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William D Paulson

Publications and source records attributed to William D Paulson.

14 recordsLinked to original sources
PubMed2005

Vascular access as a determinant of adequacy of dialysis.

Vascular accesses consist of permanent arteriovenous (AV) accesses (autogenous fistulas and synthetic grafts) and venous accesses (central venous catheters [CVCs]). AV accesses have fewer complications than venous accesses, and are therefore the preferred hemodialysis access. An important additional issue is whether the type of access influences adequacy of dialysis (i.e. Kt/V). Key limiting factors in delivering adequate Kt/V are blood pump speed (Q(B) ), access recirculation, and treatment time. In general, AV accesses support higher Q(B)S with less negative inflow arterial pressures than CVCs. Well-functioning AV accesses are also less likely to exhibit recirculation. Nevertheless, recirculation commonly develops when AV accesses (usually grafts) develop stenosis with decreased access blood flow. Although extension of treatment time can offset the effects of reduced Q(B) and recirculation, this is often impractical and poorly accepted by patients. In conclusion, AV accesses are superior to venous accesses because they are less prone to complications and are more likely to deliver prescribed Kt/V within prescribed treatment time.

Blood Vessel Prosthesis Implantation↗
PubMed2005

Mathematical model for pressure losses in the hemodialysis graft vascular circuit.

Stenosis-induced thrombosis and abandonment of the hemodialysis synthetic graft is an important cause of morbidity and mortality. The graft vascular circuit is a unique low-resistance shunt that has not yet been systematically evaluated. In this study, we developed a mathematical model of this circuit. Pressure losses (deltaPs) were measured in an in vitro experimental apparatus and compared with losses predicted by equations from the engineering literature. We considered the inflow artery, arterial and venous anastomoses, graft, stenosis, and outflow vein. We found significant differences between equations and experimental results, and attributed these differences to the transitional nature of the flow. Adjustment of the equations led to good agreement with experimental data. The resulting mathematical model predicts relations between stenosis, blood flow, intragraft pressure, and important clinical variables such as mean arterial blood pressure and hematocrit. Application of the model should improve understanding of the hemodynamics of the stenotic graft vascular circuit.

Animals↗
PubMed2005

Access monitoring does not really improve outcomes.

It is widely accepted that hemodialysis access monitoring combined with preemptive percutaneous transluminal angioplasty (PTA) improves outcomes. The many studies that have evaluated monitoring during the last decade provide an opportunity to examine whether this hypothesis is valid. Because synthetic grafts are more likely than autogenous arteriovenous fistulas to benefit from monitoring, this review is restricted to grafts. Recent studies show that monitoring does not accurately predict graft thrombosis or failure, nor does it prolong graft life. However, monitoring can reduce thrombosis, and thereby reduce access-related hospitalizations and use of central venous dialysis catheters. Because preemptive PTA is expensive, however, monitoring does not reduce the cost of access-related care. The limited benefit that monitoring provides emphasizes the urgent need to develop better approaches to solving the problem of graft thrombosis and failure.

Angioplasty, Balloon, Coronary↗
PubMed2003

In vivo validation of glucose pump test for measurement of hemodialysis access flow.

BACKGROUND: The glucose pump test (GPT) is a recently introduced method of measuring hemodialysis access blood flow (Qa). A validation of GPT during dialysis has not yet been done, and performance characteristics of the method have not yet been fully analyzed. METHODS: The authors studied 33 patients (25 synthetic grafts, 8 autogenous arteriovenous fistulae). Qa measurements by ultrasound dilution (UD) and GPT were done in triplicate during dialysis. In GPT, a baseline blood sample (C(1)) was obtained, followed by infusion of a 10% glucose solution (C(i)) through the arterial needle into the access at 16 mL/min (Q(i)). After 11 seconds, a downstream blood sample (C(2)) was aspirated from the venous needle. C(1) and C(2) glucose were measured by glucometer. Qa was computed by the equation: Qa = Q(i)(C(i) - C(2))/(C(2) - C(1)). A model of the access vascular circuit was used to determine the influence of C(2) aspiration on the Qa measurement. RESULTS: Mean Qa was 1413 mL/min by UD versus 1,496 mL/min by GPT (P = 0.11). There was a strong linear correlation between the 2 methods (r = 0.905; P <0.001). The pooled coefficient of variation was 6.4% for UD and 9.6% for GPT. The circuit model showed that aspiration of C(2) causes an increase in Qa (DeltaQa) that depends on the aspiration rate (Q(ASP)) and fraction of resistance in the circuit that is downstream to the venous needle: DeltaQa = Q(ASP)(Downstream resistance)/(Total resistance). The model predicts the overestimate is approximately 62 mL/min for grafts and 120 mL/min for fistulae but may vary depending on the balance of resistances upstream and downstream to the venous needle. CONCLUSION: This study shows that GPT closely correlates with UD, and the method has adequate precision. GPT is an inexpensive method that may help make Qa measurements more widely available than previously possible.

