Access Types

Cognitive Networks have been proposed to opportunistically discover and exploit licensed spectrum bands, in which the secondary users' (SU) activity is subordinated to primary users (PU). Depending on the nature of interaction between the SU and PU, there are two frequently encountered types of spectrum access: \emph{underlay} and \emph{interweave}. While a lot of research effort has been devoted to each mode, there is no clear consensus about which type of access performs better in different scenarios and for different metrics. To this end, in this paper we approach this question analytically, and provide closed-form expressions that allow one to compare the performance of the two types of access under a common network setup. We focus on the average delay as the key metric, which we analyze using queueing theory. This allows an SU to decide when one type of access technique provides better performance, as a function of the metric of interest and key network parameters. What is more, based on this analysis, we propose a dynamic (hybrid) policy, that can decide at any point to switch from one type of access to the other, offering up to 50% of additional performance improvement, compared to the optimal static policy in the scenario at hand. We provide extensive validation results using a wide range of realistic simulation scenarios.

Influence of the Type of Thoracic Access on Postesophagectomy Respiratory Complications

Data on hemodialysis (HD)-related organism specific bacteremia rates by type of access over an extended period are scant in the literature. Using a registry data base we examined all positive blood cultures by organisms for each type of HD access over 14 years. The IRB-approved registry data collection of prevalent patients at our HD unit from 1/1/1999 through 12/31/2012 was analyzed. All positive blood cultures were recorded and expressed as episodes/1,000 days by access type: arteriovenous fistula (AVF), arteriovenous graft (AVG), and central venous catheter (CVC). The rate of positive blood cultures in patients with CVCs was 1.86/1,000 days and was much higher than in patients with an AVF (0.08/1,000 days, p<0.001) or an AVG (0.31/1,000 days, p<0.002). There was considerable fluctuation in the bacteremia rate in CVCs with a spike during 2004-2008, due predominately to coagulase-negative staphylococcus (CNS) bacteremia. The rate subsequently decreased after retraining of staff. The exit site infection (ESI) rate of CVCs was low, suggesting this was not contributing to the cause of the increase rate of CNS bacteremia. Those patients using a CVC had a markedly increased risk of multiple episodes compared to those using an AVF. Bacteremia with Pseudomonas, polymicrobial, and fungal organisms occurred only in those with a CVC. The frequency and type of positive blood culture in HD patients are highly associated with type of access used. The high rate of CNS bacteremia with CVC in conjunction with low ESI rate suggests that contamination at the time of accessing the catheter may be the problem. Staff training was followed by a decrease in infection rates. Trending organism-specific bacteremia infection rates in HD units may provide important clues to bacteremia causality and thus prevention.

People with a temporary or permanent physical impairment are often excluded from bathing activities due to the difficulties of getting in and out of the water. This paper explores pool design, specifically the design of the access to the tank, which is the key to pools’ inclusivity. In trying to break down existing barriers between users, accessibility experts and designers, we interviewed physically impaired architects about their perception of four types of pool access often used by wheelchair users: ramps, transfer walls, transfer systems and lifts. The interviews revealed limitations in all four types of pool access. To compensate for the limitations identified, combining different types of access in one single pool may be of interest. Moreover, the interviews allowed the identification of another type of pool access, designed by one of the interviewees: an upper pool border connected to an underwater bed and seat allows for an easier exit than transfer walls and transfer systems. Another interviewee advanced the idea of a cane holder for physically and visually impaired people, which may contribute to freeing poolside floors from obstacles and reducing the risk of falls. These insights may contribute to making pools more inclusive, by accommodating specific temporary or permanent mobility needs of all of us.

