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Summary: The steady-state concept of Na+ homeostasis, based on short-term investigations of responses to high salt intake, maintains that dietary Na+ is rapidly eliminated into urine, thereby achieving constant total-body Na+ and water content. We introduced the reverse experimental approach by fixing salt intake of men participating in space flight simulations at 12 g, 9 g, and 6 g/day for months and tested for the predicted constancy in urinary excretion and total-body Na+ content. At constant salt intake, daily Na+ excretion exhibited aldosterone-dependent, weekly (circaseptan) rhythms, resulting in periodic Na+ storage. Changes in total-body Na+ (±200–400 mmol) exhibited longer infradian rhythm periods (about monthly and longer period lengths) without parallel changes in body weight and extracellular water and were directly related to urinary aldosterone excretion and inversely to urinary cortisol, suggesting rhythmic hormonal control. Our findings define rhythmic Na+ excretory and retention patterns independent of blood pressure or body water, which occur independent of salt intake. [Copyright &y& Elsevier]

Background: Abnormal fluid and plasma sodium concentrations are established prognostic factors for hemodialysis patients. However, the cumulative effects of abnormal salt and water and potential effect modifications and the effect of dialysate sodium remain incompletely understood., Methods: The study followed 68,196 incident hemodialysis patients from 875 dialysis clinics in 25 countries over 10 years (2010-2020) investigating dose-response patterns between cumulative exposure time of fluid overload/depletion (measured by bioimpedance spectroscopy using the Fresenius Body Composition Monitor [BCM]), abnormal plasma sodium levels, low dialysate sodium, and all-cause mortality. We calculated time-varying cumulative exposure (in months) of relative fluid overload (any degree; >7% or severe; >13 or >15% in women or men, respectively) and fluid depletion (<-7%), hypo- or hypernatremia (sodium <135 or >145 mmol/L, respectively), low dialysate sodium (≤138 mmol/L), and estimated hazard ratios (HRs) for all-cause mortality using a multivariable Cox model., Results: Of 2,123,957 patient-months, 61% were spent in any degree of fluid overload, 4% in fluid depletion, 11% in hyponatremia, and 1% in hypernatremia. Any degree of fluid overload was associated with higher all-cause mortality (HR peak at 3.42 (95% confidence intervals: 3.12-3.75) relative to no exposure), and this association with all-cause mortality appeared to be stronger with severe fluid overload. The risk pattern associated with hyponatremia was approximately linear in the first four patient-months and then plateaued after the fourth patient-month. We did not observe effect modification between fluid overload and hyponatremia., Conclusion: Even mild fluid overload was associated with higher mortality in hemodialysis patients. Whether a more stringent fluid management results in clinical improvement requires further investigation., (Copyright © 2024 by the American Society of Nephrology.)

The aim of the paper is to reflect on the current status of bioimpedance spectroscopy (BIS) in fluid management in dialysis patients. BIS identifies fluid overload (FO) as a virtual (overhydration) compartment, which is calculated from the difference between the measured extracellular volume and the predicted values based on a fixed hydration of lean and adipose tissue mass. FO is highly prevalent in both hemodialysis (HD) and peritoneal dialysis (PD) patients, while levels of FO are at a population level comparable between PD patients and HD patients when measured before the dialysis treatment. Even mild levels of FO are independently related to outcome in patients on HD, PD as well as in nondialysis patients with advanced chronic kidney disease. FO is not only related to left ventricular hypertrophy (LVH) but also forms part of a multidimensional spectrum with noncardiovascular risk factors such as malnutrition and inflammation. Even after multiple adjustments, FO remains an independent predictor of mortality. BIS-assisted adjustment of dry weight in HD patients has been shown to improve hypertension control and LVH and has resulted in a decline in intradialytic symptomatology. On the other hand, with increased fluid removal, target weight may not always be reached due to an increase in intradialytic symptomatology, and care should be applied in target weight adjustment in fluid overloaded patients with severe malnutrition and/or inflammation. Although a reduction in hospitalization rate was suggested, the effect of BIS-guided dry weight adjustment on mortality has not yet been shown, however, although available studies are underpowered. In PD patients, results have been more equivocal, which may be partly related to differences in treatment protocols or study populations. Future large-scale studies are needed to assess the full potential of BIS., (The Author(s). Published by S. Karger AG, Basel.)

