Access Blood Flow Rate Research Articles

Hemodialysis through persistent left superior vena cava. Should it be used?

Background To describe a case of hemodialysis done through persistent left superior vena cava, identified incidentally after a left jugular central venous dialysis catheter insertion, and to discuss its feasibility. Case Summary Single case: A 66-year-old woman was admitted to the ICU with a diagnosis of septic shock, severe pneumonia, and acute renal failure. Hemodialysis was required for acute renal insufficiency. Persistent left superior vena cava (PLSVC) was detected on Chest x-ray after a left jugular central venous dialysis catheter placement. Hemodialysis was uneventful. Using a permanent dialysis catheter placed later through the PLSVC was less efficient. Although no complications were seen during hemodialysis, it was technically difficult (with high pressure in access and low blood flow rate). Conclusion Hemodialysis through PLSVC should remain an exceptional and short-term therapeutic alternative in dialysis patients.

Dialysis efficacy and pain levels in relation to cannulation distance using the buttonhole technique

ObjectiveIn this study, we investigated whether there was any difference in pain and dialysis efficacy when patients who initially entered dialysis with the rope ladder technique were switched to the buttonhole technique.MethodsWe reduced the space between needles and examined the effects on access blood flow rate, dialysis efficacy, and pain levels with BH technique. Forty-four patients participated, 25with dialysis needles placed 5–7 cm apart using the BH technique, and 19 with needles placed 7–10 cm apart.ResultsThere was a significant reduction in the pain sensation in both groups from patients who passed the rope ladder technique to the buttonhole technique from the onset to the sixth month. There was no difference in dialysis efficacy between the patients who passed the lope ladder technique to the buttonhole technique; also, there was no difference in the dialysis efficacy compared to the needle entry interval in two groups of patients who were dialyzed with the BH technique.DiscussionThe BH technique continues to attract interest due to its dramatically reduced pain levels compared to the RL technique and no difference in dialysis efficacy.

P1311IMPORTANCE OF FISTULA POSITION FOR DETECTING STENOSIS WITH VASCULAR ACCESS BLOOD FLOW MEASUREMENT

Abstract Background and Aims Surveillance of vascular access function in patients on chronic hemodialysis (HD) by measuring the access blood flow rate (Qa) is a widely accepted method for early detection of dysfunction. Qa threshold can be lower in the more distal accesses than in the more proximal accesses. However, cut-off values of Qa in different access positions have not yet been established. The aim of our study is to determine the critical values of Qa indicative of stenosis in different access sites. Method Between July 2012 and July 2019, we performed 5798 Qa measurements of native arteriovenous fistulas (AVFs) (wrist [w]: 2932, forearm [fa]: 2035 and elbow/upper arm [e/ua]: 731) in 242 chronic HD patients using Fresenius 5008 and 5008 S blood temperature monitors (BTMs) at the beginning of HD sessions. As reference we performed 512 colour duplex ultrasonographies (CDUSs) and 205 angiographies (ANGs). CDUS was performed as surveillance method independently from the BTM, or at the presence of low Qa and/or clinical signs of access failure. ANG was performed only in CDUS positive cases or at clinical signs of access failure. We performed percutaneous transluminal angioplasty (PTA) in 174 cases and stent implantation in 2 cases. New AVFs were created in 25 cases. The results were evaluated retrospectively according to access positions using Receiver Operating Characteristic (ROC) curve analysis. Results The number of true positive (TP), true negative (TN), false positive (FP), false negative (FN) cases, sensitivity (SENS) and specificity (SPEC) in different AVF sites and Qas are summarised in table below. Conclusion In order to prevent the fistula occlusion, the cut-off Qas can be different in various access positions. Based on our results we suggest 600-650 mL/min for w AVFs, 650-700 mL/min for fa AVFs and 750-800 mL/min for e/ua AVFs as cut-off values.

