PREDICTIVE MEASURES OF VASCULAR ACCESS THROMBOSIS - A PROSPECTIVE-STUDY

Malfunction of permanent vascular accesses remains a cause of frequent and costly morbidity in patients receiving chronic hemodialy sis (CHD ). Several recommendations for routine monitoring of these permanent v ascular accesses for incipient failure have been proposed. In this stu dy, multiple indicators of incipient vascular access dysfunction, incl uding ''venous'' and ''arterial'' pressures at serial blood flows (200 ml/min, 300 ml/min, and 400 ml/min), percent urea recirculation, Dopp ler ultrasound, and access blood flow by ultrasound dilution technique were simultaneously evaluated in a total of 220 vascular accesses in 170 chronic hemodialysis patients in two separate study periods (6 mon ths apart). The rate of thrombosis was determined within the subsequen t 12 weeks of each study period to assess the short-term predictive po wer of access thrombosis. During the period of follow-up, there were 3 4 thrombotic events in 172 polytetrafluoroethylene (PTFE) grafts and o nly one thrombotic event in 48 arterio-venous fistulas (AVF). Therefor e, the statistical analysis was limited to the PTFE grafts. When graft s with thromboses were compared to those without thrombosis by univari ate analysis, access blood how measured either by ultrasound dilution technique (875 +/- 126 ml/min with thrombosis vs. 1193 +/- 677 ml/min without thrombosis, P = 0.001) or by Doppler ultrasound (762 +/- 420 m l/min with thrombosis vs. 1171 +/- 657 ml/min without thrombosis, P = 0.001) were significantly different in the two groups. There was good correlation (r = 0.79, P = 0.0001) between the blood flows determined by both techniques. The grade of stenosis determined by ultrasound was also a statistically significant predictor (P = 0.02). ''Venous'' and ''arterial'' pressures were numerically similar and were not statisti cally different between the accesses that did and those that did not t hrombose. When multivariate analysis was used, there was a significant ly increased risk of thrombosis only with decreasing access blood flow determined by ultrasound dilution techniques after adjusting for othe r confounding variables. When the average blood flow of all grafts (11 34 ml/min) is considered as the reference access blood flow (relative risk of 1.0), the relative risk of a PTFE thrombotic event within the subsequent 12 weeks was 1.23 at a blood flow 950 ml/min, 1.67 at a blo od flow of 650 ml/min and to 2.39 at a blood flow of 300 ml/min. In su mmary, access blood flow measured by either Dilution or Doppler is a r eliable indicator of subsequent short-term thrombosis risk. Other prop osed methods of evaluating access dysfunction were not useful in our p atients. If simple to use, cost-effective devices to measure dialysis access blood flow become readily available, the measurement of access blood flow will likely become the method of choice for screening of PT FE vascular access dysfunction in hemodialysis patients.