Optimization of high-efficiency hemodialysis by detection and correction of fistula dysfunction

Recirculation studies were performed in 103 patients treated with high-efficiency dialysis over a 14 month period. Fistulograms were performed on 22 out of 25 patients with greater than 0.15 fractional recirculation at a 400 ml/minute blood pump setting. Clinically significant abnormalities were found in 82% (N = 18) and treated in 17. Two patients had second episodes of elevated recirculations and were treated again within the period of follow-up. Treatment with angioplasty (N = 11) or surgical revision (N = 8) resulted in a fall in recirculation from 0.33 +/- 0.04 to 0.12 +/- 0.02 (P = 0.001). The fractional reduction of urea clearance due to recirculation fell from 0.20 +/- 0.03 to 0.08 +/- 0.02 (P = 0.001) and the effective urea clearance of the dialysis treatment rose by 16% from 193 +/- 7 ml/min to 224 +/- 6 ml/min (P = 0.001). Pre-dialysis BUN fell from 72 +/- 4 mg/100 ml to 62 +/- 3 mg/100 ml (P = 0.012). There was no correlation between venous pressure (VP) at 400 ml/min blood pump setting and recirculation (R2 = 0.04), although VP changed significantly comparing values before and after fistula repair (211 +/- 10 vs. 186 +/- 7 mm Hg, P = 0.012). Venous pressures in 20 of the patients in our dialysis unit with recirculations of less than 0.10 were 201 +/- 6 mm Hg (P = NS compared to patients with recirculation greater than or equal to 0.15 at 400 ml/min blood flow).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effective blood flow and recirculation rates in internal jugular vein twin catheters: measurement by ultrasound velocity dilution

The ultrasound dilution technology (Transonic Systems, Ithaca, NY) is a reliable method to assess blood flow (Qb) and recirculation rates (R) in vascular access during hemodialysis. However, the information available on these parameters for central venous dialysis catheters remains scarce at this point. Real Qb and R were evaluated in 33 well-functioning TwinCath (Medcomp, Harleysville, PA) inserted as mid- or long-term hemodialysis vascular access (mean duration since insertion, 270 +/- 253 days); all were implanted into the right internal jugular vein with their multiperforated distal tips located in the superior vena cava or right atrium. Several types of dialysis machines were used (Monitral and AK100, Hospal-Gambro, Lyon, France; 2008E and 4008E, Fresenius, Bad Homburg, Germany). Real Qb was measured with the ultrasound dilution method and compared with the set Qb (indicated by the dialysis machine); R, also evaluated by ultrasound dilution, was evaluated at various Qb with nonreversed lines; therefore, a total of 121 measures were performed. Arterial and venous pressures (PA and PV) were recorded simultaneously. The 33 measures at a set Qb of 200 mL/min showed a mean effective Qb of 210 +/- 18 mL/min and a mean R of 5.3 +/- 5.3%. At a Qb of 300 mL/min, 33 repeated measures resulted in mean effective Qb of 303 +/- 21 mL/min and R of 8.5 +/- 7.0%; 28 measures performed at a set Qb of 350 mL/min showed that the effective Qb was 336 +/- 24 mL/min and that R was 7.8% +/- 6.7%. Finally, an effective Qb of 372 +/- 26 mL/min and an R of 10.9 +/- 8.6% were found for the 27 measures performed at an indicated Qb of 400 mL/min. The difference between indicated and effective Qb was particularly significant for set Qb equal to or above 350 mL/min (P < 0.001). Variable correlations were observed between obtained parameters: Qb eff and R (r = 0.34), PV and R (r = 0.36), Qb eff and PV (r = 0.78), Qb eff and PA (r = 0.71), and PV and PA (r = 0.53). In conclusion, TwinCath delivers an effective Qb of nearly 375 mL/min when Qb is set at 400 mL/min on most dialysis machines. Mean R in TwinCath varies between 5% and 11% for Qb within the range of 200 to 400 mL/min. In well-functioning TwinCath, the ratio between PV and Qb remains usually below 0.5.     