Quantification of Blood Flow in Dialysis Access Using Custom-Acquisition Protocol and Imaging Methods: A Clinical Validation Study

PurposeTo determine access blood flow (ABF) rate using 2D image sequences acquired with digital subtraction angiography (DSA) and fluoroscopy. Materials and MethodsA total of 23 patients with known or suspected malfunctioning accesses were imaged using 2 filming modes: DSA at 3 or 6 frames/s (F/s), and fluoroscopy at 10 or 15 pulses/s (P/s). ABF rates were quantified using a bolus tracking method based on cross-correlation algorithm and compared with catheter-based thermal dilution (TD) flow measurements. The indicator-dilution curves were fitted with a gamma-variate (GV) curve fitting model to assess the effect on accuracy. Radiation doses were calculated to examine any increased susceptibility to tissue reactions and stochastic effects. ResultsFor DSA images, the absolute percent deviations (mean ± standard error of mean) in computed flow vs TD flow measurements at 3 F/s and 6 F/s were 34% ± 4.5% and 20% ± 4.7%, respectively, without curve fitting, and 31% ± 3.3% and 20% ± 4.1%, respectively, with curve fitting. For fluoroscopic images, the deviations at 10 P/s and 15 P/s were 44% ± 7.3% and 68% ± 10.7%, respectively, without curve fitting and 36% ± 6.4% and 48% ± 7.1%, respectively, with curve fitting. The mean peak skin dose and effective dose at 6 F/s were 3.28 mGy and 75 μSv, respectively. ConclusionsDigital subtraction angiography images obtained at 6 F/s offered the highest accuracy for dialysis access blood flow quantification.

Haemodialysis vascular access function in dialysis patients at the Kenyatta National Hospital

Background: The number of patients requiring renal replacement therapy (RRT) worldwide has been on the rise. Vascular access is the lifeline for these patients when haemodialysis (HD) is the treatment of choice. Access-related morbidity is a leading cause of hospitalization so that the function and patency of access are essential for the optimal management of patients. There is a need to recognize when a vascular access is dysfunctional because intervention must maintain function as well as preserve future vascular access sites. Methods: This was a cross-sectional study that evaluated the haemodialysis vascular access function in patients undergoing chronic haemodialysis at the Kenyatta National Hospital, Nairobi, Kenya. Peak access blood flow rates, urea reduction ratio (URR) and Kt/V were analysed in 150 patients.Results: The temporary (non-tunnelled) central venous dialysis catheters had poor function, with only 48% achieving a mean blood flow rate > 300 mL/min. The comparable rate for arteriovenous fistulae (AVF) was 88% and for tunnelled dialysis catheters 82%. One-quarter of the patients had a URR < 65%. Higher mean blood flow rates were associated with higher URR (P = 0.004) and Kt/V (P = 0.009) values. AVF stenosis was present in 12.5% and thrombosis in 3% of patients. Aneurysms were the commonest AVF complication (47%) but were not haemodynamically significant. Conclusions: Tunnelled haemodialysis catheters offered adequate blood flows and achieved adequate delivered dialysis, comparable to arteriovenous fistulae. Non-tunnelled catheters delivered poor blood flow rates and dialysis dose. Greater blood flow rates were associated with a higher delivered dialysis dose. There is a need for routine surveillance and affordable interventional procedures to prevent loss of vascular access.

Clinical effects of buttonhole cannulation method on hemodialysis patients

Although the buttonhole cannulation method is now widely used as an alternative to the rope-ladder method in most countries, only the latter method is used in Korea. This study was performed to investigate clinical benefit of the buttonhole technique for arteriovenous fistula (AVF) cannulation in maintenance hemodialysis (HD) patients. Thirty-two patients receiving HD via mature AVF were included and AVF cannulation was performed by 20 experienced nurses. During the 8 weeks, AVFs were cannulated by the rope-ladder method with 15-gauge sharp needles. After creating of 2 pairs of tunnel tracks by sharp needles for 7 weeks, AVFs were cannulated by the buttonhole method using 15-gauge blunt needles during the 16 weeks. Vascular access blood flow rate (BFR), dialysis venous pressure (DVP), and dialysis adequacy (Kt/V) were measured within the first week of the two cannulation methods. Cannulation pain, hemostasis time, and nurse's stress were evaluated at the end of the two methods. There were no statistical differences in vascular access BFR (P = 0.139), DVP (P = 0.152), and dialysis adequacy (P = 0.343) between the two methods. However, the buttonhole method shortened hemostasis time (P = 0.001) and decreased cannulation pain (P = 0.001) as well as nurse's stress (P = 0.001) compared with the rope-ladder method. In conclusion, the buttonhole cannulation method improves hemostasis time, cannulation pain, and nurse's stress without a change in vascular access BFR and dialysis adequacy in HD patients.

