Dynamic venous access pressure ratio test for hemodialysis access monitoring [PubMed]

Stanley Frinak, Gerard Zasuwa, Thomas Dunfee, Anatole Besarab, Jerry Yee

Department of Medicine, Division of Nephrology and Hypertension, Henry Ford Hospital, Detroit, Michigan, USA.

American Journal of Kidney Diseases, Vol 40 (4, 2002). pp 760-786

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. CONCLUSION: The VAPRT is a valuable tool to prospectively monitor for adverse AVG events.

Prevention of hemodialysis fistula thrombosis, Early detection of venous stenoses [PubMed]

Steve J. Schwab, John R. Raymond, Moshin Saeed, Glenn E. Newman, Patricia A. Dennis, R. Randal Bollinger

Division of Nephrology, Department of Medicine, Radiology and Surgery, Duke University Medical Center, Durham, North Carolina, USA.

Kidney International, Vol 36 (4, 1989). pp 707-711

Venous dialysis pressures were measured consecutively in 168 chronic hemodialysis patients for 265 patient-years of monitored dialysis. Venous dialysis pressure greater than 150 mm Hg measured by the protocol were considered elevated. Seventy-three patients had elevated venous dialysis pressures and 58 agreed to undergo elective venography (fistulogram). Fifty of 58 patients studied (86%) had significant venous stenoses. A combination of percutaneous transluminal angioplasty (PTA) and surgical revision were used to electively treat these stenoses. Early detection and treatment of these stenoses decreased fistula thrombosis and fistula replacement threefold compared with our earlier experiences. Patients with elevated venous dialysis pressure who were venogramed and treated had an occurrence of fistula thrombosis similar to patients with normal dialysis pressure (0.15 and 0.13 episodes per patient year of dialysis respectively, P = NS). In contrast patients with elevated venous dialysis pressure who refused elective fistulogram and treatment averaged 1.4 episodes of thrombosis per patient year of dialysis (P less than 0.001) compared to both other groups). We conclude that elevated venous dialysis pressure is a reliable method of detecting fistula stenoses and that the elective treatment of these stenoses significantly decreases fistula thrombosis and fistula loss.

Simplified measurement of intra-access pressure [PubMed]

A Besarab, S Frinak, RA Sherman, J Goldman, F Dumler, MV Devita, T Kapoian, F Al- Saghir and T Lubkowski

Department of Medicine, Henry Ford Hospital, Detroit, Michigan, USA.

Journal of the American Society of Nephrology, Vol 9, 284-289, Copyright © 1998 by American Society of Nephrology

The measurement of intra-access pressure (P[IA]) normalized by mean arterial BP (MAP) helps detect venous outlet stenosis and correlates with access blood flow. However, general use of P(IA)/MAP is limited by time and special equipment costs. Bernoulli's equation relates differences between P(IA) (recorded by an external transducer as PT) and the venous drip chamber pressure, PDC; at zero flow, the difference in height (deltaH) between the measuring sites and fluid density determines the pressure deltaPH = P(IA) - P(DC) Therefore, P(DC) and PT measurements were correlated at six different dialysis units, each using one of three different dialysis delivery systems machines. Both dynamic (i.e., with blood flow) and static pressures were measured. Changes in mean BP, zero calibration errors, and hydrostatic height between the transducer and drip chamber accounted for 90% of the variance in P(DC), with deltaPH = -1.6 + 0.74 deltaH (r = 0.88, P < 0.001). The major determinants of static P(IA)/MAP were access type and venous outflow abnormalities. In grafts, flow averaged 555 +/- 45 ml/min for P(IA)/MAP > 0.5 and 1229 +/- 112 ml/min for P(IA)/MAP < 0.5. DeltaPH varied from 9.4 to 17.4 mmHg among the six centers and was related to deltaH between the drip chamber and the armrest of the dialysis chair. Concordance between values of P(IA)/MAP calculated from PT and from P(DC) + deltaPH was excellent. It is concluded that static P(DC) measurements corrected by an appropriate deltaPH can be used to prospectively monitor hemodialysis access grafts for stenosis.

Utility of intra-access pressure monitoring in detecting and correcting venous outlet stenoses prior to thrombosis [PubMed]

Anatole Besarab, Kevin L. Sullivan, Richard P. Ross, and Michael J. Moritz

Division of Nephrology and Hypertension, Department of Medicine, Henry Ford Hospital Detroit, Michigan and the Departments of Radiology and Surgery, College of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.

Kidney International, Vol. 47 (1995), pp. 1364-1373

Vascular access thrombosis is a major problem for hemodialysis patients. Over 7.75 years, we performed intra-access venous pressure monitoring at zero dialyzer blood flow (VP0), correlated VP0 with access anatomy angiographically, and examined the effect of two levels of stenosis, 50% and > 65% luminal diameter reduction (% D) as selection criteria for referral and elective angioplasty or surgical revision upon access outcomes. Summary receiver outcome curves for absolute intra-access pressure (VP0) and intra-access pressure normalized for systemic pressure (VP0/systolic BP) were constructed to evaluate sensitivity and specificity and compared to recirculation and duplex color-flow Doppler. Access outcomes included thrombosis, revision, replacement, and angioplasty rates that were normalized per 100 patient years (100 pt-yrs). During the 7.75 year long study period totaling 832 patient-access years of risk, the percentage of prosthetic bridge grafts increased from 65% to 80%. SROC showed better sensitivity for normalized (VP0/systolic BP) than absolute intra-access pressure (VP0) in grafts. Recirculation had poor predictive power in prosthetic bridge grafts compared to VP0. Predictive power of recirculation was superior to VP0 in native arteriovenous fistulae. The angioplasty rate correlated inversely with the degree of luminal reduction used as selection criterion for referral for angioplasty or surgical revision. A strong inverse relationship between thrombosis rate and the angioplasty rate (R2 = 0.99) but not between thrombosis rate and the number of angiograms performed (R2 = 0.39) was noted. A consistent, yet evolving, intensive graft maintenance protocol produced a 70% decrease in the thrombosis rate, a 79% decrease in the access replacement rate, and an increase in the average age of patent usable vascular accesses from 1.97 to 2.98 years that was associated with a 13-fold increase in the angioplasty rate. We conclude that vascular access monitoring with VP0/systolic BP provides excellent selection criteria for angiographic referral. Intervention for stenotic lesions > 50% D using angioplasty or surgical revision markedly reduces thrombosis and access replacement rates.