Extracorporeal Dialysis Circuit Research Articles

Percutaneous Creation of Dialysis Arteriovenous Fistula: Patient Selection and Ultrasound Mapping.

Approximately, 550,000 patients with end-stage kidney disease rely on maintenance dialysis in the United States, and nearly 90% receive hemodialysis.[1] Providing hemodialysis requires a conduit to the bloodstream (vascular access) that can reliably deliver a high blood flow into the extracorporeal dialysis circuit. A surgical arteriovenous fistula (AVF) is created by a direct surgical anastomosis between a peripheral artery and vein. AVFs are considered the preferred type of vascular access, because they have better survival and require fewer interventions to maintain long-term patency for dialysis, once they are successfully cannulated for dialysis.[2] [3] [4]

An iterative run-to-run learning model to derive continuous brachial pressure estimates from arterial and venous lines during dialysis treatment

Objective:Non-invasive continuous blood pressure monitoring is not yet part of routine practice in renal dialysis units but could be a valuable tool in the detection and prevention of significant variations in patient blood pressure during treatment. Feasibility studies have delivered an initial validation of a method which utilises pressure sensors in the extra-corporeal dialysis circuit, without any direct contact with the person receiving treatment. Our main objective is to further develop this novel methodology from its current early development status to a continuous-time brachial artery pressure estimator. Methods:During an in vivo patient feasibility study with concurrent measurement validation by Finapres Nova experimental physiological measurement device, real-time continuous dialysis line pressures, and intermittent occluding arm cuff pressure data were collected over the entire period of (typically 4-hour) dialysis treatments. There was found to be an underlying quasi-linear relationship between arterial line and brachial pressure measurements which supported the development of a mathematical function to describe the relationship between arterial dialysis line pressure and brachial artery BP. However, unmodelled non-linearities, dynamics and time-varying parameters present challenges to the development of an accurate BP estimation system. In this paper, we start to address the problem of physiological parameter time variance by novel application of an iterative learning run-to-run modelling methodology originally developed for process control engineering applications to a parameterised BP model. Results:The iterative run-to-run learning methodology was applied to the real-time data measured during an observational study in 9 patients, supporting subsequent development of an adaptive real-time BP estimator. Tracking of patient BP is analysed for all the subjects in our patient study, supported only by intermittent updates from BP cuff measurements. Conclusion:The methodology and associated technology is shown to be capable of tracking patient BP non-invasively via arterial line pressure measurement during complete 4-hour treatment sessions. A robust and tractable method is demonstrated, and future refinements to the approach are defined.

A Feasibility Study of Non-Invasive Continuous Estimation of Brachial Pressure Derived From Arterial and Venous Lines During Dialysis.

Objective: Intradialytic haemodynamic instability is a significant clinical problem, leading to end-organ ischaemia and contributing to morbidity and mortality in haemodialysis patients. Non-invasive continuous blood pressure monitoring is not currently part of routine practice but may aid detection and prevention of significant falls in blood pressure during dialysis. Brachial blood pressure is currently recorded intermittently during haemodialysis via a sphygmomanometer. Current methods of continuous non-invasive blood pressure monitoring tend to restrict movement, can be sensitive to external disturbances and patient movement, and can be uncomfortable for the wearer. Additionally, poor patient blood circulation can lead to unreliable measurements. In this feasibility study we performed an initial validation of a novel method and associated technology to continuously estimate blood pressure using pressure sensors in the extra-corporeal dialysis circuit, which does not require any direct contact with the person receiving dialysis treatment. Method: The paper describes the development of the measurement system and subsequent in vivo patient feasibility study with concurrent measurement validation by Finapres Nova physiological measurement device. Real-time physiological data is collected over the entire period of (typically 4-hour) dialysis treatment. Results: We identify a quasi-linear mathematical function to describe the relationship between arterial line pressure and brachial artery BP, which is confirmed in a patient study. The results from this observational study suggest that it is feasible to derive a continuous measurement of brachial pressure from continuous measurements of arterial and venous line pressures via an empirically based and updated mathematical model. Conclusion: The methodology presented requires no interfacing to proprietary dialysis machine systems, no sensors to be attached to the patient directly, and is robust to patient movement during treatment and also to the effects of the cyclical pressure waveforms induced by the hemodialysis peristaltic blood pump. This represents a key enabling factor to the development of a practical continuous blood pressure monitoring device for dialysis patients.