Increasing blood flow increases kt/V(urea) and potassium removal but fails to improve phosphate removal

BACKGROUND: Hyperphosphatemia and hyperkalemia are major determinants of morbidity and mortality in hemodialysis patients. Half of the dialysis population suffers from hyperphosphatemia which is now recognized as an important cardiovascular disease risk factor. It is, therefore, necessary to improve the removal of these molecules. In this study, we investigated the effect of enhancing blood flow on Kt/V for urea (Kt/Vu), potassium and phosphate removal. METHODS: Thirteen patients were investigated in a randomized, cross-over, prospective study using 3 blood flows (Qb) of 200,250 and 300 ml/min which gave 39 standardized high-flux hemodialysis treatments. Effective blood flows were measured by ultrasonic flow meter. Quantification of delivered dialysis dose was performed by partial dialysate and ultrafiltrate collection for the determination of potassium and phosphate removal and by blood urea concentrations for determination of Kt/Vu. RESULTS: Kt/Vu rose significantly from 1.10 +/- 0.14 to 1.22 +/- 0.14 and finally to 1.39 +/- 0.16 (p = 0.0001) with increasing Qb similar to the increase in potassium removal from 53.0 +/- 2.4 to 63.4 +/- 2.6 and to 74.2 +/- 3.8 mMol (p = 0.01). Phosphate removal only improved from 28.1 +/- 1.3 to 31.4 +/- 1.5 (p = 0.050) when Qb was increased from 200 to 250 ml/min but remained unchanged at 31.2 +/- 1.5 mMol (NS compared to phosphate removal at Qb = 250 ml/min) when Qb was increased to 300 ml/min. CONCLUSIONS: Increasing delivered Kt/Vu and potassium removal with higher Qb fails to produce the same desired effect with phosphate removal during high-flux hemodialysis.     

Expected flow parameters within hemodialysis access and selection for remedial intervention of nonmaturing conduits

BACKGROUND: Persistent poor patency rates of arteriovenous fistulae and bridge grafts for dialysis access prompted us to investigate whether flow parameters derived from an initial postconstruction, precannulation duplex study could predict access longevity or direct remedial procedures to salvage nonmaturing conduits. METHODS: We analyzed 125 consecutive dialysis access conduits (34 forearm fistulae, 53 arm fistulae, 38 prosthetic bridge grafts, 108 patients, 82 male/26 female, average age 58 years) over the past 5 years having early (2 to 8 weeks) duplex scanning done prior to attempted hemodialysis cannulation. Velocity waveforms were recorded in the arterial inflow, arterial and venous anastomoses, mid-conduit, and in the venous outflow with averaging of volume flow rate (product of average velocity and cross-sectional area) measured at 3 mid-conduit sites. Conduits were deemed "adequate" for dialysis cannulation or "nonmaturing" by the presence of detected high-grade stenoses (peak systolic velocity >400cm/s, velocity ratio >3, and minimal diameter <2 to 3 mm) and subjected to remedial interventions (endovascular or open). Subsequent access function for hemodialysis use and late patency were recorded and correlated with early duplex findings. RESULTS: Average flow rates (forearm fistula 784 +/- 623 mL/min, arm fistula 1400 +/- 850, bridge graft 1270 +/- 604) and mid-conduit peak-systolic velocities (215 +/- 214 cm/s forearm fistula vs 312 +/- 194 arm fistula) differed between conduit type and location. Remedial interventions were needed in 10 (26%) bridge grafts and 18 (21%) fistulae "nonmaturing" due to occlusive lesions. Conduit flow rates differentiated "nonmaturing" (606 +/- 769 mL/min) and "maturing" (1140 +/- 857) fistulae (P = .01). A threshold conduit flow rate of 800 mL/min better discriminated failing and functional fistulae and bridge grafts (accuracy 77%) than a flow rate greater or less than 500 mL/min (accuracy 67%). Remedial interventions doubled average flow rates of "nonmaturing" accesses (from 605 to 1159 mL/min) to values similar to "mature, functional" conduits (1374 mL/min) and facilitated a mean duration of patency (12.9 months) equivalent to conduits not needing remedial interventions (11.5 months). CONCLUSIONS: Duplex-derived hemodynamic parameters characterized early dialysis access conduit function, prognosticated access patency, guided necessary remedial interventions, and facilitated favorable access longevity.     

