Hemodialysis access failure: a call to action

Extracorporeal pressure monitoring and the detection of vascular access stenosis

Prospective monitoring of static venous pressure is an established tool to detect outflow stenoses in a vascular access. However, with this method it is not possible to identify vascular stenoses which are localized between the arterial and venous dialysis needle. We describe a new approach based on both static arterial and venous extracorporeal pressures. Pressure data of 9 dialysis patients with normal vascular access function and 9 patients with stenotic access were analyzed. Extracorporeal pressure was found to depend on the position of the heart relative to the extracorporeal blood circuit. All patients with venous outflow stenoses had an elevated ratio of arterial and venous intra-access pressure to mean arterial pressure. In case of access stenosis between arterial and venous needle the ratio of venous pressure to mean arterial pressure was normal, and only the arterial pressure ratio was elevated. We conclude that combined arterial and venous intraaccess pressure measurement normalized by mean blood pressure detects venous stenosis as well as stenosis between the arterial and venous dialysis needle. To minimize the rate of access thrombosis both arterial and venous intra-access pressure should be monitored.

In vitro evaluation of hemolysis and sublethal blood trauma in a novel subcutaneous vascular access system for hemodialysis

Hemodialysis requires reliable frequent access to the patients' vasculature, with blood flow rates of > 300 ml/min. Currently in the U.S. market, there are three types of hemodialysis access systems: the native arteriovenous fistula, generally using 15G needles; the synthetic arteriovenous (AV) graft, also generally using 15G needles; and the percutaneous catheter. Some of the problems with current vascular access technologies include insufficient blood flow, blood trauma, thrombosis, infection, cardiac load, and venous stenosis. The LifeSite System (Vasca, Inc.) represents an alternative for vascular access, and consists of a subcutaneous valve and 12F cannula accessed by a standard 14G needle. The LifeSite valve is implanted in the upper torso with the cannula generally entering the right internal jugular vein. The purpose of this study was to compare the LifeSite System with two known vascular access systems: the 10F dialysis catheter (Tesio-Cath, MedComp) and the 15G A.V. Fistula Needle Set (JMS Co., Ltd.) with regard to blood damage produced by these devices in use. Mechanical hemolysis and sublethal blood trauma were evaluated by means of in vitro blood pumping through a circulating loop incorporating a hemodialysis vascular access system. Sublethal blood damage was examined by using a hemorheologic assay that included parameters such as erythrocyte mechanical fragility, plasma total protein and fibrinogen concentrations, and blood viscosity. The tests demonstrated that, at both studied flow rates of 300 ml/min and 450 ml/min, the LifeSite produced lower hemolysis and less sublethal damage to blood than either the Tesio-Cath catheter or the A.V. Fistula Needle Set.

Vascular access use in Europe and the United States: results from the DOPPS

BACKGROUND

A direct broad-based comparison of vascular access use and survival in Europe (EUR) and the United States (US) has not been performed previously. Case series reports suggest that vascular access practices differ substantially in the US and EUR. We report on a representative study (DOPPS) which has used the same data collection protocol for> 6400 hemodialysis (HD) patients to compare vascular access use at 145 US dialysis units and 101 units in five EUR countries (France, Germany, Italy, Spain, and the United Kingdom).

METHODS

Logistic analysis evaluated factors associated with native arteriovenous fistula (AVF) versus graft use or permanent access versus catheter use for prevalent and incident HD patients. Times to failure for AVF and graft were analyzed using Cox proportional hazards regression.

RESULTS

AVF was used by 80% of EUR and 24% of US prevalent patients, and was significantly associated with younger age, male gender, lower body mass index, non-diabetic status, lack of peripheral vascular disease, and no angina. After adjusting for these factors, AVF versus graft use was still much higher in EUR than US (AOR=21, P < 0.0001). AVF use within facilities varied from 0 to 87% (median 21%) in the US, and 39 to 100% (median 83%) in EUR. For patients who were new to HD, access use was: 66% AVF in EUR versus 15% in US (AOR=39, P < 0.0001), 31% catheters in EUR vs. 60% in US, and 2% grafts in EUR vs. 24% in US. In addition, 25% of EUR and 46% of US incident patients did not have a permanent access placed prior to starting HD. In EUR, 84% of new HD patients had seen a nephrologist for> 30 days prior to ESRD compared with 74% in the US (P < 0.0001); pre-ESRD care was associated with increased odds of AVF versus graft use (AOR=1.9, P=0.01). New HD patients had a 1.8-fold greater odds (P=0.002) of starting HD with a permanent access if a facility's typical time from referral to access placement was < or =2 weeks. AVF use when compared to grafts was substantially lower (AOR=0.61, P=0.04) when surgery trainees assisted or performed access placements. When used as a patient's first access, AVF survival was superior to grafts regarding time to first failure (RR=0.53, P=0.0002), and AVF survival was longer in EUR compared with the US (RR=0.49, P=0.0005). AVF and grafts each displayed better survival if used when initiating HD compared with being used after patients began dialysis with a catheter.

CONCLUSION

Large differences in vascular access use exist between EUR and the US, even after adjustment for patient characteristics. The results strongly suggest that a facility's preferences and approaches to vascular access practice are major determinants of vascular access use.

