New hemodialysis access system.

A new blood access system for hemodialysis (HD) addresses the major shortcomings of current accessing techniques and helps overcome patient adversity with available choices. The system uses new methods, devices and compositions comprising several novel elements: (1) totally implanted port, elementally simple in design, small and robust with improved safety features, (2) engineered transcutaneous tissue tract (TTT) to precisely guide a tubular conduit to engage the implanted port, (3) viscoelastic gel prophylaxis for internal passages and surface interfaces of the port and TTT, (4) the tool kit aligns the TTT with the port and initiates TTT formation at the time of port placement, (5) an integrated external bloodline circuit comprising the interface between the implanted port and HD machine which can be reused for several treatment sessions. The system provides bloodless, painless, and fail-safe connections with redundant sealing along the complete blood path. It is substantially more robust than current access options and more convenient to use. TTT construct is durable, permanently aligned and fixed to the port enabling non-compromised tissue integrity during access penetration. A bullet-pointed tubular assembly enters and passes through the TTT confining the tubular device to advance towards the port and entering it to engage a solid tactually sensed stop indicating the correct position. The system may be used within a few days of port placement. The access is unobtrusive and preserves patient self-image.

Blood volume-monitored regulation of ultrafiltration in fluid-overloaded hemodialysis patients: study protocol for a randomized controlled trial.

BACKGROUND: Data generated with the body composition monitor (BCM, Fresenius) show, based on bioimpedance technology, that chronic fluid overload in hemodialysis patients is associated with poor survival. However, removing excess fluid by lowering dry weight can be accompanied by intradialytic and postdialytic complications. Here, we aim at testing the hypothesis that, in comparison to conventional hemodialysis, blood volume-monitored regulation of ultrafiltration and dialysate conductivity (UCR) and/or regulation of ultrafiltration and temperature (UTR) will decrease complications when ultrafiltration volumes are systematically increased in fluid-overloaded hemodialysis patients. METHODS/DESIGN: BCM measurements yield results on fluid overload (in liters), relative to extracellular water (ECW). In this prospective, multicenter, triple-arm, parallel-group, crossover, randomized, controlled clinical trial, we use BCM measurements, routinely introduced in our three maintenance hemodialysis centers shortly prior to the start of the study, to recruit sixty hemodialysis patients with fluid overload (defined as ≥15% ECW). Patients are randomized 1:1:1 into UCR, UTR and conventional hemodialysis groups. BCM-determined, 'final' dry weight is set to normohydration weight -7% of ECW postdialysis, and reached by reducing the previous dry weight, in steps of 0.1 kg per 10 kg body weight, during 12 hemodialysis sessions (one study phase). In case of intradialytic complications, dry weight reduction is decreased, according to a prespecified algorithm. A comparison of intra- and post-dialytic complications among study groups constitutes the primary endpoint. In addition, we will assess relative weight reduction, changes in residual renal function, quality of life measures, and predialysis levels of various laboratory parameters including C-reactive protein, troponin T, and N-terminal pro-B-type natriuretic peptide, before and after the first study phase (secondary outcome parameters). DISCUSSION: Patients are not requested to revert to their initial degree of fluid overload after each study phase. Therefore, the crossover design of the present study merely serves the purpose of secondary endpoint evaluation, for example to determine patient choice of treatment modality. Previous studies on blood volume monitoring have yielded inconsistent results. Since we include only patients with BCM-determined fluid overload, we expect a benefit for all study participants, due to strict fluid management, which decreases the mortality risk of hemodialysis patients. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01416753.

A novel method for measuring catheter lock spillage: an in vitro study.

