Prediction of failure of native arteriovenous fistulas using 'on-line' fistula flow measurements

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.

Vascular access surveillance by ultrasound dilution blood flow rate (Qa) measurement is widely recommended; however, optimal criteria for detecting stenosis and predicting thrombosis in arteriovenous fistulae (AVFs) are still not clearly defined. In a blinded trial, we evaluated the accuracy of single Qa measurement, Qa adjusted for mean arterial pressure (Qa/MAP), and decrease in Qa over time (dQa) in detecting stenosis and predicting thrombosis in an unselected population of 120 hemodialysis subjects with native forearm AVFs (91 AVFs, located at the wrist; 29 AVFs, located at the midforearm). All AVFs underwent fistulography, which identified greater than 50% stenosis in 54 cases. Receiver operating characteristic curve analysis showed that dQa, Qa, and Qa/MAP have a high stenosis discriminative ability with similar areas under the curve (AUCs), ie, 0.961 +/- 0.025, 0.946 +/- 0.021, and 0.912 +/- 0.032, respectively. In the population as a whole, optimal thresholds for stenosis were Qa less than 750 mL/min alone and in combination with dQa greater than 25% (efficiency, 90%); however, the best threshold depended on anastomotic site; it was Qa less than 750 mL/min for an AVF at the wrist and Qa less than 1,000 mL/min for an AVF in the midforearm. Qa was the best predictor of incipient thrombosis (AUC, 0.981 +/- 0.013) with an optimal threshold at less than 300 mL/min (efficiency, 94%). Pooled intra-assay and interassay variation coefficients were 8.2% for MAP, 7.9% for Qa, and 11.2% for Qa/MAP. Our study shows that ultrasound dilution Qa measurement is a reproducible and highly accurate tool for detecting stenosis and predicting thrombosis in forearm AVFs. Neither Qa/MAP nor dQa improve the diagnostic performance of Qa alone, although its combination with dQa increases the test's sensitivity for stenosis.

Measurement of access blood flow is the preferred noninvasive screening test for hemodialysis arteriovenous (AV) fistula stenosis. However, performance characteristics of the 2 most frequently used ultrasound techniques compared with fistulography remain elusive. We evaluated 59 hemodialysis patients with native forearm AV fistulae who underwent all 3 measurements in a prospective order: the ultrasound dilution technique (UDT), color Doppler ultrasonography (CDUS), and fistulography. Patients with angiographically diagnosed access stenosis underwent angioplasty and were followed up by means of monthly UDT measurements until restenosis occurred within the first 6 months. Both ultrasound techniques predicted access stenosis (P < 0.01). Performance was similar between both techniques, evaluated by receiver operating characteristic curves. Areas under the curve averaged 0.79 (95% confidence interval [CI], 0.66 to 0.91) for UDT and 0.80 (95% CI, 0.65 to 0.94) for CDUS. Correlation between measured UDT and CDUS blood flow rates was 0.37 (Spearman's rho, rho = 0.004). The calculated optimal cutoff value for the prediction of stenosis was 465 mL/min for the UDT and 390 mL/min for the CDUS technique. Access stenosis was diagnosed in 41 patients who subsequently underwent percutaneous angioplasty (PTA), which was successful in 34 patients. Restenosis occurred in 13 patients within the first 6 months after PTA. UDT access blood flow after PTA was significantly lower in these 13 patients compared with the other 21 patients. Our data suggest that blood flow monitoring of AV hemodialysis access by ultrasound provides a reasonable prediction of access stenosis and restenosis.