Prevalence of anaemia, iron, and vitamin deficiencies in the health system in the Republic of Ireland: a retrospective cohort study.

BACKGROUND: Anaemia is a common but treatable condition that predicts adverse clinical outcomes. However, standards of anaemia management vary considerably. AIM: To estimate the prevalence of anaemia and extent of screening for common underlying causes in the healthcare system in the Republic of Ireland. DESIGN & SETTING: We conducted a retrospective cohort study of 112 181 adult patients, aged ≥18 years, who had a full blood count performed in 2013, using data from the National Kidney Disease Surveillance System. METHOD: The prevalence of anaemia was determined across demographic and clinical subgroups, according to World Health Organization (WHO) definitions. The proportion screened for iron, vitamin B12, and folate deficiency was determined within a 3-month follow-up period and the corresponding prevalence for each deficiency determined. RESULTS: The overall prevalence of anaemia was 12.0% (95% confidence interval [CI] = 11.8% to 12.2%) and was higher in women than men (13.2% versus 10.5%, P<0.001). Anaemia increased with advancing age (33.4% for those aged >75 years) and worsening kidney function (8.2%, 10.9%, 33.2%, and 63.8% for each estimated glomerular filtration rate [eGFR] categories >90, 60-89, 30-59 and <30 ml/min/1.73 m², respectively, P<0.001). After 3-months' follow-up, the proportion screened for iron deficiency was 11.2% based on transferrin saturation and 33.7% using serum ferritin. Screening for folate and B12 deficiency was 17.6% and 19.8%, respectively. Among screened patients, the prevalence of iron deficiency, B12, and folate deficiency was 37.0%, 6.3%, and 5.8%, respectively. CONCLUSION: The burden of anaemia in the healthcare system is substantial especially for older patients and those with advanced kidney disease. Low screening rates for iron, B12, and folate deficiency are common and warrant quality improvement initiatives.

Impact of serum sodium concentrations, and effect modifiers on mortality in the Irish Health System.

BACKGROUND: Abnormalities of serum sodium are associated with increased mortality risk in hospitalised patients, but it is unclear whether, and to what extent other factors influence this relationship. We investigated the impact of dysnatraemia on total and cause-specific mortality in the Irish health system while exploring the concurrent impact of age, kidney function and designated clinical work-based settings. METHODS: A retrospective cohort study of 32,666 participants was conducted using data from the National Kidney Disease Surveillance System. Hyponatraemia was defined as < 135 mmol/L and hypernatraemia as > 145 mmol/L with normal range 135-145 mmol/L. Multivariable Cox proportional hazards regression was used to estimate hazard ratios (HR's) and 95% Confidence Intervals (CIs) while penalised spline models further examined patterns of risk. RESULTS: There were 5,114 deaths (15.7%) over a median follow up of 5.5 years. Dysnatraemia was present in 8.5% of patients overall. In multivariable analysis, both baseline and time-dependent serum sodium concentrations exhibited a U-shaped association with mortality. Hyponatremia was significantly associated with increased risk for cardiovascular [HR 1.38 (1.18-1.61)], malignant [HR: 2.49 (2.23-2.78)] and non-cardiovascular/non-malignant causes of death [1.36 (1.17-1.58)], while hypernatremia was significantly associated with cardiovascular [HR: 2.16 (1.58-2.96)] and non-cardiovascular/ non-malignant deaths respectively [HR: 3.60 (2.87-4.52)]. The sodium-mortality relationship was significantly influenced by age, level of kidney function and the clinical setting at baseline (P < 0.001). For hyponatraemia, relative mortality risks were significantly higher for younger patients (interaction term P < 0.001), for patients with better kidney function, and for patients attending general practice [HR 2.70 (2.15-3.36)] than other clinical settings. For hypernatraemia, age and kidney function remained significant effect modifiers, with patients attending outpatient departments experiencing the greatest risk [HR 9.84 (4.88-18.62)] than patients who attended other clinical locations. Optimal serum sodium thresholds for mortality varied by level of kidney function with a flattening of mortality curve observed for patients with poorer kidney function. CONCLUSION: Serum sodium concentrations outside the standard normal range adversly impact mortality and are associated with specific causes of death. The thresholds at which these risks appear to vary by age, level of kidney function, and are modified in specific clinical settings within the health system.