Use of ACE inhibitors is associated with prolonged survival of arteriovenous grafts

Vascular access complications are common in hemodialysis patients. To investigate whether the use of angiotensin-converting enzyme (ACE) inhibitors influences the rate of polytetrafluoroethylene (PTFE) graft complications, we compared the rate of intervention-free graft survival among patients treated versus not treated with ACE inhibitors. We retrospectively analyzed the survival of grafts placed at our institution between January 1, 1995, and October 31, 1999. Among 121 grafts, 25 grafts were placed in 19 patients treated with ACE inhibitors and 96 grafts were placed in 68 patients not treated with ACE inhibitors. Follow-up ranged from 1 month to 5 years. Ten of 25 grafts failed in the ACE-inhibitor group and 62 of 95 grafts failed in the non-ACE-inhibitor group. Actuarial intervention-free access survival rates (Kaplan-Meier) were significantly greater in the ACE-inhibitor than non-ACE-inhibitor group (71% versus 53% at 6 months, 58% versus 35% at 12 months, and 44% versus 22% at 24 months; P = 0.04). Using a Cox model adjusting for age, race, sex, and diabetes, the relative risk (RR) for access failure in the ACE-inhibitor group was 53% less than in the non-ACE-inhibitor group (RR, 0.47; p < 0.03). In a more complex Cox model with additional adjustment for comorbid conditions, the RR was even lower (RR, 0.32; P = 0.003) for the ACE-inhibitor compared with non-ACE-inhibitor group (reference = 1.00). The lower RR was observed for patients with and without congestive heart failure. These results suggest that ACE inhibitors offer clinical promise in the prevention of PTFE graft failure. A prospective randomized trial is warranted to confirm the benefit of ACE inhibitors.

Buzz in the axilla: a new physical sign in hemodialysis forearm graft evaluation

The value of physical signs in predicting flow rates or polytetrafluoroethylene (PTFE) hemodialysis graft survival is not well known. Simultaneous physical examination and flow measurements were performed in 67 dialysis patients with PTFE grafts over a period of 1 month. Physical signs included the presence and location of a palpable thrill, location and auscultatory nature of the bruit, and presence or absence of a pulsation. Patients were followed up for 1 year to detect the time to failure defined by angioplasty, clotting, or surgical revision. There was a fair correlation between physical signs and graft flow rates. In a multivariate model, systolic blood pressure, location of the thrill, and patient age were the best predictors of graft flow. During follow-up, there were 68 graft failures (30 grafts, angioplasty alone; 38 grafts, thrombosis followed by interventional or surgical revisions). The median survival of a graft without a thrill in the axilla was 154 days compared with 321 days when a thrill was present (P = 0.05, log-rank test). Dialysis graft physical examination is a useful test to predict graft flows, as well as graft failure. The single best test is the location of the thrill along the venous limb of the graft. Average flow rates for no thrill, thrill but distal to the midarm, and axillary buzz were approximately 500, 750, and 1,000 mL/min, respectively. This single physical sign also correlated with subsequent graft failure and should be incorporated into physical examinations of all dialysis grafts.

Vascular access survival and incidence of revisions: a comparison of prosthetic grafts, simple autogenous fistulas, and venous transposition fistulas from the United States Renal Data System Dialysis Morbidity and Mortality Study

OBJECTIVE

The study's aim was to evaluate access patency and incidence of revisions in patients initiating hemodialysis and to determine differences in access performance by type of access among patient subgroups.

METHODS

The study used data from the United States Renal Data System Dialysis Morbidity and Mortality Study Wave 2, which contained a random sample of dialysis patients initiating dialysis in 1996 and early 1997. Failures and revisions were evaluated among 2247 newly placed hemodialysis accesses by using Cox proportional hazards regression model and Poisson regression. Primary and secondary patency rates were estimated using the Kaplan-Meier method.

RESULTS

Fifteen hundred seventy-four prosthetic grafts, 492 simple autogenous fistulas, and 181 venous transposition fistulas were available for evaluation. Prosthetic grafts had a 41% greater risk of primary failure compared with simple fistulas (relative risk, 1.41; 95% CI, 1.22-1.64; P < .001) and a 91% higher incidence of revision (relative risk, 1.91; 95% CI, 1.60-2.28; P <.001). At 2 years, autogenous fistulas demonstrated superior primary patency (39.8% versus 24.6%, P < .001) and equivalent secondary patency (64.3% versus 59.5%, P = .24) compared with prosthetic grafts. When compared with simple fistulas, vein transpositions demonstrated equivalent secondary patency at 2 years (61.5% versus 64.3%, P = .43) but inferior primary patency (27.7% versus 39.8%, P = .008) and had a 32% increased incidence of revision (P = .04). Autogenous fistulas had superior primary patency compared with prosthetic grafts in all patient subgroups except for patients with previously failed access. Vein transpositions showed the greatest benefit in terms of patency and incidence of revision in women and in patients with previously failed access.

CONCLUSIONS

The preferential placement of autogenous fistulas may increase primary patency and decrease the incidence of revisions. Vein transpositions had similar secondary patency compared with simple fistulas, but required more revisions. The greatest benefit of a vein transposition fistula was seen in women and in patients with a history of access failure.

Type of vascular access and mortality in U.S. hemodialysis patients

BACKGROUND

Vascular access (VA) complications account for 16 to 25% of hospital admissions. This study tested the hypothesis that the type of VA in use is correlated with overall mortality and cause-specific mortality.

METHODS

Data were analyzed from the U.S. Renal Data System Dialysis Morbidity and Mortality Study Wave 1, a random sample of 5507 patients, prevalent on hemodialysis as of December 31, 1993. The relative mortality risk during a two-year observation was analyzed by Cox-regression methods with adjustments for demographic and comorbid conditions. Using similar methods, cause-specific analyses also were performed for death caused by infection and cardiac causes.

RESULTS

In diabetic mellitus (DM) patients with end-stage renal disease, the associated relative mortality risk was higher for those with arteriovenous graft (AVG; RR = 1.41, P < 0.003) and central venous catheter (CVC; RR = 1.54, P < 0.002) as compared with arteriovenous fistula (AVF). In non-DM patients, those with CVC had a higher associated mortality (RR = 1.70, P < 0.001), as did to a lesser degree those with AVG (RR = 1.08, P = 0.35) when compared with AVF. Cause-specific analyses found higher infection-related deaths for CVC (RR = 2.30, P < 0.06) and AVG (RR = 2.47, P < 0.02) compared with AVF in DM; in non-DM, risk was higher also for CVC (RR = 1.83, P < 0.04) and AVG (RR = 1.27, P < 0.33). In contrast to our hypothesis that AV shunting increases cardiac risk, deaths caused by cardiac causes were higher in CVC than AVF for both DM (RR = 1.47, P < 0.05) and non-DM (RR = 1.34, P < 0.05) patients.