Chapter 37 - Intravenous Access

Retroperitoneal Versus Direct Femoral Artery Approach for Thoracic Endovascular Aortic Repair Access: A Case–Control Study

La influencia del tipo de abordaje torácico sobre el desarrollo de complicaciones respiratorias tras la esofagectomíaesofagectomía

Background: The influence of intravenous drug abuse (IVDA) on hemodialysis access placement practices and access survival in HIV-infected patients is unknown. Methods: We conducted a retrospective study of 60, HIV seropositive, maintenance hemodialysis patients. Type of access and assisted access survival (measured from date of placement) were compared in those with (77%) and without (23%) a history of IVDA. Results: Mean age was 37.8 years, mean baseline serum albumin was 2.9 g/dl and median CD4 count was 222 cells/mm³. Fifteen patients, all IVDA, were dialyzed using only tunneled catheters (median number of catheters per person (range): 2.5 (1–11)). There were longer delays in creation of a permanent access (p = 0.08), but no difference in the type of permanent access placed in IVDA versus the non-IVDA group. Over 1,051 cumulative months of access follow-up, 134 tunneled catheters, 28 grafts and 19 fistulae were placed, with observed failure rates of 1 per 4.7 access-months, 1 per 19.7 access-months, 1 per 38.2 access-months, respectively. The adjusted relative hazard of access failure for grafts versus catheters was 0.41 (95% CI: 0.23, 0.72; p = 0.002) and for fistulae versus catheters was 0.21 (95% CI: 0.08, 0.52; p = 0.001). Thirty-two percent of accesses were removed due to infection, an infection removal rate for catheters of 1 per 7.8 access-months and for grafts of 1 per 62.5 access-months; all graft infections occurred in the IVDA group. No fistula was removed due to infection. Conclusion: Fistulae are the first line of choice for hemodialysis access in HIV-seropositive patients regardless of IVDA history; if not feasible, graft placement in non-IVDA or abstinent IVDA patients is recommended. In those with active IVDA, the optimal method of renal replacement therapy and type of hemodialysis access remain uncertain.

Introduction: The type of vascular access used by haemodialysis patients is thought to be one of the predictors of patient survival. However, many previous studies have been unable to separate the effect of access type from the effects of other differences between patients groups or have included incident patients. Some centres report excellent outcomes using dialysis catheters in stable prevalent patients and challenge the current guidelines about the use of long term catheters. This is an observational UK centre level study reporting on the relationship between the percentage of established prevalent patients using definitive access and the subsequent 1 year survival. Method: Vascular access audit data from 2005 and UKRR survival data at 1 year for patients who had been on HD for over 3 months was obtained from the UKRR database. Regression analysis was used to assess the amount of variation in 1 year survival that could be explained by the percentage of patients using an AVF or AVG in a centre. Results: From the renal centres reporting to the UKRR in 2005, 16,984 patients had vascular access data. The mean centre level 1 year survival was 86.4% (95% CI: 82.2–90.9) and was 86.9% (95% CI: 82.8–91.2) after censoring for transplantation. The mean percentage of haemodialysis patients using definitive access (AVF or AVG) in a centre was 69.8% (SD 10.4). A small positive association was found between the percentage of HD patients using an AVF or AVG in a centre and 1 year uncensored survival (β = 0.06, p = 0.04). The type of access in use was able to explain 6% of the variation in centre level survival. Conclusions: To some extent, this study has repeated work done by DOPPS and in the US but for the first time has studied only prevalent dialysis patients and looked at the UK dialysis population. Whilst increased venous catheter use was associated with an increase in one year mortality of prevalent established haemodialysis patients, this effect was very small and only accounted for some 6% of the variation in one year mortality between renal centres. Further work using data from the current large vascular access audit needs to be done to further elucidate best practice within the UK.