Effect of Regional Citrate Anticoagulation vs Systemic Heparin Anticoagulation During Continuous Kidney Replacement Therapy on Dialysis Filter Life Span and Mortality Among Critically Ill Patients With Acute Kidney Injury

Although current guidelines suggest the use of regional citrate anticoagulation (which involves the addition of a citrate solution to the blood before the filter of the extracorporeal dialysis circuit) as first-line treatment for continuous kidney replacement therapy in critically ill patients, the evidence for this recommendation is based on few clinical trials and meta-analyses. To determine the effect of regional citrate anticoagulation, compared with systemic heparin anticoagulation, on filter life span and mortality. A parallel-group, randomized multicenter clinical trial in 26 centers across Germany was conducted between March 2016 and December 2018 (final date of follow-up, January 21, 2020). The trial was terminated early after 596 critically ill patients with severe acute kidney injury or clinical indications for initiation of kidney replacement therapy had been enrolled. Patients were randomized to receive either regional citrate anticoagulation (n = 300), which consisted of a target ionized calcium level of 1.0 to 1.40 mg/dL, or systemic heparin anticoagulation (n = 296), which consisted of a target activated partial thromboplastin time of 45 to 60 seconds, for continuous kidney replacement therapy. Coprimary outcomes were filter life span and 90-day mortality. Secondary end points included bleeding complications and new infections. Among 638 patients randomized, 596 (93.4%) (mean age, 67.5 years; 183 [30.7%] women) completed the trial. In the regional citrate group vs systemic heparin group, median filter life span was 47 hours (interquartile range [IQR], 19-70 hours) vs 26 hours (IQR, 12-51 hours) (difference, 15 hours [95% CI, 11 to 20 hours]; P < .001). Ninety-day all-cause mortality occurred in 150 of 300 patients vs 156 of 296 patients (Kaplan-Meier estimator percentages, 51.2% vs 53.6%; unadjusted difference, -2.4% [95% CI, -10.5% to 5.8%]; unadjusted hazard ratio, 0.91 [95% CI, 0.72 to 1.13]; unadjusted P = .38; adjusted difference, -6.1% [95% CI, -12.6% to 0.4%]; primary adjusted hazard ratio, 0.79 [95% CI, 0.63 to 1.004]; primary adjusted P = .054). Of 38 prespecified secondary end points, 34 showed no significant difference. Compared with the systemic heparin group, the regional citrate group had significantly fewer bleeding complications (15/300 [5.1%] vs 49/296 [16.9%]; difference, -11.8% [95% CI, -16.8% to -6.8%]; P < .001) and significantly more new infections (204/300 [68.0%] vs 164/296 [55.4%]; difference, 12.6% [95% CI, 4.9% to 20.3%]; P = .002). Among critically ill patients with acute kidney injury receiving continuous kidney replacement therapy, anticoagulation with regional citrate, compared with systemic heparin anticoagulation, resulted in significantly longer filter life span. The trial was terminated early and was therefore underpowered to reach conclusions about the effect of anticoagulation strategy on mortality. ClinicalTrials.gov Identifier: NCT02669589.

Efficacy of enoxaparin in preventing coagulation during high-flux haemodialysis, expanded haemodialysis and haemodiafiltration.

