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

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          Background/Aim: The measurement of the vascular access blood flow rate (Q<sub>a</sub>) 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<sub>a</sub> 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<sub>a</sub> was evaluated by the Diascan<sup>®</sup> ionic dialysance (Q<sub>a-id</sub>) method and by the ultrasound dilution technique (Q<sub>a-us</sub>; Transonic<sup>®</sup>) 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<sub>a-id</sub> and Q<sub>a-us</sub> were not significantly different, showing a difference in Q<sub>a</sub> at 32 ± 469 ml/min. Q<sub>a-id</sub> 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<sub>a</sub> <500 ml/min by Q<sub>a-id</sub>, 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<sub>a</sub> is needed and that a Q<sub>a</sub> <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<sub>a-id</sub> method has a clinical relevance to the detection of vascular access stenosis. An intervention program based on the Q<sub>a-id</sub> has to be evaluated.

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          Change in access blood flow over time predicts vascular access thrombosis.

          Vascular access thrombosis accounts for at least $1 billion dollars in annual expenses and 25% of hospitalizations for chronic hemodialysis patients. Low vascular access blood flow (less than 800 ml/min) has been shown to modestly increase the relative risk for thrombosis in the subsequent three months. In this study, it is hypothesized that a time-dependent decrease in vascular access blood flow may be more predictive of subsequent thrombosis especially in vascular accesses with flows more than 800 ml/min, since it would indicate the development of a critical outlet stenosis in the graft. Ninety-five accesses in 91 CHD patients were prospectively followed over 18 months. Vascular access blood flow was measured every six months by the ultrasound dilution technique. Thrombotic events were recorded during the three study periods. A total of 34 thrombotic events in 95 accesses were documented through the total study duration. Accesses that thrombosed had a 22% decrease in vascular access blood flow during the first observation period and a further 41% decrease during the second observation period as compared to 4% drop and 15% increase during the first and second observation periods, respectively, for accesses that did not thrombose. There was an estimated 13.6-fold (95%, confidence interval 2.68 to 69.16) increase in the relative risk of thrombosis for accesses with more than 35% decrease in vascular access blood flow compared to those accesses with no change in blood flow. There was no statistical difference in the average vascular access blood flow of all patients over the study period. Accesses that show a large (>15%) decrement in vascular access blood flow are associated with a high risk of thrombosis. Serial measurements of vascular access blood flow predict access thrombosis.
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            Graft flow as a predictor of thrombosis in hemodialysis grafts.

            The effort to reduce the incidence of graft thrombosis is mainly based on predicting venous stenosis by measuring venous drip chamber pressures. In this study we evaluated whether graft flow measurements, using an ultrasound dilution technique, would be of additional value to identify patients at risk for thrombosis. In fifty consecutive patients with a bridge graft we measured graft flow and venous drip chamber pressure at a dialyzer blood flow of 200 ml/min. The results of these flow measurements were not used for selection of patients, nor for a diagnostic or therapeutic procedure. All thrombotic events and (radiological or surgical) interventions were registered. A total of 17 patient-years were analyzed. In 17 patients an intervention was done, and in 18 patients thrombosis occurred. The incidence rate of thrombosis was higher in patients with a flow 600 ml/min (N = 37; rate ratio 7. 2; 95% CI, range 2.84 to 18.24, P 600 ml/min. In the remaining 32 patients only two developed spontaneous thrombosis. Remarkably, venous drip chamber pressure measurements did not discriminate between patients with graft flow > or < 600 ml/min, and showed a wide range in patients who developed spontaneous thrombosis within two months. We suggest that graft flow measurements are helpful in selecting patients at risk for graft thrombosis.
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              Color doppler ultrasonography imaging to guide transluminal angioplasty of venous stenosis.

              The objective of access surveillance is the early recognition of dysfunction in order to be able to correct the stenosis by angioplasty or surgery before access thrombosis occurs. The advent of color Doppler imaging has enabled studies of color Doppler ultrasonography (CDU) for the guidance of percutaneous transluminal angioplasty (PTA). The aim of the present study was to investigate whether color Doppler imaging alone can be safely and effectively used to diagnose vascular graft access stenoses and guide subsequent PTA. Using the ultrasound velocity dilution method, we measured access blood flow (Qa) during the first hour of hemodialysis every month in patients with grafts as vascular access. When the decrease in Qa from the baseline value was 40% or more, CDU was performed and immediately followed by PTA in the presence of a stenosis of more than 50%. The Qa was then measured during the first dialysis after PTA and one month later. Repeated-measure analysis of variance was applied to evaluate the early and late (after one month) effect of PTA. Twelve PTAs were performed under CDU guidance in nine patients and led to the elimination of the stenosis or its reduction (two cases). The mean Qa was 809 +/- 263 mL/min at baseline, 468 +/- 153 before PTA, and 820 +/- 281 after PTA. The difference between the pre-PTA and post-PTA values was highly significant (P < 0.001), and the mean value after PTA was not different from baseline (P = 0.672). There were no relevant complications directly related to the procedure. The CDU procedure is effective for the diagnosis of vascular access stenosis and as a guide during the PTA procedure. It could improve stenosis screening by avoiding the risks of exposure to ionizing radiation and of adverse reactions to contrast media.

                Author and article information

                Blood Purif
                Blood Purification
                S. Karger AG
                30 January 2002
                : 20
                : 2
                : 177-181
                Departments of a aNephrology, bRadiology, and cUrology, Pitié-Salpêtrière Hospital, Paris, France
                47006 Blood Purif 2002;20:177–181
                © 2002 S. Karger AG, Basel

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