title: Dynamic venous access pressure ratio test for hemodialysis access monitoring.
abstract: 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 (VDP(0)) was recorded at blood flow rates (Q(b)s) from 0 to 600 mL/min and hematocrits varied in steps from 38.4% to 18.2%. An equation for VDP(0) was developed. VAP in patients was calculated as VAP = VDP - VDP(0). VAP ratio (VAPR) was defined as VAP/mean arterial pressure (MAP). VAPR was calculated only if MAP was greater than 75 mm Hg, Q(b) 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.
  
  
  CONCLUSIONS
  The VAPRT is a valuable tool to prospectively monitor for adverse AVG events.
mesh_terms: D000465:Algorithms; D001164:Arteriovenous Fistula / Q000097:blood; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory / Q000295:instrumentation / Q000379:methods*; D001807:Blood Vessel Prosthesis; D002408:Catheters, Indwelling / Q000009:adverse effects; D006083:Graft Occlusion, Vascular / Q000503:physiopathology / Q000517:prevention & control / Q000601:surgery; D006801:Humans; D008432:Mathematical Computing; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011673:Pulsatile Flow; D012039:Regional Blood Flow / Q000502:physiology; D006435:Renal Dialysis / Q000009:adverse effects / Q000379:methods; D018570:Risk Assessment / Q000379:methods; D012680:Sensitivity and Specificity; D014655:Vascular Resistance / Q000502:physiology; D014690:Venous Pressure / Q000502:physiology*