Arteriovenous Shunt, Surgical↗
PubMed2003

A randomized controlled trial of blood flow and stenosis surveillance of hemodialysis grafts.

BACKGROUND: It is widely accepted that hemodialysis graft surveillance combined with correction of stenosis reduces thrombosis and prolongs graft survival. Nevertheless, few randomized controlled trials have evaluated this approach. METHODS: In this randomized controlled trial, 101 patients were assigned to control, flow (Qa), or stenosis groups, and were followed for up to 28 months. All patients had monthly Qa measured by ultrasound dilution and quarterly percent stenosis measured by duplex ultrasound. Referral for angiography was based on the following criteria: (1) control group (N = 34), clinical criteria; (2) flow group (N = 32), Qa <600 mL/min or clinical criteria; and (3) stenosis group (N = 35), stenosis>50% or clinical criteria. Stenosis >or=50% during angiography was corrected by preemptive percutaneous transluminal angioplasty (PTA). RESULTS: The preemptive PTA rate in the control group (0.22/patient year) was two thirds the rate in the flow group (0.34/patient year), and was highest in the stenosis group (0.65/patient year, P < 0.01). The percentage of grafts that thrombosed was similar in the control (47%) and flow groups (53%), but reduced in the stenosis group (29%, P = 0.10). Two-year graft survival was similar in the control (62%), flow (60%), and stenosis groups (64%) (P = 0.89). CONCLUSION: Qa and stenosis surveillance were not associated with improved graft survival, although thrombosis was reduced in the stenosis group. The most important factors in this result may be that monthly Qa and quarterly stenosis measurements were not accurate or timely indicators of risk of thrombosis or progressive stenosis. This study does not support the concept that Qa or stenosis surveillance are superior to aggressive clinical monitoring.

Angioplasty, Balloon↗
PubMed2002

Association between blood pressure, ultrafiltration, and hemodialysis graft thrombosis: a multivariable logistic regression analysis.

Although a low blood flow (Q(a)) is the most important cause of graft thrombosis, several studies have shown that Q(a) measurements do not accurately predict thrombosis. This suggests that additional variables may influence thrombosis. Identification of such variables may be essential to designing surveillance protocols that accurately predict thrombosis. In this nested case-control study, we prospectively followed 105 patients for up to 2.5 years in order to test the association of a number of variables with thrombosis. These included Q(a) (monthly by ultrasound dilution), percentage stenosis (quarterly by duplex ultrasound), mean arterial pressure (MAP), percentage ultrafiltration (%UF) during dialysis (%UF = 100[liters]/[kilogram of weight]), and other variables that defined patient and graft characteristics. Patients were divided into patent (n = 53) and thrombosed groups (n = 52), and MAP and %UF from seven consecutive dialysis sessions were analyzed. In the thrombosed group, the last session was the final session before thrombosis. A multivariable logistic regression model showed that Q(a), MAP (the predialysis average of seven sessions), and %UF (from the last session) were independently associated with thrombosis, whereas all other variables were not. The model yielded the following odds ratios for thrombosis: for a single Q(a) value (reduction of 1,000 mL/min), 12.0 (P < 0.01); for %UF (increase of 4%), 5.3 (P < 0.01); for MAP (reduction of 30 mm Hg), 4.1 (P = 0.02); and for percentage decrease in Q(a) (> or =20% versus <20%), 2.4 (P = 0.12). We conclude that in addition to Q(a), both %UF at the last session before thrombosis and average predialysis MAP from seven sessions are independently associated with thrombosis. These results help explain why Q(a) alone does not accurately predict thrombosis. A prospective study is needed to determine whether %UF at each session and a moving average MAP from seven sessions improve the prediction of thrombosis. However, it should be recognized that a large %UF is a preterminal event that likely provides too short a warning for intervention before thrombosis.

Blood Pressure↗
PubMed2002

Vascular access: anatomy, examination, management.

A systematic approach to managing vascular access problems is the key to reducing current high rates of access thrombosis and failure. This approach begins with a thorough knowledge of vascular access anatomy that, when combined with the physical examination, can help optimize access planning and maintenance. Because of the high complication rate of synthetic grafts, there has been increased emphasis on creating autogenous arteriovenous (AV) fistulae, which, once established, are more trouble-free. The benefit of increased fistula creation will not be realized, however, until the high rate of early fistula failure is reduced. It is widely recommended that graft surveillance programs be implemented and that stenosis be corrected when accompanied by graft dysfunction. Graft blood flow (Q(a)) is the preferred surveillance method, but has a poor accuracy in predicting thrombosis. Most studies that have evaluated the benefit of Q(a) surveillance have used historical control groups, or have been retrospective or nonrandomized. Consequently, we believe it is not currently possible to make definitive, evidence-based recommendations concerning Q(a) surveillance. The most important factor in access survival may be a team approach with an organized commitment to access planning followed by recognition and treatment of access problems.