CONCLUSION

This case-mix adjusted analysis suggests that CVC and AVG are correlated with increased mortality risk when compared with AVF, both overall and by major causes of death.

Vascular access blood flow monitoring reduces access morbidity and costs

BACKGROUND

Vascular access morbidity results in suboptimal patient outcomes and costs more than $8000 per patient-year at risk, representing approximately 15% of total Medicare expenditures for ESRD patients annually. In recent years, the rate of access thrombosis has improved following the advent of vascular access blood flow monitoring (VABFM) programs to identify and treat stenosis prior to thrombosis. To define further both the clinical and financial impact of such programs, we used the ultrasound dilution method to study the effects of VABFM on thrombosis-related morbid events and associated costs, compared with both dynamic venous pressure monitoring (DVPM) and no monitoring (NM) in arteriovenous fistulas (AVF) and grafts.

METHODS

A total of 132 chronic hemodialysis patients were followed prospectively for three consecutive study phases (I, 11 months of NM; II, 12 months of DVPM; III, 10 months of VABFM). All vascular access-related information (thrombosis rate, hospitalization, angiogram, angioplasty, access surgery, thrombectomy, catheter placement, missed treatments) was collected during the three study periods.

RESULTS

During the three study phases, graft thrombosis rate was reduced from 0.71 (phase I), to 0.67 (phase II), to 0.16 (phase III) events per patient-year at risk (P < 0.001 phase III vs. phases I and II). Similarly, hospital days, missed treatments, and catheter use related to thrombotic events were significantly reduced during phase III compared to phases I and II. Hospital days related to vascular access morbidity and adjusted for patient-year at risk were 1.8, 1.6, and 0.4 and missed dialysis treatments were 0.98, 0.86, and 0.26 treatments per patient-year at risk for phases I, II, and III, respectively (P < 0.001 for phase III vs. phases I and II). Catheter use was also significantly reduced during phases II and III, from 0.29 (phase I) to 0.17 and further to 0.07 catheters per patient-year at risk, respectively (P < 0.05 for phase III vs. phase I). Percutaneous angioplasty procedures increased during phases II and III from 0.09 to 0.32 to 0.54 procedures per patient-year at risk for phases I, II, and III, respectively (P < 0.01 for phase III vs. phase I). When the total cost of treatment for thrombosis-related events for grafts was estimated, it was found that during phase III, the adjusted yearly billed amount was reduced by 49% versus phase I and 54% versus phase II to $158,550. Similar trends in reduced thrombosis-related morbid events and cost were observed for AVFs.

CONCLUSIONS

VABFM for early detection of vascular access malfunction coupled with preventive intervention reduces thrombosis rates in both polytetrafluoroethylene (PTFE) grafts and native AVFs. While there was a significant increase in the number of angioplasties done during the flow monitoring phase, the comprehensive cost is markedly reduced due to the decreased number of hospitalizations, catheters placed, missed treatments, and surgical interventions. Vascular access blood flow monitoring along with preventive interventions should be the standard of care in chronic hemodialysis patients.

Timing of nephrologist referral and arteriovenous access use: the CHOICE Study

Recent clinical practice guidelines recommend the creation of an arteriovenous (AV) vascular access (ie, native fistula or synthetic graft) before the start of chronic hemodialysis therapy to prevent the need for complication-prone dialysis catheters. We report on the association of referral to a nephrologist with duration of dialysis-catheter use and type of vascular access used in the first 6 months of hemodialysis therapy. The study population is a representative cohort of 356 patients with questionnaire, laboratory, and medical record data collected as part of the Choices for Healthy Outcomes in Caring for End-Stage Renal Disease Center Study. Patients who reported being seen by a nephrologist at least 1 month before starting hemodialysis therapy (75%) were more likely than those referred later to use an AV access at initiation (39% versus 10%; P < 0.001) and 6 months after starting hemodialysis therapy (74% versus 56%; P < 0.01). Patients referred within 1 month of initiating hemodialysis therapy used a dialysis catheter for a median of 202 days compared with 64, 67, and 19 days for patients referred 1 to 4, 4 to 12, and greater than 12 months before initiating hemodialysis therapy, respectively (P trend < 0.001). Patients referred at least 4 months before initiating hemodialysis therapy were more likely than patients referred later to use an AV fistula, rather than a synthetic graft, as their first AV access (45% versus 31%; P < 0.01). These associations remained after adjustment for age, sex, race, marital status, education, insurance coverage, comorbid disease status, albumin level, body mass index, and underlying renal diagnosis. These data show that late referral to a nephrologist substantially increases the likelihood of dialysis-catheter use at the initiation of hemodialysis therapy and is associated with prolonged catheter use. Regardless of the time of referral, only a minority of patients used an AV access at the initiation of treatment, and greater than 25% had not used an AV access 6 months after initiation. Thus, further efforts to improve both referral patterns and preparation for dialysis after referral are needed.