BackgroundLow-molecular-weight heparins (LMWHs) are easily dialysable with high-flow membranes; however, it is not clear whether the LMWH dose should be adjusted according to the membrane type and dialysis technique. This study aimed to evaluate the influence of the dialyser on anticoagulation of the extracorporeal dialysis circuit.MethodsThirteen patients received the same dose of LMWH through the arterial port via three dialysis techniques: high-flux haemodialysis (HF-HD), online haemodiafiltration (HDF) and expanded haemodialysis (HDx). All dialysis was performed under similar conditions: duration, 4 h; blood flow, 400 mL/min; and dialysate flow, 500 mL/min. Antifactor Xa (aXa) activity and activated partial thromboplastin time (APTT) were measured before and after the dialysis. Clotting time of the vascular access site after haemodialysis, visual clotting score of the dialyser and any complications with the extracorporeal circuit or bleeding were registered.ResultsPost-dialysis aXa activity in HF-HD (0.26 ± 0.02 U/mL) was significantly different from that in HDF (0.21 ± 0.02 U/mL, P = 0.024), and there was a trend in HDx (0.22 ± 0.01 U/mL, P = 0.05). APTT post-dialysis in HF-HD (30.5 ± 0.7 s) was significantly different from that in HDx (28.2 ± 0.64 s, P = 0.009) and HDF (28.8 ± 0.73 s, P = 0.009).ConclusionsAXa activity in HDF was significantly lower than that in HF-HD, possibly because of more losses of LMWH through the dialyser. Given the higher anticoagulant loss in HDF and probably in HDx than in HF-HD, the enoxaparin dose administered may be adjusted according to the dialysis technique.

Safety and Efficacy of Tinzaparin Anticoagulation during Nocturnal Hemodialysis

Background: The safety and efficacy of low-molecular-weight heparin in the prevention of extracorporeal dialysis circuit clotting among in-center extended duration nocturnal hemodialysis (INHD) patients are unknown. The aim of this study was to determine the safety and efficacy of 2 doses of tinzaparin, among INHD patients receiving 6–8 h hemodialysis, 3 times per week. Methods: We conducted a retrospective cohort study to examine antifactor Xa levels at time 0, 2 h, 4 h mid-hemodialysis (mid-HD), 6 h, and at end of each INHD session for 4 weeks and to determine extracorporeal dialysis circuit clotting and bleeding events after switching from unfractionated heparin to tinzaparin, using a standard protocol of tinzaparin delivery at the initiation and midpoint of HD. Results: All 16 patients in The Ottawa Hospital INHD program were converted to tinzaparin and followed for 177 INHD sessions. Mean antifactor Xa level at 2 h of HD was 0.41 ± 0.21 (SD) IU/mL, at 4 h (mid-HD) 0.19 ± 0.17 IU/mL, at 6 h 0.44 ± 0.21 IU/mL, and at dialysis end 0.26 ± 0.14 IU/mL. Antifactor Xa levels were undetectable at the start of INHD, suggesting no tinzaparin accumulation. Five patients required an increase in tinzaparin due to extracorporeal dialysis circuit clotting. There were no bleeding events. One patient required a switch to fondaparinux due to an adverse reaction. Conclusion: Tinzaparin was safe and efficacious for most INHD patients without accumulation or bleeding. The conversion from unfractionated heparin to tinzaparin required an increased tinzaparin dose for 31% of INHD patients.

Novel Extracorporeal Dialysis Circuit to Improve the Removal Efficiency of High and Middle Molecular Weight Toxins.

A new extracorporeal circuit for hemodialysis was designed with the goal of improving the middle and high molecular weight toxins removal. A recirculation pathway was added to the hemodialysis circuit and relevant pressure regulation was performed along the circuit in order to keep the ultrafiltration rate as zero. The influence of increasing the recirculation to dialysate flow rate ratio on the removal of urea, vitamin B12, and hemoglobin was investigated. This removal was also modeled by an analytical method and solved by MATLAB software. A significant increase in removal of vitamin B12 (34%) and especially hemoglobin (228%) was achieved using the recirculation flow in an adjusted hemodialysis circuit. The model showed an acceptable agreement with the experimental results which shows its applicability for prediction of different toxin removal in this circuit.