Differential Impact of Central Venous Catheters versus Arteriovenous Fistulae on Quality of Life among Irish Haemodialysis Patients.

Background: Arteriovenous fistulae (AVF) have superior clinical outcomes compared with central venous catheters (CVC) among patients undergoing hemodialysis (HD). Yet, there is increasing recognition that health-related quality of life (HRQoL) may be more important to patients than survival and that differences may exist between AVF and CVCs in this regard. This study compared HRQoL between AVF and CVC in an Irish cohort. Methods: We conducted a cross-sectional survey among prevalent patients undergoing hemodialysis (N=119) dialyzing with either an AVF or CVC at a regional program. The Short Form 36 (SF-36) and a validated Vascular Access Questionnaire (SF-VAQ) compared QoL between AVF and CVC in domains of physical functioning, social functioning, and dialysis complications. Multivariable logistic regression compared differences between groups for outcomes of physical functioning, social functioning, and dialysis complications expressed as adjusted odds ratios and 95% CI. Results: Mean age was 66.6 years; 52% were using an AVF and 48% had a CVC. Patients dialyzing with an AVF were more satisfied with their access when asked directly (6.2 versus 5.0; P<0.01). Physical functioning scores for bleeding, swelling, and bruising were significantly higher for AVF than CVC (P=0.001, P=0.001, and P<0.001, respectively). In contrast, patients with a CVC reported greater difficulties in bathing and showering than those using an AVF (4.4 versus 2.0; P<0.001), whereas patients with an AVF expressed greater concerns with physical appearances. Compared with AVF, CVC users were less likely to report difficulties in physical functioning (OR=0.35; 95% CI, 0.12 to 0.94; P=0.04) but more likely to report dialysis complications (OR=1.94; 95% CI, 0.69 to 5.87; P=0.22). Conclusions: Vascular access contributes to HRQoL in hemodialysis. CVCs are associated with fewer difficulties from bleeding and bruising but greater negative effect on social activities, including bathing and showering. Overall, patients with a CVC had lower dissatisfaction scores than patients with an AVF when all three domains were added. Innovation in vascular access design and engineering may confer benefits and improve patient comfort on HD.

Serum uric acid and mortality thresholds among men and women in the Irish health system: A cohort study.

BACKGROUND: Elevation of serum uric acid (SUA) is associated with increased mortality; however, controversy exists regarding the nature of the relationship and differences between men and women. We explored relationships of SUA levels with all-cause mortality in a large cohort of patients within the Irish health system. METHODS: A retrospective cohort study of 26,525 participants was conducted using data from the National Kidney Disease Surveillance System. SUA was modelled in increments of 59.48 µmol/L (1 mg/dL), Cox's proportional hazards model estimated hazard ratios (HRs) and 95% Confidence Intervals (CI), median lifetimes were also computed separately for men and women. Mortality patterns were further explored using penalised splines. RESULTS: There were 1,288 (4.9%) deaths over a median follow-up of 5.1 years. In men, the risk of mortality was greatest for the lowest (<238 µmol/L) and highest (>535 µmol/L) categories [HR 2.35 (1.65-3.14) and HR 2.52 (1.87-3.29) respectively]; the corresponding median lifetimes for men were reduced by 9.5 and 11.7 years respectively compared to the referent. In women, mortality risks were elevated for SUA >416 mol/L [HR 1.69 (1.13-2.47) and beyond; the corresponding median lifetime for women were reduced by 5.9 years compared to the referent. Spline analysis revealed a U-shaped association between SUA and mortality in men, while for women, the pattern of association was J-shaped. CONCLUSION: Mortality patterns attributed to SUA differ between men and women. Optimal survival was associated with SUA concentrations of 304-454 µmol/L for men and < 409 µmol/L for women.

Evolution of Vascular Access Use among Incident Patients during the First Year on Hemodialysis: A National Cohort Study.