Screening for subclinical stenosis in native vessel arteriovenous fistulae

Guidelines recommend the use of ultrasound dilution techniques (UDT), including measurement of access recirculation (AR) and access blood flow (Q(a)), to screen for subclinical vascular access dysfunction. Although these techniques are efficacious in polytetrafluoroethylene grafts, data in native vessel arteriovenous fistulae (AVF) are lacking. A prospective observational study was conducted to evaluate the utility of UDT screening in AVF. Q(a) and AR were measured bimonthly. Positive studies required fistulograms and were defined by Q(a) < 500 ml/min, DeltaQ(a) > 20% from baseline or AR > 5%. Accesses with stenosis underwent percutaneous angioplasty. After 1 yr, there were 1355 mo of follow-up in 177 patients. There were 44 positive studies in 40 patients. Q(a) was <500 ml/min in 36 (82%), DeltaQ(a) was >20% in 5 (11%), and AR was >5% in 6 (14%). Of patients with Q(a) < 500 ml/min, 29 (81%) had stenosis. Only two patients (40%) with DeltaQ(a) > 20% but Q(a) > 500 ml/min had stenosis. No patient with AR > 5% had stenosis unless Q(a) was also <500 ml/min. Immediate patency rate was 93% post-PTA. Mean Q(a) increased from 303 +/- 154 ml/min to 602 +/- 220 ml/min (P < 0.0001), and mean urea reduction ratio increased from 70.4 +/- 8.4% to 74.6 +/- 6.5% (P = 0.003) post-PTA. The results demonstrate that UDT could detect subclinical stenoses in AVF, and most lesions were amenable to angioplasty. AVF that underwent PTA delivered higher Q(a) and urea reduction ratio, and immediate patency rates were acceptable. Access failure after negative UDT was unusual. Measuring AR increases the time required to perform UDT but does not improve utility. Serial measurements of Q(a) alone may be the best strategy for screening AVF.

Clinical performance characteristics of hemodialysis graft monitoring

BACKGROUND

Regular monitoring of dialysis grafts is recommended, but the value of dialysis graft blood flow monitoring and venous pressures in predicting subsequent outcomes are controversial.

METHODS

Over a period of one month, we performed simultaneous flow and venous pressure monitoring in 71 dialysis patients with polytetrafluoroethylene (PTFE) grafts. These patients were prospectively followed for one year. Receiver operating characteristic (ROC) curves were constructed to evaluate the performance of the various monitoring techniques.

RESULTS

During the period of follow-up, there were 71 graft failures (30 angioplasty alone and 41 thrombosis followed by interventional or surgical revisions). Failed grafts had a lower blood flow rate [799 +/- 452 (SD) mL/min] when compared with those without failure (1019 +/- 485 mL/min, P = 0.05) Single static or dynamic venous-pressure monitoring were not predictive of graft failure. ROC analysis showed poor performance of graft flows in predicting graft failures over the short (30 days, AUC = 0.726, 95% CI, 0.509 to 0.942) and long term (one year, AUC = 0.630, 95% CI, 0.499 to 0.761). An adjustment of graft flows for systolic blood pressure or classification of graft based both on flows and venous pressure did not improve test performance.

CONCLUSIONS

Although dialysis graft blood flow rates are statistically different in patients who have graft failure (graft angioplasty and surgery or thrombosis) versus those who do not, the performance characteristics preclude clinical decision-making from an isolated blood flow or venous pressure study.

Assessment of a policy to reduce placement of prosthetic hemodialysis access

BACKGROUND

The aim of this study was to evaluate the determinants of access patency and revision, including the effects of reducing the placement of prosthetic hemodialysis access.

METHODS

A retrospective cohort study of all hemodialysis accesses placed at the Veteran's Administration Puget Sound Health Care System between 1992 and 1999 was conducted. A policy was instituted in 1996 that maximized the use of autogenous hemodialysis access. The impacts of the policy change, demographics, and comorbid factors on access type and patency, were examined. Primary and secondary patency rates were examined using the Kaplan--Meier method, and factors associated with failure and revision were examined using Cox proportional hazard models and Poisson regression.

RESULTS

During the study, 104 accesses (61 prosthetic grafts and 43 autogenous fistulas) were placed prior to 1996, and 118 (31 prosthetic grafts and 87 autogenous fistulas) were placed after 1996. There was a significant increase in autogenous fistulas placed after 1996 (87 out of 118) compared with before 1996 (43 out of 104, P < 0.001). At one year, autogenous fistulas demonstrated superior primary patency (56 vs. 36%, P = 0.001) and secondary patency (72 vs. 58%, P = 0.003) compared with prosthetic grafts. After adjustment for age, race, side of access placement, and history of prior access placement, patients with a prosthetic graft were estimated to experience a 78% increase in the risk of primary access failure when compared with similar patients having an autogenous access [adjusted relative risk (aRR) = 1.78, 95% CI 1.21--2.62, P = 0.003)]. Similarly, the adjusted relative risk of secondary access failure for comparing prosthetic grafts with autogenous fistulas was estimated to be 2.21 (95% CI 1.38--3.54, P = 0.001). The adjusted risk of access revision was 2.89-fold higher for prosthetic grafts than for autogenous fistulas (95% CI 1.88--4.44, P < 0.001).

CONCLUSIONS

Autogenous conduits demonstrated superior performance when compared with prosthetic grafts in terms of primary and secondary patency and number of revisions. A policy emphasizing the preferential placement of autogenous fistulas over prosthetic grafts may result in improved patency and a reduction in the number of procedures required to maintain dialysis access patency.

Blood flow surveillance of hemodialysis grafts and the dysfunction hypothesis

It is widely recommended that hemodialysis graft surveillance programs should be implemented and that significant stenosis should be corrected when it is accompanied by graft dysfunction. The rationale for surveillance depends on the dysfunction hypothesis, which states that stenosis causes graft dysfunction [such as a decrease in graft blood flow (Qa)], and this dysfunction reliably precedes and accurately predicts thrombosis. The usefulness of Qa surveillance depends on accurate prediction of thrombosis so that stenosis can be corrected prior to thrombosis. An analysis of the dysfunction hypothesis indicates that some or all of its underlying assumptions are invalid. Most importantly, the presence of wide hemodynamic variation during Qa measurements makes Qa a relatively inaccurate predictor of thrombosis. A number of studies have evaluated the value of surveillance with intervention in reducing thrombosis rates and prolonging graft life. Review of these studies show that few have been prospective and randomized, and many have included historical control groups. It is debatable whether these studies have established that Qa surveillance with intervention should be applied to all grafts. Data from several studies suggest that severity of stenosis may be at least as accurate as Qa in predicting thrombosis. Consequently, inclusion of stenosis measurements (e.g., by duplex ultrasound) may improve the results of surveillance. These unresolved issues indicate it is premature to recommend routine Qa surveillance with intervention of all hemodialysis patients with grafts.