Is There a Necessity for Individual Blood Water Corrections when Conductivity-Based Access Blood Flow Measurements Are Made?

Background/Aims:Access blood water flow rate (Qaw) can be measured during hemodialysis using an online effective ionic dialysance (EID) methodology. Fresenius employ this methodology in their 2008K dialysis machine. The machine computer converts Qaw to an access blood flow rate (Fresenius Qa) using a generic blood water constant (BWC). We wished to validate this BWC. Methods: 18 patients had Fresenius Qa measurements using the EID and these were compared with a ‘gold standard’ ultrasound dilution methodology (Transonic Qa). Qa values were also obtained by removing the BWC from Fresenius Qa values to obtain the Qaw and recorrecting it with individualized patient factors using hematocrit and total protein values (HctTp Qa). The measurements were repeated after 1 h. Results:There were no significant differences between Fresenius and Transonic, nor between HctTp and Transonic Qa values (p > 0.17). There were strong correlations between both sets of values (r > 0.856; p < 0.001). There was a significant correlation between the pairs of Transonic Qa values (r = 0.823; p < 0.007), but not for Fresenius Qa pairs (r = 0.573; p > 0.07). It was surmised that the BWC was not valid post-dialysis. Conclusion:The generic BWC is comparable to individualized blood water correction factors when Qa measures are made early in dialysis and prior to ultrafiltration treatment.

The influence of between‐needle cannulation distance on the efficacy of hemodialysis treatments

There is a belief that there should be a minimum of 5 cm between two cannulating needles of an arteriovenous fistula. This study examined the effect of reduction of space between needles from 5 cm to 2.5 cm on access recirculation, the measurement of access blood flow rate (by indicator dilution technology), and dialysis efficiency (by effective ionic dialysance). Twelve patients were studied, with half having their dialysis needles placed 2.5 cm apart for five consecutive dialysis treatments followed by placing needles 5 cm apart for a further five consecutive treatments. The other half initiated with 5 cm followed by 2.5 cm distance for a similar number of treatments. All 120 dialyses had successful cannulations with access recirculation excluded. Access blood flow (Qa mL/min) measurement was attempted for each patient twice, with each of the two needle positions. The Qa with needles 2.5 cm apart was 1310.95 ± 525.7 mL/min (M ± SD, n = 21) and was 1001.0 ± 240.4 mL/min when 5 cm apart (n = 22) (p = 0.014). There was a correlation between these two sets of Qa values (r = 0.554; p = 0.011). The effective ionic dialysance values obtained with needles 2.5 cm or 5 cm apart were similar and correlated strongly (r = 0.71; p = 0.000). Hemodialysis treatments using arteriovenous fistulae and two needles as close as 2.5 cm apart are possible without access recirculation and impairment of clearance. Indicator dilution access blood flow measurements are not recommended under these circumstances.

Dysfunctional stenotic hemodialysis arteriovenous fistulae: Effect of percutaneous transluminal angioplasty

Purpose: To study effect of percutaneous transluminal balloon angioplasty (PTA) on dysfunctional stenotic arteriovenous fistulae (AVF). Methods: Between June 2008 to January 2010, 22 patients with dysfunctional stenotic hemodialysis native AVF for whom technically successful PTA were done, were enrolled in the study. AVF dysfunction was shown by a decrease in blood pump flow (Qb) below prescribed level (300-350 ml/min), a decrease in access blood flow rate (Qa) below 400 ml/min and a decrease in urea reduction rate (URR) below 65%. AVF stenoses were diagnosed by duplex ultrasound study and significant stenoses (more than 50% of luminal diameter) were treated by PTA. After PTA, measurements of Qb, Qa, and URR were done and were compared to pre- intervention levels. All AVF were kept on access surveillance program and primary patency rates were assessed at 1, 3, 6 and 12 months. Results: PTA was associated with improvement of AVF hemodynamics as shown by returning of Qb to the prescribed levels with a significant increase by mean of 76(± 26) ml/min (P<0.001) and a significant increase of Qa by mean of 407 (± 92) ml/min (P<0.001) compared to pre- intervention levels. Also PTA was associated with improvement of adequacy of dialysis as shown by a significant increase of URR by a mean of 24.6(± 6.1) % (P<0.001) compared to pre- intervention levels. Primary patency rates of AVF were 95.4%, 68.2 %, 45.4% and 22.7% at 1, 3,6 and 12 months, respectively. Also, primary patency rates were significantly superior in less severe stenoses compared to more severe stenoses with 6 months patency rate of 66.7% versus 20%, respectively (P=0.029). Conclusion: PTA is an effective and safe procedure in the treatment of dysfunctional stenotic haemodialysis native AVF. When successful, it improves AVF haemodynamics, adequacy of dialysis and primary patency rates at short and intermediate terms. Our findings also support the importance of hemodialysis access surveillance programs for early detection of AVF stenosis causing access dysfunction and the pre-emptive PTA which improves access survival