Background: Although the arteriovenous fistula (AVF) confers superior benefits over central venous catheters (CVCs), utilization rates remain low among prevalent patients on hemodialysis (HD). The goal of this study was to determine the evolution of vascular access type in the first year of dialysis and identify factors associated with conversion from CVC to a functioning AVF. Methods: We studiedadult patients (n=610) who began HD between the January 1, 2015 and December 31, 2016 and were treated for at least 90 days, using data from the National Kidney Disease Clinical Patient Management System in the Irish health system. Prevalence of vascular access type was determined at days 90 and 360 after dialysis initiation and at 30-day intervals. Multivariable logistic regression explored factors associated with CVC at day 90, and Cox regression evaluated predictors of conversion from CVC to AVF on day 360. Results: CVC use was present in 77% of incident patients at day 90, with significant variation across HD centers (from 63% to 91%, P<0.001), which persisted after case-mix adjustment. From day 90 to day 360, AVF use increased modestly from 23% to 41%. Conversion from CVC to AVF increased over time, but the likelihood was lower for older patients (for age >77 years versus referent, adjusted hazard ratio [HR], 0.43; 95% CI, 0.19 to 0.96), for patients with a lower BMI (per unit decrease in BMI, HR, 0.95; 95% CI, 0.93 to 0.98), and varied significantly across HD centers (from an HR of 0.25 [95% CI, 0.08 to 0.74] to 2.09 [95% CI, 1.04 to 4.18]). Conclusion: CVCs are the predominant type of vascular access observed during the first year of dialysis, with low conversion rates from CVC to AVF. There is substantial center variation in the Irish health system that is not explained by patient-related factors alone.

Propensity score matched mortality comparisons of peritoneal and in-centre haemodialysis: systematic review and meta-analysis.

BACKGROUND: Accurate comparisons of haemodialysis (HD) and peritoneal dialysis (PD) survival based on observational studies are difficult due to substantial residual confounding that arises from imbalances between treatments. Propensity score matching (PSM) comparisons confer additional advantages over conventional methods of adjustment by further reducing selection bias between treatments. We conducted a systematic review of studies that compared mortality between in-centre HD with PD using a PSM-based approach. METHODS: A sensitive search strategy identified all citations in the PubMed, Cochrane and EMBASE databases from inception through November 2018. Pooled PD versus HD mortality hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated through random-effects meta-analysis. A subsequent meta-regression explored factors to account for between-study variation. RESULTS: The systematic review yielded 214 citations with 17 cohort studies and 113 578 PSM incident dialysis patients. Cohort periods spanned the period 1993-2014. The pooled HR for PD versus HD was 1.06 (95% CI 0.99-1.14). There was considerable variation by country, however, mortality risks for PD versus HD remained virtually unchanged when stratified by geographical region with HRs of 1.04 (95% CI 0.94-1.15), 1.14 (95% CI 0.99-1.32) and 0.98 (0.87-1.10) for European, Asian and American cohorts, respectively. Subgroup meta-analyses revealed similar risks for patients with diabetes [HR 1.09 (95% CI 0.98-1.21)] and without diabetes [HR 0.99 (95% CI 0.90-1.09)]. Heterogeneity was substantial (I2 = 87%) and was largely accounted for by differences in cohort period, study type and country of origin. Together these factors explained a substantial degree of between-studies variance (R2 = 90.6%). CONCLUSIONS: This meta-analysis suggests that PD and in-centre HD carry equivalent survival benefits. Reported differences in survival between treatments largely reflect a combination of factors that are unrelated to clinical efficacy.

Use of Compositional Data Analysis to Show Estimated Changes in Cardiometabolic Health by Reallocating Time to Light-Intensity Physical Activity in Older Adults.