Bridging to a high flow upper arm native fistula for hemodialysis with the LifeSite Hemodialysis Access System

Permanent vascular access for chronic hemodialysis requires a reliable structure with adequate blood flow. Endogenous arteriovenous (AV) fistulas offer the best outcomes, but standard radiocephalic fistulas are not always feasible. A reliable alternative is a transposed basilic vein-brachial artery AV fistula, which offers a number of advantages over synthetic AV grafts. The transposed basilic vein fistula provides high flow rates along with low rates of infection, thrombosis, and other complications; however, longer maturation times may be nec-essary. This longer maturation time may necessitate the use of a "bridge device" for access. The new, fully subcutaneous vascular access device - the LifeSite(R) hemodialysis Access System - offers several significant advantages over a standard dialysis catheter as a bridge device: higher flow rates without recirculation, as well as lower rates of infection, thrombosis, and hospitalization. This article describes the surgical procedure for the creation of the transposed basilic vein fistula and the implantation procedure for the LifeSite System. We report on the use of this combined sequential approach to vascular access in 14 patients with excellent results. All 14 patients initially implanted with the LifeSite System were successfully bridged to a functional transposed basilic vein fistula. The mean flow rate with the LifeSite System was 450 ml/min; only one device had to be removed due to infection in an HIV-positive patient, and no other complications were observed. The mean time to maturation of the transposed basilic vein fistula was 6 months; the upper arm fistulas delivered a mean flow rate of 1100 ml/min with a 100% patency rate at 6 months. The sequential use of the LifeSite System and a transposed basilic vein fistula represents a valuable approach to increasing the usage of a high flow native AV fistula.     

Prevention of hemodialysis fistula thrombosis. Early detection of venous stenoses

Venous dialysis pressures were measured consecutively in 168 chronic hemodialysis patients for 265 patient-years of monitored dialysis. Venous dialysis pressure greater than 150 mm Hg measured by the protocol were considered elevated. Seventy-three patients had elevated venous dialysis pressures and 58 agreed to undergo elective venography (fistulogram). Fifty of 58 patients studied (86%) had significant venous stenoses. A combination of percutaneous transluminal angioplasty (PTA) and surgical revision were used to electively treat these stenoses. Early detection and treatment of these stenoses decreased fistula thrombosis and fistula replacement threefold compared with our earlier experiences. Patients with elevated venous dialysis pressure who were venogramed and treated had an occurrence of fistula thrombosis similar to patients with normal dialysis pressure (0.15 and 0.13 episodes per patient year of dialysis respectively, P = NS). In contrast patients with elevated venous dialysis pressure who refused elective fistulogram and treatment averaged 1.4 episodes of thrombosis per patient year of dialysis (P less than 0.001) compared to both other groups). We conclude that elevated venous dialysis pressure is a reliable method of detecting fistula stenoses and that the elective treatment of these stenoses significantly decreases fistula thrombosis and fistula loss.     

In Vivo Measurement of Blood Recirculation During “Y” Type Single Needle Dialysis

A method has been described and validated for obtaining a sample of blood, without separate venapuncture, which has the same urea and creatinine composition as systemic venous blood during hemodialysis. Using this technique, recirculation in vivo during “Y” type single needle dialysis, measured in 20 bovine fistulas, ranged from 6.9% to 56.5% and averaged 19.4% of blood flow rate as calculated from blood urea nitrogen; and averaged 22.0% with a range of 3.3% to 62.1% of blood flow rate as calculated from serum creatinine concentration. These results suggest that fistula puncture methods and devices that eliminate recirculation in the ex vivo blood circuit should be used to maximize dialysis efficiency.     