Vascular Access Practice in Hemodialysis: Instrumental in Determining Patient Mortality

Authors’ reply

BackgroundThere is a lack of contemporary data describing global variations in vascular access for hemodialysis (HD). We used the third iteration of the International Society of Nephrology Global Kidney Health Atlas (ISN-GKHA) to highlight differences in funding and availability of hemodialysis accesses used for initiating HD across world regions.MethodsSurvey questions were directed at understanding the funding modules for obtaining vascular access and types of accesses used to initiate dialysis. An electronic survey was sent to national and regional key stakeholders affiliated with the ISN between June and September 2022. Countries that participated in the survey were categorized based on World Bank Income Classification (low-, lower-middle, upper-middle, and high-income) and by their regional affiliation with the ISN.ResultsData on types of vascular access were available from 160 countries. Respondents from 35 countries (22% of surveyed countries) reported that > 50% of patients started HD with an arteriovenous fistula or graft (AVF or AVG). These rates were higher in Western Europe (n = 14; 64%), North & East Asia (n = 4; 67%), and among high-income countries (n = 24; 38%). The rates of > 50% of patients starting HD with a tunneled dialysis catheter were highest in North America & Caribbean region (n = 7; 58%) and lowest in South Asia and Newly Independent States and Russia (n = 0 in both regions). Respondents from 50% (n = 9) of low-income countries reported that > 75% of patients started HD using a temporary catheter, with the highest rates in Africa (n = 30; 75%) and Latin America (n = 14; 67%). Funding for the creation of vascular access was often through public funding and free at the point of delivery in high-income countries (n = 42; 67% for AVF/AVG, n = 44; 70% for central venous catheters). In low-income countries, private and out of pocket funding was reported as being more common (n = 8; 40% for AVF/AVG, n = 5; 25% for central venous catheters).ConclusionsHigh income countries exhibit variation in the use of AVF/AVG and tunneled catheters. In low-income countries, there is a higher use of temporary dialysis catheters and private funding models for access creation.

Background and Aims Hemodialysis (HD) is the most widely used treatment modality worldwide in the care of patients with end stage renal disease (ESRD). The success of the therapy depends largely on the quality of the VA and its proper functioning, which has a bearing on the patient's quality of life. Vascular access dysfunction remains one of the leading causes of excessive morbidity, mortality, and healthcare costs in this group. A functional vascular access is mandatory to achieve good levels of dialytic efficiency, and it is considered the lifeline of patients on maintenance HD. The ideal vascular access should have specific characteristics among which the most important are the following: ease of placement; delivery of adequate blood flow for effective dialysis; good primary patency rates; low rates of complications and side effects; long-lasting life; and low economic costs. There are 3 types of vascular accesses (VAs): the internal arteriovenous fistula (IAVF); the central venous catheter, which can be tunneled (CVC-T) or not (CVC-nT); and the synthetic vascular graft. Internal arteriovenous fistula is considered the best option because it is safer, more durable, and less expensive. The catheter is essential for emergency onset in HD but is associated with a higher number of infections, higher mortality, and greater costs. Arteriovenous fistulae (AVF) have advantages over arteriovenous grafts (AVG) and central venous catheters (CVC), but whether AVF are associated independently with better survival is unclear. The aim of this study is to determine the vascular access outcomes of ESRD patients on maintenance hemodialysis. Specifically, this study (1) described the clinicodemographic profile of the patients in terms of age, sex, primary etiology of ESRD, employment status, comorbidities, hepatitis status and family history of the disease; (2) determined the vascular access used on the HD patients (AVF/AVG, CVC or IJ; (3) identified interventions performed to maintain vascular access for hemodialysis; (4) determined the categories of the vascular access site; (5) assessed the vascular access outcome; (6) determined the reason and number for vascular access change and the (7) clinical outcome of the HD patients. Method This is a single center, cross-sectional study of ESRD patients on maintenance hemodialysis enrolled in Perpetual Succour Hospital Hemodialysis Unit from April 1, 2021, to November 30, 2023. Results There were 260 hemodialysis patients included, with successful vascular access outcome (73.13%) and were younger (57.2 ± 14.1). Those who had failed vascular access were females (54.2%), unemployed (61.4%) and had diabetes mellitus (50.6%) as the primary etiology of their ESRD. Those with failed vascular access were hypertensive (86.7%), with history of CAD and MI (57.8%) and were having diabetes mellitus (56.6%). Proportion of those with failed and successful vascular access significantly differ among hypertensives $(p = .012)$, diabetics $(p = .039)$, with chronic glomerulonephritis $(p = .011)$, and among those with malignancy $(p = .003)$. Most of those who were alive had successful vascular access (76.8%), however, among those who had failed vascular access died (57.6%). And the association of clinical outcomes (death or not) and failure or success of vascular access is statistically significant, $(p = .001)$. Conclusion Our study showed that failed vascular access were more associated with female gender, diabetes mellitus as the primary etiology of ESRD and with other co-morbid conditions such as hypertension and CAD or MI. Successful vascular outcome were among those of younger age group compared to those whose vascular access failed, probably due to better vascular condition and fewer co-morbidities. As shown in Table 2, type of access, interventions performed, and vascular access site significantly differ among HD patients with failed vascular access outcome and with those who were successful $(p = .001)$Those with failure on the vascular access were changed to CVC (44.6%) while others had changed to IJ (22.9%). Eighty of those with failed vascular (96.4%) access has changed site due to no bruit (65.0%) and thrombosis (33.8%).