BACKGROUND: All physical activity (PA) behaviours undertaken over the day, including sleep, sedentary time, standing time, light-intensity PA (LIPA) and moderate-to-vigorous PA (MVPA) have the potential to influence cardiometabolic health. Since these behaviours are mutually exclusive, standard statistical approaches are unable to account for the impact on time spent in other behaviours. OBJECTIVE: By employing a compositional data analysis (CoDA) approach, this study examined the associations of objectively measured time spent in sleep, sedentary time, standing time, LIPA and MVPA over a 24-h day on markers of cardiometabolic health in older adults. METHODS: Participants (n =366; 64.6 years [5.3]; 46% female) from the Mitchelstown Cohort Rescreen Study provided measures of body composition, blood lipid and markers of glucose control. An activPAL3 Micro was used to obtain objective measures of sleep, sedentary time, standing time, LIPA and MVPA, using a 7-day continuous wear protocol. Regression analysis, using geometric means derived from CoDA (based on isometric log-ratio transformed data), was used to examine the relationship between the aforementioned behaviours and markers of cardiometabolic health. RESULTS: Standing time and LIPA showed diverging associations with markers of body composition. Body mass index (BMI), body mass and fat mass were negatively associated with LIPA (all p <0.05) and positively associated with standing time (all p <0.05). Sedentary time was also associated with higher BMI (p <0.05). No associations between blood markers and any PA behaviours were observed, except for triglycerides, which were negatively associated with standing time (p < 0.05). Reallocating 30 min from sleep, sedentary time or standing time, to LIPA, was associated with significant decreases in BMI, body fat and fat mass. CONCLUSION: This is the first study to employ CoDA in older adults that has accounted for sleep, sedentary time, standing time, LIPA and MVPA in a 24-h cycle. The findings support engagement in LIPA to improve body composition in older adults. Increased standing time was associated with higher levels of adiposity, with increased LIPA associated with reduced adiposity; therefore, these findings indicate that replacing standing time with LIPA is a strategy to lower adiposity.

Temporal trends in acute kidney injury across health care settings in the Irish health system: a cohort study.

BACKGROUND: Complete ascertainment of the true rates of acute kidney injury (AKI) and emerging trends are essential for planning of preventive strategies within health systems. METHODS: We conducted a retrospective cohort study from 2005 to 2014 using data from regional laboratory information systems to determine incidence rates of AKI and severity Stages 1-3 in the Irish health system. Multivariable models were developed to explore annual trends and the contributions of demographic factors, clinical measures, geographic factors and location of medical supervision expressed as adjusted odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: From 2005 to 2014, incidence rates of AKI increased from 6.1% (5.8-6.3) to 13.2% (12.7-13.8) per 100 patient-years in men and from 5.0% (4.8-5.2) to 11.5% (11.0-12.0) in women, P < 0.001. Stage 1 AKI accounted for the greatest growth in incidence, from 4.4% (95% CI 4.3-4.6) in 2005 to 10.1% (95% CI 9.8-10.5) in 2014 (P < 0.001 for trend). Compared with 2005, patients in 2014 were more likely to experience AKI [OR 4.53 (95% CI 4.02-5.1) for Stage 1, OR 5.22 (4.16-6.55) for Stage 2 and OR 4.11 (3.05-5.54) for Stage 3], adjusting for changing demographic and clinical profiles. Incidence rates of AKI increased in all locations of medical supervision during the period of observation, but were greatest for inpatient [OR 19.11 (95% CI 17.69-20.64)] and emergency room settings [OR 5.97 (95% CI 5.56-6.42)] compared with a general practice setting (referent). CONCLUSION: Incidence rates of AKI have increased substantially in the Irish health system, which were not accounted for by changing demographic patterns, clinical profiles or location of medical supervision.

Determinants and outcomes of access-related blood-stream infections among Irish haemodialysis patients; a cohort study.

BACKGROUND: Infections are the second leading cause of death and hospitalisation among haemodialysis (HD) patients. Rates of access-related bloodstream infections (AR-BSI) are influenced by patient characteristics and local protocols. We explored factors associated with AR-BSI in a contemporary cohort of HD patients at a tertiary nephrology centre. METHODS: A retrospective cohort of 235 chronic HD patients was identified from a regional dialysis programme between Jan 2015 and Dec 2016. Data on demographics, primary renal disease, comorbid conditions and dialysis access type were obtained from the Kidney Disease Clinical Patient Management System (KDCPMS). Data on blood cultures were captured from the microbiology laboratory. Poisson regression with robust variance estimates was used to compare infection rates and relative risk of AR-BSI according to the site and type of vascular access. RESULTS: The mean age was 65 (± 15) years, 77% were men, and the median follow up was 19 months (IQR: 10-24 months), accumulating 2030 catheter-months and 1831 fistula-months. Overall rates of AR-BSI were significantly higher for central venous catheter (CVC) compared to arteriovenous fistula (AVF), (2.22, 95% (CI): 1.62-2.97) versus 0.11 (0.01-0.39) per 100 patient-months respectively), with a rate ratio of 20.29 (4.92-83.66), p < 0.0001. This pattern persisted across age, gender and diabetes subgroups. Within the CVC subgroup, presence of a femoral CVC access was associated with significantly higher rates of AR-BSI (adjusted RR 4.93, 95% CI: 2.69-9.01). Older age (75+ versus < 75 years) was not associated with significant differences in rates of AR-BSI in the unadjusted or the adjusted analysis. Coagulase negative Staphylococcus (61%) and Staphylococcus aureus (23%) were the predominant culprits. AR-BSIs resulted in access loss and hospitalisation in 57 and 72% of events respectively, and two patients died with concurrent AR-BSI. CONCLUSIONS: Rates of AR-BSI are substantially higher in CVC than AVF in contemporary HD despite advances in catheter design and anti-infective protocols. This pattern was consistent in all subgroups. The policy of AVF preference over CVC should continue to minimise patient morbidity while at the same time improving anti-infective strategies through better care protocols and infection surveillance.

