Predictive value of access blood flow and stenosis in detection of graft failure.

AIMS: Low access flow and the diagnosis of high degrees of venous stenosis have been recommended as indications for prophylactic angioplasty. However, recent studies have shown that prophylactic angioplasty for > 50% stenosis did not prolong graft patency, and that a single flow measurement may not accurately predict graft failure. In this study we compared the value of monthly measurement of access flow and of the maximal degree of stenosis in the detection of graft failure over a three-month period. METHODS: Thirty-nine hemodialysis patients with polytetrafluoroethylene (PTFE) grafts were evaluated by Doppler ultrasound at monthly intervals for three months. Graft failures were defined as thrombosis, or surgical and angioplastic revisions required because of the presence of access recirculation, and patients with graft failure were followed within the subsequent one-month periods of observation. RESULTS: Twelve graft failures occurred during the three-month period of observation. The risk for subsequent graft failure significantly increased at flows < 300 ml/min. Nine (20%) graft failures occurred with stenoses of 30 to 50%, and three (13%) with stenoses of> 50%. The grafts that failed in the second and the third study months had a 25.8% (380 +/- 62 vs. 287 +/- 190 ml/min, p < 0.05) and a 36.5% (393 +/- 142 vs. 226 +/- 41 ml/min, p < 0.05) decrease in access flow, respectively. There was no significant change in access flow for the grafts patent throughout the study (911 +/- 333, 794 +/- 302, and 919 +/383 ml/min, p = ns). No significant increases in maximal stenosis were found for the grafts that failed in the second month (44 +/- 6.1 vs. 48 +/- 15%, p = ns) and the third month (48 +/- 9 vs. 51 +/- 16%, p = ns). There were no significant changes in the maximum stenosis for the grafts patent throughout the three-month study periods (37 +/- 15,43 +/- 11, and 44 +/- 15%, p = ns). CONCLUSIONS: Access flow is a more sensitive predictor of graft failure than stenosis. Examination of trend in decline of access flow is a more powerful indicator to detect graft dysfunction than an individual single flow value.

Predictive value of access blood flow in detecting access thrombosis.

The aim of this study was to evaluate whether repeated measurement of access blood flow (Qac) using the ultrasound dilution technique could predict access failure in patients on hemodialysis. One hundred thirty-one patients were evaluated at intervals of 8 weeks for a period of 6 months. The incidence of thrombosis was determined within each study period. During the 6 month follow-up, 36 thrombotic events occurred in 27 of 68 polytetrafluoroethylene (PTFE) grafts, and only six thrombotic events in 5 of 63 arteriovenous (AV) fistulas. The relative risk for access thrombosis for patients with PTFE grafts was 5.6 times greater than for patients with AV fistulas. Qac was significantly lower in thrombotic compared with patent PTFE grafts (958 +/- 506 ml/min vs 1141 +/- 482 ml/min, p < 0.05). A significant relationship was found between the incidence of subsequent PTFE graft thrombotic events and Qac (p < 0.001). Compared with accesses with high blood flow (1100-1400 ml/min), the risk for subsequent thrombosis tripled in grafts with a Qac of less than 500 ml/min. This relationship was not seen with AV fistulas. In patent PTFE grafts, Qac remained unchanged within each 2 month interval, whereas it decreased in thrombotic PTFE grafts. Thus, repeated measurements of Qac have the potential to predict future access failure in PTFE grafts; however, an increased measuring frequency might improve the predictive value of graft failure with high Qac.

The measurement of blood density to investigate protein deposition at the blood/hollow fiber membrane interface during ultrafiltration.

Concentration polarization and secondary membrane formation change the membrane hydraulic permeability of capillary filters during hemofiltration reducing initial value filtration rates up to 50%. This leads to a significant loss of filter efficiency which must be taken into consideration when designing filters for long-term application such as in implantable artificial kidneys. By measuring blood density uninterrupted over a period of time using the mechanical oscillatory technique it is possible to follow the dynamics of protein deposition at the interface between the blood and capillary walls. The resulting picture of the deposition behaviour can lead to a better understanding of time-dependent filtration where flow and pressure conditions change. Protein deposition (Pt) with polysulfone membranes in relation to the effective capillary surface was in the range of 2.2. mg/(h x cm2) according to a logarithmic function (Pt = a + b x log(t)).