Hans D. Polaschegg

NEW ACCESS DEVICE FOR HEMODIALYSIS

A new subcutaneous device (Dialock; Biolink Corp., Middleboro, MA) provides vascular access to patients who currently require hemodialysis (HD). The device consists of a port-like valve, implanted subcutaneously below the clavicle, which provides a linear flow passage to two catheters placed in the right atrium via the jugular vein. The valve is accessed percutaneously with needle-cannulas that functionally convert the device to twin catheters for connecting the patient to the HD lines. Interdialytic patency is maintained using a standard heparin lock. The device has been implanted in 10 outpatients under local anesthesia, with almost immediate use for HD (median, 3 days) and has functioned successfully for more than 6 months (mean +/- SD, 4.0 +/- 1.7; > 400 dialysis sessions). Blood flows over 300 ml/min were consistently achieved (average, 320 +/- 50) with venous and arterial pressures of 197 +/- 42 mmHg and -241 +/- 31 mmHg, respectively. After 40 patient-months, condition of the needle puncture sites remains satisfactory. Four systemic infections have occurred in three patients; all have resolved without the need for device removal. There have been no infections at the puncture sites. One patient whose heparin lock was not changed for 23 days (for reasons unrelated to the device) required fibrin sheath stripping of his catheters. Patient and nurse acceptance has been excellent. The device may offer substantial improvement over conventional devices for HD access.

Dialock: Pilot Trial of a New Vascular Port Access Device for Hemodialysis

Vascular access (VA), an essential tool for end stage renal disease (ESRD) patients, remains a weak component of extracorporeal renal replacement therapy (RRT) (1, 2). VA related problems are the primary cause of hospitalization accounting for most of the morbidity cost in ESRD patients (3, 4). Native and/or prosthetic arteriovenous fistulas (AVF), considered the “gold standard” for permanent VA in dialysis, have some limitations (5, 6). AVF may not be functional or usable on short notice in newly recruited or late referred ESRD patients (7). Dysfunction of mature AVF may occur for several reasons: stenosis; thrombosis; low flow or high recirculation. AVF may also be contraindicated in patients with severe heart failure or peripheral arteritis (8). Infection is another condition that compromises the use of native or prosthetic AVF. Permanent catheters, proposed as an alternative to AVF in these conditions (9, 10), are associated with a significantly higher risk of infection (11–16). Whatever the causes of catheter infection (patientor staff-related), one of the main predisposing factors is the external location of the catheter. First, the catheter breaks the skin integrity and facilitates the migration of bacteria in the subcutaneous tunnel. Second, the catheter gives a permanent access to blood stream facilitating the bacteria contamination and migration from the internal lumen. Third, the tubing is made of synthetic elastomer, a foreign material facilitating the adhesion and the proliferation of bacteria (17, 18). A totally implantable device, in keeping with the permanent port concept, appears highly desirable. It has been shown that the VA port used for chemotherapy significantly reduced the risk of infection (19). To satisfy blood flow requirements of extra-corporeal renal replacement therapy (high flow, low resistance) a new subcutaneous port device (Dialock®) has been developed (20). This hemodialysis VA device consists of a metallic port-like valve implanted subcutaneously in the chest area and connected to a dual silastic right jugular vein catheter. This study reports additional results of the international pilot trial clinical trial with the Dialock hemodialysis access device (21).

In vivo verification of an automatic noninvasive system for real time Kt evaluation.

It is generally accepted that morbidity and mortality of hemodialysis patients is related to dialysis quantitation. Currently available methods for the quantitation of dialysis require blood sampling or a continuous measurement of changes in urea concentration during treatment. These maneuvers are time consuming and expensive, and are generally performed, at most, once per month. The authors introduce an on-line, automated method for measurement of dialyzer electrolyte clearance comparable to urea clearance by using dialysate conductivity sensors placed pre and post dialyzer, and measuring conductivity at three different pre dialyzer levels. Conditions that reduce clearance, such as recirculation or fiber clotting, are automatically taken into account so that the method measures effective clearance rather than dialyzer clearance. In vitro and in vivo studies validate the method. Results are immediately available and can be used to address problems such as improper needle placement and access recirculation. In addition, repetitive electrolyte clearance data can serve to enhance quality assurance programs with respect to verifying the function of reused or new dialyzers. Appropriate algorithms can be used to calculate delivered Kt/V.

Solute Disequilibrium and Multicompartment Modeling

Mathematical models that simulate the exchange of solute between multiple body compartments have been used to study the distribution, elimination, and transport of urea, water, electrolytes, and other substances in the dialysis patient. Within a compartment, such substances are assumed to be uniformly distributed while exchange between compartments or with the environment may occur in a number of different ways. Diffusion in response to concentration gradients between, for example, intracellular and extracellular spaces, and convection due to blood flow have been identified as the most important transport mechanisms. Any system with more than one compartment may develop nonuniform solute distribution or solute disequilibrium between compartments. The minimum number of compartments required to model a kinetic process such as urea removal during hemodialysis depends on the accuracy and temporal resolution required, with higher resolution calling for more compartments. A two-compartment model is adequate for most clinical purposes. The physiological meaning or anatomic counterparts of the mathematical compartments remain uncertain as both flow and diffusion transport mechanisms contribute to the disequilibrium. Processes such as access and cardiopulmonary recirculation may be represented as additional compartments with small distribution volumes and high mass transport rates. Failure to recognize the effect of multiple compartments will result in an inaccurate measurement of dialysis dose and an inadequate hemodialysis prescription with a predictably poor clinical outcome. Allowance for compartment effects is particularly important in patients receiving treatment with a high ratio of dialyzer clearance to total body water, now commonly encountered during short-time, high-efficiency dialysis.

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.