Children with chronic renal failure (CRF) generally maintain sodium and water balance until the GFR is reduced very severely (< 10 ml/min/1.73m2). However the kidneys lose their ability to excrete a sodium or water load and patients are advised to avoid excessive intakes of salt or water.
Similarly, they are unable to cope with dehydration. Patients with CRF continue to need to excrete an osmotic load to balance their dietary intake. In the face of CRF, the renal concentrating ability is reduced and therefore the volume of urine which must be passed to excrete this solute load is increased. This must be matched by an increase in fluid intake. An inadequate fluid intake will therefore lead to dehydration, but equally, the impaired kidney function means that they are unable to excrete a high water load. Excessive fluid intake may lead to hyponatraemia. Animal experiments have suggested that water restriction may accelerate progression of CRF by increasing glomerular filtration pressure.
The advice is therefore to maintain a good fluid intake, but avoiding fluid overload.