Enhancing patency, safety and cost effectiveness of catheters.

Catheters are generally known to be the last resort for blood access in dialysis. Because of the many problems related to catheter use, catheters are banned from vascular access courses organized by professional societies and the development of catheters and catheter related equipment relies on a few interested medical doctors with limited knowledge of hydraulics and material science. Rather than accepting the need for catheters and the need for improving catheters and catheter related procedures, vascular access meetings typically begin and end with statements saying that the use of fistulas must be increased and catheters must be banned. Several small companies have developed new catheters and catheter related equipment, which potentially overcome many of the problems related to the use of catheters. The authors had the privilege of participating in one of these developments and report about basic features and clinical experience of the DIALOCK blood access port and an antimicrobial catheter locking solution (CLS) which is used with conventional catheters as well as with the DIALOCK.

Pressure drops in cannulas for hemodialysis.

UNLABELLED: Pressure drops in cannulas for hemodialysis have been measured in vitro in both flow directions for five different viscosities and up to 600 mL/min flow Cannula dimensions were 15, 16 and 17 gauge and 15, 20 and 25 mm nominal length. The measurements were taken at room temperature with glycerin solutions as test fluid. RESULTS: The pressure drops can be described by a second order function but not by the Hagen-Poiseuille law even when corrected for inlet and outlet effects as described by Bernoulli's law. Pressure drops depend on flow direction. Back-eyes and cannula tips have no influence on the pressure drop. Pressure drops and especially flow direction asymmetry are influenced by the hydraulic design of the connection piece between cannula and tubing. The results can be used for prediction of pressure drops in cannulas allowing better use of pressures already measured in the extracorporeal circuit of hemodialysis machines.

Pressure and flow in the extracorporeal circuit.

The impact of pressure and flow changes in the extracorporeal circuit on dialysis efficiency in response to altered hematocrit is discussed in the light of the known properties of blood, published studies and the author's as yet unpublished measurements. Increasing the hematocrit from 0.35 to 0.45 must be expected to reduce the efficiency of urea elimination by 3-5%, which can be offset by increasing dialysis time or blood flow. The change in physical parameters thus represents no obstacle to normalizing the hematocrit. However, basing the erythropoietin dose on the predialysis hematocrit should be reconsidered.

Challenges for chronic dialysis in the new millennium.

Although significant technical advances have occurred in the dialysis industry in the last 20 to 30 years, their collective impact on clinical outcomes has been less well-documented than their commercial successes. This article delineates the technical, administrative, and socioeconomic challenges which must be overcome in the next millennium in order to incorporate predicted technological advances into substantive improvements in quality of life, patient satisfaction, and adequacy of renal replacement therapy in the end-stage renal disease population. Technological advances envisioned include new athrombogenic materials for dialyzers and blood lines; membranes with absorptive properties; more efficient dialyzers; biofeedback sensor systems for physiological control of dialysis, on-line screening, and trend analysis; increased utilization of frequent dialysis; new vascular access techniques; increasing use of practice guidelines; global capitation; and attention to patients' views on standards of care, quality of life, and operation of dialysis facilities. Whereas many new technologies will be available, their application will largely depend on both fundamental research and socioeconomic factors.

Dialock: a new vascular access device for extracorporeal renal replacement therapy. Preliminary clinical results.