Ultrahigh-pressure versus High-pressure Angioplasty for Treatment of Venous Anastomotic Stenosis in Hemodialysis Grafts: Is There a Difference in Patency?

Ultrahigh-pressure (UHP) balloon catheters were compared with high-pressure (HP) balloon catheters to determine if there was a difference in patency after percutaneous transluminal angioplasty (PTA) of venous anastomotic stenoses. A retrospective study was conducted from January 2001 to September 2005 that included 22 patients with synthetic hemodialysis grafts who underwent 110 PTA procedures for venous anastomotic stenoses. Data collected included graft configuration and location, percent stenosis, balloon type used, residual stenosis, and total access blood flow before and after intervention. Patency from time of initial PTA to the next intervention was estimated with the Kaplan-Meier technique, with initial failures included in the analysis. A total of 55 PTAs were performed in each group. Technical success rate was 96% (n = 106) and clinical success rate was 100%. Median survival times were 4.6 months for the UHP cohort and 5.4 months for the HP group. When each event was considered independent, the difference was significant (P = .014). However, when each PTA event was considered dependent on earlier PTA events, no significant difference in patency was observed (P = .64). The mean increases in access blood flow rate by ultrasound dilution (available for 71 events) after PTA were 264 mL/min with UHP and 524 mL/min with HP (P = .14, Student t test). One minor complication (0.9%) of focal extravasation after PTA occurred and resolved with prolonged balloon inflation. Routine use of UHP for PTA of venous anastomotic stenoses in synthetic hemodialysis grafts was not associated with any significant change in patency compared with routine HP balloon angioplasty.

Vascular access blood flow for hemodialysis: A risk factor for development of cardiovascular complications in hemodialysis patients

Vascular access blood flow rate of 100-350 cm/s and between 500 and 1000 ml/min, points to normal vascular access function and adequate hemodialysis. High blood flow through the arteriovenus fistula overloads the left ventricle inducing left ventricular remodiling. The aim of the study was to establish the degree of correlation between blood flow through the vascular access for hemodialysis and echocardiographic parameters for the assessment of left ventricular hypertrophy and left ventricular dilatation and left ventricular function. The research included 115 patients (M:F 71:44), average age 53.30+/-12.17 years, average length of dialysis 4.51 +/- 4.01 years and average Kt/Vsp index 1.17+/-0.23. The average blood flow through the vascular access for hemodialysis was 662.27+/-301.59 ml/min. EDDLV 54.52+/-6.42 mm, and EDVi 100.80+/-34.62 ml/m2. There is a statistically significant positive correlation between blood flow through vascular access for hemodialysis and EDDLV and EDVi. High blood flow through the vascular access for hemodialysis is an independent risk factor for the development of cardiovascular complications in patients on hemodialysis.

How much can we learn from long-term extension trials in multiple sclerosis?

