Medial fibrosis, vascular calcification, intimal hyperplasia, and arteriovenous fistula maturation

BACKGROUND

Arteriovenous fistulas (AVFs) for hemodialysis frequently fail to mature because of inadequate dilation or early stenosis. The pathogenesis of AVF nonmaturation may be related to pre-existing vascular pathologic states: medial fibrosis or microcalcification may limit arterial dilation, and intimal hyperplasia may cause stenosis.

STUDY DESIGN

Observational study.

SETTING & PARTICIPANTS

Patients with chronic kidney disease (N = 50) undergoing AVF placement.

PREDICTORS

Medial fibrosis, microcalcification, and intimal hyperplasia in arteries and veins obtained during AVF creation.

OUTCOME & MEASUREMENTS

AVF nonmaturation.

RESULTS

AVF nonmaturation occurred in 38% of patients despite attempted salvage procedures. Preoperative arterial diameter was associated with upper-arm AVF maturation (P = 0.007). Medial fibrosis was similar in patients with nonmaturing and mature AVFs (60% ± 14% vs 66% ± 13%; P = 0.2). AVF nonmaturation was not associated with patient age or diabetes, although both variables were associated significantly with severe medial fibrosis. Conversely, AVF nonmaturation was higher in women than men despite similar medial fibrosis in both sexes. Arterial microcalcification (assessed semiquantitatively) tended to be associated with AVF nonmaturation (1.3 ± 0.8 vs 0.9 ± 0.8; P = 0.08). None of the arteries or veins obtained at AVF creation had intimal hyperplasia. However, repeated venous samples obtained in 6 patients during surgical revision of an immature AVF showed venous neointimal hyperplasia.

LIMITATIONS

Single-center study.

CONCLUSION

Medial fibrosis and microcalcification are frequent in arteries used to create AVFs, but do not explain AVF nonmaturation. Unlike previous studies, intimal hyperplasia was not present at baseline, but developed de novo in nonmaturing AVFs.

The spectrum of infections in catheter-dependent hemodialysis patients

BACKGROUND AND OBJECTIVES

Catheter-dependent hemodialysis patients may develop access-related and nonaccess-related infections that may be managed in the outpatient arena or in the hospital. The goal of this study was to quantify infections in such patients, to characterize their clinical presentations, and to evaluate factors determining need for hospitalization.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We collected prospective data on the clinical management of catheter-dependent hemodialysis patients with suspected infection at a large dialysis center. We documented the presenting symptoms, type of infection, pathogen, and whether hospitalization occurred.

RESULTS

An infection was suspected in 305 separate cases and confirmed in 88%. The 268 diagnosed infections included catheter-related bacteremia (69%), another access-related infection (19%), and nonaccess-related infection (12%). The overall frequency of infection was 4.62 per 1000 catheter-days. Hospitalization occurred in 37% of all infections, but it varied greatly (72% for nonaccess-related infection, 34% for catheter-related bacteremia, and 4% for exit-site infection). Among patients with catheter-related bacteremia, the likelihood of hospitalization varied by pathogen, being 53% for Staphylococcus aureus, 30% for Enterococcus, 23% for Staphylococcus epidermidis, and 17% for gram-negative rods (P < 0.001). The likelihood of hospitalization was not associated with age, gender, or diabetes. Fever was a presenting symptom in only 47% of cases of catheter-related bacteremia.

CONCLUSIONS

Catheter-dependent patients have a high burden of infection. It is important to evaluate patients with suspected infection for various access-related and nonaccess-related infections. A low threshold is indicated for suspecting catheter-related bacteremia because the patients frequently present without fever.

Arteriovenous graft placement in predialysis patients: a potential catheter-sparing strategy

BACKGROUND

When predialysis patients are deemed unsuitable candidates for an arteriovenous fistula, current guidelines recommend waiting until just before or after initiation of dialysis therapy before placing a graft. This strategy may increase catheter use when these patients start dialysis therapy. We compared the outcomes of patients whose grafts were placed before and after dialysis therapy initiation.

STUDY DESIGN

Retrospective analysis of a prospective computerized vascular access database.