Catheters are widely used for blood purification, parenteral nutrition, and for the infusion of drugs. Previous work on catheter lock spillage has focused on the theory and in vitro demonstration of catheter lock spillage caused by the laminar flow profile and by fluid exchange caused by density differences. This work describes an in vitro test with a method that potentially allows measurement of catheter lock spillage in vivo without sampling. The method is based on the change of the electrical resistance of the catheter when the lock solution is injected. This method was tested in vitro with human blood at 36°C using 46.7% trisodium citrate as catheter lock solution. The catheter tip was placed in a beaker filled with whole blood. A stainless steel rod in the beaker served as one electrode and an Arrow-Johans ECG adapter, which was placed on the distal end of the catheter, served as a second electrode. Conductivity was measured with a 5V (rms) 310 Hz sinus voltage and a 10 kOhm resistor in series to the catheter. The driving voltage and the voltage drop at the catheter was continuously measured with a program written under LabView (National Instruments), and the results were converted into mean trisodium citrate concentrations. Within 20 min, the mean trisodium citrate concentration in the catheter decreased to less than 5%. Unlike the previous methods used for catheter lock spillage measurement, this principle can be employed to measure the time course of catheter lock spillage in vivo.

Trisodium citrate induced protein precipitation in haemodialysis catheters might cause pulmonary embolism.

BACKGROUND: The locking anticoagulant plays a decisive role in the patency of central venous catheters (CVCs) used for haemodialysis. During injection, the hydraulic effects inevitably cause lock solution to spill into the systemic circulation. Density differences between whole blood (WB) and the lock solution cause further gravity-induced seepage of lock solution. This is followed by an influx of WB into the catheter, also described for trisodium citrate, which is a common agent for serum protein precipitation. Embolic complications from haemodialysis catheters locked with hypertonic trisodium citrate have been reported. We aimed to investigate protein precipitation in trisodium citrate locked catheters as a possible cause of pulmonary embolisms. METHODS: In vitro, WB and trisodium citrate (concentrations ranging from 4.7 to 46.7%) mixtures in a ratio of 1:4 were used to assess protein precipitation. Additionally, WB/trisodium citrate mixture was pumped through a 20-µm mesh filter, simulating pulmonary vessels, and filtrate pressure was measured. In vivo, listed filling volumes of haemodialysis catheters locked with trisodium citrate 4% (n=10), 10% (n=10), 20% (n=10) or 46.7% (n=10) were aspirated and then analysed for protein precipitation. RESULTS: In vitro, protein precipitation capable of causing filter occlusion was observed in test solutions containing trisodium citrate above a concentration of 12%. In vivo, protein precipitation was detected in all samples from the CVCs filled with trisodium citrate 46.7% (n=10) and 20% (n=10). In contrast, there were no signs of precipitation in samples from the catheters filled with trisodium citrate 4% (n=10) or 10% (n=10). CONCLUSIONS: Our in vitro results demonstrate that protein precipitates inside haemodialysis catheters when trisodium citrate is used above the concentrations of 12%. Precipitated protein may have contributed to the pathophysiology of reported embolisms from haemodialysis catheters filled with hypertonic trisodium citrate. Based on our findings, we suggest that trisodium citrate lock solution up to the concentration of 10% can be used safely.

Wearable dialysis: what is missing?

In this chapter, unanswered questions regarding the safety and usability of the wearable artificial kidney (WAK) are discussed. This will cover issues such as safe blood access, risks related to the operation of the WAK, temporary disconnection or separation during sleep, and reloading dialysate regeneration cartridges.

Hemodialysis machine technology: a global overview.

The market for hemodialysis machines, the background, the current products of manufacturers and the features of hemodialysis machines are described in this article. In addition to the established companies and their products, Chinese manufacturers, and new developments for home hemodialysis, are outlined based on publications available on the internet and patent applications. Here, a critical review of the state of the art questions the medical usefulness of high-tech developments, compared with the benefits of more frequent and/or longer dialysis treatment with comparable simple machines.

Venous needle dislodgement: the pitfalls of venous pressure measurement and possible alternatives, a review.