<h3>Summary</h3> <h3>Background and objectives</h3> Given different sites of stenosis and access blood flow rates (Qa), the criteria for diagnosing fistula stenosis might vary according to anastomotic site. To test this, we analyzed the database of a prospective blinded study seeking an optimal bedside screening program for fistula stenosis. <h3>Design, setting, participants, &amp; measurements</h3> Several methods used during dialysis (physical examination [PE], dynamic and derived static venous pressure [VAPR], dialysis blood pump flow/arterial pressure ratio, and Qa measurement) to diagnose angiographically-proven &gt;50% stenosis were assessed in an unselected population of hemodialysis patients with mature fistulae (43 at the wrist [distal fistulae], 76 at mid-forearm or the elbow [proximal fistulae]). <h3>Results</h3> Prevalence of inflow stenosis was uninfluenced by anastomotic site, whereas outflow stenoses were more prevalent in proximal fistulae. The best test for inflow stenosis was Qa &lt;650 ml/min in distal fistulae and a combination of a positive PE and Qa &lt;900 ml/m in proximal fistulae. In proximal fistulae, PE and VAPR &gt;0.5 were both equally highly diagnostic of outflow stenosis. Tailoring choice of test to site of the anastomosis may also contain the screening-associated workload, by reducing the need to perform PE and measure VAPR, compared with a screening approach regardless of the access location. <h3>Conclusions</h3> Our study shows that an effective bedside screening program with ≥85% accuracy for fistula stenosis can be tailored to the site of the anastomosis, Qa being the tool of choice for the wrist, and PE alone or combined with Qa and VAPR measurements for more proximally-located accesses.

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CHAPTER 4

Access Flow after Angioplasty Predicts Subsequent Arteriovenous Graft Survival

The effectiveness of angioplasty can be assessed by access blood flow (ABF) measurements after the procedure; however, ABF after angioplasty is highly variable. The purpose of this study was to determine if the level of ABF achieved after angioplasty of arteriovenous (AV) grafts was predictive of subsequent graft outcomes. Retrospective review was performed of 51 shunt images in 31 patients who were receiving dialysis via functioning AV grafts. Patients were referred for shunt imaging because of low ABF rates, increased venous pressure, or clinical indications. Only those patients with ABF measurements performed less than 1 month after angioplasty were included. Patients were then followed for at least 12 months after the initial angioplasty and access-related events were recorded (eg, thrombosis, repeat angioplasty, infection, loss of access). Average ABF rates increased from 655 mL/min+/-45 before angioplasty to 946 mL/min+/-50 after angioplasty. The median ABF rate after the procedure was 1,040 mL/min. Grafts with an ABF rate after angioplasty of less than 1,000 mL/min were more likely to require repeat intervention and to exhibit thrombosis within the first 6 months compared with those with ABF rates greater than 1,000 mL/min. They also had a lower 1-year assisted patency rate (ie, graft survival). The most important determinant of flow after angioplasty was the ABF before angioplasty. Grafts with an ABF rate greater than 1,000 mL/min after prophylactic angioplasty required fewer repeat interventions and had longer assisted patency after prophylactic angioplasty than those with ABF rates less than 1,000 mL/min.

Factors Associated With Urea Reduction Ratio in Acute Renal Failure

Prescription and delivery of hemodialysis (HD) in acute renal failure (ARF) may be affected by patient-related factors such as hemodynamic instability, catabolism, variable extracellular fluid volume, and coagulation disturbances. This study was undertaken in a cohort of patients with ARF requiring HD, to quantify patient- and dialysis-related variables that influence dialysis delivery. The urea reduction ratio (URR) was calculated for each HD session. Patient-related variables included age, gender, weight, mean arterial pressure, and Acute Physiological and Chronic Health Evaluation (APACHE) II and Multiple Organ Failure (MOF) scores. Dialysis-related variables were dialyzer characteristics (membrane type, surface area, KoA, and K(UF)), blood flow rate (Qb), session length, anticoagulant use, vascular access, and ultrafiltration volume. The analysis of factors associated with URR was performed using mixed linear statistical models. The cohort consisted of 81 adult patients with ARF who underwent 419 consecutive dialysis sessions. Mean (+/- SD) age was 60 +/- 18 years; 57% were male. At dialysis initiation, APACHE II score was 23 +/- 8 and MOF score 2 +/- 1. The number of HD treatments averaged 5.5 +/- 6.1/patient and 0.8 +/- 0.2/patient/day, mean URR was 54 +/- 15%, and session length 3.2 +/- 1.1 h; 58% used a femoral venous catheter, and 92% polysulfone dialyzers. Among patient-related variables, the only independent predictor of delivered dose of dialysis, as measured by URR was the predialysis weight (P < 0.01). Among the dialysis-related variables, treatment time (P < 0.01), dialyzer surface area (P < 0.01), dialyzer K(UF) (P = 0.04), blood flow rate (P < 0.01), and the use of a femoral venous catheter (P < 0.01) were also independently associated with URR. An interaction between vascular access site and blood flow rate was also found to be significant (P < 0.01). This study underscores the importance of the dialysis prescription parameters and vascular access site in influencing the dialysis dose in critically ill patients, and argues against the importance of patient-related characteristics such as disease severity.