Acute Symptoms During and Between Hemodialysis: The Relative Role of Speed, Duration, and Biocompatibility of Dialysis

Abstract: The relationship between hemodialysis (HD) symptoms and dialyzer membrane composition and area, blood–flow, treatment duration, urea removal, ultrafiltration volume, leukocyte activation, and complement generation (C3a) was studied in 20 patients undergoing 234 HD treatments by 12 different modes in random order using Cuprophan, hemophane, or polyamide membranes with small or large membrane areas with high Qb (400 ml/min) and short duration (2 h) or low Qb (200 ml/min) and long duration (4 h). Fewer symptoms occurred during the 2–h HD at high Qb than during the 4–h HD with low Qb (19% vs. 32%, p = 0. 0351). No differences were observed between different dialyzer membranes or areas. More intradialytic symptoms occurred when urea elimination was high than it was low (p = 0. 0044). Leukocyte activation (leukocyte drop) after 15 min of dialysis and complement generation did not influence symptom incidence. Blood pressure changes were mainly influenced by ultrafiltration volume (p < 0. 001). Symptoms between dialyses were determined by urea removal and ultrafiltration. Membrane, area, or Qb were of no importance. Thus, duration of dialysis, urea removal, and demand for ultrafiltration, but not membrane composition, area, or biocompatability, are important for the development of HD–related symptoms.     

Vascular access for hemodialysis

A well-functioning vascular access for hemodialysis plays a key role in the quality of life and clinical outcome of dialysis patients. A vascular access for dialysis is considered to be adequate when it provides a blood flow of at least 250 ml/min in the standard dialysis and up to 350-400 ml/min in the high-efficiency dialysis. So far, Cimino-Brescia arterio-venous fistula still remains the gold standard among the available vascular accesses. It should be the first-choice vascular access. Unfortunately, due to the growing age of patients requiring dialysis, to the late-referral phenomenon, to the poor forearm vascular district, and to the increase in acute forms of renal disease, the use of vascular prostheses and central venous catheter becomes more and more frequent. The most important complications of vascular access are stenoses, thromboses, infections. Infections, more frequent in synthetic vascular access than in native fistulas, are responsible for the increase in patients' morbidity and, consequently, in public health costs. An integrated multi-professional approach of vascular access, involving nephrologists, vascular surgeons, interventional radiologists, and trained dialysis nurses should be implemented in order to early detect vascular access complications and failure.     

ACCESS RECIRCULATION

A 72-year-old white female with end-stage renal disease (ESRD) secondary to chronic glomerulonephritis has been on chronic hemodialysis for the past one and a half years. She has a history of congestive heart failure which has not been symptomatic since she began dialysis. She weighs 47 kg (103.4 lbs) and receives 3 hr of "conventional" hemodialysis with a blood flow rate of 350 ml/min which is well tolerated. Treatments are provided using a left upper arm polytetraflourethylene (PTFE) graft. Monthly percentage reduction in urea (PRU) values have been approximately 65%. However, her most recent PRU was 57% (predialysis blood urea nitrogen (BUN) 82 mg/dl, postdialysis BUN 35 mg/dl). Since her treatment parameters had not been changed, recirculation studies were obtained. The BUN values were: peripheral vein (P)—58 mg/dl, arterial line (A)—48 mg/dl, venous line (V)—23 mg/dl. Calculated recirculation was 29% ([P - A]/[P - V], 158 - 48]/[58 - 23]). The high level of recirculation prompted radiologic evaluation of the access. A fistulogram, including views of arterial inflow and central veins, showed no stenotic lesions. Needle placement was reviewed and found to be satisfactory. Repeat recirculation studies yielded similar results .     

超声稀释法监测血液透析患者的内瘘功能

目的对维持性血液透析患者进行内瘘血流量（Qb）及再循环率（R％）测定，了解血液透析患者的内瘘功能状态。方法在患者血液透析开始后30min及结束前1h采用超声稀释法测定内瘘功能。对内瘘血流量过低（Qb〈600ml／min）及过高（Qb〉1800ml／min）的患者进行彩色多普勒超声检查。测量内瘘头静脉内径、桡动脉内径、肱动脉内径及平均血流速度并排除血管腔有无狭窄。结果180例患者中的163例成功进行了内瘘功能测定，3例再循环率〉0，占0．02％。平均Qb（1010．3±662．6）ml／min，40例Qb〈600ml／min（24．5％，低流量组），104例Qb为600-1800ml／min（63.8％，正常流量组），19例Qb〉1800ml／min（11．7％，高流量组）。多普勒超声检查低流量组10例，高流量组7例。两组比较在头静脉内径、桡动脉内径、流速、肱动脉流速方面差异均有统计学意义。结论超声稀释法评定血管内瘘功能有较好的敏感性和特异性，是血管通路（包括自身血管和人造血管）功能监测的一种良好的手段。     