The historical development of the use of pressure sensors as protective system against blood loss to the environment is reviewed. In spite of early warnings about the deficiency of such sensors, the venous pressure sensor is still formally accepted as protective system against blood loss to the environment in case of leaks or needle dislodgement. The early warnings were corroborated by publications and accident reports. Several alternative methods have been developed or described in the literature recently. These methods are critically reviewed. The conclusion is that external monitors are currently the only available alternatives, although long-time clinical experience is missing. Methods employing sensors integrated into dialysis machines have been described but it is unlikely that any of these methods will become available in the immediate future.

Red blood cell damage from extracorporeal circulation in hemodialysis.

Blood damage is an unavoidable side effect of extracorporeal circulation. The effects of blood damage on patients' hematocrit and erythropoietin requirement as well as other potential side effects have not been studied for uneventful treatments. Comparing long nocturnal dialysis with regular 4-hour, three times per week dialysis allows for the conclusion that the influence of blood damage caused by extracorporeal circulation is small compared with biochemical effects. Acute hemolysis is one of the few remaining mechanical problems of dialysis. Acute hemolysis is caused by obstructions within the extracorporeal circuit caused by manufacturing errors, kinking of blood tubing or user errors, or by a combination of excessive flow and improper cannula or catheter dimensions. The risk of acute hemolysis can be further reduced by industrial quality control, better design of dialysis equipment, and hemodialysis machine control. Adverse effects caused by chronic mechanical hemolysis need to be studied.

Catheter locking-solution spillage: theory and experimental verification.

UNLABELLED: A theory was developed allowing the prediction of the spillage volume after injection of locking solution into a catheter. This theory was corroborated by in-vitro measurements using colorized fluid injected automatically by a micropump into a stirred container with clear fluid. The amount of spilled solution was measured with a fiberoptic spectrometer equipped with a dip probe. Straight cylindrical tubing was used as catheter. RESULTS: The theory predicts the beginning of spillage when 50% of the catheter filling volume is injected. When the nominal filling volume is injected, 25% of the solution is spilled and the mean concentration at the catheter tip is 50% of the locking solution concentration. EXPERIMENTS: Spillage was slightly less than predicted (20-25% at nominal filling volume). During the experiments it was recognized that a small air bubble trapped in the Luer connection during connection reduces the spillage volume to 10-15%.

Technical aspects of online hemodiafiltration.

The chapter describes and analyzes the most commonly used systems for online substitution fluid production in hemofiltration and hemodiafiltration, covering in detail systems comprising 2 multiuse filters, or 2 multiuse filters in combination with 1 disposable filter. A generally applicable risk analysis for the process of online substitution fluid preparation is provided. It is concluded that both system variants discussed perform in a safe manner, provided the operator fully complies with the manufacturer's instructions for use.

Loss of catheter locking solution caused by fluid density.

The avoidance of clotting in catheter lumina between treatments usually entails locking with an anticoagulant solution such as heparin. In a previous work, it was shown that approximately 20% of locking solution flows from the catheter during instillation of the lock equal in volume to the lumen volume. Furthermore, the locking solution may spill into the blood stream under the influence of gravity. This work investigates the influence of density and viscosity of the locking solution on the volume and speed of locking solution loss from the catheter lumen. A large fraction of the catheter locking solution spills under the influence of gravity if the locking solution's density is higher than the fluid it spills to (blood). Locking solution lost is replaced by blood. Viscosity delays this process, but at 90 minutes after injection, the loss is completed even when highly viscous lock solutions are used. Slow administration of the lock has negligible influence upon the dynamics of the loss.

Machines for hemodialysis.

Basic functions of hemodialysis machines are described. The paper focuses on essential treatment parameters and safety aspects. The cause of safety hazards and protective systems for amelioration of these hazards are described. With the exception of hemolysis caused by obstructions in the extracorporeal circuit and blood losses caused by user errors machine related accidents are rare. Foreseeable improvements of next generation hemodialysis machines will reduce the likelihood of accidents further. The accuracy of adjusted or monitored treatment parameters that may influence outcome (dialysate concentration, ultrafiltration, blood flow and on-line measured clearance) is discussed.