Chronic renal failure

Chronic renal failure (CRF) is the progressive irreversible destruction of kidney tissue by disease which, if not treated by dialysis or transplant, will result in the death of the patient. The aetiology of CRF encompasses the spectrum of known kidney diseases. The end result of progressive renal damage is the same no matter what the cause of the disease may have been. The major effects of renal failure all occur because of the loss of functioning nephrons. It is a feature of CRF that patients may have few if any symptoms until the glomerular filtration rate falls below 15 mL/minute (i.e. to 10% of normal function), and the disease is far advanced.

Consequences of CRF

Sodium and water metabolism

Most CRF patients retain the ability to reabsorb sodium ions, but the renal tubules may lose their ability to reabsorb water and so concentrate urine. Polyuria, although present, may not be excessive because the GFR is so low. Because of their impaired ability to regulate water balance, patients in renal failure may become fluid overloaded or fluid depleted very easily.

Hyperkalaemia is a feature of advanced CRF and poses a threat to life (Fig 19.1). The ability to excrete potassium decreases as the GFR falls, but hyperkalaemia may not be a major problem in CRF until the GFR falls to very low levels. Then, a sudden deterioration of renal function may precipitate a rapid rise in serum potassium concentration. An unexpectedly high serum potassium concentration in an outpatient should always be investigated with urgency.