Comparison of Enoxaparin Sodium and Standard Heparin for Hemodialysis Anticoagulation

Background: Low-molecular-weight heparin (LMWH) has been suggested as an effective and safe anticoagulant for hemodialysis. The aim of our study was to investigate the effects of LMWH including minor bleeding, clotting formation in the extracorporeal dialysis circuit and their effect on the lipid profile in comparison with heparin. Methods: This randomized, crossover study with parallel design was conducted in 45 patients who required maintenance hemodialysis due to end-stage renal failure. Four patients with known bleeding disorders, receiving anticoagulant drugs and receiving drugs which could affect heparin activity were excluded. All patients were randomly assigned to receive either enoxaparin sodium (0.7 mg/kg) or standard heparin for a duration of 12 weeks, after which patients were crossed over to another therapy for a further 12 weeks. Enoxaparin sodium was administered 5 minutes before dialysis, injected into the arterial line pre- dialyser and heparin was administered 50 U/kg intravenously into the pre- dialyser arterial line followed by a maintenance dose of 1000 U per hour. Results: The mean age of the study population was of 65.18 (SD = 12.15) years. From these patients 22 (53%) were male and 19 (47%) were female. At the end of the first study phase, minor bleeding in patients receiving enoxaparin with dose of 0.25 mg/kg was significantly decreased in comparison to the patients receiving heparin (P: 0.03), although vascular compression time did not significantly differ between the heparin and enoxaparin groups. At the end of the second study phase, the enoxaparin group showed a significant increase in minor bleeding in comparison with the heparin group (P: 0. 04). In the enoxaparin arm, recurrent blood oozing from puncture sites led to the idea to reduce the dose of enoxaparin. After enoxaparin dose reduction, the frequency of minor bleeding decreased to 10% (from 19% to 10%) (P: 0.01). Vascular compression time was not statistically different in heparin and enoxaparin at the end of study (P: 0.1). There were no significant changes in serum lipids with either anticoagulant neither at the end of the 12th week nor at the end of the 24th week. Conclusions: This study suggests that a single-dose of enoxaparin is an effective and convenient alternative to standard heparin. The recommended dose of this study in Iranian patients is 0.25 mg/kg.

Assessment of the Adminstration of Low Molecular Weight Heparin for Hemodialysis Anticoagulation in Comparison to Standard Unfractionated Heparin

Background and Aim of Study : The use of Low - molecular - weight heparin (LMWH) for hemodialysis anticoagulation has been proposed as effective and safe for hemodialysis (HD) anticoagulation as standard unfraction ated heparin (UFH). The aim of our study was to assess the use of LMWH for hemodialysis anticoagulation in comparison to UFH, including hemorrhagic events and clotting of the extracorporeal dialysis circuit and their effect on lipids profile. Method s : This prospective, randomized study conducted on 44 patients (31 males, 13 females; mean age 53.7.9±14.2 years ) with end - stage renal disease on regular hemodialysis. The hemodialysis patients were subjected to UFH and followed prospectively for 16 weeks (4 8 dialyses sessions) and the same patients were subjected to LMWH (enoxaparin sodium; 40 mg) for a further 16 weeks , clotting of the extracorporeal dialysis circuit and hemorrhagic events were evaluated by visual inspection of the air trap, blood lines and dialyzers and the time required for arterio - venous fistula compression. Kt/V was calculated to determine whether UFH or LMWH had any effect on the adequacy of dialysis and lipid profile were measured at the end of each arm of the study to determine whethe r UFH or LMWH had any effect on the lipid profile levels. Results : The present study showed that, compared with UFH, the effect of LMWH (enoxaparin Original Research Article

Safety and Efficacy of Low Molecular Weight Heparins for Hemodialysis in Patients with End-Stage Renal Failure