Oxidative stress and increased expression of growth factors in lesions of failed hemodialysis access

The pathological role of oxidative stress in patients treated by hemodialysis has gained increasing recognition in recent years. Because complications related to vascular access are a major source of morbidity, immunohistochemical evidence of oxidative stress and activation of growth factors were examined in native arteriovenous (AV) fistulae (n = 11) and expanded polytetrafluoroethylene (ePTFE) grafts (n = 15) recovered from hemodialysis patients at the time of surgical revision or resection. To show the presence of oxidative stress in tissues, three markers were chosen: N(epsilon)(carboxymethyl)lysine, a structurally identified advanced glycation end product; 4-hydroxy-2,3-nonenol, a lipid peroxidation product; and redox-active transition metals bound to proteins, a source of Fenton chemistry-generated free radicals. Markers of cell growth and proliferation were endothelin-1 (ET-1), a potent mitogenic peptide implicated in the formation of intimal hyperplasia; transforming growth factor-beta (TGF-beta), a stimulus to vascular cell growth and matrix production; and platelet-derived growth factor (PDGF), a mediator of intimal hyperplasia. All specimens studied showed significant intimal hyperplasia. In general, the neointima close to the vascular lumen of the AV fistula and the pseudointima close to the lumen of the ePTFE graft were positive for oxidative stress markers. At sites of injury, especially in the presence of histological evidence of inflammation and healing, expression of oxidative markers was particularly intense. Prominent staining of PDGF was shown at sites of anastomotic hyperplasia and in neovasculature. TGF-beta was associated with proliferation or repair in both AV fistulae and ePTFE grafts. ET-1 staining was most intense in the neointima and pseudointima. This study showed histochemical colocalization of markers of oxidative stress with growth factors known to contribute to intimal hyperplasia.

Identifying patients at risk for hemodialysis underprescription

Underprescription of hemodialysis is an important barrier to adequate delivery of dialysis. We sought to determine which patient factors are associated with hemodialysis underprescription and to examine variation in prescription across facilities. For 721 randomly selected patients from all 22 chronic hemodialysis units in northeast Ohio, we calculated prescribed Kt/V based on dialyzer urea clearance at prescribed blood and dialysate flow (K), prescribed treatment time (t), and anthropometric volume (V). A minimum 'prescribed Kt/V' of 1.3 has been recommended to ensure an adequate 'delivered Kt/V' of 1.2. Using this criterion, 15% of patients had a low prescribed Kt/V. Prescribed Kt was strongly related to patient anthropometric volume but not to other patient characteristics (age, gender, race, cause of renal failure, number of years on dialysis, number of comorbid conditions). A 10-liter increase in V was associated with an 8.3-liter increase in prescribed Kt. However, a 13-liter increase in prescribed Kt would be needed to maintain a prescribed Kt/V of 1.3. As a result, the proportion of patients with low prescriptions increased from 2% of patients with V <35 liters to 42% of patients with V > or =50 liters. In addition, the prevalence of low prescriptions varied dramatically across facilities (range 0-47%) even after accounting for volumes of individual patients. Of the 109 patients with low prescription, 75% would achieve a prescribed Kt/V of 1.3 with less than 30 min of additional treatment time. In conclusion, large patients and patients at specific facilities are at increased risk for underprescription of hemodialysis. Most patients with low prescriptions would achieve a prescribed Kt/V of 1.3 with a modest increase in treatment time.

Hemodynamic reproducibility during blood flow measurements of hemodialysis synthetic grafts

We have previously shown that graft blood flow (Qa) has a poor accuracy in predicting graft thrombosis. In this study, we determined whether hemodynamic variation helps explain this poor predictive accuracy. We also determined whether standardized timing of Qa measurements, which is widely recommended, will promote measurement reproducibility. We analyzed variations in mean arterial pressure (MAP) in seven consecutive dialysis sessions for 51 patients and determined the influence of MAP on Qa (by ultrasound dilution). We used a pooled coefficient of variation (CV) to summarize MAP variation within individual patients (computed as +/-2 CVs). MAPs from the seven sessions varied widely, and most variation was present with the first MAPs at the beginning of the sessions. These first MAPs varied by +/-23%, whereas variation for the entire session was +/-28%. The influence of MAP on Qa was determined by measuring the two together during consecutive thirds of a single session. The percentage of change in MAP (DeltaMAP) and Qa (DeltaQa) from the first to middle or last thirds of the session varied over wide ranges: -37% to 86% and -43% to 78%, respectively. The DeltaQa versus DeltaMAP correlation was relatively strong for changes between the first and middle thirds (r = 0.666) and first and last thirds (r = 0.646) of the session (both P: < 0.01). We conclude that MAP varies far more widely during dialysis than previously recognized. This variation is associated with large changes in Qa that may impair accuracy in predicting thrombosis. This wide MAP variation also indicates hemodynamic reproducibility is not feasible when measuring Qa. Thus, we do not recommend standardized timing of Qa measurements during dialysis. A practical method of addressing poor Qa reproducibility may be to take frequent measurements so that trends can be recognized before thrombosis occurs.