BACKGROUND: Vascular access, a vital tool for end-stage renal disease patients, remains a weak component of extracorporeal renal replacement therapy (RRT) and the first cause of morbidity. Permanent catheters proposed as an alternative to permanent AV fistulae are associated with a significant risk of infection. A subcutaneously implantable chamber connected to permanent catheter appears highly desirable to reduce such hazards. METHODS: Dialock, a metallic port-like valve device connected to permanent silicone twin catheters has been developed (Biolink Corp, Middleboro, MA, USA). After being implanted subcutaneously below the clavicle, Dialock provides a linear flow passage to two Silastic catheters placed in the right atrium via the right internal jugular vein. The valve is accessed percutaneously each dialysis session with needle cannulae that functionally convert the device into twin catheters. Interdialytic patency of the catheters is ensured by antithrombotic lock (heparin or low-molecular-weight heparin). RESULTS: Dialock was implanted in 10 ESRD patients (64+/-12 years) under general anaesthesia, with almost immediate use for HD. RRT consisted of three HD sessions per week lasting 4 h; 699 HD sessions were performed. Average duration of use was 5.7 patient-months (1.3-9.6 months). Patient satisfaction was evident in all cases. Three episodes of bacteraemia occurring in the early phase of the study were cured by appropriate antibiotics. No device was removed because of infection. Skin condition at the puncture sites has remained satisfactory in all patients. Nurse training for cannulating was brief (2-3 x). Effective blood flow was 307+/-3.3 ml/min, with a venous pressure of 195+/-39 mmHg and a recirculation rate of 6.7+/-0.8%. Effective Kt/V dp delivered was 1.36+/-0.03 with a nPCR of 1.20+/-0.005 g/kg/day. Haematoma and a small amount of bleeding of the skin puncture sites observed in the initial period of the study were effectively prevented by reducing heparin lock volume. CONCLUSIONS: The Dialock device offers a new and interesting vascular access alternative for haemodialysis bridging the 'gap' between permanent catheters and arteriovenous fistulae. Dialock's place in the vascular access strategy for haemodialysis patients deserves further long-term clinical studies.

Initial results of a new access device for hemodialysis technical note.

BACKGROUND: A new subcutaneous device (DIALOCKtrade mark) 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 internal or external 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. METHODS: The device was implanted in 10 outpatients under local anesthesia. Patients used the device during dialysis 3 times/week, and data were collected on blood flow, pressures, adverse events and patient and nurse satisfaction. RESULTS: The device was used for HD almost immediately (median 3 days after implantation) and functioned successfully for more than nine months (mean +/- SD 7.3 +/- 1.5) in all but one patient who died of unrelated causes after one month; there were >800 dialysis sessions total. Blood flows over 300 ml/min were consistently achieved (average 326 +/- 40) with venous and arterial pressures of 200 +/- 44 and -246 +/- 29 mm Hg, respectively. After 66 patient-months, condition of the needle puncture sites remained satisfactory. Five systemic infections occurred in four patients, producing 2.3 bacteremic episodes per 1000 patient-days. All resolved without the need for device removal. There were no infections at the puncture sites. Two patients required fibrin sheath stripping of their catheters, one whose heparin lock was not changed for 23 days (for reasons unrelated to the device). Patient and nurse acceptance was excellent. CONCLUSION: The device represents a positive improvement in the area of HD access.

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.

The acu-men: a new device for continuous renal replacement therapy in acute renal failure.

BACKGROUND: We sought to design a simple machine to safely provide continuous veno-venous hemofiltration to acute renal failure patients. RESULTS: The acu-men device uses a pneumatic blood pump with tidal blood flow as the driving force. A volumetric balancing system balances the filtrate with the replacement fluid, and the blood-air interface is eliminated by replacing the conventional venous drip chamber with two air-separating membranes. The extracorporeal circuit is integrated in a disposable cartridge, which is inserted into the machine at the beginning of treatment. The priming and rinsing is done automatically. CONCLUSION: While preliminary data from an ongoing clinic trial on the efficacy of the device are encouraging, further long-term studies are necessary to evaluate its potential to decrease morbidity and mortality in acute renal failure patients.

Effects of controlled blood cooling on hemodynamic stability and urea kinetics during high-efficiency hemodialysis.

