Repeated single-point measurements of thoracic bioimpedance at a single (low) frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multi-frequency measurements may add in-depth information on the distribution between intra- and extracellular fluid. This study aimed to investigate the feasibility of semi-continuous multi-frequency thoracic bioimpedance measurements by a wearable device in hemodialysis patients. Therefore, thoracic bioimpedance was recorded semi-continuously (i.e., every ten minutes) at nine frequencies (8–160 kHz) in 68 patients during two consecutive hemodialysis sessions, complemented by a single-point measurement at home in-between both sessions. On average, the resistance signals increased during both hemodialysis sessions and decreased during the interdialytic interval. The increase during dialysis was larger at 8 kHz (∆ 32.6 Ω during session 1 and ∆ 10 Ω during session 2), compared to 160 kHz (∆ 29.5 Ω during session 1 and ∆ 5.1 Ω during session 2). Whereas the resistance at 8 kHz showed a linear time pattern, the evolution of the resistance at 160 kHz was significantly different (p < 0.0001). Measuring bioimpedance semi-continuously and with a multi-frequency current is a major step forward in the understanding of fluid dynamics in hemodialysis patients. This study paves the road towards remote fluid monitoring.

Abstract Background and Aims Hemodialysis patients face a high hemodynamic variability in blood pressure and fluid status, which contributes to their cardiovascular mortality. Currently, intradialytic hemodynamic monitoring has to rely on cuff-based blood pressure measurements. During the interdialytic interval, no monitoring system is applied. An interesting alternative to monitor hemodynamics continuously can be found in the bioimpedance technique, and more specifically in bioimpedance measurements of the thoracic segment. Repeated single-point measurements of thoracic bioimpedance at single (low)-frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multifrequency measurements may add in-depth information on the distribution between intra- and extracellular fluid. This study aims to investigate the feasibility of semi-continuous multifrequency thoracic bioimpedance measurements by a wearable device in hemodialysis patients. Method Thoracic bioimpedance was recorded semi-continuously (i.e. every ten minutes) at nine frequencies (8–160 kHz) in 68 patients during two consecutive hemodialysis sessions, complemented by an interdialytic single-point measurement at home. The wearable bioimpedance device was provided by imec, The Netherlands (Fig. 1). A linear mixed model was built to integrate all measurements at frequencies 8 and 160 kHz, incorporating the different dialysis sessions up until 240 minutes after the start of dialysis as well as the home measurement that was performed. Results On average, the thoracic resistance signals increased during the first hemodialysis session, decreased during the interdialytic interval, and increased again during the second hemodialysis session, at all frequencies. The average intradialytic increase was larger at 8 kHz (∆ 32.6 Ω during session 1 and ∆ 10 Ω during session 2) compared to 160 kHz (∆ 29.5 Ω during session 1 and ∆ 5.1 Ω during session 2). By measuring semi-continuously and at multiple frequencies, a different time pattern became clear within and between frequencies. The resistance at 8 kHz followed a linear time pattern, whereas the evolution of the resistance at 160 kHz showed a significant quadratic trend in the first dialysis session (p < 0.0001). During the first interdialytic interval (from the end of the first dialysis session towards the home measurement), the decrease in resistance was more distinct at 8 kHz (∆ −2.27 Ω) compared to a small increase of 0.84 Ω in 160 kHz. This finding reveals a certain inertia in the higher frequencies, mirroring the changes in intracellular volume. Finally, the statistical model could create individual predicting profiles over time, including as well the intradialytic as the interdialytic interval (Fig. 2). Conclusion In this study, we showed that it is feasible to perform semi-continuous and multifrequency bioimpedance measurements by a wearable device during hemodialysis. Semi-continuous and multifrequency measurements provided a broader, and respectively profounder knowledge on the trend of the bioimpedance signal during fluid changes compared to single-point and single-frequency measurements. Measuring thoracic bioimpedance semi-continuously and with a multifrequency current is a major step forward in the understanding of fluid dynamics in hemodialysis patients, by which the road is paved towards remote fluid monitoring and the prevention of hemodynamic instabilities.

