Dynamic venous access pressure ratio test for hemodialysis access monitoring

Background: Early recognition of arteriovenous graft (AVG) dysfunction in hemodialysis (HD) patients followed by prompt corrective procedures reduces AVG thrombosis rates and lengthens access survival. We developed a method to prospectively monitor AVGs that uses an algorithm to calculate venous access pressure (VAP) during HD from the venous drip chamber pressure (VDP). Methods: Sham HD with blood was performed using standard blood tubing and a 1-in. 15-G needle. The pressure needed to overcome circuit resistance at an intra-access pressure of zero (VDP0) was recorded at blood flow rates (QbS) from 0 to 600 mL/min and hematocrits varied in steps from 38.4% to 18.2%. An equation for VDP0 was developed. VAP in patients was calculated as VAP = VDP - VDP0. VAP ratio (VAPR) was defined as VAP/mean arterial pressure (MAP). VAPR was calculated only if MAP was greater than 75 mm Hg, Qb was greater than 200 mL/min, and VDP was greater than 20 mm Hg. A positive VAPR test (VAPRT) result was defined as three consecutive treatments with VAPR exceeding 0.55 during a given month. Sensitivity and specificity of VAPRT to predict a graft event, defined by AVG occlusion or requirement for angioplasty, were calculated. Results: During a 3-month interval, 120 HD patients with AVGs underwent 359 VAPRTs while access outcomes were monitored for 6 months. After 3 months, sensitivity and specificity for detection of a graft event were 70% ± 8% and 88% ± 2% and increased to 74% ± 5% and 92% ± 3% at 6 months, respectively. Conclusion: The VAPRT is a valuable tool to prospectively monitor for adverse AVG events. © 2002 by the National Kidney Foundation, Inc.