Prevalence and treatment of gout among patients with chronic kidney disease in the Irish health system: A national study.

BACKGROUND: Gout is a common inflammatory arthritis associated with adverse clinical outcomes. Under treatment is common in the general population. The aim of this study was to determine the prevalence of gout and its treatment among patients with chronic kidney disease (CKD). METHODS: We conducted a multi-centre cross sectional study of patients (n = 522) who attended specialist nephrology clinics in Ireland. Standardized data collection tool recorded clinical characteristics and medication use at clinic visits and kidney function was assessed with standardised creatinine measurements and Estimated Glomerular Filtration Rate (eGFR). The prevalence of gout and the corresponding use of urate lowering therapies (ULT) were determined. Multivariate logistic regression explored correlates of gout expressed as Odds Ratios (OR) and 95% Confidence Intervals (CI) adjusting for demographic and clinical characteristics. RESULTS: Overall prevalence of gout was 16.6% and increased significantly from 7.5% in Stage 1-2 CKD to 22.8% in stage 4-5 CKD, P< 0.005. Prevalence increased with age (P < 0.005) and was higher in men than women (19.1% versus 10.3% P< 0.005). Overall, 67.9% of gout patients with CKD were treated with ULT, and the percentage increased with advancing stage of CKD from 55.6% in Stage 1-2 to 77.4% in Stage 4-5, P<0.005. Multivariable modelling identified men (vs women), OR, 1.95 (0.95-4.03), serum albumin, OR 1.09 (1.02-1.16) per 1 g/L lower, poorer kidney function, OR 1.11 (1.01-1.22) per 5 ml/min/1.73m2 lower, and rising parathyroid hormone levels, OR 1.38 (1.08-1.77) per 50 pg/ml higher as disease correlates. CONCLUSIONS: Gout is common in CKD and increases with worsening kidney function in the Irish health system. Over two thirds of patients with gout were receiving ULT, increasing to 77% of patients with advanced CKD. Greater awareness of gout in CKD, its treatment and the effectiveness of treatment strategies should be vigorously monitored to improve patient outcomes.

Real-World Variability in the Prediction of Intracranial Aneurysm Wall Shear Stress: The 2015 International Aneurysm CFD Challenge.

PURPOSE: Image-based computational fluid dynamics (CFD) is widely used to predict intracranial aneurysm wall shear stress (WSS), particularly with the goal of improving rupture risk assessment. Nevertheless, concern has been expressed over the variability of predicted WSS and inconsistent associations with rupture. Previous challenges, and studies from individual groups, have focused on individual aspects of the image-based CFD pipeline. The aim of this Challenge was to quantify the total variability of the whole pipeline. METHODS: 3D rotational angiography image volumes of five middle cerebral artery aneurysms were provided to participants, who were free to choose their segmentation methods, boundary conditions, and CFD solver and settings. Participants were asked to fill out a questionnaire about their solution strategies and experience with aneurysm CFD, and provide surface distributions of WSS magnitude, from which we objectively derived a variety of hemodynamic parameters. RESULTS: A total of 28 datasets were submitted, from 26 teams with varying levels of self-assessed experience. Wide variability of segmentations, CFD model extents, and inflow rates resulted in interquartile ranges of sac average WSS up to 56%, which reduced to < 30% after normalizing by parent artery WSS. Sac-maximum WSS and low shear area were more variable, while rank-ordering of cases by low or high shear showed only modest consensus among teams. Experience was not a significant predictor of variability. CONCLUSIONS: Wide variability exists in the prediction of intracranial aneurysm WSS. While segmentation and CFD solver techniques may be difficult to standardize across groups, our findings suggest that some of the variability in image-based CFD could be reduced by establishing guidelines for model extents, inflow rates, and blood properties, and by encouraging the reporting of normalized hemodynamic parameters.