We examined the role of whole body and thoracic bioimpedance in hemodynamic changes during hemodialysis. Whole body and thoracic bioimpedance signals were strongly related to ultrafiltration volume and moderately, negatively, to changes in blood pressure. This work supports the further development of a wearable device measuring thoracic bioimpedance longitudinally in patients on hemodialysis. As such, it may serve as an innovative tool for continuous hemodynamic monitoring during hemodialysis in hospital or in a home-based setting.

ABSTRACT Acute kidney injury is a common and important complication following hematopoietic stem cell transplantation. In the nephrology community, acute kidney injury is no longer viewed as a simple temporary and potentially reversible decline in kidney clearance as acute kidney injury imposes a risk for immediate and future complications. Therefore, stratifying patients for the risk of acute kidney injury following stem cell transplantation would be very helpful to optimize peri-stem cell transplant management and could potentially improve outcomes in this patient population. In the current issue of CKJ, Mancianti et al. report on the testing of the kidney's functional reserve in patients planned for stem cell transplantation and demonstrate that stem cell transplant candidates with a preserved kidney response on a protein load had a higher chance of full kidney recovery after an episode of acute kidney injury. In this editorial, we discuss the kidney's functional reserve test and its limitations.

AimsTo study loop diuretic response and effect of loop diuretic omission in ambulatory heart failure (HF) patients on chronic low‐dose loop diuretics.Methods and resultsUrine collections were performed on two consecutive days in 40 ambulatory HF patients with 40–80 mg furosemide (day 1 with loop diuretic; day 2 without loop diuretic). Three phases were collected each day: (i) first 6 h; (ii) rest of the day; and (iii) night. On the day of loop diuretic intake, the total natriuresis was 125.9 (86.9–155.0) mmol/24 h and urine output was 1650 (1380–2025) mL/24 h. There was a clear loop diuretic response with a natriuresis of 9.4 (6.7–15.9) mmol/h and a urine output of 117 (83–167) mL/h during the first 6 h, followed by a significant drop in natriuresis and urine output during the rest of the day [2.6 (1.8–4.8) mmol/h and 55 (33–71) mL/h] and night [2.2 (1.6–3.5) mmol/h and 44 (34–73) mL/h]. On day 2, after loop diuretic omission, the natriuresis and urine output remained similarly low the entire day, resulting in a 50% reduction in natriuresis [55.1 (33.5–77.7) mmol/24 h; P < 0.001] and a 31% reduction in urine output [1035 (875–1425) mL/24 h; P < 0.001] compared with the day of loop diuretic intake.ConclusionPatients with HF on chronic loop diuretic treatment still have a clear diuretic response phase, while loop diuretic omission leads to a significant drop in natriuresis and urine output, arguing against routine cessation of low‐dose loop diuretics.

Abstract Background and Aims Blood pressure (BP) variability is an important cardiovascular risk factor that contributes to the high burden of cardiovascular mortality in hemodialysis (HD) patients. Ultrafiltration rate (UFR) and plasma refill rate modify the extracellular volume (ECV), which is a major determinant of the systolic BP. Segmental bioimpedance of the thoracic region addresses the central volume compartment of the body. We hypothesize that changes in bioimpedance reflect changes in BP and that thoracic measurements are more accurately in detecting intradialytic BP changes compared to whole body bioimpedance. Method During two consecutive short-term interval HD sessions, thoracic bioimpedance signal was registered continuously from predialysis until the end of the session. Corresponding BP, whole body bioimpedance and ultrafiltration volume (UFV) after the start and at the end of dialysis was registered. After outlier detection, valid raw bioimpedance data [Ohm] at 8 and 160 kHz for thoracic measurements, and 5 and 200 kHz for whole body measurements, were taken into further analysis. Dialysis sessions were divided into 3 groups according to the development of the systolic BP: a drop ≥ than 20 mmHg was defined as a hypotensive session, an increase ≥ 10 mmHg was considered as a hypertensive session. Pearson correlation analysis was applied (r, p-value) to the relative data, calculated as a percentage from the start value. Results From 2 dialysis centres, a total of 46 HD patients were enrolled in the study (65.2% male, mean age 71 ± 12.6 years, mean dialysis vintage 4 ± 3.9 years), which resulted in 89 dialysis sessions to analyse. Mean systolic BP after start of dialysis was 133.2 ± 20.7 mmHg and mean UF volume was 1817.5 ± 801.5 mL. 23 sessions showed a hypotensive gradient from the start till the end of dialysis, and 13 sessions progressed with an increase of more than 10 mmHg. When the 8 kHz curve was plotted according to the 3 BP groups, a more plane increase in thoracic bioimpedance signal was observed in the group with a normal tension course (Figure 1). There was a significant relationship between UFR and changes in relative bioimpedance data, as well as thoracic (r = .49 at 8 kHz, r = .46 at 160 kHz, all ps < .001), as whole body bioimpedance (r = .58 at 5 kHz, r = .52 at 200 kHz, all ps < .001). UFV correlated with changes in systolic BP (r = -.31, p < .01). Both bioimpedance techniques correlated with each other (r = .38, p = .001 for low frequencies; r = .29, p < .01 for high frequencies). Where the relative thoracic bioimpedance signal correlated with changes in systolic BP (r = -.35 at 8kHz, -.32 at 160 kHz, all ps < .01) (Figure 2), whole body did not. Conclusion Thoracic bioimpedance is associated with intradialytic BP changes, whereas whole body bioimpedance is not. Thoracic bioimpedance has the potential to function as an important diagnostic and predictive tool in BP variability during HD.