Introduction: Circumstances such as gender, age, diabetes mellitus (DM) and renal failure impact on the body composition of patients. However, we use nutritional parameters such as lean and fat tissue with reference values from healthy subjects to assess the nutritional status of haemodialysis (HD) patients., Aims: To analyse body composition by bioimpedance spectroscopy (BIS) of 6395 HD patients in order to obtain reference values of lean tissue index (LTI) and fat tissue index (FTI) from HD patients; and to confirm its validity by showing that those patients with LTI below the 10th percentile calculated for their group have greatest risk of death., Material and Methods: We used the BIS to determine the LTI and FTI in our cohort of HD patients in Spain. We calculated the 10th percentile and 90th percentile of LTI and FTI in each age decile for patients grouped by gender and presence of DM. We collected clinical, laboratory and demographic parameters., Results: The LTI/FTI 10 and 90 percentile values varied by group (age, gender and presence of DM) and, after adjusting for other risk factors such as fluid overload, those patients with LTI lower than percentile 10 had a higher relative risk of death (OR 1.57) than those patients with higher values., Conclusions: Monitoring the LTI and FTI of patients on HD using suitable reference values may help to identify risk in this patient population., (Copyright © 2016 Sociedad Española de Nefrología. Published by Elsevier España, S.L.U. All rights reserved.)

Blood pressure (BP) response to volume depletion induced by hemodialysis (HD) treatment may be important to understand the pathophysiology of the increased mortality in HD patients with vascular calcification. In the present study a comparison between end stage renal disease (ESRD) patients affected by peripheral vascular disease (PVD) and ESRD patients without PVD was performed. Continuous blood pressure was recorded at the beginning and at the end of HD. BP and heart rate variability (HRV) were analyzed to quantify the autonomic nervous system regulation of heart beat and peripheral resistance. PVD patients showed an increase of pulse pressure (PP) during HD, an altered autonomic peripheral control, a lower sympathetic activity, with respect to ESRD patients without PVD.

A crucial point in the haemodialysis (HD) treatment is the reliable assessment of hydration status. An inadequate removed volume may lead to chronic fluid overload which can lead to hypertension, left ventricular hypertrophy and heart failure. Therefore, the estimation of the hydration state and the management of a well-tolerated water removal is an important challenge. This exploratory study aims at identifying new parameters obtained from continuous Blood Volume Monitoring (BVM) allowing a qualitative evaluation of hydration status for verifying the adequacy of HD setting parameters (e.g UFR, target dry weight). The percentage of blood volume reduction (BVR%) during HD was compared against a gold standard method for hydration status assessment. The slope of the first 30 minute of blood volume reduction (BVR) was proposed as a useful parameter to identify overhydrated patients.

This work aims at studying the autonomic nervous system (ANS) response to hemodialysis (HD) treatment in a population of end stage renal disease (ESRD) patients. ECG Holter recordings and whole body bioimpedance spectroscopy measurements were performed for each patient. Patients were classified according to the fluid overload (FO) values and the systolic blood pressure (SBP) measured before HD. Time domain and frequency domain indices from heart rate variability (HRV) signals were measured for the first 30 minutes and last 30 minutes of HD, the first hour after HD, and night (12.00 p.m.-4 a.m.). Significant differences were obtained in fluid overloaded but normotensive patients (Group IV) with respect to fluid overloaded and hypertensive patients (Group I) and normohydrated and normotensive patients (Group N+Dx). In particular, SDNN, RMSSD, SDSD, pNN50%, indices resulted significantly higher in Group IV with respect to the other groups. Overhydrated patients with hypertension (Group I) showed a blunted parasympathetic activity, which is supposed to contribute to hypertension.