Low molecular weight heparins (LWMH) are the preferred initial treatment for many thromboembolic disorders but are renally excreted and relatively contraindicated in patients with renal failure because of concerns of increased bleeding risks. The purpose of this study was to evaluate the safety and efficacy of LMWH compared with unfractionated heparin (UFH) for preventing thrombosis of the extracorporeal dialysis circuit. Studies were identified with the use of MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and FirstSearch; reference lists were reviewed; and pharmaceutical companies were contacted. Randomized, controlled trials that compared an LMWH with another anticoagulant during hemodialysis in patients with ESRD and reported at least one of bleeding, extracorporeal circuit thrombosis, or anti-Xa levels were chosen. Two reviewers independently extracted data on methodologic quality, study design, clinical outcomes, and anti-Xa levels. Seventeen trials were included in this systematic review, 11 of which were included in the meta-analysis. It was found that LMWH did not significantly affect the number of bleeding events (relative risk, 0.96; 95% confidence interval [CI], 0.27 to 3.43), bleeding assessed by vascular access compression time (weighted mean difference, -0.87; 95% CI, -2.75 to 1.02), or extracorporeal circuit thrombosis (relative risk, 1.15; 95% CI, 0.70 to 1.91) as compared with UFH. LMWH seem to be as safe as UFH in terms of bleeding complications and as effective as UFH in preventing extracorporeal circuit thrombosis. However, inferences from these trials assessing anticoagulation for patients who undergo hemodialysis will continue to be weak until larger, more rigorous randomized trials are conducted.

Safety and Efficacy of Low Molecular Weight Heparins for Hemodialysis in Patients with End-Stage Renal Disease: A Meta-Analysis of Randomized Trials.

Background: The anticoagulant management of patients with thromboembolic disease who also have end-stage renal disease is a frequently encountered and unresolved clinical problem. Low molecular weight heparins (LWMHs) are the preferred initial treatment for these disorders but are renally excreted, and generally avoided in patients with renal failure due to concerns of bioaccumulation and increased bleeding risks. Unfractionated heparin (UFH) remains the primary anticoagulant used in this patient population despite the efficacy and convenience of LMWHs. Although LMWHs are typically not used to treat thrombosis in patients with end-stage renal disease, they are frequently used during hemodialysis to prevent thrombosis of the extracorporeal dialysis circuit. While there are no randomized data evaluating the safety and efficacy of LMWHs in these patients, randomized trials have been performed using LMWHs in the setting of hemodialysis. We performed a systematic review and meta-analysis of these randomized trials summarizing this data.Purpose: To evaluate the safety and efficacy of LMWHs compared to UFH for preventing thrombosis of the extracorporeal dialysis circuit.Data sources: We identified studies using MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials and FirstSearch, reviewed reference lists and contacted pharmaceutical companies.Study selection: We included randomized, controlled trials that compared a LMWH with another anticoagulant during hemodialysis in patients with end-stage renal disease, and reported at least one of the following outcomes: bleeding, extracorporeal circuit thrombosis, or anti-Xa levels.Data extraction: Two reviewers independently extracted data on methodologic quality, study design, clinical outcomes, and anti-Xa levels.Data synthesis: We included 17 trials in this systematic review, 11 of which were included in the meta-analysis. We found that LMWH did not significantly affect the number of bleeding events (relative risk [RR] 0.96, 95% CI, 0.27 to 3.43), bleeding assessed by vascular access compression time (weighted mean difference −0.87, 95% CI, −2.75 to 1.02) or extracorporeal circuit thrombosis (RR 1.15, 95% CI, 0.70 to 1.91) as compared with UFH.Conclusions: LMWHs appear to be as safe as UFH in terms of bleeding complications, and as effective as UFH in preventing extracorporeal circuit thrombosis. However, inferences from these trials assessing anticoagulation for patients undergoing hemodialysis will continue to be weak until larger, more rigorous randomized trials are conducted.