Intra-abdominal hypertension (IAH) causes severe organ dysfunction. Our aim is to evaluate the effect of increased intra-abdominal pressure (IAP) on renal function, hypothesizing that venous congestion may increase proteinuria and fluid retention without endothelial dysfunction. Three urine samples were collected from 32 non-pregnant women undergoing laparoscopic-assisted vaginal hysterectomy (LAVH) and from 10 controls placed in Trendelenburg position for 60 min. Urine sampling was done before (PRE), during or immediately after (PER), and two hours after (POST) the procedure. Urinary albumin, protein and creatinine concentrations were measured in each sample, and ratios were calculated and compared within and between groups. During LAVH, the albumin/creatinine ratio (ACR) increased and persisted POST-procedure, which was not observed in controls. A positive correlation existed between the LAVH duration and the relative change in both ACR and protein/creatinine ratio (PCR) PER- and POST-procedure. Iatrogenic IAH increases urinary ACR and PCR in non-pregnant women via a process of venous congestion. This mechanism might explain the presentation of one specific subtype of late-onset preeclampsia, where no drop of maternal cardiac output is observed.

The importance of physical activity has become evident since a sedentary lifestyle drives cardiovascular disease progression and is associated with increased morbidity and mortality. The favorable effects of exercise training in chronic heart failure (HF) and chronic kidney disease (CKD) are widely recognized and exercise training is recommended by European and American guidelines. However, the application of exercise intervention in HF patients hospitalized for acute decompensation or acute worsening in cardiac function has not been explored extensively and, as a result, knowledge about the effects of exercise training in the inpatient setting of acute HF is limited. Acute HF is often accompanied by signs and symptoms of congestion, termed acute decompensated heart failure (ADHF), which leads to worsening renal function (WRF) and eventually negatively affects both thoracic and abdominal organs. Therefore, we first provide a comprehensive overview of the impact of exercise training in hospitalized patients demonstrating acute decompensating HF. In the second part, we will focus on the effects of exercise training on congestion in a setting of ADHF complicated by renal dysfunction. This review suggests that exercise intervention is beneficial in the inpatient setting of acute HF, but that more clinical studies focusing on the application of exercise training to counteract venous congestion are needed.

In this study, the effects of moderate intense endurance exercise on heart and kidney function and morphology were studied in a thoracic inferior vena cava constricted (IVCc) rat model of abdominal venous congestion. After IVC surgical constriction, eight sedentary male Sprague-Dawley IVCc rats (IVCc-SED) were compared to eight IVCc rats subjected to moderate intense endurance exercise (IVCc-MOD). Heart and kidney function was examined and renal functional reserve (RFR) was investigated by administering a high protein diet (HPD). After 12 weeks of exercise training, abdominal venous pressure, indices of body fat content, plasma cystatin C levels, and post-HPD urinary KIM-1 levels were all significantly lower in IVCc-MOD versus IVCc-SED rats (P < 0.05). RFR did not differ between both groups. The implementation of moderate intense endurance exercise in the IVCc model reduces abdominal venous pressure and is beneficial to kidney function.