Arteriovenous fistulae (AVF) have advantages over arteriovenous grafts (AVG) and central venous catheters (CVC), but whether AVF are associated independently with better survival is unclear. Recent studies showing such a survival benefit did not include early access experience or account for changes in access type over time and did not include data on some important confounders. Reported here are survival rates stratified by the type of access in use up to 3 yr after initiation of hemodialysis among 616 incident patients who were enrolled in the Choices for Healthy Outcomes in Caring for ESRD (CHOICE) Study. A total of 1084 accesses (185 AVF, 296 AVG, 603 CVC) were used for a total of 1381 person-years. At initiation, 409 (66%) patients were using a CVC, 122 (20%) were using an AVG, and 85 (14%) were using an AVF. After 6 mo, 34% were using a CVC, 40% were using an AVG, and 26% were using an AVF. Annual mortality rates were 11.7% for AVF, 14.2% for AVG, and 16.1% for CVC. Adjusted relative hazards (RH) of death compared with AVF were 1.5 (95% confidence interval, 1.0 to 2.2) for CVC and 1.2 (0.8 to 1.8) for AVG. The increased hazards associated with CVC, as compared with AVF, were stronger in men (n = 334; RH = 2.0; P = 0.01) than women (n = 282; RH = 1.0 for CVC; P = 0.92). These results strongly support existing clinical practice guidelines and suggest that the use of venous catheters should be minimized to reduce the frequency of access complications and to improve patient survival, especially among male hemodialysis patients.

Background: The incidence of end-stage renal disease (ESRD) is increasing considerably worldwide; moreover, most of the patients start their therapy by hemodialysis (HD). Arteriovenous fistula (AVF) is the best type of vascular access for use in such therapy, due to its decreased rate of complications, followed by arteriovenous graft (AVG) and finally, central venous catheters, which are associated with, increased mortality and morbidity. In this study, we aim to find out the proportion of the current to initial vascular access used, the timing of creating permanent access, and any complications experienced. Patients and Methods: A cross-sectional study was conducted on two hundred eighteen patients currently on regular hemodialysis program. Their records were reviewed and the data was analyzed for vascular accesses type used at the start of hemodialysis and at the current time, the timing of the creation of permanent access, and the complications occurred. Data collected were statistically analyzed using IBM-SPSS statistics software Inc. Chicago, IL, USA. Results: Out-of-the 218 patients on hemodialysis, 193 patients (88.5%) started hemodialysis via Central venous catheters (CVC), 23 patients (10.5%) had an arterio-venous fistula (AVF), and only two patients (0.9%) used tunneled CVC, while no one has AV-graft. Currently, 82.1% of patients have AVF, 7.8% have chronic CVC, 5.9% have acute CVC and only 4.1% have AV-Graft, Many complications are noted in all types of access with different percentages of occurrence. Conclusion: We concluded that although a high percentage of patients have AVF, still pre-emptive AVF counts very low percentage, serious complications are still happening and we recommend the establishment of joined pre-dialysis clinic with surgeons and psychologists in each dialysis center.