Haemodialysis recirculation detected by the three-sample method is an artefact

The efficiency of haemodialysis may be limited by recirculationof blood between venous and arterial needles. Recirculationcan be detected directly using a saline dilution method butis most commonly calculated from the urea concentrations ofsimultaneous samples from venous and arterial lines and a peripheralvein (three-sample method). The methods detect markedly differentrates of recirculation in similar study populations. To investigatethe possibility that the methods detect different phenomena,we performed both tests on 16 haemodialysis patients at variousextracorporeal blood flow rates (Qb). The saline dilution methodshowed no recirculation in any of the patients, whereas thethree-sample method indicated recirculation in all patients.The three-sample method indicated a mean recirculation fractionof 12.5% (SD 6.1) and was not influenced by changing Qb, suggestingthat it was not detecting fistula recirculation. The three-samplemethod detects a solute concentration difference between arterialblood and peripheral blood during dialysis. There appears tobe a disequilibrium between a central pool, represented by thearterial sample, and a poorly perfused peripheral pool, relativelyisolated from the dialysis process, represented by the peripheralvenous sample. The three-sample method for detecting recirculationshould be abandoned.     

Comparison of arteriovenous fistula recirculation by thermodilution and urea - based method

Objective: To compare arteriovenous fistula recirculation by thermodilution technique and urea based two needle slow flow method. Design: Comparative cross-sectional study. Place and Duration of Study: Hemodialysis Unit of Nephrology Department of Shaikh Zayed Hospital, Lahore, from October 2005 to December 2005. Patients and Methods: Thirty one patients with end stage renal disease on maintenance hemodialysis through arteriovenous fistula were selected on purposive design. Hemodialysis was done on Fresenius 4008 S machines with in-built blood temperature monitoring module to measure recirculation by thermodilution method. Recirculation by the thermodilution method was calculated with the blood flow rate of 300 milliliter /minute and dialysate flow of 500ml /minute. Access recirculation by urea based method was calculated by taking three blood samples for blood urea nitrogen. Two samples were taken simultaneously from the arterial and venous ports respectively. Third sample was taken from the arterial port after slowing the blood flow pump to 50 milliliter/minute and waiting for 30 seconds. Relationship of thermodilution and urea based method was assessed by calculating Pearson correlation coefficient (r). Results: Out of 31 patients, 18 (58.1%) were males, whereas 13 (41.9%) were females. Their mean age was 47.29 +/- 13.42 years. Mean access recirculation by thermodilution method was 7.31 +/- 3.03 and by urea based method was 9.55 +/- 6.64. Correlation coefficient (r) was 0.706 with p-value of < 0.001, which was highly significant. Conclusion: Arteriovenous fistula recirculation calculated by thermo-dilution technique has a strong correlation with the recirculation calculated by the two-needle urea based method.     

Factors influencing permanent catheter performance

Permanent dual lumen catheters (PDLC) provide an alternative vascular access in patients considered unsuitable for arteriovenous fistula, graft or peritoneal dialysis. However, the use of PDLC is often complicated by inadequate blood flow. The aim of this study was to identify catheter dysfunctions. We studied prospec-tively 57 chronic hemodialyzed patients, 73+/-11 years of age, with PDLC for 18+/-14 (1-48) months. Catheters were tunneled in silicone (MedComp Tesio n= 40) or in polyurethane (Permcath Quinton n = 11, GamCath Gambro n = 6) in left or right internal jugular (n = 49), in left or right subclavian (n = 3) and in right femoral vein (n = 5). We studied the blood viscosity indices (hematocrit, total protein, cholesterol and triglycerides), catheter intra-dialytic parameters (pre-pump and venous pressure), localization of the catheter tip (superior vena cava = SVC, right atrium = RA, inferior vena cava = IVC), blood pressure before and after hemodialysis during the 3 last dialyses, use of anticoagulant (ACT) or antiaggregant therapy (AAT) and previous infectious episodes. The mean blood flow was 269+/-37 ml/min (median 280 ml/min). The patients were divided according to the median value into groups I (Qb < 280, n = 28) and group II (Qb > 280, n =29). Results: Blood viscosity, patients' mean arterial pressure and venous catheter line pressure did not differ between the two groups. Pre-pump pressure, at the start and at the end of treatment, was higher in group I. ACT, AAT and previous infectious episodes could not explain the low-performance. Blood flows of catheters localized in RA, SVC, and in IVC were respectively 287+/-20, 268+/-39, 244+/-27 ml/min. In the first case the Qb was significantly higher than IVC (p = 0.03) and SVC (p = 0.04). In conclusion, the most important factor influencing blood flow rates seems to be the position of the catheter tip in the venous system. The best blood flows were found in catheters with the tip localized in the right cardiac cavities, while PLDC placed in inferior vena cava showed lower blood flow.     