The influence of patient- and facility-specific factors on nutritional status and survival in hemodialysis

Background Parameters of nutritional status, including serum albumin, serum creatinine, and body mass index (BMI), are powerful predictors of mortality and hospitalization in patients with end stage renal disease (ESRD). Patient-specific characteristics and facility-related practice patterns modify certain parameters of nutritional status. We aimed to determine whether patient and facility characteristics modify the risk profiles associated with malnutrition in hemodialysis patients. Methods We analyzed data on 5,234 prevalent hemodialysis patients from the Dialysis Morbidity and Mortality Study (DMMS) Wave 1 for whom information on demographic, clinical, nutritional, and facility-related characteristics were available. We evaluated the associations among facility characteristics and serum albumin, serum creatinine, and BMI, adjusting for the effects of age, sex, race/ethnicity, diabetes, and dialysis vintage. We determined correlates of mortality and hospitalization, focusing on nutritional parameters, facility effects, and the interactions among patient-specific and facility-specific characteristics, albumin, creatinine, and BMI. Results Serum albumin was lower with older age, diabetes, nonblack race, and hemodialysis using a catheter. Serum albumin was higher with annual vascular access surveillance, higher BMI among women, higher urea reduction ratio, among patients in whom dialyzers were reprocessed (particularly with bleach), among dialysis units in which water purification was used, and when vascular access blood flow rates were ≥350 mL/min. Overall survival was decreased with lower albumin, creatinine, and BMI. There were interactions among albumin, age, and vintage. Whereas lower serum albumin concentrations consistently were associated with an increased risk of death, the differences were attenuated among older patients and accentuated among patients of longer vintage. Conclusion Some facility-specific factors are associated with nutritional parameters including serum albumin, serum creatinine, and BMI. The associations of nutritional parameters with mortality and hospitalization vary by age, sex, and vintage but not by facility-specific factors, including those associated with the nutritional parameters themselves.

Detection of Vascular Access Stenosis by Measurement of Access Blood Flow from Ionic Dialysance

Background/Aim: The measurement of the vascular access blood flow rate (Q_a) in chronic hemodialyzed patients was proposed to predict access thrombosis. We have recently presented a new method based on the measurements of ionic dialysance at normal and reversed positions of the blood lines. We evaluate the reliability of the measurement of Q_a by this method in detecting significant access stenoses. Methods: Twenty-five patients on chronic hemodialysis and having a vascular access cannulated with two needles were studied. The Q_a was evaluated by the Diascan^® ionic dialysance (Q_a-id) method and by the ultrasound dilution technique (Q_a-us; Transonic^®) during the same dialysis session. The measurements were available for 23 patients. In addition, the patients had ultrasonography of their fistula followed by angiography, if a stenosis was detected. Results: Q_a-id and Q_a-us were not significantly different, showing a difference in Q_a at 32 ± 469 ml/min. Q_a-id was significantly different between patients with or without stenosis (508 ± 241 vs. 1,125 ± 652 ml/min, p < 0.05). Among patients with a Q_a <500 ml/min by Q_a-id, 5 had a stenosis detected by ultrasonography (sensitivity 83%), and 3 had no stenosis (false-positive rate 18%). Of these 3 patients, 2 had a thrombotic event at 1 and 3 months, suggesting that a more sensitive detection of stenosis for this range of Q_a is needed and that a Q_a <500 ml/min has a higher power to predict thromboses than a stenosis by ultrasonography. Conclusions: The measurement of the access flow rate by the Q_a-id method has a clinical relevance to the detection of vascular access stenosis. An intervention program based on the Q_a-id has to be evaluated.

