Year : 2008 | Volume
: 19 | Issue : 5 | Page : 781--784
Predicting Hemodialysis Access Failure with the Measurement of Dialysis Access Recirculation
Javad Salimi, Effat Razeghi, Hossein Karjalian, Alipasha Meysamie, Moosa Dahhaz, Majid Dadmehr
Sina Trauma & Surgery Research Center, School of Medicine, Medical Sciences/University of Tehran, Iran
Sina Trauma and Surgery Research Center, Sina Hospital, Hassan Abad Sq. Tehran 11364
Clinical practice guidelines recommend regular monitoring of hemodialysis (HD) vascular access using methods such as vascular access recirculation (AR), for early detection and correction of access dysfunction. We measured access recirculation using low blood flow method in 51 chronic HD patients. Of these patients, 42 had arteriovenous fistulas and nine had synthetic arteriovenous grafts. The mean access recirculation rate was 8.75%. We conclude that AR reflects the access blood flow and patients with high AR rate due to stenosis should be referred for intervention or revision for prolonging the life of the access.
|How to cite this article:|
Salimi J, Razeghi E, Karjalian H, Meysamie A, Dahhaz M, Dadmehr M. Predicting Hemodialysis Access Failure with the Measurement of Dialysis Access Recirculation.Saudi J Kidney Dis Transpl 2008;19:781-784
|How to cite this URL:|
Salimi J, Razeghi E, Karjalian H, Meysamie A, Dahhaz M, Dadmehr M. Predicting Hemodialysis Access Failure with the Measurement of Dialysis Access Recirculation. Saudi J Kidney Dis Transpl [serial online] 2008 [cited 2020 May 30 ];19:781-784
Available from: http://www.sjkdt.org/text.asp?2008/19/5/781/42458
With an increasing number of elderly patients as well as patients with co-morbid conditions such as vascular disease and diabetes mellitus in the hemodialysis (HD) population, a wellfunctioning mature arteriovenous fistula (AVF) is essential for the delivering HD in these patients. , Malfunction of permanent vascular accesses remains a cause of frequent and costly morbidity among these patients. 
Stenosis of the HD vascular access is common with an occlusion rate of 17–45% at one year. , Therefore, periodic monitoring of the access is recommended; early detection and correction of stenotic lesions can reduce the frequency of thrombosis and the need for highrisk therapy, increase the life of the access and help to reduce the rate of access failure. ,
A variety of techniques such as physical examination, venous pump pressure, percent access recirculation, transonic flow and others are helpful in detecting vascular access dysfunction and improve assessment of the vascular access site. , There is currently no consensus as to the optimum method of screening for stenosis; the most widely used method of screening for stenosis has been the percent access recirculation (%AR) measurement. 
Vascular access recirculation (AR) is defined as the return of dialyzed blood to the arterial segment of the access bypassing the systemic recirculation, thereby resulting in reducing the efficiency of dialysis.  High degrees of recirculation can lead to a significant discrepancy between the amount of HD prescribed and the amount of HD delivered.  Some investigators have suggested that AR of 15% or higher reliably suggests significant stenosis. 
The purpose of the present study was to evaluate AR in chronic renal failure patients for early detection of access stenosis and subsequent intervention or revision to prolong the life of the access.
Materials and Methods
The present single center study was carried out on 51 chronic HD patients with permanent vascular accesses in a university-based HD unit. The medical ethics committee of the Tehran University of Medical Sciences approved this study. Patients' demographic information was collected by research assistants and study nurses.
Vascular access recirculation was measured using blood urea nitrogen (BUN) as the indicator with the low blood flow method as follows. Approximately 30 minutes after the initiation of HD, ultrafiltration was turned off and dialyzer afferent and efferent samples were obtained. Immediately thereafter, the blood flow was reduced to 50 ml/min. A blood sample was drawn from the arterial blood line after sufficient time had been passed to clear 150 percent of the volume between the arterial needle and the sampling point, but no later than 30 seconds after the reduction of access flow to 50 ml/min. The blood samples were sent to the laboratory soon after for measuring the BUN; all measurements were made in one laboratory. The percent recirculation was calculated using the formula %R = (P-A) / (P-V) ×100, where P, A and V refer to urea concentrations in the peripheral blood, pre-dialyzer arterial line and post-dialyzer venous circuit.
A total of 51 patients (30 males and 21 females) with end-stage renal disease receiving maintenance HD were studied; the mean age of the patients was 55.33 ± 15.77 years (range 17 to 85 years). Thirteen patients (25.55) had diabetes mellitus as the cause of ESRD. A history of hypertension was present in 38 patients (74.5%).
The types of HD vascular access in the study patients included native AVF in 82.4% and synthetic arteriovenous grafts in 17.6% of the patients. Forearm fistulas were present in 9.8% while 72.55% of the patients (n = 37) had native fistulas in the upper arm. Synthetic arteriovenous grafts were created in the upper arm in three patients and in the thigh in six other patients. The mean age of the access was 34.19 months (range 1 to 204 months) for AVF and 16 months (range 3 to 30 months) for synthetic arteriovenous grafts. The mean duration on dialysis among the study patients was 46.6 months (2 to 204 months).
The mean systolic blood pressure was 127.25 mmHg and the mean diastolic blood pressure was 77.16 mmHg. Mean recirculation rate was 8.745 with a median value of 4.40. A total of 80.4% of the patients had recirculation rate less than 15%.
