Overhydration, underhydration, and total body sodium: A tricky "ménage a trois" in dialysis patients.

Overhydration is a frequent complication in dialysis patients. It has been linked with hypertension, left ventricular hypertrophy, arterial stiffness, atherosclerosis uremic cardiomyopathy, and all-cause mortality or cardiovascular morbidity. In addition, predialysis underhydration is also associated with increased risk of death in ESRD patients. In this context, the optimal evaluation of hydration status is a must. However, this mission is not easy or accurate. In the last 10 years, several new methods have been tested in dialysis patients, particularly bioimpedance and lung ultrasonography. The precise clinical value of these techniques in the daily care of hemodialysis patients is not obvious yet. Sodium is also an important piece of this puzzle. Salt intake and/or removal of sodium during dialysis are essential determinants of optimal hydration status. Recent studies have revealed that salt and water homeostasis is also dependent of tissue sodium storage-increased in hemodialysis patients. However, the significance of increased sodium tissue storage as a cardiovascular risk factor and the relationship between tissue sodium content and hard CV endpoint have not yet been elucidated yet.