SETTING & PARTICIPANTS

Patients with chronic kidney disease receiving their first arteriovenous graft (n = 248) at a large medical center.

PREDICTOR

Timing of graft placement (before or after initiation of dialysis therapy).

OUTCOME & MEASUREMENTS

Primary graft failure, cumulative graft survival, catheter dependence, and catheter-related bacteremia.

RESULTS

The first graft was placed predialysis in 62 patients and postdialysis in 186 patients. Primary graft failure was similar for pre- and postdialysis grafts (20% vs 24%; P = 0.5). Median cumulative graft survival was similar for pre- and postdialysis grafts (365 vs 414 days; HR, 1.22; 95% CI, 0.81-1.98; P = 0.3). Median duration of catheter dependence after graft placement in the postdialysis group was 48 days and was associated with 0.63 (95% CI, 0.48-0.79) episodes of catheter-related bacteremia per patient.

LIMITATIONS

Retrospective analysis, single medical center.

CONCLUSION

Grafts placed predialysis have primary failure rates and cumulative survival similar to those placed after starting dialysis therapy. However, postdialysis graft placement is associated with prolonged catheter dependence and frequent bacteremia. Predialysis graft placement may decrease catheter dependence and bacteremia in selected patients.

Use of aspirin associates with longer primary patency of hemodialysis grafts

Extended-release dipyridamole plus low-dose aspirin (ERDP/ASA) prolongs primary unassisted graft patency of newly created hemodialysis arteriovenous grafts, but the individual contributions of each component are unknown. Here, we analyzed whether use of aspirin at baseline associated with primary unassisted graft patency among participants in a randomized trial that compared ERDP/ASA and placebo in newly created grafts. We used Cox proportional hazards regression, adjusting for prespecified baseline comorbidities and covariates. Of all participants, 43% reported use of aspirin at baseline; of these, 82% remained on nonstudy aspirin (i.e., excluding ERDP/ASA) at 1 year. After 1 year of follow-up, the incidence of primary unassisted patency among participants using aspirin at baseline was 30% (95% CI: 24 to 35%) and among those not using aspirin was 23% (95% CI: 18 to 27%). Use of aspirin at baseline associated with a dose-dependent prolongation of primary unassisted graft patency that approached statistical significance (adjusted HR, 0.83; 95% CI: 0.68 to 1.01; P=0.06). Use of aspirin at baseline did not associate with prolongation of cumulative graft patency or participant survival. In conclusion, use of aspirin associates with a trend toward longer primary unassisted patency of newly placed hemodialysis grafts similar to that observed for ERDP/ASA.

Whether and when to refer patients for predialysis AV fistula creation: complex decision making in the face of uncertainty

Patients who initiate chronic dialysis with a functional arteriovenous (AV) fistula survive longer and experience fewer complications after initiation of dialysis than those who require a catheter. However, more than 80% of patients in this country begin chronic dialysis with a catheter rather than a fistula, either because they do not have a permanent access or their permanent access is not ready for use. Increasing rates of predialysis AV fistula placement is thus considered a priority area for predialysis care in this country. However, achievement of a functional AV fistula by the time of dialysis initiation is not always an easy proposition. We here outline the limitations of currently recommended approaches toward timing of AV fistula placement. We also highlight the potential complexity of patient and clinician decision making in this area. Particularly in the presence of advanced age and a high burden of comorbidity and disability, it is often uncertain whether patients will need, want, or benefit from chronic dialysis. Adding to this uncertainty, it is often not known whether, when, and after how many revisions an AV fistula will be sufficiently mature to support dialysis. We argue that it is important to acknowledge the complexity of medical decision making in this area and the limitations of currently available prognostic tools to guide such decision making. We conclude that initiation of dialysis with a catheter is appropriate for patients in whom the perceived harms of preemptive fistula placement outweigh the expected benefit.