Efficacy of Heat Disinfection With the Aksys Personal Hemodialysis System

The first objective of this study was to validate the use of water at 85°C ± 5°C to achieve high-level disinfection of a clean-in-place extracorporeal dialysis circuit. The second objective was to demonstrate that applying this hot water method to the entire fluid pathways of a newly designed dialysis instrument, including an integral reverse-osmosis membrane, routinely allowed the production of back-filtered dialysate meeting the U.S. Pharmacopeia (USP) standard for the water for injection (WFI). In a first study, six dialyzers were inoculated with P. aeruginosa, incubated, and subjected to 75°C water for 30 minutes. No organisms could be recovered from the experimental dialyzers nor from three negative controls, but they were recovered from three positive controls. In a second study, the carbon tanks in the water inlet line and the dialysate tank were both inoculated with massive amounts of dialysis water-adapted Gram-negative organisms, followed by seven dialysis treatments using bovine blood, where the fifth and sixth procedures were separated by 2 idle days and the sixth and seventh procedures were separated by 3 idle days. In addition, the bovine blood used in each treatment was highly contaminated. In every case, the back-filtered dialysate met the WFI standard. From the above results we conclude that a hot water disinfection process is efficacious in reducing even grossly exaggerated contamination in the Aksys personal hemodialysis system to the point where it can produce water and dialysate that greatly exceed the Association for the Advancement of Medical Instrumentation (AAMI) standards and priming and rinse-back solution (back-filtered dialysate) that meets the USP standard for WFI.

Efficacy of Heat Disinfection With the Aksys Personal Hemodialysis System.

The first objective of this study was to validate the use of water at 85°C ± 5°C to achieve high-level disinfection of a clean-in-place extracorporeal dialysis circuit. The second objective was to demonstrate that applying this hot water method to the entire fluid pathways of a newly designed dialysis instrument, including an integral reverse-osmosis membrane, routinely allowed the production of back-filtered dialysate meeting the U.S. Pharmacopeia (USP) standard for the water for injection (WFI). In a first study, six dialyzers were inoculated with P. aeruginosa, incubated, and subjected to 75°C water for 30 minutes. No organisms could be recovered from the experimental dialyzers nor from three negative controls, but they were recovered from three positive controls. In a second study, the carbon tanks in the water inlet line and the dialysate tank were both inoculated with massive amounts of dialysis water-adapted Gram-negative organisms, followed by seven dialysis treatments using bovine blood, where the fifth and sixth procedures were separated by 2 idle days and the sixth and seventh procedures were separated by 3 idle days. In addition, the bovine blood used in each treatment was highly contaminated. In every case, the back-filtered dialysate met the WFI standard. From the above results we conclude that a hot water disinfection process is efficacious in reducing even grossly exaggerated contamination in the Aksys personal hemodialysis system to the point where it can produce water and dialysate that greatly exceed the Association for the Advancement of Medical Instrumentation (AAMI) standards and priming and rinse-back solution (back-filtered dialysate) that meets the USP standard for WFI.

Ribosome and free amino acid content in muscle during hemodialysis

Patients (N = 8) with chronic renal failure and uremia treated with hospital hemodialysis were in a pilot study investigated before and after a single hemodialysis session. The extracorporeal dialysis circuit was flushed regularly with saline to avoid clotting and the use of heparin. Percutaneous skeletal muscle biopsies were taken before and after the dialysis to determine the content of free amino acids together with the concentration and size distribution of ribosomes before and after dialysis. After dialysis the alanine concentration in muscle decreased by 20% (P less than 0.05), while all other amino acids were unaffected. The total ribosome concentration per mg of DNA decreased by 31% (P less than 0.01) and the relative proportion of polyribosomes by 7% (P less than 0.05) after the dialysis compared to predialytic values. All individual plasma amino acids decreased during the dialysis procedure except for threonine and arginine, which were unaltered, and leucine and isoleucine, which increased. The decline in ribosome and polyribosome content together with the changes in amino acid levels indicate a low capacity for protein synthesis and increased catabolism in muscle of hemodialyzed patients.