Morphological and hemodynamical alterations in brachial artery and cephalic vein. An image-based study for preoperative assessment for vascular access creation.

The current study aims to computationally evaluate the effect of right upper arm position on the geometric and hemodynamic characteristics of the brachial artery (BA) and cephalic vein (CV) and, furthermore, to present in detail the methodology to characterise morphological and hemodynamical healthy vessels. Ten healthy volunteers were analysed in two configurations, the supine (S) and the prone (P) position. Lumen 3D surface models were constructed from images acquired from a non-contrast MRI sequence. Then, the models were used to numerically compute the physiological range of geometric (n = 10) and hemodynamic (n = 3) parameters in the BA and CV. Geometric parameters such as curvature and tortuosity, and hemodynamic parameters based on wall shear stress (WSS) metrics were calculated with the use of computational fluid dynamics. Our results highlight that changes in arm position had a greater impact on WSS metrics of the BA by altering the mean and maximum blood flow rate of the vessel. Whereas, curvature and tortuosity were found not to be significantly different between positions. Inter-variability was associated with antegrade and retrograde flow in BA, and antegrade flow in CV. Shear stress was low and oscillatory shear forces were negligible. This data suggests that deviations from this state may contribute to the risk of accelerated intimal hyperplasia of the vein in arteriovenous fistulas. Therefore, preoperative conditions coupled with post-operative longitudinal data will aid the identification of such relationships.

Temporal trends in hyperuricaemia in the Irish health system from 2006-2014: A cohort study.

BACKGROUND: Elevated serum uric acid (sUA) concentrations are common in the general population and are associated with chronic metabolic conditions and adverse clinical outcomes. We evaluated secular trends in the burden of hyperuricaemia from 2006-2014 within the Irish health system. METHODS: Data from the National Kidney Disease Surveillance Programme was used to determine the prevalence of elevated sUA in adults, age > 18 years, within the Irish health system. Hyperuricaemia was defined as sUA > 416.4 µmol/L in men and > 339.06 µmol/L in women, and prevalence was calculated as the proportion of patients per year with mean sUA levels above sex-specific thresholds. Temporal trends in prevalence were compared from 2006 to 2014 while general estimating equations (GEE) explored variation across calendar years expressed as odds ratios (OR) and 95% Confidence intervals (CI). RESULTS: From 2006 to 2014, prevalence of hyperuricaemia increased from 19.7% to 25.0% in men and from 20.5% to 24.1% in women, P<0.001. The corresponding sUA concentrations increased significantly from 314.6 (93.9) in 2006 to 325.6 (96.2) in 2014, P<0.001. Age-specific prevalence increased in all groups from 2006 to 2014, and the magnitude of increase was similar for each age category. Adjusting for baseline demographic characteristics and illness indicators, the likelihood of hyperuricemia was greatest for patients in 2014; OR 1.45 (1.26-1.65) for men and OR 1.47 (1.29-1.67) in women vs 2006 (referent). Factors associated with hyperuricaemia included: worsening kidney function, elevated white cell count, raised serum phosphate and calcium levels, elevated total protein and higher haemoglobin concentrations, all P<0.001. CONCLUSIONS: The burden of hyperuricaemia is substantial in the Irish health system and has increased in frequency over the past decade. Advancing age, poorer kidney function, measures of nutrition and inflammation, and regional variation all contribute to increasing prevalence, but these do not fully explain emerging trends.

The Role of Shear Stress in Arteriovenous Fistula Maturation and Failure: A Systematic Review.

