Vascular access outcomes in the elderly hemodialysis population: A USRDS study

Arteriovenous fistulae (AVF) are widely regarded as the preferred vascular access in hemodialysis (HD) patients due to their primary patency and patient survival benefits. Recent scholarship has suggested that the elderly population differs significantly from the general population in terms of inflammatory markers. What is more, recent studies have suggested that the elderly HD population is less likely to have an AVF placed as the initial vascular access compared to a younger cohort. The purpose of this study is to investigate the applicability of current vascular access guidelines to the elderly HD population. We hypothesized that the elderly HD population would derive less patency and survival benefit from AVF placement relative to arteriovenous graft (AVG) than the general population is known to derive. We performed a retrospective analysis using the US Renal Data System (USRDS) Wave II dataset to explore significant predictors of referral for intervention or access failure, and patient survival in the elderly US HD population using Cox regression corrected for race, gender, peripheral vascular disease, diabetes mellitus, and nutritional status. Of the 1471 HD patients with AVF or AVG, 764 patients were >65 years. Elderly diabetics had no significant mortality benefit from the use of AVF compared to AVG [odds ratio (OR) 1.34 (95% CI 0.92-1.95), p = 0.123]. Likewise, elderly nondiabetics had no significant mortality benefit from the use of AVF compared to AVG [OR 1.05 (95% CI 0.81-1.36), p = 0.735]. Elderly diabetics had no difference in odds for intervention referral for AVF compared to AVG [OR 1.49 (95% CI 0.76-2.9), p = 0.24]. Elderly nondiabetics had no difference in odds for intervention referral for AVF compared to AVG [OR 1.48 (95% CI 0.95-2.3), p = 0.08]. We conclude that the potential benefits derived from AVFs compared with AVGs and central venous catheters (CVC) may not apply universally. The recommendations of vascular access choice stipulated by national guidelines may need to be modified for elderly patients.     

How I do it: preferential use of the right external jugular vein for tunneled catheter placement

We describe a case in which the right external jugular vein (REJ) was preferentially used to place a tunneled catheter, even though the left internal jugular vein (LIJ) was widely patent. The possible advantage of placing REJ catheters over LIJ is that doing so may function to preserve better the left-sided vasculature in general, and, in particular, when future left-sided access is planned. Contrast venography was required. While REJ is a viable option for catheter insertion, the effect of REJ vs. LIJ catheter placement on long-term vessel patency as well as catheter function must be more rigorously defined to conclusively establish the superiority of one over the other.     

How I do it: directional atherectomy for in-stent restenosis of a PTFE arteriovenous graft

We describe the use of directional atherectomy (DA) to restore patency of a thrombosed polytetrafluoroethylene arteriovenous graft with an in-stent restenosis at the venous anastomosis. Technically, the procedure described is not an atherectomy per se, but rather the removal of fibrosis and intimal hyperplasia with sharp endoluminal dissection. Certainly, the operator must be cautious when performing DA directly adjacent to a previously deployed stent. Nevertheless, our report suggests that there may be a role for DA in the treatment of severe, resistant in-stent stenosis. Further investigation is necessary to evaluate the safety and efficacy of the described technique.     

Plasticity in representations of environmental sounds revealed by electrical neuroimaging

The rapid and precise processing of environmental sounds contributes to communication functions as well as both object recognition and localization. Plasticity in (accessing) the neural representations of environmental sounds is likewise essential for an adaptive organism, in particular humans, and can be indexed by repetition priming. How the brain achieves such plasticity with representations of environmental sounds is presently unresolved. Electrical neuroimaging of 64-channel auditory evoked potentials (AEPs) in humans identified the spatio-temporal brain mechanisms of repetition priming involving sounds of environmental objects. Subjects performed an 'oddball' target detection task, based on the semantic category of stimuli (living vs. man-made objects). Repetition priming effects were observed behaviorally as a speeding of reaction times and electrophysiologically as a suppression of the strength of responses to repeated sound presentations over the 156-215 ms post-stimulus period. These effects of plasticity were furthermore localized, using statistical analyses of a distributed linear inverse solution, to the left middle temporal gyrus and superior temporal sulcus (BA22), which have been implicated in associating sounds with their abstract representations and actions. These effects are subsequent to and occur in different brain regions from what has been previously identified as the earliest discrimination of auditory object categories. Plasticity in associative-semantic, rather than perceptual-discriminative functions, may underlie repetition priming of sounds of objects. We present a multi-stage mechanism of auditory object processing akin to what has been described for visual object processing and which also provides a framework for accessing multisensory object representations.     