Successful use of central venous catheter as permanent hemodialysis access: 84-month follow-Up in lucania

Cuffed tunneled venous access catheters are commonly used for temporary and permanent access in hemodialysis (HD) patients. These catheters serve an essential role in providing permanent access in subjects in whom all other access options have been exhausted. The predominant complications are catheter thrombosis, catheter fibrin sheating and infection. The aim of this study was to evaluate long-term survival and complications of permanent venous catheters (PVC) placed for the purpose of HD during the period from January 1992 to December 1998, at the Dialysis Units of Lucania (a southern Italian region). A total of 98 PVC were placed in 88 patients during this period. The catheters used were of three types: (a) 72 VasCath Soft Cell catheters (Bard Instrument Company, Toronto, Ont., Canada); (b) 22 PermCath catheters (Quinton Instrument Company, Seattle, Wash., USA), and (c) 4 Tesio catheters (Bellco SpA, Mirandola, Italy). Survival curves of catheters were calculated using the Kaplan-Meier product-limit estimator. The patient survival was 60% at the 78th month. Actually, 52 patients (27 males, 25 females) are still alive: 15 (26.9%) of these patients have diabetes mellitus and 1 has been transplanted. The actuarial survival rate of PVC was 89% in the whole population studied and 82% in subjects alive after 84 months. Twenty-five patients (28.4%) had PVC as the first reliable vascular access. Long-term complications occurred 27 times (1 episode every 44.81 month/patient) as: breakage (3.1%); thrombosis (10.2%); displacement (2.0%); subcutaneous tunnel bleeding (3.1%); inadequate blood flow (7.1%), and infection (10.2%). In conclusion, our data confirm that PVC might represent an effective long-term blood access route for HD. Again, PVC are getting the access of choice for selected patients (i.e., older subjects with cardiovascular diseases and cancer patients) and are enjoying a dramatic increase in use for subjects who are terrified of repetitive venopuncture.

Initial experience of a nephrologist-operated vascular access center

A nephrology practice in Alabama did not feel in control of vascular access management. Scheduling delays, as well as variable techniques and outcomes, leading to high morbidity and mortality, caused frustration with the existing care system for vascular access. Our objective was to develop an integrative system of vascular access care, involving nephrologists along with the other caregivers, and to demonstrate an improvement in outcomes. Nephrology Vascular Labs (NVL), a recent RMS-Lifeline acquisition, opened a vascular access center (VAC) as an extension of the nephrology practice. Both pre-ESRD and ESRD patients are evaluated and treated in the VAC. Treatment is rendered in a timely fashion, to the benefit of the patients. Nephrologists serve as the interventionists. More than 90% of vascular access problems detected at dialysis are treated at the VAC. More than 2000 procedures have been performed over 2 years. Procedures carried out include thrombolysis with angioplasty, fluoroscopy alone or with angioplasty, placement of cuffed and noncuffed catheters, removal of cuffed catheters, and minor surgeries. Success rates have been high. Minor and major complications have been relatively low. Referrals to both surgeons and radiologists are shown to emphasize the role of the VAC as part of an integrative system of vascular access care. Results of a patient satisfaction survey were excellent. The VAC has fulfilled the vision of creating a seamless integration of care for vascular access. Hospitalization rate has been reduced and it is suspected that the global cost of access care is markedly lower than prior to the VAC. Multiple nephrologists can rotate as the VAC's interventionist and jointly obtain good outcomes and have little variability among them. Several reasons for using a nephrologists as the interventionist are discussed.

Vascular access for haemodialysis

BACKGROUND

The recent expansion of renal replacement therapy programmes has been associated with an increase in the number and complexity of patients requiring permanent vascular access. The introduction of strategies designed to maximize secondary access patency is, therefore, increasingly important as a means of prolonging patient survival on dialysis, reducing morbidity and reducing the escalating cost of such programmes.

METHODS

A review of the current literature on the planning of vascular access, access surveillance methods and treatment of the most common complications was performed.

RESULTS

Multidisciplinary vascular access planning, increased use of preoperative imaging and the preferential use of autogeneous vein are essential to obtain the best long-term results. While vascular access surveillance, in particular protocols involving direct measurement of access flow, enables the prospective detection and treatment of venous stenosis, the precise indications for treating venous stenosis remain unclear. Surgical revision remains the gold standard for the treatment of failing arteriovenous fistulas, but recent advances in interventional radiological techniques along with the suitability of arteriovenous fistulas for percutaneous intervention may offer an effective alternative. The effect of both these interventions on access patency requires comparison in a randomized trial.

CONCLUSION

The introduction of strategies to improve access patency rates will change vascular access surgical practice away from the construction of new fistulas towards an increase in outpatient percutaneous intervention and surgical revisional procedures. The role of surgical interventions requires clearer definition.

Introduction of a switch that can reverse blood flow direction on-line during hemodialysis

In several circumstances in hemodialysis, the regular direction of blood flow has to be reversed or changed, such as in access dysfunction or insufficient blood flow being obtained through the arterial port, as well as to measure actual access blood flow in fistulas or grafts by using the formula Qa = Qb((1-R)/R), where R represents recirculation in the reversed line configuration. We invented a disposable switch device made from standard blood line tubing that can be introduced into the dialysis circuit and allows for on-line reversal of lines, without needing to manually disconnect and reconnect tubing or interrupt the hemodialysis procedure. Over a period of eight months, 16 patients (8 arteriovenous fistula, 8 PTFE) underwent 193 hemodialysis sessions with the switch in place. Circuit pressures, pump, and actual blood flows measured with ultrasound dilution were monitored before and after reversing the lines. Switching was accomplished within 1-2 seconds. Arterial circuit (r = 0.99), venous circuit pressures (r = 0.6), and actual pump flow (364 +/- 56 vs. 350 +/- 57 ml/min; r = 0.73) correlated very well preswitching and postswitching (p < 0.0001). Dialysis circuit flow measured with an ultrasound dilution technique decreased from 364 +/- 56 (230-480) ml/min preswitching to 350 +/- 57 (220-490) ml/min postswitching (p < 0.001). No difficulties or complications were observed. This switch device is a useful addition to the technology of hemodialysis in that it greatly facilitates the procedure of reversing the lines in an extracorporeal circuit while not significantly interfering with circuit pressures and connections.