INTRODUCTION: Non-maturation and post-maturation venous stenosis are the primary causes of failure within arteriovenous fistulae (AVFs). Although the exact mechanisms triggering failure remain unclear, abnormal hemodynamic profiles are thought to mediate vascular remodelling and can adversely impact on fistula patency. AIM: The review aims to clarify the role of shear stress on outward remodelling during maturation and evaluate the evidence supporting theories related to the localisation and development of intimal hyperplasia within AVFs. METHODS: A systematic review of studies comparing remodelling data with hemodynamic data obtained from computational fluid dynamics of AVFs during and after maturation was conducted. RESULTS: Outward remodelling occurred to reduce or normalise the level of shear stress over time in fistulae with a large radius of curvature (curved) whereas shear stress was found to augment over time in fistulae with a small radius of curvature (straight) coinciding with minimal to no increases in lumen area. Although this review highlighted that there is a growing body of evidence suggesting low and oscillating shear stress may stimulate the initiation and development of intimal medial thickening within AVFs. Further lines of evidence are needed to support the disturbed flow theory and outward remodelling findings before surgical configurations and treatment strategies are optimised to conform to them. This review highlighted that variation between the time of analysis, classification of IH, resolution of simulations, data processing techniques and omission of various shear stress metrics prevented forming pooling of data amongst studies. CONCLUSION: Standardised measurements and data processing techniques are needed to comprehensively evaluate the relationship between shear stress and intimal medial thickening. Advances in image acquisition and flow quantifications coupled with the increasing prevalence of longitudinal studies commencing from fistula creation offer viable techniques and strategies to robustly evaluate the relationship between shear stress and remodelling during maturation and thereafter.

Experimental and Numerical Analysis of the Bulk Flow Parameters Within an Arteriovenous Fistula.

The creation of an arteriovenous fistula for hemodialysis has been reported to generate unstable to turbulent flow behaviour. On the other hand, the vast majority of computational fluid dynamic studies of an arteriovenous fistula use low spatial and temporal resolutions resolution in conjunction with laminar assumptions to investigate bulk flow and near wall parameters. The objective of the present study is to investigate if adequately resolved CFD can capture instabilities within an arteriovenous fistula. An experimental model of a representative fistula was created and the pressure distribution within the model was analysed for steady inlet conditions. Temporal CFD simulations with steady inflow conditions were computed for comparison. Following this verification a pulsatile simulation was employed to assess the role of pulsatility on bulk flow parameters. High frequency fluctuations beyond 100 Hz were found to occupy the venous segment of the arteriovenous fistula under pulsatile conditions and the flow within the venous segment exhibited unstable behaviour under both steady and pulsatile inlet conditions. The presence of high frequency fluctuations may be overlooked unless adequate spatial and temporal resolutions are employed. These fluctuations may impact endothelial cell function and contribute to the cascade of events leading to aggressive intimal hyperplasia and the loss of functionality of the vascular access.

One-stage vs. two-stage brachio-basilic arteriovenous fistula for dialysis access: a systematic review and a meta-analysis.

INTRODUCTION: A brachiobasilic arteriovenous fistula (BB-AVF) can provide access for haemodialysis in patients who are not eligible for a more superficial fistula. However, it is unclear whether one- or two-stage BB-AVF is the best option for patients. AIM: To systematically assess the difference between both procedures in terms of access maturation, patency and postoperative complications. METHODS: Online search for randomised controlled trials (RCTs) and observational studies that compared the one-stage versus the two-stage technique for creating a BB-AVF. RESULTS: Eight studies were included (849 patients with 859 fistulas), 366 created using a one-stage technique, while 493 in a two-stage approach. There was no statistically significant difference between the two groups in the rate of successful maturation (Pooled risk ratio = 0.95 [0.82, 1.11], P = 0.53). Similarly, the incidence of postoperative haematoma (Pooled risk ratio = 0.73 [0.34, 1.58], P = 0.43), wound infection (Pooled risk ratio = 0.77 [0.35, 1.68], P = 0.51) and steal syndrome (Pooled risk ratio = 0.65 [0.27, 1.53], P = 0.32) were statistically comparable. CONCLUSION: Although more studies seem to favour the two-stage BVT approach, evidence in the literature is not sufficient to draw a final conclusion as the difference between the one-stage and the two-stage approaches for creation of a BB-AVF is not statistically significant in terms of the overall maturation rate and postoperative complications. Patency rates (primary, assisted primary and secondary) were comparable in the majority of studies. Large randomised properly conducted trials with superior methodology and adequate sub-group analysis are needed before making a final recommendation.

