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8 Four different types anastomotic configurations: A) Side-to-side anastomosis, B) End-to-end anastomosis, C) End-to-side anastomosis, and D) Side-to-end anastomosis
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Therapeutic options for patients suffering from end-stage renal disease have improved tremendously over the last decades and can be divided into three categories: hemodialysis, peritoneal dialysis and kidney transplantation. Transplantation remains the treatment of choice, however, lack of donor organs results in the necessity of performing-tempora...
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Context 1
... of access placement to access thrombosis or time of measurement of patency, including intervening manipulations (surgical or endovascular interventions) designed to maintain the functionality of a patent access Secondary patency: Secondary patency (access survival until abandonment) is defined as the interval from time of access placement to access abandonment or time of measurement of patency, including intervening manipulations (surgical or endovascular interventions) designed to reestablish the functionality of thrombosed access According to the NKF-K/DOQI guidelines (NKF-K/DOQI 2001), a direct surgical connection between an artery and a vein as distal as possible in the upper extremity on the non-dominant side is preferred in patients requiring long-term HD. In case distal vascular diameters are not suitable for creation of an AVF, more proximal vessels are utilized (see Fig. 5.6). When proximal vascular diameters are still not suitable or in case autologous vessels are no longer available, the second option is the creation of an AVG, where prosthetic material is used to make the connection. When HD therapy needs to be initiated before either an AVF or AVG is created, a CVC can be used as a temporary VA. However, CVC use should be minimized because of increased risk of sepsis, increased mortality, and development of central venous stenosis or thrombosis which comprises future VA procedures in the ipsilateral upper limb. Unfortunately, many patients require a CVC either to start dialysis or as a bridge between AVF failure and the creation of a new VA. A distal radiocephalic arteriovenous fistula (RC-AVF) is considered the best option for initial VA in the vast majority of patients. Although creation of a RC-AVF may be compromised by insufficient vascular diameters or a diseased cephalic vein, post-operative flow enhancement and dilatation of the venous cannulation traject are usually sufficient to meet the demands for dialysis prescription. Furthermore, it leaves more proximal sites for future procedures in the event of failure. To preserve the possibility of distal RC-AVF creation, it is crucial to avoid cannulation of the cephalic vein after the diagnosis ESRD has been established. After successful creation of a RC-AVF it may function for years with a minimum of complications, revisions and interventions. On the long term, RC-AVFs have a low incidence of thrombosis (0.2 events per patient per year) and infection (2%) compared to more proximal AVFs and the use of grafts. However, relatively high numbers of early thrombosis and nonmaturation are important disadvantages of this fistula configuration. Observational studies report early failure rates varying from 5% to 46% and secondary patency rates from 42% to 83% after one year of follow-up (Silva et al. 1998; Golledge et al. 1999; Wolowczyk et al. 2000; Gibson et al. 2001; Allon et al. 2001; Dixon et al. 2002; Ravani et al. 2002; Rooijens et al. 2004; Biuckians et al. 2008; Huijbregts et al. 2008) (see Table 5.2). Older studies incorporated in the meta-analysis performed by Rooijens et al (2004) identified lower primary failure rates (17%), which might be explained by the increase in comorbidities in the ESRD patient population nowadays. Compared to men, women have poorer patency rates which might advocate more proximal AVF creation if the cephalic vein or radial artery is small. When a wrist RC-AVF has failed or is impossible to create, a more proximally located anastomosis from the mid-forearm to the elbow between the radial artery and cephalic vein may be employed before re- sorting to secondary autologous VA. The patient is positioned on the operating table with the arm in 90 de- grees of abduction. Subsequently, venous congestion pressure is applied after which the radial artery and the cephalic vein together with their first order side branches are marked on the skin: the preferred location for the incision is identified. After release of the tourniquet disinfection of the arm can take place. Ideally this procedure is carried out under local or regional anesthesia instead of general anesthesia which is associated with decreased blood pressures during surgery. This procedural drop in blood pressure re- stricts post-operative flow enhancement and increases the risk of immediate post-operative thrombosis. A local subcutaneous injection of lido- caine 1% (without epinephrine) is usually sufficient to create this type of VA. Some studies have described a beneficiary effect of regional anesthesia: peripheral vasodilatation which potentially results a larger post- operative flow enhancement (Malinzak and Gan 2009; Yildirim et al. 2006). After a longitudinal or transverse incision near the wrist, the cephalic vein and radial artery are dissected from their surrounding tissue. Next, the cephalic vein is mobilized towards the radial artery where the anastomosis will be created (see Fig. 5.7). For the RC-AVF, four types of anastomosis can be employed (see Fig. ...