There was no significant correlation between AR and gender, age, history of hypertension, diabetes mellitus, type of access, localization of access, access age and duration on dialysis therapy.
The native AVF is considered the vascular access (VA) of choice for HD because of its greater patency and lower complication rates. It is nevertheless prone to dysfunction and failure; mostly due to the occurrence of stenosis.  Vascular access failure secondary to thrombosis is a major cause of morbidity and mortality among patients on HD. The limited number of potential access sites makes access preservation a high priority. 
While it is known that vascular access-related morbidity represents a major portion of the ESRD-related costs (responsible for approximately 15–25% of all hospital admissions), recent data also suggest that this cost associated with vascular access care may be rising.  Because access stenosis is so common and its impact so severe, it is important to identify a safe, reliable and cost-effective method of screening for stenosis. 
Early detection and treatment of stenosis by means of percutaneous transluminal angioplasty has been shown in the literature, to be highly successful in the prevention of HD access thrombosis thereby prolonging the life of the access.  A number of non-randomized studies have shown that prophylactic repair of accesses at risk, either surgically or with interventional angioplasty, prior to thrombosis, significantly prolongs the useful life of the access and reduces the rate of future thrombosis when compared to accesses repaired surgically after a thrombotic event.  Clinical practice patterns for detection and treatment of stenosis in AVFs varies widely and is largely dictated by local customs and expertise.  The most widely used method of screening for stenosis has been the %AR measurement. In contrast, some authors have found %AR to be inaccurate and that it may have a large analytical error.  Tonelli et al  believe that, because measuring AR did not improve utility and is time consuming, AR is not ideally suited for routine screening for access dysfunction in native vessel AVF. According to Tessitore et al,  AR is one of the surrogate markers of access inflow problems and is monitored by about 64% of HD facilities. Nephrologists generally rely on percent urea recirculation test to detect stenosis (two- and three-site method); nevertheless both methods suffer from artifacts and neither has been shown to be superior to the other in detecting stenosis. 
Tonelli et al  suggested that low access blood flow (Qa), and high AR are both associated with access failure and based on recently published Canadian guidelines, recommend regular bi-monthly screening of native vessel AVF, using ultrasound dilution techniques (UDT) to measure both Qa and AR. These guidelines suggest that AR > 5% (in non-urea based method) should be investigated with angiography. In contrast, May et al  believe that (as also recently suggested by others) access blood flow may not be a good predictor of thrombosis of native AVF and that access recirculation may still have a role as a screening test in patients with native AVF.
Hemodialysis access recirculation occurs when dialyzed blood returning through the venous needle reenters the extracorporeal circuit through the arterial needle rather than returning to the systemic circulation. As a result, the efficacy of dialysis is reduced and high degrees of recirculation can lead to a significant discrepancy between the amount of HD prescribed and the amount of HD delivered. High degrees of access recirculation indicate the presence of access stenosis, the most common cause of access thrombosis.  Access recirculation is usually due to high grade venous stenosis which obstruct venous out flow, leading to back flow into the arterial needle. There are two other less common causes. First, access recirculation can be induced by inadequate arterial inflow; in this setting backflow from the venous limb of the access is necessary to support the extracorporeal blood flow rate set by pump. Second, access recirculation can result from improper needle placement. Close proximity of the needles will increase the reentry of dialyzed blood into the arterial needle. In some centers, misplacement of needles is a common source of recirculation, even after such placement had been previously recognized. 
In our study, the mean recirculation rate was 8.7%. Bay et al  have reported recirculation rate of 11.8 ± 9.9% in their patients and Besarab et al  found an average recirculation value of 5.5 ± 0.8% in their patients. Both groups used urea-based method for measurement of recirculation.
Tonelli et al  suggested that AR does not occur until Qa is significantly reduced and is not acceptably sensitive even at very low Qa. According to Besarab,  AR (in the absence of reversed needles) occurs only when access blood flow rates (ABFR) are less than dialyzer blood flow rates (DBFR). It means that recirculation will not occur until ABFR is severely impaired, well below levels of 600 to 800 ml/min at which stage arteriovenous grafts first develop an increased risk for thrombosis. The previous threshold value of urea recirculation of greater then 15 to 20% was based on studies utilizing the traditional peripheral veinthree needle method. Current threshold values for the evaluation of possible stenosis are based upon more accurate methods. Fistulography should be performed if recirculation is greater than 10% by two-needle urea-based method or 5% using non-urea method.  Many nephrologists recommended that urea recirculation be determined quarterly to permit early identification of access stenosis. 
This prospective pilot study has several limitations include the lack of a control group and our inability to calculate sensitivity and specificity for this technique. The size of the study population is small and the follow-up period is limited. Operator error or technical measurement error might have occurred in this study. In addition, our results may not apply to units that currently screen for access dysfunction using other methods. Finally, we were not able to determine the optimal frequency of screening, because all patients were studied only once.
Additional work should be done to confirm the diagnostic importance of, and the optimal screening frequency, in this population.
To summarize, patients on HD in whom indirect methods of assessing access function such as physical examination, venous pump pressure, percent urea recirculation and others, are either borderline or equivocal, Doppler ultrasound may play an adjuvant role to confirming or ruling out the presence of significant stenosis before exposing the patient to the more expensive and invasive angiography.
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