Medicare reimbursement policies and hemodialysis vascular access outcomes: a need for change

In March 2010, the Center for Medicare and Medicaid Services (CMS) convened several clinical technical expert panels (C-TEP) to provide recommendations for improving various aspects of hemodialysis management. One of the C-TEPs was tasked with recommending measures to decrease vascular access-related infections. The members of this C-TEP, who are the authors of this manuscript, concluded unanimously that the single most important measure would be to remove financial and regulatory barriers to timely placement and revision of hemodialysis fistulas and the concurrent avoidance of catheter use. The following position paper outlines the financial barriers to improved vascular access outcomes and our proposals for a future CMS demonstration project.

Saving Infected Catheters: Why and How

Conventional management of dialysis catheter-related bacteremia involves administration of systemic antibiotics, as well as removal of the infected catheter. This approach adds burdensome and expensive procedures, and creates short-term problems for dialysis access. Recent research has shown that bacterial biofilms form routinely in the catheter lumen, and act as the nidus for bacteremic episodes. Instillation of a concentrated antibiotic-anticoagulant solution into the catheter lumen ('antibiotic lock') may permit successful treatment of the infection, while salvaging the patient's catheter. A number of recent studies have reported the success of an antibiotic lock protocol in about two thirds of cases of catheter-related bacteremia. Catheter replacement is only performed in those patients with protocol failures (persistent fever or positive surveillance blood cultures). In conclusion, routine application of an antibiotic lock protocol may reduce substantially the need for routine catheter replacement in hemodialysis patients with catheter-related bacteremia.

Decreased cumulative access survival in arteriovenous fistulas requiring interventions to promote maturation

BACKGROUND AND OBJECTIVES

New arteriovenous fistulas (AVF) are frequently unsuitable for hemodialysis because of AVF nonmaturation. Aggressive endovascular or surgical interventions are often undertaken to salvage nonmaturing AVFs. The effect of early interventions to promote AVF maturation on subsequent long-term AVF outcomes is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We evaluated 173 hemodialysis patients from two academic centers who received a new AVF. Of these, 96 (56%) required no further intervention, 54 (31%) required one intervention, and 23 (13%) required two or more interventions to achieve suitability for dialysis. We calculated AVF survival and frequency of postmaturation interventions in each group.

RESULTS

Cumulative AVF survival (access cannulation to permanent failure) in patients with two or more versus one versus zero interventions before maturation was 68% versus 78% versus 92% at 1 year, 57% versus 71% versus 85% at 2 years, and 42% versus 57% versus 75% at 3 years. Using Cox regression analysis with interventions before maturation, age, sex, race, diabetes, peripheral vascular disease, access site, and obesity in the model, intervention before maturation (two or more) was the only factor associated with cumulative AVF survival. The number of interventions required to maintain patency after maturation was 3.51 ± 2.20 versus 1.37 ± 0.31 versus 0.76 ± 0.10 per year in patients with two or more versus one versus zero interventions before maturation.

CONCLUSIONS

Compared with AVF that mature without interventions, AVF that require interventions have decreased cumulative survival and require more interventions to maintain their patency for hemodialysis.

Warfarin dosing in patients with impaired kidney function

BACKGROUND

In patients with kidney impairment, warfarin, a drug metabolized primarily by the cytochrome P-450 system, is initiated at similar doses and managed similarly as in the general medical population. Unfortunately, few data exist to guide dose adjustment in patients with decreased kidney function. Here, we determine the degree of warfarin dose reduction associated with kidney impairment and make recommendations for warfarin dosing.

STUDY DESIGN

Cross-sectional analysis.

SETTING & PARTICIPANTS

Long-term warfarin users followed up at anticoagulation clinics (n = 980); 708 participants from the University of Alabama (UAB) and 272 participants from the University of Chicago (UIC).

PREDICTOR

No/mild (estimated glomerular filtration rate [eGFR] ≥ 60 mL/min/1.73 m(2)), moderate (eGFR, 30-59 mL/min/1.73 m(2)), and severe (eGFR < 30 mL/min/1.73 m(2)) kidney impairment; CYP2C9 and VKORC1 genotype; age; race; sex; body mass; sociodemographic factors; smoking status; alcohol; vitamin K intake; comorbid conditions (eg, congestive heart failure); and drug interactions (eg, amiodarone and statins).

OUTCOME & MEASUREMENT

Warfarin dose (milligrams per day) was evaluated using linear regression after adjustment for clinical, demographic, and genetic factors.