Analysis of variable flow doppler hemodialysis access flow measurements and comparison with ultrasound dilution

The variable flow (VF) Doppler method determines access blood flow from the pump speed-induced change in Doppler signal between the arterial and venous needles. This study evaluated 35 patients in two analyses to assess VF Doppler measurement reproducibility (54 paired measurements) and compared VF Doppler and ultrasound dilution flow measurements (24 paired measurements). VF Doppler measurement variations were 4% for access flow less than 800 mL/min (n = 17), 6% for access flow of 801 to 1,600 mL/min (n = 22), and 11% for access flow greater than 1,600 mL/min (n = 15). The mean measurement coefficient of variation was 7% for VF Doppler compared with 5% for ultrasound dilution. Correlation coefficients (r) between VF Doppler and ultrasound dilution access flow measurements were 0.79 (n = 24; P < 0.0001), 0.84 for access flow less than 2,000 mL/min (n = 20; P < 0.0001), and 0.91 for access flow less than 1,600 mL/min (n = 18, P < 0.0001). VF Doppler measurements using indicated versus measured pump flow rates correlated highly (r = 0.99; P < 0.0001). VF Doppler therefore yields reproducible access volume flow measurements that correlate with ultrasound dilution measurements. The VF Doppler method is dependent on the pump-induced change in access Doppler signal and therefore is inherently most accurate and reproducible at lower access blood flow rates. This method appears capable of determining access flow rates in the clinically useful range. © 2001 by the National Kidney Foundation, Inc.

Noninvasive transcutaneous determination of access blood flow rate

Current indicator dilution techniques for determining the vascular access blood flow rate (Qa) require reversal of the dialysis blood lines and are time consuming. We have recently described an indicator dilution technique for determining Qa using a novel optical transcutaneous hematocrit (Hct) sensor that does not require reversal of the dialysis lines, and have validated the accuracy of this method (TQa) in vitro. This study compared results using the TQa method with those obtained using a similar indicator dilution technique but which required reversal of the dialysis lines (HD01 Monitor, Transonic Systems, Ithaca, NY, USA) during routine hemodialysis in 59 patients (25 native fistulas and 34 synthetic grafts). The sensor for the TQa method was placed on the skin directly over the access to measure changes in Hct approximately 25 mm downstream of the venous needle. A single 30 mL bolus of saline was infused into the dialyzer venous line over approximately six seconds without reversal of the dialysis blood lines, and the vascular access flow rate was calculated using indicator dilution methods from the time-dependent decrease in the Hct downstream of the venous needle. Two additional small-scale studies were performed to assess the effect skin pigmentation and to evaluate further the reproducibility of the TQa method. Qa values determined by the TQa method were highly correlated with those determined by the HD01 method (N = 72, R2 = 0.948, P < 0.001) over the range of 153 to 2,042 mL/min. There was no significant difference between vascular access flow rates determined by the TQa method and those determined by the HD01 Results from one small-scale study showed that the relationship between Qa values determined by the TQa and the HD01 methods was similar when tested only among black patients (N = 12), suggesting that skin pigmentation is not an important determinant of the accuracy of the TQa The second small-scale study showed that the intratreatment coefficient of variation for the TQa method was 7.8 +/- 5.6% (N = 14). : These results show that transcutaneous measurement of Qa is an accurate, simple, and fast technique for determining Qa without requiring the reversal of the dialysis blood lines.

Variable flow Doppler for hemodialysis access evaluation: theory and clinical feasibility.

Access thrombosis remains an enormous problem for patients on hemodialysis. Current evidence suggests that decreasing access blood flow rate is an important predictor of future access thrombosis and failure. This article describes a method for determining access volume flow and detecting access pathology. The Doppler ultrasound signal downstream from the arterial needle as a function of the variable hemodialysis blood pump flow rate, is used to determine access blood flow. By using this variable flow (VF) Doppler technique compared with duplex volume flow estimates measured in 18 accesses (16 patients with 12 polytetrafluorethylene [PTFE] grafts and 6 autogenous fistulas), the results showed a correlation of 0.83 (p < 0.0001) between these methods. In grafts with lower blood flow rates, aberrant flow patterns were observed, including stagnant or reversed flow during diastole while forward flow was maintained during systole. When reversed diastolic flow was severe, it was accompanied by access recirculation. In conclusion, we report the theory and clinical feasibility of determining access blood flow by using a VF Doppler technique. Measurements are made without the need to determine the access cross sectional area required for duplex volume flow calculations and without the need to reverse the lines required for various indicator dilution techniques. Important information is also obtained about aberrant flow patterns in patients at risk of access failure.