Citations
... Upper-extremity veins are important in ESRD because they may be used to create vascular accesses [114]. However, unlike the arteries, the contribution of CKD-related factors to chronic venous remodeling and transcriptomic changes in CKD veins has been poorly studied. ...
Most patients with end-stage renal disease (ESRD) and advanced chronic kidney disease (CKD) choose hemodialysis as their treatment of choice. Thus, upper-extremity veins provide a functioning arteriovenous access to reduce dependence on central venous catheters. However, it is unknown whether CKD reprograms the transcriptome of veins and primes them for arteriovenous fistula (AVF) failure. To examine this, we performed transcriptomic analyses of bulk RNA sequencing data of veins isolated from 48 CKD patients and 20 non-CKD controls and made the following findings: (1) CKD converts veins into immune organs by upregulating 13 cytokine and chemokine genes, and over 50 canonical and noncanonical secretome genes; (2) CKD increases innate immune responses by upregulating 12 innate immune response genes and 18 cell membrane protein genes for increased intercellular communication, such as CX3CR1 chemokine signaling; (3) CKD upregulates five endoplasmic reticulum protein-coding genes and three mitochondrial genes, impairing mitochondrial bioenergetics and inducing immunometabolic reprogramming; (4) CKD reprograms fibrogenic processes in veins by upregulating 20 fibroblast genes and 6 fibrogenic factors, priming the vein for AVF failure; (5) CKD reprograms numerous cell death and survival programs; (6) CKD reprograms protein kinase signal transduction pathways and upregulates SRPK3 and CHKB; and (7) CKD reprograms vein transcriptomes and upregulates MYCN, AP1, and 11 other transcription factors for embryonic organ development, positive regulation of developmental growth, and muscle structure development in veins. These results provide novel insights on the roles of veins as immune endocrine organs and the effect of CKD in upregulating secretomes and driving immune and vascular cell differentiation.
... In this metric the K represent the clearance performance, a %, t represents the time of operation, in minutes, and V is the volumetric flow rate through the device, mL/min. Since the flow rate of blood coming into the kidneys is ∼1000 mL/min, a typical dialysis machine would process about 1/3rd of that (e.g., ∼350 mL/min for hemodialysis machine) [167]. However, since hemodialysis is only connected 12-15 hours/ week, so a device which is continuously operating (assuming roughly the same filtration efficiency) could have a much lower average flow rate, something on the order of ∼30-40 mL/min. ...
Globally, around 2.6 million people receive renal replacement therapy (RRT), and a further 4.9-9.7 million people need, but do not have access to, RRT [1]. The next generation RRT devices will certainly be in demand due to the increasing occurrence of diabetes, atherosclerosis and the growing population of older citizens. This review provides a comprehensive, yet concise overview of the cleared and remaining hurdles in the development of artificial kidneys to move beyond traditional dialysis technology–the current baseline of renal failure treatment. It compares and contrasts between new concepts in cell-based and non-cell-based approaches. Based on this study, a new engineering perspective on the future of artificial kidneys is described. This review suggests that stem-cell-based artificial kidneys represent a long-term, complete solution but it can take years of development due to the limitations of current cell seeding technology, viability and complicated behavior control. Alternatively, there is much potential for near- and medium- term solutions with the development of non-cell-based wearable and implantable devices to support current therapies. Based on recent fundamental advances in microfluidics, membranes and related research, it may be possible to integrate these technologies to enable implantable artificial kidneys (iAK) in the near future.