Hyperparathyroidism in chronic kidney disease: a retrospective cohort study of costs and outcomes

Hyperparathyroidism may play a role in the excess morbidity and mortality in chronic kidney disease. This study examined utilization and outcomes of patients with hyperparathyroidism and chronic kidney disease. In a US health maintenance organization (HMO), patients with chronic kidney disease were identified from the electronic medical record. Patients included in the study had at least one intact parathyroid hormone (iPTH) measurement ordered by a nephrologist and were at least 20 years of age with no history of renal replacement therapy (RRT, n = 455). Cohorts were determined by index iPTH level and were followed for 1 year. Rates of health care utilization were compared between cohorts using Poisson regression; costs comparisons were made using linear regression; mortality and RRT were evaluated using Cox regression. Increasing levels of iPTH were associated with a significantly elevated risk of mortality and RRT, even after adjustment for potential confounders such as stage of chronic kidney disease. Compared to iPTH of <110 pg/ml, we found a 66% increase combined mortality-RRT risk (HR 1.66, 95% CI 1.41–1.97) for those with iPTH 110–199 pg/ml, and a HR of 4.57 (95% CI 3.86–5.43) for iPTH ≥300 pg/ml. We did not find a convincing association between iPTH level and utilization. While this study provides no evidence that treating patients with higher levels of iPTH will ameliorate poor outcomes, it suggests that iPTH levels beyond the targets suggested by clinical guidelines are associated with increased harm in patients with chronic kidney disease. This work was presented in part at the National Kidney Foundation 2006 annual meeting and at the 2006 International Society for Pharmacoeconomics and Outcomes Research meeting.     

Right hemispheric dominance for echo suppression

When two sounds are presented sequentially within a short delay (∼10 ms), the listener perceives a single auditory event, the location of which is dominated by the directional information conveyed by the leading sound (the precedence effect, PE). The PE is not always instantaneous, but has been shown to build-up across repetitions of lead-lag pairs. Here, we investigated the contributions of lateralization cue (interaural time and intensity differences; ITD and IID, respectively) and the side of lateralization of the leading sound on the spatio-temporal activity associated with the PE. We applied electrical neuroimaging analyses to compare auditory evoked potentials (AEPs) in response to physically identical click pairs presented early and late within a stimulus train and perceived as two segregated events or as one fused auditory event. Significant topographic AEP modulations associated with the PE were observed over the 70-117 ms post-stimulus period, with one topography characterizing fused perceptions and another segregated perceptions. The specific pattern of effects varied as a function of lateralization cue and the lateralization of the leading sound. The PE for ITD stimuli built-up during the stimulus train irrespective of the lateralization of the leading sound. The PE for IID stimuli did not exhibit build-up over the course of the stimulus train, but instead was generally affected by the lateralization of the leading sound. Source estimations further suggested that bilateral temporal networks were engaged when perceptions were segregated, whereas fused perceptions resulted in decreased activity in left temporal and increased activity in right temporo-parietal cortices.     

Stent Migration and Folding in the Subclavian Vein during Subclavian Hemodialysis Catheter Placement

The role of stent placement in hemodialysis (HD) access intervention continues to evolve. As more stents are placed, new and unusual complications are coming to light. We describe a case in which an unsuccessful attempt to place a left subclavian dialysis catheter resulted in the inadvertent migration and folding of a previously deployed subclavian stent. Attempts to remove the stent with a snare were unsuccessful. Patency was restored to the access circuit by placing a new stent through the struts of the folded one. Clinical vascular practice guidelines for vascular access on the use of fluoroscopy for temporary HD catheter placement may need to be re-evaluated with the reported increase in stent placement in the US HD population.     

How I do it: endovascular stent deployment using a novel technique that obviates the need for introducer-sheath upsizing

A case is presented and a novel technique is described by which an endovascular stent is deployed in the venous outflow system of an arteriovenous fistula without the traditional exchange to a larger diameter introducer sheath.