Background: Magnesium (Mg) is an essential cation for multiple processes in the body. The kidney plays a major role in regulating the Mg balance. In a healthy individual, totalbody Mg content is kept constant by interactions among intestine, bones and the kidneys. Summary: In case of chronic kidney disease (CKD), renal regulatory mechanisms may be insufficient to balance intestinal Mg absorption. Usually Mg remains normal; however, when glomerular filtration rate declines, changes in serum Mg are observed. Patients with end-stage renal disease on dialysis are largely dependent on the dialysate Mg concentration for maintaining serum Mg and Mg homeostasis. A low Mg is associated with several complications such as hypertension, and vascular calcification, and also associated with an increased risk for both cardiovascular disease (CVD) and non-CVD mortality. Severe hypermagnesaemia is known to cause cardiac conduction defects, neuromuscular effects and muscle weakness; a slightly elevated Mg has been suggested to be beneficial in patients with end-stage renal disease. Key Messages: The role of both low and high Mg, in general, but especially in relation to CKD and dialysis patients is discussed.

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.