In vivo validation of the in silico predicted pressure drop across an arteriovenous fistula.

The creation of an arteriovenous fistula offers a unique example of vascular remodelling and adaption. Yet, the specific factors which elicit remodelling events which determine successful maturation or failure have not been unambiguously determined. Computational fluid dynamic (CFD) simulations are increasingly been employed to investigate the interaction between local hemodynamics and remodelling and can potentially be used to assist in clinical risk assessment of maturation or failure. However, these simulations are inextricably linked to their prescribed boundary conditions and are reliant on in vivo measurements of flow and pressure to ensure their validity. The study compares in vivo measurements of the pressure distribution across arteriovenous fistulae against a representative numerical model. The results of the study indicate relative agreement (error ≈ 8-10%) between the in vivo and CFD prediction of the mean pressure drop across the AVFs. The large pressure drop across the AVFs coincided with a palpable thrill (perivascular vibration) in vivo and fluctuations were observed in the numerical pressure drop signal due to flow instabilities arising at the anastomosis. This study provides a benchmark of the pressure distribution within an AVF and validates that CFD solutions are capable of replicating the abnormal physiological flow conditions induced by fistula creation.

Role of far infra-red therapy in dialysis arterio-venous fistula maturation and survival: systematic review and meta-analysis.

INTRODUCTION: A well-functioning arteriovenous fistula (AVF) is the best modality for vascular access in patients with end-stage renal disease (ESRD) requiring haemodialysis (HD). However, AVFs' main disadvantage is the high rate of maturation failure, with approximately one third (20%-50%) not maturing into useful access. This review examine the use of Far-Infra Red therapy in an attempt to enhance both primary (unassisted) and secondary (assisted) patency rates for AVF in dialysis and pre-dialysis patients. METHOD: We performed an online search for observational studies and randomised controlled trials (RCTs) that evaluated FIR in patients with AVF. Eligible studies compared FIR with control treatment and reported at least one outcome measure relating to access survival. Primary patency and secondary patency rates were the main outcomes of interest. RESULTS: Four RCTs (666 patients) were included. Unassisted patency assessed in 610 patients, and was significantly better among those who received FIR (228/311) compared to (185/299) controls (pooled risk ratio of 1.23 [1.12-1.35], p = 0.00001). In addition, the two studies which reported secondary patency rates showed significant difference in favour of FIR therapy--160/168 patients--compared to 140/163 controls (pooled risk ratio of 1.11 [1.04-1.19], p = 0.003). CONCLUSION: FIR therapy may positively influence the complex process of AVF maturation improving both primary and secondary patency rates. However blinded RCTs performed by investigators with no commercial ties to FIR therapy technologies are needed.

Variability of computational fluid dynamics solutions for pressure and flow in a giant aneurysm: the ASME 2012 Summer Bioengineering Conference CFD Challenge.

Stimulated by a recent controversy regarding pressure drops predicted in a giant aneurysm with a proximal stenosis, the present study sought to assess variability in the prediction of pressures and flow by a wide variety of research groups. In phase I, lumen geometry, flow rates, and fluid properties were specified, leaving each research group to choose their solver, discretization, and solution strategies. Variability was assessed by having each group interpolate their results onto a standardized mesh and centerline. For phase II, a physical model of the geometry was constructed, from which pressure and flow rates were measured. Groups repeated their simulations using a geometry reconstructed from a micro-computed tomography (CT) scan of the physical model with the measured flow rates and fluid properties. Phase I results from 25 groups demonstrated remarkable consistency in the pressure patterns, with the majority predicting peak systolic pressure drops within 8% of each other. Aneurysm sac flow patterns were more variable with only a few groups reporting peak systolic flow instabilities owing to their use of high temporal resolutions. Variability for phase II was comparable, and the median predicted pressure drops were within a few millimeters of mercury of the measured values but only after accounting for submillimeter errors in the reconstruction of the life-sized flow model from micro-CT. In summary, pressure can be predicted with consistency by CFD across a wide range of solvers and solution strategies, but this may not hold true for specific flow patterns or derived quantities. Future challenges are needed and should focus on hemodynamic quantities thought to be of clinical interest.