Arteriovenous Shunt, Surgical↗
PubMedDate not supplied

Blood flow surveillance of hemodialysis grafts: insights from two case reports.

It is widely recommended that all hemodialysis grafts undergo blood flow (Qa) surveillance, and that stenosis be corrected when accompanied by a low Qa or decrease in Qa (deltaQa). This recommendation has, however, become increasingly controversial. Studies have shown that although there is an association between Qa and thrombosis, the accuracy of Qa in predicting thrombosis within individual patients is poor. We describe two cases that demonstrate common causes of poor predictive accuracy. These cases also show that application of Qa surveillance algorithms is often complex and ambiguous. Most studies reporting that surveillance with intervention reduces thrombosis or prolongs graft life have used historical or sequential control groups, or have been retrospective. Accurate assessment of the benefit of graft surveillance must await studies that are fully prospective and randomized with concurrent control groups. Until such studies have demonstrated sufficient benefit, we do not recommend periodic Qa surveillance with intervention of all hemodialysis grafts.

Aged↗
PubMedDate not supplied

Stenosis surveillance of hemodialysis grafts by duplex ultrasound reduces hospitalizations and cost of care.

Most recent randomized controlled trials (RCTs) have found that hemodialysis graft surveillance combined with preemptive correction of stenosis does not prolong graft survival. Nevertheless, such programs may be justified if they reduce other adverse outcomes or decrease the cost of care. This study tested this hypothesis by applying a secondary analysis to our original RCT. This study of 101 patients evaluated correction of stenosis based upon blood flow (Q) and stenosis surveillance. Patients were randomly assigned to control, flow, or stenosis groups, and were followed for up to 28 months. Q was measured monthly by ultrasound dilution; stenosis was measured quarterly by duplex ultrasound. Stenosis of 50% was corrected by percutaneous transluminal angioplasty (PTA) after referral for angiography. Referral criteria were: control group, clinical criteria; flow group, Q < 600 ml/min or clinical criteria; stenosis group, stenosis > 50% or clinical criteria. We compared access-related hospitalizations and cost of care, and use of central venous dialysis catheters (CVCs), among the three groups. Hospitalization rates were higher in the control and flow groups than in the stenosis group (0.50, 0.57, 0.18/patient-year, respectively [p < 0.01]), and hospitalization costs were lowest in the stenosis group (p = 0.026). The stenosis group had a trend toward lowest CVC rates (0.44, 0.32, 0.20/patient-year, respectively [p = 0.20]). The costs of care were higher in the control and flow groups than in the stenosis group (dollar 3727, dollar 4839, dollar 3306/patient-year, respectively [p = 0.015]). The costs of stenosis (dollar 142/patient-year) and Q (dollar 279/patient-year) measurements were minimal compared to the total cost of access-related care. In conclusion, stenosis surveillance by duplex ultrasound combined with preemptive correction yielded reduced hospitalization rates and costs, reduced total cost of access-related care, and a trend of reduced CVC rates. In contrast, flow surveillance did not yield a significant benefit. Stenosis surveillance provides important benefits that may justify application of such programs.

Analysis of Variance↗
PubMedDate not supplied

Thresholds for significant decrease in hemodialysis access blood flow.

During hemodialysis access surveillance, referral for evaluation and correction of stenosis is based upon determination that a significant decrease in blood flow (Q) has occurred. However, criteria for determining when a decrease is statistically significant have not yet been established. In this study we established such criteria by analyzing Q variation with the glucose pump test (GPT). We took nine Q measurements in each of 25 patients (18 grafts, 7 fistulas) during three dialysis sessions within a 2-week period (predialysis and during hours 1 and 3). We determined thresholds that define a significant percentage decrease in Q (deltaQ) for various p values. In order to confirm the general applicability of these thresholds, we computed the average within-patient Q variation during the three sessions (computed as a coefficient of variation and referred to as short-term variation). We then determined the relative influences of biological (true) variation and analytical error on short-term variation. We found that deltaQ must be > 33% to be significant at p < 0.05, whereas the threshold is > 17% for p < 0.20. Measuring Q at uniform versus different times during the sessions did not significantly reduce these thresholds. We also found that biological variation was nearly as large as short-term Q variation, whereas analytical error contributed minimally to short-term variation. In conclusion, this study defines thresholds for a significant deltaQ that have wide application in determining access referral for evaluation and correction of stenosis. Selection of a particular threshold should consider the relative importance of avoiding thrombosis versus avoiding unnecessary procedures. If avoiding unnecessary procedures is a priority, then we recommend a threshold of > 33%. These thresholds apply to other methods of measuring Q, provided analytical error is significantly less than biological variation.

Arteriovenous Shunt, Surgical↗