Influence of uremia and hemodialysis on circulating interleukin-1 and tumor necrosis factor α

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) were determined in the plasma of long-term hemodialysis (HD) patients and uremic (UR) patients undergoing their first dialysis session using either cellulosic (CUP) or synthetic (PAN-AN 69) membrane-equipped dialyzers. In long-term HD patients, plasma IL-1 and TNF alpha levels were significantly increased compared to their levels in normal subjects. During a single dialysis session, a significant increase in IL-1 but not in TNF alpha was observed. In not yet dialyzed UR patients, IL-1 plasma levels did not differ from those observed in normal subjects. By contrast, TNF alpha was found significantly increased although less than in long-term HD patients. During the first dialysis session, no significant increase was observed in the levels of either monokine. Lastly, regardless of the group of patients, no significant influence of the dialysis membrane could be detected, suggesting that the observed changes are not exclusively secondary to the activation of complement. Altogether, these results suggest that the passage of the blood through the extracorporeal dialysis circuit triggers the secretion of IL-1 and further exacerbates that of TNF alpha by monocytes. The presence of increased TNF alpha in the plasma of first-dialysis UR patients suggests that factors unrelated to dialysis contribute to the activation of monocytes in these patients. Lastly, the concomitant presence of IL-1 and TNF alpha in the plasma of long-term HD patients could be responsible for some of the clinical features observed in these patients, and provides strong evidence favoring the concept that HD can be assimilated to a recurrent acute-phase inflammatory response.

Hemodialysis without anticoagulation: One-year prospective trial in hospitalized patients at risk for bleeding

This prospective study evaluated a protocol for hemodialysis without anticoagulation in a diverse group of hospitalized patients in unstable condition with relative contraindications to anticoagulation. Of 262 attempts at hemodialysis without anticoagulation in 49 patients, 239 hemodialysis treatments (91 percent) were successfully completed. Approximately 7 percent of the attempts required conversion to a low-dose heparin regimen because of clotting in the extracorporeal dialysis circuit. Fewer than 2 percent of the dialysis treatments resulted in clotting in the extracorporeal circuit sufficient to interrupt hemodialysis. Partial thromboplastin times and activated clotting times did not change during these hemodialysis treatments. Solute clearance, ultrafiltration rate, and decrements in arterial oxygen concentration and platelet count were not different from those in patients who underwent hemodialysis with anticoagulation. There were no episodes of accelerated bleeding associated with this dialysis method. This study indicates that hemodialysis without anticoagulation can be reliable and effective in closely monitored situations.

Shunt haemodynamics and extracorporeal dialysis: an electrical resistance network analysis

A time-dependent resistance model is used to study haemodynamic aspects of haemodialysis treatment. In the first part of the paper one model circuit, consisting of a pressure source, upstream and downstream resistances and a branching resistance, is shown to represent the haemodynamics of any type of arteriovenous fistula (AVF). Simple algebraic relations are derived for the haemodynamic determinants of AVFs, including finger ischaemia and AVF-maturation. The second part of the paper analyses the influences of a two-needle extracorporeal dialysis (ECD) circuit on the systemic vascular haemodynamics. The main result of the analysis is that the ECD-circuit can be considered as virtually independent of the systemic circulation. Consequently the dialysis flow does not depend on systemic vascular determinants and there are no instantaneous changes in the systemic circulation after switching on the ECD circuit. The ECD flow at onset of AVF collapse is shown to be (slightly) larger than the undisturbed AVF flow. Hence, onset of collapse strongly depends on the systemic blood pressure and vascular resistances. It can be used diagnostically to assess AVF capacities. Optimisation of haemodialysis through the ECD circuit is predicted to be inefficient.