Arterio-Venous Fistulas (avf) are the most popular form of vascular access used for hemodialysis. However they continue to present complications leading to early and late failure. To understand the reasons for failure, it is necessary to analyze the hemodynamics involved. Wall shear stress (wss) is commonly studied in avfs as it often relates to cardiovascular disease, although there is dispute over whether high or low wss is detrimental to avf patency. The goal of this paper is to investigate velocity flow conditions in a rigid, patient-specific brachio-cephalic avf model in both steady flow (Re = 1817) and patient-specific pulsatile flow (Reav=1817, Remax=2233). Particle Image Velocimetry (piv) measurements were performed at the anastomosis to capture the complex 3D-3C flow present. The results from this study found regions of recirculation and high velocity fluctuations in the distal artery and proximal vein, and flow impingement at the anastomosis toe. Steady and pulsatile flow demonstrated similar flow features, possibly owed to the low pulsatility index. In addition, the recirculation zone did not vary along the waveform. The directional variability was seen to be the highest at the regions of recirculation and flow impingement suggesting regions of high transWSS while the coefficient of variation was greatest at the walls and in areas of flow separation indicating high temporal wall shear stress.
Acute kidney injury (AKI) is a common condition amongst critically ill patients in the medical intensive care unit (ICU) and is associated with increased morbidity and mortality. There are several areas of ongoing debate regarding management of AKI, specifically the initiation and timing of renal replacement therapy (RRT). In this review, we aim to concisely discuss epidemiology, current evidence with regards to optimal vascular access, timing of initiation and modality of renal replacement therapy in acute kidney injury in critically ill patients.
The dialysis population has grown rapidly in the past decade, as a consequence of government support for catastrophic illness and broadening of the indications for patient selection. Progress in the management of patients on hemodialysis has resulted in a steady increase in the number of surviving long-term patients with end stage renal disease. As a result, this population includes large numbers of older subjects, as well as individuals with systemic diseases, in whom establishment and maintenance of adequate vascular access is particularly difficult. The success of vascular access in the elderly patients depends upon proper selection of the type and location of the A-V fistula, and upon prompt and aggressive management of any developing complications. While experience with transplantation in elderly patients has significantly improved in recent years, careful evaluation of the elderly potential allograft recipient may improve patient and graft survival, by identifying those patients in whom the risk involved may be prohibitive. In addition, growing knowledge and judicious use of immunosuppressive medications have further improved the outcome following transplantation. In the absence of any obvious contraindications, transplantation is a safe, effective treatment modality for end-stage renal disease in elderly patients.
Introduction:
Inadequate flow enhancement on the one hand, and excessive flow enhancement on the other hand, remain frequent complications of arteriovenous fistula (AVF) creation, and hamper hemodialysis therapy in patients with end-stage renal disease. In an effort to reduce these, a patient-specific computational model, capable of predicting postoperative flow, has been developed. The purpose of this study was to determine the accuracy of the patient-specific model and to investigate its feasibility to support decision-making in AVF surgery.
Methods:
Patient-specific pulse wave propagation models were created for 25 patients awaiting AVF creation. Model input parameters were obtained from clinical measurements and literature. For every patient, a radiocephalic AVF, a brachiocephalic AVF, and a brachiobasilic AVF configuration were simulated and analyzed for their postoperative flow. The most distal configuration with a predicted flow between 400 and 1500 ml/min was considered the preferred location for AVF surgery. The suggestion of the model was compared to the choice of an experienced vascular surgeon. Furthermore, predicted flows were compared to measured postoperative flows.
Results:
Taken into account the confidence interval (25(th) and 75(th) percentile interval), overlap between predicted and measured postoperative flows was observed in 70% of the patients. Differentiation between upper and lower arm configuration was similar in 76% of the patients, whereas discrimination between two upper arm AVF configurations was more difficult. In 3 patients the surgeon created an upper arm AVF, while model based predictions allowed for lower arm AVF creation, thereby preserving proximal vessels. In one patient early thrombosis in a radiocephalic AVF was observed which might have been indicated by the low predicted postoperative flow.
Conclusions:
Postoperative flow can be predicted relatively accurately for multiple AVF configurations by using computational modeling. This model may therefore be considered a valuable additional tool in the preoperative work-up of patients awaiting AVF creation.
