameters averaged over the rough/smooth sections are similar; however, the rough surface experiences a much wider range, with maximum wall shear stress greater than 6 Pa compared to the approximately 3 Pa on the smooth segment. This suggests the smooth-walled assumption may neglect important near-wall haemodynamics. While rheological models lack sufficient definition to truly encompass the micro-scale effects occurring over the rough surface, single-phase models (Newtonian and non-Newtonian) provide numerically stable and comparable results to other coronary simulations. Multiphase models allow for phase interactions between plasma and red blood cells which is more suited to such multi-scale models. These models require additional physical laws to govern advection/aggregation of particulates in the near-wall region.

Use of electron microscopy to study platelets and thrombi

Electron microscopy has been a valuable tool for the study of platelet biology and thrombosis for more than 70 years. Early studies using conventional transmission and scanning electron microscopy (EM) provided a foundation for our initial understanding of platelet structure and how it changes upon platelet activation. EM approaches have since been utilized to study platelets and thrombi in the context of basic, translational and clinical research, and they are instrumental in the diagnosis of multiple platelet function disorders. In this brief review, we provide a sampling of the many contributions EM based studies have made to the field, including both historical highlights and contemporary applications. We will also discuss exciting new imaging modalities based on EM and their utility for the study of platelets, hemostasis and thrombosis into the future.

Effect of the expression of CD62P and thrombin generation on patients using central venous catheters for hemodialysis

The formation of thrombi in medical devices that come into contact with blood is a common cause of increased morbidity and mortality. Prolonged use of central venous catheters (CVCs) may cause high infection rates or compromise CVC patency due to thrombus development. In this study, we sought insights into possible changes in the hemostatic system during prolonged use of inserted CVCs for hemodialysis by assessing platelets by CD62P and CD41a expression and the potential for thrombin generation (TG). This study included patients with chronic renal failure who were undergoing hemodialysis three times a week using a CVC, and healthy subjects as controls. The participants were distributed into three groups: Group 1: clinically and laboratorially healthy individuals matched by sex and age to the patients (controls); Group II: patients who had completed 1 month of CVC insertion; and Group III: the same patients after they had completed 4 months of CVC insertion. Platelet activation analysis and TG evaluation were performed using blood samples obtained through two different accesses, that is, through a peripheral vein and directly from the CVC lumen. The data showed platelet activation and an increase in the generation of thrombin, particularly after 4 months of CVC use. The results also indicated that insertion of the catheter into the blood stream stimulated the intrinsic rather than the extrinsic pathway. Taken together, the data showed a direct relationship between the use of CVCs in hemodialysis patients and a state of hypercoagulability, most likely associated with endothelial damage and the contact of the medical device with blood components such as platelets and coagulation factors.

Microstructural evaluation by confocal and electron microscopy in thrombi developed in central venous catheters

Abstract OBJECTIVE Evaluating thrombi microstructure developed in central venous catheters using confocal and electron microscopy. METHOD An experimental, descriptive study carrying out a microstructural evaluation of venous thrombi developed in central venous catheters using Scanning Electron Microscopy and Confocal Laser Scanning Microscopy. RESULTS A total of 78 venous catheters were collected over a period of three months. Different fibrin structures were distinguished: fibrin plates, fibrin network, and fibrin fibers. It was observed that the thrombus had thick fibrin plates adhered to the catheter wall openings in both a catheter with three days of permanence as well as in a catheter with 20 days of insertion in the patient. However, a greater amount of erythrocytes and fibrin fibers were found in the central region of the thrombus. CONCLUSION This study contributes to improving health care and can have a positive impact on clinical practice, as easy adherence of platelets and fibrins to the catheter wall demonstrated in this study makes it possible to adopt thrombus prevention strategies such as therapy discontinuation for an extended period, blood reflux by a catheter, slow infusion rate and hypercoagulo pathyclinical conditions.

Monitoring Central Venous Catheter Resistance to Predict Imminent Occlusion: A Prospective Pilot Study

BACKGROUND

Long-term central venous catheters are essential for the management of chronic medical conditions, including childhood cancer. Catheter occlusion is associated with an increased risk of subsequent complications, including bloodstream infection, venous thrombosis, and catheter fracture. Therefore, predicting and pre-emptively treating occlusions should prevent complications, but no method for predicting such occlusions has been developed.

METHODS

We conducted a prospective trial to determine the feasibility, acceptability, and efficacy of catheter-resistance monitoring, a novel approach to predicting central venous catheter occlusion in pediatric patients. Participants who had tunneled catheters and were receiving treatment for cancer or undergoing hematopoietic stem cell transplantation underwent weekly catheter-resistance monitoring for up to 12 weeks. Resistance was assessed by measuring the inline pressure at multiple flow-rates via a syringe pump system fitted with a pressure-sensing transducer. When turbulent flow through the device was evident, resistance was not estimated, and the result was noted as "non-laminar."

RESULTS

Ten patients attended 113 catheter-resistance monitoring visits. Elevated catheter resistance (>8.8% increase) was strongly associated with the subsequent development of acute catheter occlusion within 10 days (odds ratio = 6.2; 95% confidence interval, 1.8-21.5; p <0.01; sensitivity, 75%; specificity, 67%). A combined prediction model comprising either change in resistance greater than 8.8% or a non-laminar result predicted subsequent occlusion (odds ratio = 6.8; 95% confidence interval, 2.0-22.8; p = 0.002; sensitivity, 80%; specificity, 63%). Participants rated catheter-resistance monitoring as highly acceptable.

CONCLUSIONS

In this pediatric hematology and oncology population, catheter-resistance monitoring is feasible, acceptable, and predicts imminent catheter occlusion. Larger studies are required to validate these findings, assess the predictive value for other clinical outcomes, and determine the impact of pre-emptive therapy.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01737554.