Congestion (i.e., backward failure) is an important culprit mechanism driving disease progression in heart failure. Nevertheless, congestion remains often underappreciated and clinicians underestimate the importance of congestion on the pathophysiology of decompensation in heart failure. In patients, it is however difficult to study how isolated congestion contributes to organ dysfunction, since heart failure and chronic kidney disease very often coexist in the so-called cardiorenal syndrome. Here, we review the existing relevant and suitable backward heart failure animal models to induce congestion, induced in the left- (i.e., myocardial infarction, rapid ventricular pacing) or right-sided heart (i.e., aorta-caval shunt, mitral valve regurgitation, and monocrotaline), and more specific animal models of congestion, induced by saline infusion or inferior vena cava constriction. Next, we examine critically how representative they are for the clinical situation. After all, a relevant animal model of isolated congestion offers the unique possibility of studying the effects of congestion in heart failure and the cardiorenal syndrome, separately from forward failure (i.e., impaired cardiac output). In this respect, new treatment options can be discovered.

Venous congestion is an important contributor to worsening renal function in heart failure and the cardiorenal syndrome. In patients, it is difficult to study the effects of isolated venous congestion on organ function. In this study, the consequences of isolated abdominal venous congestion on morphology and function of the kidneys, liver and heart were studied in a rat model. Twelve shamoperated (SHAM) male Sprague Dawley rats were compared to eleven inferior vena cava-constricted (IVCc) rats for twenty-one weeks. Abdominal venous pressure was significantly higher in the IVCc versus SHAM group (p < 0.0001). Indices of liver and kidney weight, function and morphology, inflammation as well as collagen deposition were significantly increased in the IVCc compared to SHAM group, (p < 0.05). Echocardiographic and hemodynamic parameters were largely unaffected by abdominal venous congestion. In this rat model of isolated abdominal venous congestion, retrogradely conducted glomerular hypertension without a concomitant change in glomerular filtration rate was observed. Adverse short-term hepatic morphological alterations were developed which explain the observed organ function dysfunction. Importantly, cardiac function remained comparable between both groups. This study provides relevant insight in the pathophysiology of abdominal congestion on organ function.

Renal stimulation tests document the dynamic response of the glomerular filtration rate (GFR) after a single or a combination of stimuli, such as an intravenous infusion of dopamine or amino acids or an oral protein meal. The increment of the GFR above the unstimulated state has formerly been called the renal functional reserve (RFR). Although the concept of a renal reserve capacity has not withstood scientific scrutiny, the literature documenting renal stimulation merits renewed interest. An absent or a blunted response of the GFR after a stimulus indicates lost or diseased nephrons. This information is valuable in preventing, diagnosing and prognosticating acute kidney injury and pregnancy-related renal events as well as chronic kidney disease. However, before renal function testing is universally practiced, some shortcomings must be addressed. First, a common nomenclature should be decided upon. The expression of RFR should be replaced by renal functional response. Second, a simple protocol must be developed and propagated. Third, we suggest designing prospective studies linking a defective stimulatory response to emergence of renal injury biomarkers, to histological or morphological renal abnormalities and to adverse renal outcomes in different renal syndromes.

Over the past ten year period, there has been a sharp increase in the age distribution of dialysis patients. The mean age of patients entering dialysis therapy in 1995 was 69 years, rising to 75 years by 2005 (Figure 1). Of this group of patients, there is a 20% mortality rate within 6 months of commencing dialysis (Figure 2). Renal replacement therapy (RRT) is considered a bridge to transplantation. However, what if the patient is not eligible for transplantation because of age, co-morbidity or refusal?

The pros and cons of subclavian vein hemodialysis catheters are reviewed. The subclavian vein catheter offers rapid and adequate vascular access. Other advantages are preservation of patient mobility and the ease with which the dressing can be secured. In contrast, subclavian vein stenosis has recently been identified as an important long-term complication of subclavian vein catheters that seriously compromises the creation and long-term viability of later ipsilateral arteriovenous fistulas. For this reason, we recommend restricting use of the subclavian hemodialysis catheter for acute situations and preferential use of internal jugular catheters for more chronic approaches because they better preserve venous integrity.