Although the use of cooled dialysate during hemodialysis is associated with stabilization of intradialytic BP, the effects of blood cooling on hemodynamics and urea kinetics in high-efficiency hemodialysis have not been completely studied. In particular, the effects of blood cooling have not been elucidated in very short-time, high K/V dialysis treatments, in which postdialysis urea rebound is maximized. In theory, blood cooling could increase urea compartmentalization during treatment and decrease dialysis efficacy. Measurements of cardiovascular hemodynamics and urea kinetics were performed in 15 patients (56 studies) during dialysis, using a blood temperature monitor with control of dialysate temperature. Dialysate temperature was adjusted to either lower the core temperature or raise the core temperature by, respectively, producing negative heat-energy exchange (cooled dialysis) or keeping heat-energy exchange in the extracorporeal circuit neutral (thermoneutral dialysis) so that energy was not transferred to or from the patient. Each subject was studied on both protocols, thereby allowing each individual to act as his own control. In cooled dialysis, heat-energy exchange in the extracorporeal circuit was -266+/-15 kJ per treatment, and dialysate temperature averaged 35.7+/-0.02 degrees C. In thermoneutral dialysis, heat-energy exchange in the extracorporeal circuit averaged 5+/-31 kJ per treatment, and dialysate temperature averaged 37.1+/-0.02 degrees C. Dialysate cooling resulted in a reduction in mean body temperature compared with thermoneutral therapy (-0.22+/-0.04 versus +0.31+/-0.05 degrees C). Cooling resulted in a greater increase in peripheral vascular resistance index (+515+/-160 versus + 114+/-92 dyn.sec/cm5 per m2), an increase in mean arterial pressure (+4+/-3 versus -4+/-4 mmHg), a reduction in the maximum intradialytic fall in mean arterial pressure (-10+/-2 versus -18+/-3, mmHg), and a reduction in staff interventions for hypotension or dialytic symptoms (6 of 28 versus 12 of 28 studies). These differences occurred without differences in the change in blood volume (-14.3+/-1.8% versus -13.9+/-2.2%) or cardiac index (-0.4+/-0.1 versus -0.4+/-0.2, L/min per m2). Urea rebound (37+/-4% versus 38+/-3%) and effective Kt/V (1.29+/-0.05 versus 1.32+/-0.06) were not different between groups. Thus, body temperature cooling can be used to stabilize BP and reduce intradialytic events requiring staff intervention without compromising the efficacy of treatment in high-efficiency dialysis.

Dynamic pressure measurement for detection of blood access stenosis.

A novel method for detection of access failure has been developed. It is based on the continuous evaluation of pre-pump arterial and venous pressure in the extracorporeal circuit. Knowing the flow resistance properties of the arterial and venous branches of the extracorporeal circuit from in-vitro measurements and the height differences, calculating the fistula pressure dynamically is possible. The fistula pressure allows identification of access failure as has been shown by other authors. The dynamic measurement however allows identification of bad needle placement. Dynamic measurement at different flow rates and comparison with static measurements allow for the identification of intra-access stenosis. The mathematical algorithm is described and pressure-flow curves for two sets of extracorporeal circuits are shown. In-vivo examples show a "normal" fistula and a fistula with intra-access stenosis.

The use of heated citric acid for dialyzer reprocessing.

Dialyzer reprocessing with heated water (100 to 105 degrees C) for 20 h can be used safely in lieu of chemical methods for disinfection. All infective agents including spores are destroyed and depyrogenation may occur. However, these temperatures may result in structural damage to the dialyzer, limiting reuse. Dialyzer reprocessing by using 1.5% citric acid heated to 95 degrees C for 20 h is an alternative method that produces equivalent microbiologic effects. Citric acid is well known as a disinfecting agent used for dialysis equipment. Because there is little structural damage to dialyzer components at 95 degrees C, reuse statistics are improved (mean reuse increased to 12.8). Both small and large molecule clearances and the sieving coefficient for protein are insignificantly altered by the process. Whereas the procedure is relatively simple, quality-assurance indicators are essential. The method has appeal because it avoids the use of chemical germicides. However, at present it has only been tested thoroughly in polysulfone dialyzers with heat-resistant polycarbonate casings and polyurethane resin. The clinical experience is favorable.

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.