Accuracy of decrease in blood flow in predicting hemodialysis graft thrombosis

We recently showed that a single low graft blood-flow measurement (Qa) does not accurately predict graft thrombosis. In this study, we prospectively determined whether percentage of decrease in Qa (DeltaQa) or adjustment of Qa for mean arterial pressure (Qa/MAP; Delta(Qa/MAP)) provides greater predictive accuracy than a single Qa. We monitored 83 grafts from 80 patients for thrombosis over periods up to 12 months. Qa (by ultrasound dilution) and MAP were measured monthly during the study. Receiver operating characteristic curves were used to determine whether Qa, DeltaQa, Qa/MAP, or Delta(Qa/MAP) provided the combination of high sensitivity (>80%) and low false-positive rate (FPR; <20%) needed for clinical use. This level of predictive accuracy requires an area under the curve (AUC) of approximately 0.90. We analyzed the four predictors by a number of criteria and found that all AUCs were less than 0.90 and adjustment for MAP reduced the AUC. In predicting thrombosis within 1 month, for example, AUCs for Qa and net DeltaQa (over 3 months) were 0.84 and 0.82, respectively, whereas AUCs for Qa/MAP and net Delta(Qa/MAP) were 0.78 and 0.75, respectively. At a sensitivity of 80%, FPRs for all predictors were at least 30%. Thus, a high sensitivity always required a high FPR. These results show that DeltaQa and adjustment for MAP are not more accurate than a single low Qa in predicting thrombosis. None of these predictors provide enough predictive accuracy to be the sole criterion for clinical decision making. A successful monitoring and intervention program will likely require the inclusion of other predictors that, together with Qa, may provide the needed accuracy.

The function of permanent vascular access

BACKGROUND

Complications arising from vascular access (VA) are major causes of morbidity in patients on renal replacement therapy (RRT). They contribute to frustration of health care providers and to high medical cost. To prevent failures in the future it will be helpful to identify the factors that are related to VA malfunction.

METHODS

In a retrospective analysis we analysed the types, duration and primary rate of patency of 1033 permanent vascular accesses in 544 consecutive patients established during a 13-year period in a tertiary care hospital. Patient characteristics, incidence, and risk factors related to VA failure were registered. In addition, VA outcomes in patients who started haemodialysis with a catheter and in whom initial VA failure occurred were analysed separately.

RESULTS

Forty-five per cent of patients required a central catheter at the start of HD, but 92% of them were being dialysed with an a-v fistula at the last observation. The total number of complications was 0.24 episodes per patient per year at risk and the rate of thrombosis 0.1. A total of 52% of patients were dialysed throughout the observation period with their initial a-v fistula; 9.3% had more than three episodes of VA failure. The radiocephalic a-v fistula was the VA with the best median duration, exceeding 7 years, but also the type that had the highest initial failure rate, i.e. 25% of patients and 13% of the events. The brachiocephalic a-v fistula was the second most frequent type of VA, with a median duration of function of 3.6 years, in contrast to the humerobasilic a-v fistula, which exceeded 5 years. Average patency of the different types of grafts did not exceed 1 year, with the exception of the autologous saphenous graft with a median duration of function of 1.4 years. Patients with glomerulonephritis had the best function rates for their VA, the median exceeding the duration of the study, whereas in half of the diabetic patients it was less than 1 year. The duration of patency of the VA was twice in patients below age 65 years and in elderly males compared to elderly females. Patients who started HD with a catheter, as well as those with initial VA failure, had a higher rate of VA failure in the subsequent course on RRT.

CONCLUSION

The radiocephalic and the humerobasilic a-v fistulae are the two types of VA with the longest duration of function, although a high rate of initial failure is seen with the radiocephalic a-v fistula. Age, female gender, presence of diabetic nephropathy, start of dialysis with a catheter, and failure to wait for initial maturation of the VA are risk factors, and account for the majority of VA failures during RRT.

Use of standardized ratios to examine variability in hemodialysis vascular access across facilities. Medical Review Board of The Renal Network, Inc

The type of hemodialysis vascular access (catheter, fistula, graft) is an important determinant of patient morbidity and dialysis efficiency. The relative importance of patient versus provider factors in determining type of vascular access is unclear. We sought to develop a quality improvement tool that adjusts for differences in patient characteristics, thereby allowing examination of provider-related variability in types of vascular access used across facilities. We examined 15,339 patients from 216 chronic hemodialysis units in Indiana, Kentucky, Ohio, and Illinois and found that 20% of patients had catheters, 24% had fistulas, and 56% had grafts. Young, male, and white patients were more likely to have fistulas, whereas old, female, and black patients were more likely to have grafts. Diabetics were more likely to have catheters and less likely to have fistulas. New patients were more likely to have catheters and less likely to have grafts. A facility specific standardized catheter ratio (SCR), standardized fistula ratio (SFR), and standardized graft ratio (SGR) were calculated based on the actual number of patients with each type of vascular access divided by the expected number adjusted for patient characteristics. Facility SCRs ranged from 0.00 to 2.87. Of the 216 facilities, 38 (18%) had an SCR significantly less than 1.00, and 32 (15%) had an SCR significantly greater than 1.00. Similar variability was observed in SFRs and SGRs. In conclusion, the type of vascular access varies greatly across facilities. Use of standardized access ratios adjusted for patient characteristics may help providers examine processes of care that contribute to variability in access use. Analogous to the standardized mortality ratio, the SCR, SFR, and SGR should be effective quality improvement tools.