Arteriovenous fistulas for dialysis: Blood flow,viscosity, and long-term patency

A prospective study of the influence of blood flow at the time of operation on subsequent performance of dialysis fistulas is reported. Flow was measured in 33 consecutive arteriovenous fistulas using an electromagnetic flowmeter. During the mean follow-up time of 7 months (range, 2–12 months), 19 fistulas were used for dialysis, 9 have not yet been used, 4 were never used because of thrombosis or failure to develop adequately, and 1 patient died before using the fistula for hemodialysis. There were 9 complications (thrombosis, stenosis, and failure to develop). Operative blood flow for these 9 fistulas averaged 221 ml/min as compared to 214 ml/min for the group with no subsequent problems. No critical flow rate below which the fistula would not develop could be defined. An analysis of influences on flow rate at the time of operation showed that there was a significant correlation between flow and blood pressure, vessel dimensions, and whole blood viscosity, but it was not possible to predict fistula failure from these data.     

Inflow reduction by distalization of anastomosis treats efficiently high-inflow high-cardiac output vascular access for hemodialysis

The arteriovenous fistula used for vascular access for hemodialysis may contribute to development of congestive heart failure. Theses patients can present with frequent episodes of congestive hear failure. Traditional management of high-inflow, a high-cardiac-output fistula generally involves either closure or banding. Although high-output state can be controlled, the lifeline of the patient is lost. We describe a series of 17 hemodialysis patients (10 men and 7 women) in whom a novel inflow reduction method was employed. All patients had symptoms of heart failure (15 brachiocephalic fistulas and two brachioaxillary bypass grafts) and a fistula inflow rate above 1600 ml/min. The inflow reduction procedure included ligation of the brachial anastomosis and reconstruction of the fistula by using an expanded polytetrafluoroethylene (Gore-Tex Intering) vascular graft in a bypass from the radial artery. The mean (+/- SD) time between fistula creation and the inflow reduction procedure was 30 +/- 17 months. The mean access inflow rate decreased significantly after the inflow reduction procedure, from 3135 +/- 692 to 1025 +/- 551 ml/min (p =0.0001). The mean cardiac output rate decreased from 8 +/- 3.1 to 5.6 +/- 1.7 l/min (p = 0.001) with resolution of symptoms. During the follow-up period thrombosis or stenosis developed in seven patients, three of whom underwent surgical revision. Thirteen of the seventeen accesses (77%) subjected to the inflow reduction procedure remained patent. Access loss was due to failed fistuloplasty or thrombosis. To our knowledge, this is the first report demonstrating that inflow reduction obtained by distalization of the anastomosis of the access fistula is feasible and safe for managing high-inflow, high-cardiac-output fistulas. Longer and larger studies of the inflow reduction procedure and its benefits are needed.     

Optimal Hemodialysis Access

The optimal provision of vascular access for the ESRD patient involves the following: early identification of such patients so that either a primary a/v fistula or a PTFE graft may be created; prospective monitoring of VDP and urea recirculation to detect venous stenoses; intervention with either angio-plasty or surgical revision in cases found to have venous stenosis; and development of a quality assurance plan that monitors thrombosis and fistula replacement rates and seeks causes of fistula thrombosis in patients without an anatomic basis for the clotting.