RESULTS

Prevalences of moderate (31.8% and 27.6%) and severe kidney impairment (8.9% and 6.6%) were similar in the UAB and UIC cohorts. Warfarin dose requirements were significantly lower in patients with moderate and severe kidney impairment compared with those with no/mild kidney impairment in the UAB (P < 0.001) and UIC (P < 0.001) cohorts. Compared with patients with no/mild kidney impairment, patients with moderate kidney impairment required 9.5% lower doses (P < 0.001) and patients with severe kidney impairment required 19% lower doses (P < 0.001).

LIMITATIONS

No measurement of warfarin, serum albumin, vitamin K, and coagulation factors; no evaluation of other markers (eg, cystatin).

CONCLUSION

Moderate and severe kidney impairment were associated with a reduction in warfarin dose requirements.

Comparison of radiocephalic fistulas placed in the proximal forearm and in the wrist

Non-maturation is a common problem in patients receiving an arteriovenous fistula. The first vascular access choice is a distal radiocephalic fistula (dRCF) at the wrist. Patients with a failed dRCF or with vessels unsuitable for dRCF, the recommendation is to place a brachiocephalic fistula in the upper arm. Proximal forearm radiocephalic fistulas (pRCF) are created infrequently, but may permit a second forearm fistula before proceeding to the upper arm. The goal of the present study was to compare the outcomes of them. We retrospectively analyzed a computerized access database to compare the outcomes of 19 RCF and 39 dRCF placed during a 6-month period. The baseline characteristics were similar, except those with a pRCF were more likely to have previous access and be male. Primary failure (non-maturation) was lower for pRCF than dRCF (32 vs. 59%, p = 0.05); and excluding secondary failures, cumulative fistula survival was similar (92 vs. 86% at 1 year and 74 vs. 76% at 2 years, p = 0.56). pRCF may be an attractive alternative to a brachiocephalic fistula in patients who cannot receive a dRCF. pRCF has a lower non-maturation rate than that of a dRCF, and a comparable cumulative survival once it is used successfully for dialysis.

A physiologic-based approach to the treatment of acute hyperkalemia

Hyperkalemia is a common and potentially lethal disorder. Given its variable presentation, clinicians should have a high index of suspicion, especially in patients with chronic kidney disease. The present case highlights key physiologic mechanisms in the development of hyperkalemia and provides an outline for emergent treatment. In this context, we discuss specific mechanisms of action of available treatments of hyperkalemia.

Does the heparin lock concentration affect hemodialysis catheter patency?

BACKGROUND AND OBJECTIVES

Concentrated heparin solutions are instilled into the catheter lumens after each hemodialysis session to prevent catheter thrombosis. The heparin lock concentration at many centers has been decreased recently to reduce the risk of systemic bleeding and contain costs. However, the effect of this change on catheter patency is unknown. We compared catheter patency between two heparin lock solutions: 1000 versus 5000 units/ml.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

With use of a prospective, computerized, vascular access database, 105 patients with newly placed tunneled hemodialysis catheters, including 58 patients receiving a 5000 units/ml heparin lock and 47 patients receiving a 1000 units/ml heparin lock, were retrospectively identified. The primary endpoint was cumulative catheter patency and the secondary endpoint was frequency of thrombolytic instillation.

RESULTS

Cumulative catheter survival was similar in the two groups, being 71% versus 73% at 120 days in the low- and high-concentration heparin lock groups (hazard ratio of catheter failure, 0.97; 95% confidence interval, 0.45 to 2.09; P = 0.95). The frequency of tissue plasminogen activator instillation was significantly greater in the low-concentration heparin group (hazard ratio, 2.18; 95% CI, 1.26 to 3.86; P = 0.005). No major bleeding complications were observed in either treatment group. The overall drug cost for maintaining catheter patency was 23% lower with the low-concentration heparin lock ($1418 versus $1917) to maintain catheter patency for 1000 days.

CONCLUSIONS

Low-concentration heparin lock solutions do not decrease cumulative dialysis catheter patency, but require a twofold increase in thrombolytic instillation to maintain long-term patency.