An evaluation of an integrative care approach for end-stage renal disease patients

Studies analyzing the outcome of integrative care of end-stage renal disease (ESRD) patients, whereby patients are transferred from one renal replacement modality to another according to individual needs, are scant. In this study, we analyzed 417 files of 223 hemodialysis (HD) and 194 peritoneal dialysis (PD) patients starting renal replacement therapy between 1979 and 1996, to evaluate the effect of such an approach. Analysis was done for survival of patients on their first modality, for intention-to-treat survival (counting total time on renal replacement therapy, but with exclusion of time on transplantation), and for total survival. Log rank analysis was used and correction for risk factors was performed by Cox proportional hazards regression. Intention-to-treat survival and total survival were not different between PD and HD patients (log rank, P > 0.05). Technique success was higher in HD patients compared to PD patients (log rank, P = 0.01), with a success rate after 3 yr of 61 and 48%, respectively. Thirty-five patients were transferred from HD to PD and 32 from PD to HD. Transfer of PD patients to HD was accompanied by an increase in survival compared to those remaining on PD (log rank, P = 0.001), whereas, in contrast, transfer of patients from HD to PD was not (log rank, P = 0.17). Survival of patients remaining more than 48 mo on their initial modality was lower for PD patients (log rank, P < 0.01). A matched-pair analysis between patients who started on PD and who were transferred to HD later (by definition called integrative care patients), and patients who started and remained on HD, showed a survival advantage for the integrative care patients. These results indicate that patient outcome is not jeopardized by starting patients on PD, at least if patients are transferred in a timely manner to HD when PD-related problems arise.

Changes in venous histology in chronic hemodialysis patients

Because most hemodialysis access fails at the venous side, we studied samples of brachial vein obtained during access creation in 15 patients with end-stage renal disease who gave consent. Veins were examined by computer-assisted histomorphometry, and the results correlated with the patients' clinical data. The mean venous medial width was 239 +/- 31 microm, and mean intimal width was 6.0 +/- 0.9 microm. Mean venous medial width was 358 +/- 74 microm and mean venous intimal width was 9.2 +/- 1.2 microm in the 4 patients who had been undergoing dialysis more than 6 months, compared with 196 +/- 23 microm and 4.9 +/- 0.8 microm, respectively, in the 11 patients undergoing dialysis less than 6 months (P < 0.01). The number of months undergoing hemodialysis correlated well with venous medial width (r = 0.79; P < 0.001). Correlation between number of months undergoing dialysis and intimal width did not reach statistical significance. Medial and intimal widths of the 4 patients with diabetes were not significantly different from those of the patients without diabetes. Serum parathyroid hormone level did not correlate with either medial or intimal venous width. We conclude there may be changes in the veins of hemodialysis patients with time that cause thickening of layers, even in veins not directly used for access. This may affect the creation or survival of subsequent vascular accesses.

Pharmacologic prevention of vascular access stenosis

Vascular access dysfunction continues to result in substantial morbidity for chronic hemodialysis patients. Pharmacologic and molecular biologic approaches to prevention of vascular access dysfunction, if clinically successful, will be cost effective and improve quality of life for chronic dialysis patients. This review summarizes currently available information and future prospects in pharmacologic and molecular biologic approaches to preventing vascular access stenosis.

Does blood flow accurately predict thrombosis or failure of hemodialysis synthetic grafts? A meta-analysis

A number of studies have reported that a single low blood flow (Qa) measurement in synthetic hemodialysis grafts predicts thrombosis or failure. In a meta-analysis of these studies, we computed receiver operating characteristic (ROC) curves that evaluated the predictive accuracy of a Qa measurement. The ROC curves plotted sensitivity versus false-positive rate for predicting thrombosis or failure at different Qa thresholds. A perfect predictor has an area under the curve (AUC) of 1.0, whereas a predictor with no discriminative ability has an AUC of 0.5. We identified studies through a literature search and included our own unpublished data. A random-effects model was used to combine the ROC curves from different studies. Of 19 identified studies, 12 were suitable for computing binormal ROC curves (6 predicted thrombosis; 6 predicted failure). The studies measured Qa and then observed outcome during periods of 1.5 to more than 6 months. The combined AUCs from these studies indicate Qa was a relatively poor predictor, with 0.70 +/- 0. 04 (range, 0.61 to 0.84) for thrombosis and 0.76 +/- 0.07 (range, 0. 62 to 0.90) for failure. The wide range of AUCs also shows there was much heterogeneity between studies. We conclude that a single Qa measurement does not appear to have enough accuracy to be a clinically useful predictor of graft thrombosis or failure. Serial Qa measurements and identification of factors that caused heterogeneity between studies may be needed to achieve sufficient accuracy.

Monitoring interposition graft venous pressures at higher blood-flow rates improves sensitivity in predicting graft failure

Monitoring the patency of hemodialysis interposition grafts is recommended to improve graft survival. Which blood flows best predict graft survival is not known. We monitored venous pressures in 32 dialysis patients over a median of 252 days at variable flow rates of the blood pump (Qb). Venous pressure trends (VPTs), maximum venous pressure (MVP), and the variability of venous pressure (percent coefficient of variation) were calculated. Kaplan-Meier curves were constructed from the time of the end of VPT monitoring to time to failure, defined as angioplasty, clotting, or surgical revision. Risk for graft failure for each 10-mm Hg increase in venous pressure was calculated by the Cox proportional hazards model. There were 12 graft failures, but no failures in 12 fistulas over the course of the study. The variability in venous pressure was less at greater Qbs. For grafts, VPTs were predictive of event only when calculated for Qbs greater than 100 mL/min. At Qbs of 400 mL/min, there was a 70% risk for graft failure with each 10-mm Hg increase in VPT. The risk for graft failure increased between 28% and 44% for each 10-mm Hg increase in MVP at all Qbs. MVP of 230 mm Hg at a Qb of 400 mL/min provided the best efficiency of test performance. Dialysis venous chamber pressure monitoring is a useful test to predict graft stenosis or thrombosis. There is a substantial variability in venous pressures in the same patient that reduces with increasing Qbs. Venous pressure monitoring at greater Qbs provides a more sensitive method for predicting access failure.