Preferred strategy for hemodialysis access creation in elderly patients.

BACKGROUND: Adequate functioning vascular access is the key to successful hemodialysis. The use of an autologous arteriovenous fistula (AVF) is advised because of good long-term patency and a low incidence of complications. However, the number of patients with AVFs is declining because of the change in the demography of the dialysis population, with increasing numbers of very old patients with multiple comorbidities. METHODS: In this vignette an elderly patient is described with calcified distal arteries and a small cephalic vein who is referred at a late stage for access creation. The results and performance of different types of vascular access (AVF; arteriovenous graft; central vein catheter), in relation to late referral and patient demographics, are described. In addition, patient morbidity and mortality versus the type of access are discussed. CONCLUSIONS: The patient described in this vignette appears to be unsuitable for the creation of a forearm AVF because of calcified distal arteries and a small cephalic vein. The risk of non-maturing autologous AVFs is high in elderly patients and this observation might justify the use of early stick grafts. High risk patients may benefit from permanent central vein catheters.

Assisting vascular access surgery planning for hemodialysis by using MR, image segmentation techniques, and computer simulations.

The surgical creation of a vascular access, used for hemodialysis treatment of renal patients, has considerable complication rates (30-50 %). Image-based computational modeling might assist the surgeon in planning by enhanced analysis of preoperative hemodynamics, and in the future might serve as platform for outcome prediction. The objective of this study is to investigate preoperative personalization of the computer model using magnetic resonance (MR). MR-angiography and MR-flow data were obtained for eight patients and eight volunteers. Blood vessels were extracted for model input by a segmentation algorithm. Windkessel elements were added at the ends to represent the peripheral beds. Monte Carlo-based calibration was used to estimate the most influential non-measurable parameters. The predicted flow waveforms were compared with the MR-flow measurements for framework evaluation. The vasculature of all subjects were segmented in on average <5 min. The Monte Carlo-calibrated simulations showed a deviation between measured and simulated flow waveforms of 9 and 10 % for volunteers and patients, respectively. The presented method accurately mimics the preoperative hemodynamic state. Furthermore, the surgeon can interactively explore the hemodynamics at any vascular tree position. This integration of measurements in a modeling approach can provide the surgeon with additional information for preoperative planning.

Cost-effectiveness of vascular access for haemodialysis: arteriovenous fistulas versus arteriovenous grafts.

BACKGROUND: The use of an arteriovenous fistula (AVF) for haemodialysis treatment may be associated with a high early failure rate, but usually good long-term patency, while using an arteriovenous graft (AVG) yields a lower early failure rate with worse long-term patency. The aim of this study was to calculate and compare the costs and outcome of AVF and AVG surgery in terms of early and long-term patencies. METHODS: A decision tree and a Markov model were constructed to calculate costs and performance of AVFs and AVGs. The model was populated with a retrospective cohort of HD patients receiving their first VA. The outcomes were determined probabilistically with a 5-year follow-up. RESULTS: AVFs were usable for a mean (95% CI) of 28.5 months (24.6-32.5 months), while AVGs showed a patency of 25.5 months (20.0-31.2 months). The use of AVFs was the dominant type of VA and € 631 could be saved per patient/per month patency compared to AVG use. Regardless of the willingness to pay, the use of AVFs yielded a higher probability of being cost-effective compared to AVGs. CONCLUSIONS: AVFs are more cost-effective than AVGs. Nonetheless, early failure rates significantly influence AVF performance and initiatives to reduce early failure can improve its cost-effectiveness.

A pulse wave propagation model to support decision-making in vascular access planning in the clinic.

The preferred vascular access for hemodialysis is an autologous arteriovenous fistula (AVF) in the arm: a surgically created connection between an artery and vein. The surgeon selects the AVF location based on experience and preoperative diagnostics. However, 20-50% of all lower arm AVFs are hampered by a too low access flow, whereas complications associated with too high flows are observed in 20% of all upper arm AVFs. We hypothesize that a pulse wave propagation model fed by patient-specific data has the ability to assist the surgeon in selecting the optimal AVF configuration by predicting direct postoperative flow. Previously, a 1D wave propagation model (spectral elements) was developed in which an approximated velocity profile was assumed based on boundary layer theory. In this study, we derived a distributed lumped parameter implementation of the pulse wave propagation model. The elements of the electrical analog for a segment are based on the approximated velocity profiles and dependent on the Womersley number. We present the application of the lumped parameter pulse wave propagation model to vascular access surgery and show how a patient-specific model is able to predict the hemodynamical impact of AVF creation and might assist in vascular access planning. The lumped parameter pulse wave propagation model was able to select the same AVF configuration as an experienced surgeon in nine out of ten patients. In addition, in six out of ten patients predicted postoperative flows were in the same order of magnitude as measured postoperative flows. Future research should quantify uncertainty in model predictions and measurements.

Feasibility of non-contrast-enhanced magnetic resonance angiography for imaging upper extremity vasculature prior to vascular access creation.

OBJECTIVES: Preoperative mapping of arterial and venous anatomy helps to prevent postoperative complications after vascular access creation. The use of gadolinium in contrast-enhanced (CE) magnetic resonance angiography (MRA) has been linked to nephrogenic systemic fibrosis in patients with end-stage renal disease (ESRD). The purpose of this study was to evaluate non-contrast-enhanced (NCE) MRA for assessment of upper extremity and central vasculature and to compare it with CE-MRA. METHODS: NCE and CE-MRA images were acquired in 10 healthy volunteers and 15 patients with ESRD. In each data set, two observers analysed 11 arterial and 16 venous segments with regard to image quality (0-4), presence of artefacts (0-2) and vessel-to-background ratio. RESULTS: More arterial segments were depicted using CE-MRA compared to NCE-MRA (99% vs. 96%, p = 0.001) with mean image quality of 3.80 vs. 2.68, (p < 0.001) and mean vessel-to-background ratio of 6.47 vs. 4.14 (p < 0.001). Ninety-one percent of the venous segments were portrayed using NCE-MRA vs. 80% using CE-MRA (p < 0.001). Mean image quality and vessel-to-background ratio were 2.41 vs. 2.21 (p = 0.140) and 5.13 vs. 3.88 (p < 0.001), respectively. CONCLUSIONS: Although arterial image quality and vessel-to-background ratios were lower, NCE-MRA is considered a feasible alternative to CE-MRA in patients with ESRD who need imaging of the upper extremity and central vasculature prior to dialysis access creation.

Surgical techniques to improve cannulation of hemodialysis vascular access.

OBJECTIVE: Successful access cannulation is of utmost importance for adequate hemodialysis treatment. Upper arm fistulae, obesity and deep or tortuous veins may impair needling and can cause significant complications and inconvenience for the patient. In the ultimate case, cannulation problems lead to temporary central vein catheter use for dialysis or even to irreversible access loss. Surgical access revision may enhance successful cannulation. METHODS: A systematic literature review of all publications related to hemodialysis vascular access, cannulation complications and treatment was performed. RESULTS: A total of 384 publications were identified, of which only 17 were related to treatment of cannulation complications in large patient populations. The clinical success rate of surgical intervention with vein elevation or transposition ranges from 85% to 91%. The 1-year primary and secondary patencies are 60% and 71%, respectively. Lipectomy results in an initial success rate of 100% with a primary and secondary patency of 71% and 98%, respectively, after 1 year of follow-up. CONCLUSION: Surgical revision to improve hemodialysis vascular access cannulation has a high clinical success rate with good long-term patency.